case study of soil pollution in india

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Home > Books > Environmental Risk Assessment of Soil Contamination

Metal Contamination of Soils and Prospects of Phytoremediation in and Around River Yamuna: A Case Study from North-Central India

Submitted: 20 September 2013 Published: 26 March 2014

DOI: 10.5772/57239

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Environmental Risk Assessment of Soil Contamination

Edited by Maria C. Hernandez-Soriano

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Author Information

Manoj s. paul *.

• Department of Botany, St. John’s College, Agra, India

Mayank Varun

Rohan d’souza, paulo j.c. favas.

• Department of Geology, School of Life Sciences and the Environment, University of Trás-os-Montes e Alto Douro, Vila Real, Portugal
• IMAR-CMA Marine and Environmental Research Centre, Faculty of Sciences and Technology, University of Coimbra, Coimbra, Portugal

João Pratas

• Department of Earth Sciences, Faculty of Sciences and Technology, University of Coimbra, Coimbra, Portugal

*Address all correspondence to: [email protected]

1. Introduction

The rapid industrialization and intensive agricultural activities over the last few decades have resulted in accumulation of various pollutants in the environment, which are distributed over wide areas by means of air and water. This has caused visible detrimental effects to the ecosystem and consequences to human health. Today, many soils throughout the world have undesirably high concentrations of heavy metals. These include lead (Pb), cadmium (Cd), zinc (Zn), mercury (Hg), arsenic (As), silver (Ag), chromium (Cr), copper (Cu), iron (Fe), and the platinum group elements. At low or background concentrations, heavy metals are not pollutants. They occur naturally in the environment due to their presence in bedrocks. Some heavy metals such as Zn and Cu are also essential micronutrients for living organisms. Therefore, the term heavy metal pollution refers to heavy metal levels that are abnormally high relative to normal background levels. All heavy metals at high concentration have strong toxic effects and are regarded as environmental pollutants.

Some heavy metals (like Fe, Zn, Ca and Mg) have been reported to be of bio-importance to man and their daily medicinal and dietary allowances have been recommended. However, some others (like As, Cd, Pb, and methylated forms of Hg) have been reported to have no known bio-importance in human biochemistry and physiology and consumption even at very low concentrations can be toxic [ 1 ]. Even for those that have bio-importance, dietary intakes have to be maintained at regulatory limits, as excesses result in poisoning or toxicity [ 2 ]. Although individual metals exhibit specific signs of their toxicity, the following have been reported as general signs associated with Cd, Pb, As, Hg, Zn, Cu and Al poisoning: gastrointestinal disorders, diarrhoea, stomatitis, tremor, ataxia, paralysis, vomiting and convulsion, depression, and pneumonia when volatile vapours and fumes are inhaled [ 3 ]. The nature of effects could be toxic (acute, chronic or sub-chronic), neurotoxic, carcinogenic, mutagenic or teratogenic.

Pb, Zn, Cu, Co, Mn, Fe, Cr and Cd have been found in the streams and rivers of the Americas, Europe, Asia, Africa and Australia [ 4 - 9 ]. In India, presence of heavy metals has been reported in the Brahmaputra [ 10 ]; the Kali and Hindon [ 11 ]; and more recently, in the Gomti [ 12 ]; the Cauvery [ 13 ]; and the Ganga [ 14 ].

The Yamuna (also Jamuna or Jumna) is the largest tributary of the Ganga in northern India, having the total length of about 1376 km. The source of Yamuna is Yamunotri in the Uttarakhand Himalaya, which is north of Haridwar in the Himalayan mountains. Yamuna river flows through the states of Uttarakhand, Delhi, Haryana and Uttar Pradesh and finally merges with river Ganges at a sacred spot known as Triveni Sangam in Allahabad. A number of prominent cities such as Delhi, Mathura and Agra lie on the bank of river Yamuna. Over 57 million people depend on the Yamuna waters. Just like the Ganges, the Yamuna too is highly venerated in Hinduism and worshipped as goddess Yamuna, throughout its course.

Due to high density population growth, rapid industrialization, today Yamuna is one of the most polluted rivers in the world, especially around New Delhi, where 15 drains discharge waste water into the river. The city dumps ~58% of its waste into it. When the river enters the city, it is already contaminated with 7500 coliform content per 100 ml. when it leaves the city, it carries with a dangerously high coliform content of 24 million per 100 ml. Even the ground water has been affected by leachates that pass down from the dumping sites. According to the Central Pollution Control Board (CPCB), 70% of the pollution in river is from untreated sewage and the remaining 30% is from industrial sources, agricultural run-off, garbage etc. The water quality of Yamuna River falls under the category "E" which makes it fit only for recreation and industrial cooling, completely ruling out the possibility for underwater life. Almost every year mass death of fishes is reported. Biological Oxygen Demand (BOD) load increased by 2.5 times between 1980 and 2005: from 117 tonnes per day in 1980 to 276 in 2005.

Although the government of India has spent nearly $500 million to clean up the river, the river continues to be polluted with garbage while most sewage treatment facilities are underfunded or malfunctioning. The Ministry of Environment and Forests (MoEF) of the Government of India (GOI) took measures to curb pollution in 12 towns of Haryana, 8 towns of Uttar Pradesh, and Delhi under an action plan (Yamuna Action Plan-YAP) which is being implemented since 1993 [ 15 ]. However in 2009, the Union government admitted the failure of the Ganga Action Plan (GAP) and the Yamuna Action Plan (YAP), saying that "rivers Ganga and Yamuna are no cleaner now than two decades ago" despite spending over Rs 1, 700 crore to control pollution [ 16 ]. In August 2009, Delhi Jal Board (DJB) initiated its plan for resuscitating a 22 km stretch of the Yamuna in Delhi by constructing interceptor sewers, at the cost of about Rs 1, 800 crore [ 17 ].

There are three main sources of pollution in the river, namely household and municipal disposal sites, agricultural run-off, and industrial effluents and run-off. Urban runoff and agricultural runoff are mainly non–point sources. The major sources of pollution from agriculture are fertilizers containing superabundant nutrients such as nitrogen and phosphorus, and heavy metals such as Cd, Cu, Pb and Zn. Water quality may also be altered by other factors, such as livestock manure, human waste, and atmospheric deposition. Atmospheric pollutants are often the largest source of waterborne metals. It is estimated that 70% of lead in water and over 50% of many of the other trace metals in the Great Lakes (USA) are derived from atmospheric transfer. In general, freshwater ecosystems have low natural background metal levels and therefore tend to be sensitive to even small additions of most trace metals. Heavy metal contamination of soils and water from industrial and traffic sources in urban environments has been studied in North America and Europe [ 18 - 22 ]. Agencies like the World Health Organization (WHO) and the United states Environment Protection Agency (USEPA) have set stringent standards for maximum permissible limits of heavy metals, but there is a paucity of detailed studies on heavy metal pollution and its remediation within industrial zones in developing countries. Yamuna outnumbers any other river in the number of industries on its bank. This is because it passes through many major industrial cities. About 22, 42, and 17 large and medium industrial units in the states of Haryana, Delhi, and Uttar Pradesh have been identified as polluting the river in the action plan area. In addition, the water in this river remains stagnant for almost 9 months in a year aggravating the situation.

According to the Agra District Industrial Centre officials, there were 226 iron foundries and about 340 metal casting units functioning in Agra in the decade of 1990-2000. Before the revised pollution control directives put the Agra diesel generator manufacturing industry off its track, the foundry industry of this town ranked among the country’s largest assemblies of metal casting industrial units, generating business of over Rs 6, 000 crores. The ban on coking coal in the blast furnaces utilized by the foundry and metal-casting industry was a serious setback and the number of industrial units reduced drastically. In August 1999, the Supreme Court ordered the closure of 53 iron foundries and 107 other factories in Agra. In September 2010, it again ordered the closure of 212 of the 1, 715 small industries that had failed to disclose their toxic emission levels to the Uttar Pradesh Pollution Control Board (UPPCB). Another 299 were required to install pollution controlling devices, failing which they too would face closure. However, the ground realities are still nowhere near the reduced pollution levels targeted in Yamuna and its adjacent areas whether Agra or elsewhere, after it leaves the Himalayan foothills. The status quo, thus, ultimately leaves much to be desired.

Phytoremediation is an emerging technology that employs the use of green plants for the clean up of contaminated environment. It takes the advantage of the fact that a living plant acts as a solar-driven pump, which can extract and concentrate certain metals from the environment [ 23 ]. This remediation method maintains the biological properties and physical structure of the soil. The technique is environmentally friendly, cost-effective, visually unobtrusive, and offers the possibility of bio-recovery of the metals. In the case of heavy metal contamination in soil, phytoremediation techniques are narrowed down to Phytoextraction, where plants remove metals from the soil by concentrating them in their harvestable parts [ 24 ], and Phytostabilization , where plants reduce the mobility and bioavailability of pollutants by immobilization [ 25 ].

Phytoremediation is becoming possible because of the successful basic and applied research much of it conducted with the productive interdisciplinary cooperation of plant biologists, soil chemists, microbiologists and environmental engineers. Extensive progress has been made in characterizing and modifying the soil chemistry of the contaminated site to accelerate phytoremediation. The greatest progress in phytoremediation has been made with metals [ 26 , 27 ]. Phytoremediation leaves the topsoil in usable condition and it is aesthetically pleasing. It requires minimal equipment and less energy inputs as plants do most of the work using solar energy. Thus, it is an eco-friendly process. The plants used can later be harvested, processed and disposed off in an environmentally sound manner. This technology has been receiving attention lately as an innovative, cost-effective alternative to the otherwise tedious and expensive methods in use which are not only a burden on the exchequer but also require efforts on recurring basis.

Phytoremediation employing indigenous species can be an ecologically viable option for sustainable and cost-effective management. Native plants often become adapted to locally elevated levels of metals in soil at contaminated sites, e.g. mines and industrial zones [ 28 - 30 ] and metal toxicity issues do not generally arise. Many native, well adapted plants have been investigated and even used for heavy metal bioindicatoring and phytoremedial purposes including lemongrass and other wild grasses, vetiver, Sesbania , Avena , Crotalaria , Crinum asiaticum, Typha latifolia and Calotropis procera etc. [ 31 - 35 , 28 ]. Native wild species are also important to remediate soils in context of the studied area due to a remark (April, 2006) of the Supreme Court prohibiting the cultivation of plants requiring fertilizers and pesticides along the Yamuna. In the light of this limitation, native wild species are a viable option since these do not require agronomic inputs.

Since the river Yamuna is the life line of Mathura and Agra, the existing pollution level has posed a serious threat not only to the environment but also to the human population. Adjacent areas are highly polluted and are a sink for a variety of chemicals including heavy metals. The present study was undertaken: (i) to get a comprehensive profile of eight metals in water and adjacent soils of the river Yamuna within Mathura, Agra and Bateshwar; (ii) to get a qualitative and quantitative estimate of the species present at test sites through phyto-sociological surveys; and (iii) to inventorize species with potential for phytoremediation present on sites by comparing with those previously reported by the authors as suitable in this context.

2. Case study

Agra (27°10’N, 78°05’E, 169 msl), on the banks of the river Yamuna, is located in Uttar Pradesh in the north central part of India. It is roughly 200 km south-east of the national capital, New Delhi. Bounded by the Thar desert of Rajasthan on its south-east, west and north-west peripheries, it is a semi-arid area. The world renowned Mughal monument, the Taj Mahal is situated here. It is world renowned for its leather industry and marble handicrafts but it also boasts a cast iron and engineering goods industry. Mathura (27.28°N 77.41°E) is located approximately 60 km north of Agra and 145 km south-east of Delhi. According to Hindu scriptures Mathura is the birthplace of Lord Krishna. It is a fast expanding city with about half a million residents. Mathura oil refinery is one of the biggest oil refineries of Asia. Textile printing, dyeing and silver ornament manufacturing are major industries. Apart from these there are units manufacturing taps, household items, and cotton materials. Bateshwar (26.93°N 78.54°E) is a village on the banks of Yamuna about 120 km downstream from Agra. It is an important spiritual and cultural centre for Hindus.

Map of the study area

The study area was divided into three zones ( Figure 1) ; all three along the course of Yamuna and covering two cities viz. Mathura (zone 1) and Agra (zone 2) and a large village i.e. Bateshwar (zone 3). The distance between zones 1 and 2 is 80 km and zones 2 and 3 is 120 km downstream. In all, a total distance of 200 km was covered along the course of river. In each zone, 5 sites were selected ~1 km apart. Five random soil samples were taken from 0-15 cm depth at each site. A total of 75 soil samples (25 from each zone) were analyzed in order to obtain a complete profile. The same number of river water samples was collected from midstream at a depth of about 0.3 m. Soil from the botanical garden of St. John’s college, Agra, was utilized as control.

The statistical significance of differences among mean metal content in water and soil was independently determined by one-way analysis of variance (ANOVA) followed by Fisher’s LSD test. Pearson’s coefficient for correlation of water and soil data was analyzed at a significance level of P < 0.05 and P < 0.01 with SPSS 16.0 statistics software.

3. Physico-chemical profile

Physico-chemical properties of the water samples collected from the study zones are mentioned in Table 1 . The pH values indicate neutral nature of river water acceptable as per BIS [ 36 ] and WHO [ 37 ] guidelines. A reading of 6.5 to 7.5 is considered neutral, suitable for general plant growth [ 38 ]. Conductance which reflects the status of major ions/inorganic pollution and is a measure of total dissolved solids and ionized species in the water, varies between 434 – 503 µmho/cm. Total dissolved solids were highest in zone 2. The hardness of water body is regulated largely by the levels of Ca and Mg salts. Other metals if present such as Fe, Al and Mn may also contribute to hardness. Most parameters were within their respective acceptable limits [ 36 , 37 ]. Electrical conductivity was low. High COD, BOD and low DO in zones 1 and 2 are due to the discharge of huge amount of the untreated urban and industrial wastewater/effluents indiscriminately. All three zones were faecally contaminated. Bacterial contamination ranged from19000—93000 coliform/100ml; the values are much higher than recommended values of 1coliform/100ml. Most of these coliforms were of faecal type due to gravity discharge of faecal wastes in adjacent areas along the river.

Physico-chemical profile of water

The soil of the study area is characterized by alluvium, which is an admixture of gravel, sand, silt and clay in various proportions deposited during the quaternary period. The area is a part of Indo-Gangetic alluvium of quaternary age and is made up of recent unconsolidated fluviatile formations comprising sand, silt, clay and kankar with occasional beds of gravel. The topsoil is coarse and angular sand with small clay fraction. The sub-soil is sandy throughout. The stabilized topsoil is reddish brown with sand and clay mixed. The minimum depth of topsoil layer is 60 cm.

Physico-chemical properties of soil samples are given in Table 2 . The topsoil in the study area is sandy loam (sand 60-80%, silt 10-24%, clay 8-16%). It has high exchangeable sodium percentage (ESP) values and moderate water retaining capacity. The sub-soil is sandy throughout. Soil pH ranged from neutral to alkaline. Zones 3, 2 and 1 were classified as very low, low and medium in organic matter, respectively.

Physico-chemical profile of soils

The electrical conductivity (EC) of soils ranged from 0.33-0.54 dS/m. Zone 1 and 2 soils fall in very high (>100 kg/ha), soils from zone 3 and control site in the high (50-100 kg/ha) phosphate availability bracket. Soils from zones 1, 3 and control displayed medium (130-330 kg/ha) potash levels while zone 2 was low (<130 kg/ha) in available potash. Nitrogen content in the soil samples ranged from 50.1 – 112.9 kg/ha.

4. Heavy metal profile

Concentrations of heavy metals in the water samples collected from different location have been summarized in Table 3 . It is clearly evident from the table that heavy metals were consistently higher in zone 2 compared to zones 1 and 3. Cr content was markedly higher among the metals in zone 2 followed by zone 1. The concentration of heavy metals in water samples ranged from 0.018 – 0.095 mg Pb l -1 , 0.025 – 0.341 mg Cd l -1 , 0.47 – 1.76 mg Zn l -1 , 0.27 – 1.58 mg Cu l -1 , 0.001 – 0.005 mg Co l -1 , 0.80 – 9.37 mg Cr l -1 and 0.078 – 0.32 mg Ni l -1 . As was not detected in any sample.

Heavy metal content of water samples (mg L -1 )

# As content below detection limit.

F value :“∗” statistically significant. Different letters in the same column denote significant statistical difference (P≤0.001) in mean metal contents in water samples from different zones

SD- Standard deviation.

WHO – World Health Organization.

USEPA – United States Environment Protection Agency.

All the metals in water samples were positively (P<0.01) correlated with each other ( Table 4) . In other words, metal concentration trends were identical and increased simultaneously for Pb, Cd, Zn, Cu, Co, Cr, and Ni.

Correlation coefficients: water heavy metal concentrations

** Correlation is significant at the 0.01 level (two-tailed) (two-tailed; n=75)

Higher concentrations of metals in zone 2 ( Figure 2) may be attributed to the discharge of industrial effluents from various sources including untreated sewage, municipal waste and agrochemical runoff from the nearby villages directly into the river. The concentrations of Co and Ni were found to be negligible at all sites. Due to the neutral to alkaline nature of river water, most of the heavy metals have precipitated and settled as carbonates, oxides, and hydroxide bearing sediments and elevated levels indicates higher exposure risks to the benthic biota of the river. Based on the WHO [ 37 ] and USEPA [ 39 ] drinking water standards ( Table 3) the results in the present investigation show that Pb, Cd and Cr at all sites and Ni at most sites far exceeded the prescribed limits. Cu values from zone 2 were above the USEPA [ 39 ] threshold. One Way ANOVA and Fisher’s LSD test indicate the difference in mean content of each metal among zones was highly significant statistically (P ≤ 0.001).

Average heavy metal content in water samples

When compared with the metal profile of the rivers around the world ( Table 5) the situation does not seem that desperate here, at least as far as heavy metal contamination is concerned. The picture, however, is quite different when we consider the WHO guidelines for drinking water and World average of trace elements in unpolluted rivers [ 56 , 57 ], the concentration ranges of Pb and Cd were well above the international guidelines and acceptable concentrations for drinking water ( Table 3) . When compared to the world average of trace elements for unpolluted rivers, the river was considered polluted by Pb, Cd, Zn and Cu.

Average heavy metal concentrations of rivers around the world (mg L -1 )

Concentrations of heavy metals in the soil samples have been summarized in Table 6 . Quantitatively the metals were observed in the sequence Pb > Zn > Cr > Ni > Cu > As > Cd > Co ( Figure 3) , though their thresholds for concern, mobility in soil and toxicity are different so this trend does not necessarily reflect the threat of individual metals. Pb and Zn were found in fairly higher concentrations at all the sampling locations. Generally, an overall linear increasing trend of metal contamination was noted from site 1, before the Yamuna enters the city of Mathura, to site 10 where the river leaves Agra. Thus, maximum values for all metals were observed in the samples pertaining to Agra. In the third zone metal concentrations were seen to decrease gradually. One-way ANOVA and Fisher’s LSD test indicate that mean Pb and Co content was different at all sites (P ≤ 0.001); while mean Cr, Cd, Cu, Ni, and As in zone 2 differed significantly from zone 1 and 3 (P ≤ 0.001). The latter did not differ significantly among themselves. Mean Zn content in zone 1 differed significantly from zone 2 and 3 (P ≤ 0.05). The difference between the latter was not significant statistically.

Heavy metal content of soil samples (mg kg -1 )

F value :‘*’ statistically significant. Different letters in the same column denote significant statistical difference (P≤0.05) in mean metal contents in soil samples from different zones.

Average heavy metal content in soil samples

All the metals in soils were positively (P<0.01) correlated with each other ( Table 7) . Significant negative correlation was observed between metal concentrations and soil pH (P<0.01). The same was observed in the case of Zn and Co with Organic matter. Phosphate is able to increase water-soluble lead forms from contaminated soils by 56.8– 100% [ 61 ]. This is clearly shown by the phosphate values ( Table 2) obtained for different samples with maximum in zone 2 followed by zone 1 which probably led to higher Pb values in zones 1 and 2 ( Table 6) . Fertilizers contain from trace to several ppm of Pb, Zn, Cu, Mg [ 62 , 63 ]. High P 2 O 5 -blended fertilizers and the pure phosphates, contain significant concentrations of several elements of potential environmental or agronomic concern [ 62 , 64 ].

Correlation coefficients: soil heavy metal concentrations

* Correlation is significant at the 0.05 level (two-tailed; n=75)

** Correlation is significant at the 0.01 level (two-tailed)

Agra is the fourth most populated city in Uttar Pradesh, India. With a population of 1.7 million (2011 census) it generates about 700 tonnes of solid wastes every day. It is also a major cause for adding contamination to soil and groundwater. Solid waste is also discharged from 200 hospitals and nursing homes along with 168 foundries, 52 tanneries, 300 shoe industries, 200 petha (a local sweet) manufacturing units, 50 dairies, 56 electroplating units, 15 silver vibrators and 15 galvanizing units. Significantly higher amount of metal pollution in the samples from the city (sites 6-10) is obviously due to untreated domestic/wastewater, sewage and industrial effluent discharged at these sites throughout the year. The increasing contamination as one proceeds downstream mirrors the extent of damage caused to the pedosphere.

Mean concentrations of heavy metals in soils at the sites studied were compared with threshold values of soil suggested by the Canadian Environmental Quality Guidelines [ 58 ]. It was observed that As (sites 1-13) and Ni (sites 6-10) crossed their respective industrial thresholds while the other metals (Pb, Zn and Cu) are well within it. Mean concentrations of As at sites 4-10 were approximately twice the thresholds suggested. Cd and Cr levels were above their thresholds only at site 10. However, the situation is drastically different in the perspective of the residential limits where in addition to these, the thresholds are exceeded even by Pb, Cd (10 sites each), Cr (5 sites) and also Zn and Cu at one site.

On comparing metal concentrations with the values suggested for soil remediation by VROM, Netherlands [ 59 ], values of Zn (sites 7-13), Ni (sites 4-10) and Cr (site 10) were above the background values but below the intervention level. It is significant to note that in studies similar to the present one, the degree of contamination and the resulting ‘hazard indices’ for soils may vary when different thresholds, existing in only a few countries, are considered [ 65 ]. To increase the reliability of risk estimation due to contaminants, global consensus on such thresholds is urgently needed.

The concentrations of As are usually low, less than 6 ppm, for geological and soil environment [ 64 ]. It is estimated that about 60% As in the environment is from anthropogenic sources including As-based pesticides, fertilizers, and wastes from mines, smelter and tannery industries [ 66 ]. The relatively high values of As in the samples seem to be directly related to the discharge of domestic and industrial effluent as well as use of phosphate fertilizers, pesticides used in the agricultural activities in the region.

Highly significant positive correlation (P<0.01) was observed between soil and water content of Pb, Cd, Cu, Co, Cr and Ni. The results also indicate that metal concentrations in soil were higher than those in the water. This distribution pattern of heavy metals between the water phase and soil is expected as most heavy metal speciation studies have reported a similar pattern of distribution both in sea water as well as in lakes [ 67 - 69 ].

Several authors have pointed out the need for a better knowledge of urban soils [ 18 , 70 ]. In the past few years, studies on urban soils in many cities have been carried out around the world. Some examples are Spanish [ 19 , 71 ] and Italian cities [ 21 , 72 ]. Other examples for European cities are Aberdeen [ 73 ], Athens [ 74 ], Oslo [ 22 ] and Belgrade [ 18 ]. The mean heavy metal contents for all zones are compared in Table 8 to those of some cities around the world. The differences concerning population, living habits, industrial activities, etc., cause significant differences in the metal contamination profile. Compared to average concentrations in urban soils in the world, the mean concentrations of Pb and Cu are up to 2—4 times higher in some cases but still less than London, Naples and Palermo. In the case of Cd, it is many times higher than Kattedan (India). Zn and Cr contents do not differ much; still they are less than those of Naples and Madrid. Ni content is more than almost all European cities, but less than Kattedan and Firozabad in India. Co values are less than those reported from other industrial regions of India. As content is less than that of Firozabad.

Average heavy metal concentrations in urban soils from different cities across the world (mg kg −1 )

It is encouraging to note that the mean concentrations of individual metals are below those reported from other industrial hubs within India i.e. Kattedan (Andhra Pradesh) [except Cd and As] and Firozabad (Uttar Pradesh). Kattedan Industrial Development Area (KIDA) is a major industrial area of Andhra Pradesh and houses 400–500 industries, including 150 large scale industries and 300 small-scale industries. Major sources of metals pollution are battery, electrode, oil refining, metal plating, textile, pharmaceutical, chemical paints, rubber, petrochemicals, glass, therapeutics, and Pb extraction facilities [ 81 ]. This is also one of the contaminated areas identified by the Central Pollution Control Board (CPCB) in New Delhi, and referred to as an ecological disaster area [ 81 ]. Firozabad is the hub of the Indian Glass industry.

5. Assessment of heavy metal contamination in soil

Assessment of soil contamination was performed by the contamination index (P i ) and integrated contamination index (P c ) as expressed by fuzzy functions [ 82 , 29 , 28 ]. Class I criteria [ 60 ] could be used as no-polluted threshold; Class II as lowly polluted threshold value; and while Class III as highly polluted threshold value. P i values ≤ 1 indicate no contamination; 1 ≤ P i ≤ 2 indicates low contamination; 2 ≤ P i ≤ 3 indicates moderate contamination; while P i > 3 indicates high contamination.

Individual elements displayed remarkably different patterns of accumulation in soils. Furthermore, observed differences in the magnitude of accumulation suggest that the relative contribution of the individual elements to total heavy metal contamination varies. Figure 4 shows the proportions of contamination levels (from P i values) in the soil samples from all the sites studied. Except for 76% samples from zone 2, which showed moderate Pb contamination, the rest exhibited low contamination zone as did all samples from zones 1 and 3. In case of Cd, all samples were in the high contamination zone. For Zn, 24% samples from zone 2 were moderately contaminated while 72%, 76%, and 100% samples from zones 1, 2, and 3, respectively were in the low contamination range. For Cu, 88% samples from zone 2 were moderately contaminated while 36% and 12% samples, from zones 1 and 2, respectively were in the low contamination range. All samples from zone 3 indicated no contamination. Except for zone 2 (20% samples) in the low contamination zone, the remaining samples did not indicate Cr contamination. For Ni, 12% and 72% samples from zones 1 and 2, respectively were moderately contaminated while 16% and 22% samples from, respectively were in the low contamination range. All samples from zone 3 indicated no contamination. In the case of As, 64%, 100%, and 60% samples from zones 1, 2, and 3 were in the low contamination range.

Contamination indices (Pi) of heavy metals in soil samples

Thus, zone 1 was found to be lowly contaminated with Pb, Zn, Cu, Ni and As but highly contaminated with Cd. Zone 2 exhibited low to moderate contamination of Pb, Zn, Cu, Ni; low Cr and As contamination; and high Cd contamination. Zone 3 was lowly polluted with Pb and Zn. As contamination ranged from none to low. No Cu, Cr and Ni contamination was observed. These results agree with the findings regarding metal contamination of soil due to the glass industry at Firozabad, India [ 29 ]. Of the nine elements studied, Zn, Cd, and As showed a greater accumulation in all soils, whereas, accumulation of Ni and Cu was high in limited samples.

Integrated Contamination Indices (P c ) were calculated for all soils to assess the extent of heavy metal contamination at the sites. P c is defined as the summation of the difference between the contamination index for each metal and 1 (one). It is categorized under the following heads: P c ≤ 0 no contamination; 0 ≤ P c ≤ 7 low contamination; 7 ≤ P c ≤ 21 moderate contamination; P c > 21 high contamination. Threshold values for Co could not be obtained hence this metals was excluded in the calculation. A clear ascending trend is visible in the P c values for all sites ( Figure 5) . P c values generally show a moderate to high contamination at studied sites. The P c indices indicate that 45% sampling locations fall in the moderate contamination while 55% of the samples fall in the high contamination range. All the samples from zone 2 fell under the high contamination category. While in zone 1, 60% samples come under moderate and 40% under high contamination level category. In zone 3, 76% and 24% samples were in the moderate and high contamination range, respectively.

Integrated contamination indices (Pc) of soil samples. Black and gray lines are the upper threshold values of moderate and low contamination, respectively

The effect of the glass industry on urban soil metal characterization was assessed at 25 test sites at Firozabad, India [ 29 ]. The area is characterized by little or no monitoring of industrial processes, usage and disposal of hazardous chemicals. A comprehensive profile of Zn, Mn, Co, Cd, Pb, Cr, Ni, Cu and As contamination was obtained. Zn, Cd, and As showed a greater accumulation in all soils, whereas, accumulation of Ni and Cu was high in limited samples. Integrated contamination indices (P c ) indicate that 60% of the sites were in the high contamination range and 28% were in the moderate contamination range with just 12% sites on the border of the moderate to low contamination range. [ 83 ] assessed the impact of both landuse and soil textures on Cd, Zn, Pb and Cu based on samples collected from the major landuse/landcover pattern of Dutch forests and aerable soils drawn from six different sites. Metal content in agricultural and industrial soil is found to be higher than the forest soil.

The fact that no P c value in the present investigation fell within the low contamination range was not surprising, given the fact that the study was being carried out in an area which has already been contaminated with metals, but moderate to high indices in zone 1 and 2 are alarming because these include heavily populated areas. The local populace is, thus, exposed to wide range of historically well established toxins and even carcinogens. The situation is surely compounded by vehicular pollution at urban sites (1-10). Vehicular emissions are a significant source of many pollutants [ 21 , 84 ].

6. Phytosociological studies

Plants show differing morpho-physiological responses to soil metal contamination. Most are sensitive to very low concentrations; others have developed tolerance, and a reduced number accumulate metals. The latter capacity has practically opened up the way to phytoextraction. Hyperaccumulation is an unusual occurrence, seen in a narrow range of species which often grow in metal-rich soils. The following thresholds for metal hyperaccumulation in shoots, without evident symptoms of toxicity, have been suggested [ 85 ]: 100 mg kg -1 for Cd, 1, 000 mg kg -1 for Ni, Cu, Co and Pb, and 10, 000 mg kg -1 for Zn and Mn. Known hyperaccumulators are generally minor vegetation components in most European and North American habitats. Currently, more than 400 hyperaccumulator species are known, belonging to 45 different botanical families, among which the most frequent are Brassicaceae and Fabaceae [ 86 ].

Lack of information on the agricultural management of hyperaccumulators, together with slow-growing and poor shoot and root growth, increase the difficulties in the practical application of these species in remediation projects [ 87 ]. Hence, the potential for any plant species to remediate successfully heavy metal contaminated sites depends on all of the following prerequisite factors: a) the amount of metals that can be accumulated by the candidate plant, b) the growth rate of the plant in question, and c) the planting density [ 88 ]. The growth rate of a plant in a chemically contaminated soil is important from the perspective of biomass. Parameters like basal area, canopy, abundance, dominance of species can help obtain a more rounded picture in the case of mixed planting or natural flora at a contaminated site. The rate of metal removal from the soils can be calculated if information on the above mentioned parameters is available. In addition, versatility of the candidate plant to tolerate and at the same time accumulate multiple metal contaminants and/or metal-organic mixtures would be an asset for any phytoremediation system.

The choice of plant species is thus, an important task in any phytoremediation based technique. Decontaminating a site in a reasonable number of harvests requires plants that are both high yielders of biomass and good metal accumulators by dry weight. It has been demonstrated [ 89 , 90 ] that, wild native plants may be better phytoremediators for waste lands than the known metal bioaccumulators like Thlaspi caerulescens and Alyssum bertolonii because the latter are slow growing with shallow root systems and low biomass. Also, the technology for their large-scale cultivation is not fully developed; therefore, their use is rather limited [ 91 ].

If soil at contaminated sites, e.g. mines, industrial zones is naturally high in a particular metal, native plants will often become adapted over time to the locally elevated levels [ 28 - 30 ] and metal toxicity issues do not generally arise. Successful establishment and colonization of several pioneer plant species tolerant to Pb/Zn mine spoils has also been demonstrated with tolerant plants including Phragmites australis, Vetiveria zizanioides, and Sesbania rostrata [ 31 , 92 ]. Many native, well adapted plants have been investigated and even used for heavy metal bioindicatoring and phytoremedial purposes including lemongrass and other wild grasses, vetiver, Sesbania , Avena , Crotalaria , Crinum asiaticum, Typha latifolia and Calotropis procera etc. [ 31 - 35 ]. Phytoremediation employing indigenous species can be an ecologically viable option for sustainable and cost-effective management.

An important component of any ecosystem is the species it contains. Species also serve as good indicators of the ecological condition of a system [ 93 ]. Ecological surveys are necessary for an adequate characterization of a plant community and also to know the diversity and dispersion status of species in the area. Phytosociology aims to characterize and classify plant communities in terms of composition and structure.

At all sampling sites within a zone, ecological indices [relative frequency, relative density, relative dominance and importance value index (IVI)] were estimated, by using a 1m 2 quadrat. Sampling was done randomly at 10 spots at each site within a zone. The data were compiled and analysed according to some workers [ 94 - 96 ].

Relative density is the proportion of density of a species (plants/unit area) to that of the stand as a whole. The dispersion of species in relation to that of all the species is termed as relative frequency of a species. Relative dominance is the proportion of the basal area of a species to the sum of the basal area of all species present. Basal area refers to area covered by the plant’s stem and leaves one inch above the ground surface. The overall picture of ecological importance of a species in relation to the community structure can be obtained by adding the values of the above three parameters [ 97 ].

A total of 22 weed species were recorded from the sites ( Table 9) . Most of the weeds recorded are herbs except Calotropis procera and Datura stramonium which are shrubby in nature. Two grasses i.e. P. annua and C. dactylon were observed. The phytosociological parameters obtained from the sites clearly indicate that there are naturally occurring plant species which have the capacity to tolerate the heavy metal content of the soils. The floral composition of the three zones varied qualitatively and quantitatively. Most species were seen to grow vigorously. Relative frequency, relative density, relative dominace and IVI indicate that Calotropis procera, Parthenium hysterophorus, Chenopodium murale, Croton bonplandianum, Rumex dentatus, Amaranthus spinosus, Datura stramonium and Withania somnifera were the most abundant weeds. All of these species have been reported as potential phytoremediators in earlier studies. It is important to note that floral diversity decreased with increasing contamination profile of the sites. Maximum species (20) were observed in zone 3, followed by zones 1 and 2.

Phytosociological parameters of flora at test sites

IVI- Importance Value Index

C. procera has been demonstrated as a potential phytoremediator species. The shrub showed good accumulation of metals and is a potential phytoextractor for As and Zn as well as a promising phytostabiliser for Pb, Cd, Cu and Mn [ 28 , 29 , 35 ]. C. procera was observed to have a high degree of sociability i.e. relative frequency, relative density, relative dominance and IVI. P. hysterophorus was also important in this context and was most dominant in zone 2. This species has been identified for As phytoextraction along with A. spinosus , C. bonplandianum, and D. stramonium [ 28 ] . The latter two have also been indicated for phytoextraction— C. bonplandianum for Mn and D. stramonium for Mn, Cr, and Cu—together with R. dentatus for Pb. Another species with high IVI, C. murale has been suggested for Zn, Cd, Pb and Cu phytoextraction [ 28 , 29 ]. Among the less dominant species, Tridex procumbens and Euphorbia hirrta have also been reported as promising tools for phytoextraction of Mn and As, respectively [ 28 ]. E. hirrta and D. stramonium were not found in zone 2.

Poa annua has been identified as a phytostabilizer for Mn, Cd, and As and phytoextractor for Cu and Pb. Cu concentrations up to 742.06 mg kg -1 dry weight have been reported in P. annua shoots [ 28 , 29 ]. Poa annua was observed only at sites in zone 1.

Other species found at the sites have also been indicated for further studies following initial field surveys. Gnaphalium luteo-album (Mn and As); Withania somnifera (Cu); and Heliotropium ellipticum (As) have shown promise as phytostabilisers for these metals and metal combinations [ 28 , 29 ].

7. Discussion

The occurrence as well as concentrations of heavy metals like Pb, Zn, Cu, Co, Mn, Fe, Cr and Cd in streams and rivers all over the world is increasing. In the present case study, heavy metal contamination was consistently higher in city of Agra, which may be attributed to the heavy industrialization combined with agricultural and urban runoff. The situation is made worse by atmospheric deposition, again attributable to industrial and vehicular pollution. In general, freshwater ecosystems have low natural background metal levels and therefore tend to be sensitive to even small additions of most trace metals. The river water far exceeded the limits of metals prescribed by WHO and USEPA for drinking water standards and Pb, Cd, and Cr content at all sites and Ni at most sites exceeded the prescribed limits. In a heavily populated country like India where a sizeable portion of the population is illiterate and resides in slums/poorly planned neighbourhoods without proper sanitation and drainage, day-to-day activities also contribute to the overall pollution load. Provision of suitable alternatives along with proper education and awareness is integral to the minimization of this problem at the source. Apart from taking measures like effluent treatment before it enters the river and subsequent treatment of river water at the most polluted sites, a steady flow of water is to be ensured throughout the year, by way of channelizing the river with canals at crucial points. Such measures can address this problem to a substantial extent. Expenditure of more than US$ 500 million without much success appears to be an unjustified proposition.

Phytoremediation has been receiving attention lately as an innovative, cost-effective alternative to the otherwise tedious and expensive methods in use, which are not only a burden on the exchequer but also, require efforts on a recurring basis. Lack of information on the agricultural management of hyperaccumulator species, together with their poor biomass and root proliferation, increases the difficulties in their practical application. It has been amply demonstrated that wild native plants may be better phytoremediating tools. These species can be an ecologically viable option for sustainable and cost-effective management especially in scenarios where expertise, technical expertise and/or funding is a limiting factor. Ecological surveys are necessary for adequate characterization of a plant community and subsequent identification of prospective candidates for phytoremedial strategies since metal toxicity issues generally do not arise in plants already established on contaminated soils. Allowing native species to remediate site is an attractive proposition since these species do not require frequent irrigation, fertilizers, and pesticide treatments, while simultaneously a plant community comparable to that existing in the vicinity can be established. The outcome is, thus site remediation, ecological restoration and addition in aesthetic value. This is also in concurrence with the ruling (2006) of the Hon’ble Supreme Court of India prohibiting cultivation of plants requiring fertilizers and pesticides along the river Yamuna. Using these perennial phytoremedial candidates without any special needs holds much promise in this context. In addition, versatility of the candidate plant to tolerate and at the same time accumulate multiple metal contaminants and/or metal-organic mixtures would be an asset for any phytoremediation strategy.

Acknowledgments

Financial support from University Grants Commission [F. no. 35-47/2008(SR)] is gratefully acknowledged. This study was partially supported by the European Fund for Economic and Regional Development (FEDER) through the Program Operational Factors of Competitiveness (COMPETE) and National Funds through the Portuguese Foundation for Science and Technology (PEST-C/MAR/UI 0284/2011, FCOMP 01 0124 FEDER 022689.

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Supporting India’s Farmers To Regenerate the Soil

• Masha Hamilton — Editor/Writer, The Rockefeller Foundation

In 2016, Vikash Abraham abandoned his work as a corporate engineer and IT security specialist and discovered his dharma.

His life’s purpose was to be part of a movement to, as he puts it, rethink agriculture back into nature’s cycles for the good of farmers, consumers, and the soil itself.

Now fluent in the worries and joys of farmers from India’s cities to forests, he is Chief Strategy Officer for Naandi Foundation . His focus is on helping develop innovative ways to bring regenerative and profitable agriculture to a country of 1.417 billion people with a poverty rate of about 16.4 percent where farmers have worked hard to alleviate hunger but struggle themselves to earn a living.

Naandi, founded in 1998 and based in Hyderabad, works in 17 states across India with the overarching goal of eradicating poverty. Its three key agricultural goals are to heal degraded soil and provide consumers with nutritious food while ensuring farming is profitable for the farmers. The Rockefeller Foundation began supporting this work in 2020.

One of Naandi’s latest initiatives is Urban Farms Co. , focused on proactively helping farmers in their fight against depleted soil by creating organic compost that is provided to farm fields quickly and inexpensively, while lining up markets for the farmers’ produce.

The nonprofit has helped about 150,000 farmers convert to regenerative agriculture practices.

Given that there are an estimated 800 million farmers in India—more farmers per capita than any country on the globe—“there is a long way to go,” Abraham acknowledges. But the movement toward sustainable farming practices—both for philosophical and practical reasons—is gaining speed. Eventually it will take off, he says, “and I think we are at that time.”

Topsoil Linked to Global Food Security

The Food and Agriculture Organization of the United Nations, which marks an annual World Soil Day on Dec. 5, says 95 percent of food eaten across the globe comes from the soil, but about 35 percent of the earth’s soils are already degraded, and 90 percent could become degraded by 2050 unless steps are taken to reverse the impacts of erosion and unsustainable agriculture practices.

(Video courtesy of Naandi Foundation)

The impact of soil degradation could total $23 trillion in losses of food, ecosystem services and income worldwide by 2050 unless land resource management practices are changed, the United Nations Convention to Combat Desertification says.

Conventional farming “is a losing proposition because the cost of cultivation is so high that the farmers spend more than they earn, and at the other end of the growing season, they don’t have good market linkages,” says Naandi’s Chief Policy Officer Rohini Mukherjee.

Conventional farming operates in part on the theory that plants get their nutrition through water-soluble chemical fertilizers. So, farmers must pay for that input each season, and conventional farmers view weeds as competing for those nutrients.

In regenerative farming, practices are based on the knowledge that plants get their nutrition through biological cycles—and the practices that renew soils can renew the very communities that tend to the land.

Thus, cover crops are valued because, through photosynthesis, they feed the soil, while also protecting it from erosion. This also offers protection from the loss of topsoil.

While large scale conventional farming has contributed to a loss of valuable topsoil, sustainability practices such as cover crops, no-till, biodiversity, crop rotation and more can restore depleted soil over time.

But when soil is severely weakened, and speed is important, additional help is needed. This is an area where Naandi is transforming the landscape.

Convenience, Cost and Results Prioritize

For farmers to change, Abraham says, three conditions must be met:

• The new approach must be convenient.
• The results must be quick.
• The financial return must at least equal what the farmer earned before transitioning.

“The farmers know better than us how depleted the soil is,” Abraham says. “But they will continue to use chemical fertilizers if it is most convenient. If we say, you have to dig a hole in the back of your garden, create a compost system, do a lot of extra work, wait three months and then carry the composted soil kilometers away to get more nutritious crops in time, they aren’t going to do it.”

It’s also critical that the farmers see near immediate results, including in their bottom line, he notes.

“In India, many farmers get their livelihood from a single acre of land. So, from Day One of converting to regenerative farming, the field has to grow the same yield and make a profit,” Abraham says. “We knew we needed to develop a model to address this challenge.”

A Topsoil Recipe to Kickstart Biology

The first step to developing that model was to devise a scalable way to make and distribute organic compost. Naandi began by creating centralized hubs to serve about 200 acres of land at once.

Step Two: They set out to create compost material that could immediately improve soil quality, combining organic matter from multiple sources. Naandi collects paddy crop residue, which is typically burned—so this practice also reduces air pollution. Then they buy cow dung from gaushalas , or shelters to care for old cows, as cows are sacred in India. Finally, they clear public land of weeds for free, gathering biodiverse green material with various micronutrients.

Step Three: These ingredients are used to create a recipe and, under watchful eyes, is turned into compost. “We have shredders, turners and a team dedicated to monitoring the temperature and aerating the mixture,” says Abraham. “We convert this into very, very high-quality organic fertilizers.”

Step Four is simply that the farmer calls the hub and Naandi supplies the topsoil.

“You can think of it like a foundation that a house is built on,” Abraham says. “When land is devoid of the biology it needs, we add a ten-ton foundation of compost. So, we immediately create the top layer of soil with the right nutrients, and that kickstarts biology. When convenience comes, people are willing to change.”

In fact, not only soil, but “seeds, saplings—the farmer can get all nature of supplies from the hub, and we also find them markets for what they grow.”

Naandi also identifies markets for the farmers, so they can focus on growing. “We supply 10 to 12 tons of vegetables every day to most of the large supermarkets and online markets in the Delhi region, and this is growing,” Abraham says.

Coffee Plants Thrive on Enriched Soil

Naandi supports farmers growing in three types of geographies: urban, rural and tribal. In the tribal areas, where Indigenous farmers are growing coffee in a forest environment, Naandi’s afforestation work is funded by investors who are interested  carbon credits  and the potential of carbon sequestration achieved through tree planting.

Naandi’s work began, in fact, with remote tribal communities in the Araku region of southern India nestled in the Eastern Ghats, where farmers were supported from seed to cup in growing world-class coffee in their fields.

As part of that regenerative effort, Naandi has planted 30 million trees in and around about 1,000 villages, pulling carbon into the soil and saving a forest that was showing clear signs of depletion.

As the soil became richer and the valley lusher, the coffee notes became more complex. In 2018, Araku Coffee won the prestigious Prix Epicures gold medal, recognizing it as one of the world’s best coffees.

Naandi dubbed its approach “ Arakunomics ” – an integrated economic model to ensure profits for farmers and quality for consumers through regenerative agriculture. For its work in Araku and vision of the future, The Rockefeller Foundation awarded Naandi as one of 10 “visionaries” in the Food System Vision 2050 Prize , culled from more than 1,300 submissions.

Naandi puts on an annual celebration called Gems of Araku , when international jurors select a winning cup of coffee made from freshly roasted beans in what is called a cupping session, and it is announced in Araku, where farmers and their families have gathered for a day of festivities.

Abraham describes being there a few years ago when the best cup was announced. He watched the tribal farmer whose land generated the winning cup walk up with his family to receive the award.

The farmer was asked, ‘now that you have won the best cup of coffee in the world, what is your aspiration?’ He answered, “I want everyone in my village to be able to produce the best cup of coffee also.’ That sense of community really touched me. I think it’s the spirit we should build on.

Abraham had no background in farming when he began working with Naandi. He was immersed in the corporate world. A course in agriculture as a hobby started him on another path. “This has been the most beautiful journey,” he says. “I’m very clear about what I’m doing with my life now.”

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Chapter 3. Sources of soil pollution

Sources of soil pollution and major contaminants in industrial and transport areas.

Industrial processes including mining and manufacturing historically have been leading causes of soil pollution. Industrial areas typically have much higher levels of trace elements and organic contaminants. This is due to intentional and unintentional releases from industrial processes directly into the environment, including to the soil, adjacent water bodies, and the atmosphere (Salles et al. , 2016; Ajmone-Marsan and Biasioli, 2010; Biasioli and Ajmone-Marsan, 2007).

Many responsible industrial companies attempt to mitigate the risks of their operations impacting on the environment and public health. Many countries have well-enforced legislation to control the industrial operations and the environmentally sound management of their emissions and wastes. The concept of using Best Available Techniques in mining, manufacturing, recycling and disposal is incorporated in many national legal frameworks. International bodies, such as UNEP, UNIDO, and the Chemical Conventions, and industry associations set standards and provide guidance to improve the safety and sustainability of each sector and minimize its impact on the environment and public health. Nevertheless, there are still current industrial operations that routinely contribute to soil pollution, especially in LMICs. Industrial accidents are also a major source of pollution. There are also legacy issues of abandoned industrial sites, historical long-term industrial pollution, and waste disposal sites that were not managed in an environmentally sound manner. These all continue to pollute soil.

Global industrial output is expected to continue to grow as is illustrated by the chemical sector. From 2000 to 2017 the global annual production of chemicals doubled to approximately 2.3 billion tonnes (Cayuela and Hagan, 2019). The majority of the chemicals were petroleum compounds, special chemicals and polymers which represent 26 percent, 27 percent and 22 percent by value (CEFIC, 2017). The use of chemicals, other than pharmaceuticals, is projected to increase by 85 percent by 2030, with China and the European Union remaining the largest consumers ( Figure 16 ). In 2011, world sales of chemicals were estimated at USD 3 500 billion, equivalent to USD 500 per year for every man, woman, and child in the world (CEFIC, 2017). Although anthropogenic chemicals have delivered enormous benefits to human civilization, these are offset by large-scale negative impacts, resulting from unintentional human and environmental exposure and toxicity.

Figure 16. Projected growth in world chemicals sales (2016 – 2030) (a–b). Chemicals exclude pharmaceuticals.

The main sources of soil pollution from industrial sources can be divided into the following categories: 1) mining and quarrying; 2) manufacture; 3) energy production; 4) construction facilities; and 5) transportation.

3.5.1. Mining, quarrying and oil extraction activities

Mining activities have been occurring for thousands of years. Mining is a potential major source of trace elements, not just from the mining operation itself, but mostly due to wastes and emissions during the processing of the extracted materials such as tailings, waste rock deposits and smelting operations (Mwesigye et al. , 2016; Odumo et al. , 2014a; Rodríguez Martín et al. , 2014). Responsible mining and mineral processing organizations attempt to mitigate the risks of their operations impacting on the environment and public health. Amongst other organizations, the International Council of Mining and Metals sets standards and provide guidance to improve the safety and sustainability of the industry and minimize its impact on the environment (International Council on Mining and Metals, 2020). Nevertheless, there are current and historic mining and metal processing operations that still contribute to soil pollution, especially in LMICs.

Many rocks are naturally rich in trace elements (Committee on Sources of Lead Contamination at or near Superfund Sites et al. , 2017), which are mobilized when extracting them from the ore reservoirs. Mining wastes still contain trace elements, but in concentrations at which it is not cost-effective to extract them, but which may still pose a risk to the environment and human health. In some instances, the use of chemicals to separate the desired resource is required, what generates large quantities of chemically enriched waste (including cyanide solutions) in precious metal extraction.

One of the major risks stem from tailings which are liquid slurries made of water and fine mineral particles that are created when mined ore is crushed, ground and processed. Tailings are collected in settling ponds, which are often constructed on site by means of a dam. The water is treated and recycled or discharged, and the solids allowed to dry out. Tailings contain the unwanted and residual trace elements of the ore enrichment process. The main pathways for soil pollution are cases where the tailings dam fails or from wind erosion that disperses the fine mineral particles from the surface unless it is adequately covered with vegetation or a capping material. This can lead to the pollution of areas at long distances from the source (Kandemir and Ankara, 2015; Karaca, Cameselle and Reddy, 2018). Rico et al. (2008) gathered information about 147 ruptures of tailing dams worldwide, pointing out that most of these accidents occurred due to a lack of maintenance during operation. Examples include accidents in Aznalcollar, Spain in 1998 (Simón et al. , 1999), Baia Mare, Romania in 2000 and in 2015 in Brazil (Hatje et al. , 2017; Queiroz et al. , 2018). These accidents released toxic waste rich in arsenic, cadmium, copper, lead and zinc that accumulated in soils and reached surface waters. Soil pollution from trace elements can also occur from leaching and wind erosion of deposits of ore and rock waste. Where mining wastes that contain reduced sulphur minerals, such as pyrites, are exposed to oxygen and water, there is the potential for the formation of acid mine drainage (AMD). The acidity enhances metal solubility from other minerals containing sulphides, gangue silicates and carbonate materials. The result is the formation of large volumes of highly acidic wastewaters containing high concentrations of sulphates, iron, and trace elements that in the event of a spillage could lead to the pollution of water bodies, groundwater and subsequent transfer to soil (Akcil and Koldas, 2006; Ribeiro et al. , 2013).

Spillages during the transfer and transport of ore concentrates to the smelter is another potential source of soil pollution. Particulate and gaseous emissions from a smelter that lacks appropriate abatement technologies is a local and distant source of trace elements pollution of soils (Ettler, 2016; Feisthauer et al. , 2006; He et al. , 2019; MacDonald et al. , 2003). Ore concentrates shipped to smelters can also be a regionally localized source of trace elements (Renoux et al. , 2013).

According to FAO and ITPS (2015a), the exploitation of coal, gold, uranium, wolfram/tungsten, tin, platinoids, and polymetallic sulphides caused the most severe cases of soil pollution whenever mining is carried out. Pollution of soil from trace elements at sites surrounding coal mines were reported to be the highest in Barapukuria in Bangladesh, Ledo in India, Ptolemais-Amynteon in Greece, and the Tibagi River in Brazil compared to all analysed sites (Sahoo, Equeenuddin and Powell, 2016). Gold mining operations can cause emissions of mercury, cyanide, arsenic, zinc, lead, nickel and other toxic elements (AMAP and UNEP, 2019; Fashola, Ngole-Jeme and Babalola, 2016; Gold.info, 2013; de Lacerda, 2003a; Odumo et al. , 2014b). Mercury is primarily used for the extraction of gold, being released together with the mining waste in tailings, from which is volatilized or enter the surrounding soils and groundwater. From the late 1980s and early 1990s, artisanal gold mining in the Amazon basin is estimated to have caused the release of 4 000 tonnes of mercury (de Lacerda, 2003b). The latest global inventory of mercury emissions estimates that mercury content of organic soils is about 150 000 tonnes due to anthropogenic activities, reaching 800 000 tonnes in mineral soils, of which up to 15 percent correspond to releases from small-scale gold mining mainly in South America and East and Southeast Asia ( Figure 17 ) (UNEP, 2019a). Large-scale gold mining is responsible for some 2 700 tonnes of mercury entering the soil each year (UNEP, 2019a).

Figure 17. Mercury emissions to air from artisanal and small-scale gold mining by region.

Uranium mining and extraction continue to produce large quantities of radioactive waste worldwide. In 2006 according to Abdelouas (2006), the global volume of uranium mill tailing was 938 million cubic metres, which contains high concentrations of trace elements and radionuclides. Mining waste is enriched in natural radionuclides and their decay by-products, such as 40 K, 232 Th, 235 U, and 238 U (Smičiklas and Šljivić-Ivanović, 2016). The issues associated with mining of phosphorus minerals is discussed in Section 3.3.2 on mineral fertilizers.

Mining sites represent a continued potential source of pollution after activities at the sites have been completed. Without appropriate long-term maintenance tailing dams and rock waste deposits can be subject to weathering, water and wind erosion that continue to disperse the contaminants onto the surrounding soils. For example, significant levels of lead and zinc linked to carbonates and occluded in readily reducible manganese and iron oxides have been found in the soils and mining waste of an abandoned mining areas in the lead district of Alto Moulouya, Morocco, which can be easily transported by erosion to nearby soils (Iavazzo et al. , 2012).

3.5.2. Manufacturing and recycling industries

The contaminants associated with manufacturing industry will vary with the product produced and the manufacturing process involved. Several examples are presented below to provide an idea of the type of contaminants that occur, the impact on the environment and human health, and the importance of their proper management.

Agrochemicals

The crop protection industry has continuously grown in past decades (Nishimoto, 2019). In most developed countries agrochemical manufacture is highly regulated and controlled to minimise its impact. The manufacturing processes tend to generate significant quantities of emissions and wastes that need to be managed in an environmentally sound manner using best available techniques. In less well-regulated countries these emissions and wastes continue to pose a threat to soil health.

The pesticide manufacturing industry has left a legacy of hazardous waste produced as by-products in the manufacturing process. The organochlorine pesticide industry is linked to the presence of highly toxic organic contaminants such as 1, 2, 3, 4, 5, 6-hexachlorocyclohexane (HCH), DDT and chlordane among others (Cong et al. , 2010; Zhang et al. , 2009). Many of these pesticides have been banned due to their environmental persistence and their carcinogenic and/or neurotoxic potential. However, residues remain in soils surrounding manufacturing and application areas (Die et al. , 2015). An example of these legacy issues is the production of the organochlorine pesticide lindane, the gamma isomer of hexachlorocyclohexane, historically one of the most widely used insecticides in the world. The manufacturing process is extremely inefficient, producing about 6-10 tonnes of by-products, mainly the alpha and beta HCH, for every tonne of active lindane (Vijgen et al. , 2011). These by-products have similar toxicity and environmental impacts as lindane, being persistent and bio-accumulative, and were listed, along with lindane, as a POP in the Stockholm Convention in 2017. The production of lindane has been banned and only pharmaceutical use against head lice and scabies is allowed (Stockholm Convention, 2021). By-products of lindane production were accumulated in open stockpiles and landfill sites, some with limited containment measures that have caused severe pollution problems ( Figure 18 ) (Abhilash and Singh, 2008; Jit et al. , 2011; Torres et al. , 2013; Tripathi et al. , 2019b; Vijgen et al. , 2018, 2019). In addition, Amirova and Weber (2015) reported severe pollution caused by polychlorinated dibenzodioxins and furans (PCDD/Fs) in a former organochlorine pesticide production facility in the Russian Federation. Similarly, large amounts of PCDD/Fs have been disposed from a pesticide factory in Hamburg, Germany (Götz, Sokollek and Weber, 2013) and Switzerland (Forter and Rheingasse, 2006).

Figure 18. Piezometer P91.03 of the Gouhenans lindane deposit, France. ©Alexandre Bourgeois (via Wikimedia Commons, CC BY-SA 4.0)

Lead Acid Battery recycling

The manufacturing and recycling of lead-acid batteries (LAB) in many developing countries does not operate with Best Available Techniques (BAT) and best environmental practice (BEP), and is an important source of lead pollution and human exposure. Today, most LAB are manufactured, used and recycled in LMICs. Pollution occurs during both the production and recycling of LAB when facilities lack proper pollution control, personal protective equipment and proper regulatory oversight, leading to emission of lead into the environment (van der Kuijp, Huang and Cherry, 2013a; Manhart et al. , 2016; UNEP, 2010). The manufacturing of LAB consumes about 85 percent of lead worldwide and is a growing market in Asian developing countries (Future Market Insights, 2018; ILA, 2019), especially in China and India. because of the rapid development of the industries that use LAB such as electric bikes, motor vehicles, photovoltaic (PV) devices, uninterruptible power supplies, telecommunications technologies, and electric power systems (Gottesfeld and Pokhrel, 2011; van der Kuijp, Huang and Cherry, 2013a). China is the world’s largest producer, refiner and consumer of lead, with more than 1.92 million tonnes per year devoted to producing LABs (van der Kuijp, Huang and Cherry, 2013a). Chen et al. (2010) observed how the production of LAB generated and released fine lead dust through atmospheric dispersion resulting in deposition on soil and tree leaves. The increase in LAB demand has required an increase in primary lead production from mines and its recycling, which contributes to approximately 80 percent of lead usage worldwide (van der Kuijp, Huang and Cherry, 2013b).

The informal recycling of used LAB is a significant source of lead in soil and threatens human health and the environment (Pure Earth, 2016; WHO, 2017b). At a typical informal recycler, the plastic box that holds the battery components is broken open with a hand axe or machete and the sulphuric acid solution inside is dumped on the ground or in a storm drain. The Pb plates are removed and placed in a hole in the ground about 30 centimetres deep. The hole is filled with charcoal and ignited. The molten lead is then ladled into ingot moulds, cooled, and sold back to battery manufacturers. In the informal sector, the process is typically conducted with no pollution control equipment or regulatory oversight. Informal and substandard LAB recycling results in large volumes of lead-contaminated waste, lead fumes and lead dust, which migrate from the recycling site into nearby communities through atmospheric deposition, wind, flooding, storm water runoff, on automobile tires, and on the clothes and hair of workers (Pure Earth, 2019a). The Toxic Sites Identification Program, run by the non-profit organization Pure Earth, has identified and assessed more than 1 250 sites in LMICs where soils are contaminated with lead (Pure Earth, 2019b). Of these sites, more than half are contaminated from the informal recycling of LAB, often in urban or suburban residential areas. A 2016 study of the prevalence of lead pollution from informal battery recycling sites estimates that there are between 10 599 and 29 241 such recycling sites across 90 LMICs (Ericson et al. , 2016).

Copper smelters and steel plants release PCDD/Fs which has resulted in pollution of soils and cattle in the surrounding with restriction of grazing up to 20 km from the industry (Esposito et al. , 2014; Weber et al. , 2018a)

Approximately 63.2 million tonnes of aluminium were produced worldwide in 2017, and global production is increasing due to continuing strong demand driven by trends towards lightweight buildings (European Aluminium, 2016). The emissions and wastes produced in aluminium extraction and production processes pose major threats to the environment when not managed appropriately. The aluminium industry has three main steps: mining of bauxite, refining of bauxite to alumina (Al 2 O 3 ) and the smelting of alumina to produce aluminium (OECD, 2012).

The main environmental risks of aluminium production are from solid waste arising during refining, and emissions to atmosphere during smelting. The Bayer refining process produces about 2-2.5 tonnes of red mud for each tonne of aluminium produced. The storage of red muds in large quantities poses an environmental threat for the population in the vicinity, because of its alkaline nature, but also a high economic cost because of maintenance requirements. Red mud is a mixture of oxides of iron (which is responsible for its colour), aluminium, titanium, trace elements and fluorine compounds. As discussed in section 3.5.1 on mining, the failure of tailings dams is a major risk for soil pollution. The failure of a dam at the Ajka aluminium mining operation released about 100 thousand cubic metres of red mud into the surrounding environment (Muravyeva and Bebeshko, 2014; Sahu and Patel, 2016; US EPA, 2017b). Smelting operations with inappropriate emission abatement and wastewater treatment can release fluorine compounds to atmosphere as gases and particulates and in the aqueous discharges. The fluoride released in the wastewaters which can cause serious negative effects to the surrounding environment and to human health (Arshad and Eid, 2018; Martin and Larivière, 2014; Melidis, 2015). An association was found between high levels of SO 2 and fluorides in children with bronchial hyper-responsiveness in an aluminium smelter town Årdal in Norway (Søyseth et al. , 1995).

Textile manufacture

The textile industry may also release dangerous substances in effluents. Large volumes of wastewater are produced in the dyeing and finishing process. Improperly treated wastewater contains trace elements, including arsenic, cadmium, cobalt, copper, lead, mercury and nickel, dyestuffs, cellulose, polyvinyl alcohol, surfactants and high chemical and biological oxygen demand (Adeel et al. , 2015; Bouatay et al. , 2016; Panigrahi and Sharma, 2014; Saeed et al. , 2016; Sivaram, Gopal and Barik, 2019)). Until its listing in the Stockholm convention, PFAS was used in the textile industry to provide waterproofing and stain resistance to fabrics (RISE, 2019). The major risk for soil pollution is spillage of untreated effluents or the use of polluted wastewater for irrigation.

Leather manufacture

Leather manufacture and tanneries produce large amounts of solid and liquid by-products that are responsible for significant pollution of soil and water, especially in developing countries. The tanning process involves a transformation of the skin to hide through the use of different chemicals followed by a second process that converts hide to leather with trivalent chromium compounds or tannins, mineral salts and colours (Alvarez-Bernal et al. , 2006). The untreated effluents from tanning industries contain a high concentration of contaminants including chromium compounds, dyes, chlorides, dissolved solids, nitrogen and suspended solids (Bosnic, Buljan and Daniels, 2000; Ramasamy and Naidu, 1998). The tanning process can oxidize trivalent chromium to its much more toxic hexavalent state (Fuck et al. , 2011). Many cases of chromium pollution reported for water bodies and soils are due to the tannery process. Tannery effluents are highly enriched in chromium, which if not properly removed from the effluent can end up in neighbouring water bodies and soils (Nur-E-Alam et al. , 2020). A study of the soil in Dhaka, Bangladesh, surrounding a tannery plant observed an accumulation of trivalent chromium at 28 000 mg/kg at 1 km distance from the waste disposal area, and an irregular distribution of hexavalent chromium, reaching 1 mg/kg, with other trace elements in the soil subsurface. Furthermore chromium was found bound to the clay minerals in the soil (Shams et al. , 2009). The risk of soil pollution by tanning effluents may occur indirectly with the irrigation of soils from water bodies contaminated with the effluents (Alvarez-Bernal et al. , 2006). Naidansuren et al. (2017) studied a 55 ha area surrounding tanneries in the capital of Mongolia, Ulaanbaatar, and identified that 12.4 ha had chromium levels that posed a health risk for the population living and working in the area.

Speciality Chemical and Pharmaceutical Manufacture

The production of polychlorinated biphenyls was banned when the Stockholm Convention came into force in 2004. However manufacturing sites have been found polluted up to a distance of 70 km, affecting local populations (Turrio-Baldassarri et al. , 2009; Wimmerová et al. , 2015). Similarly, pollution of soils and the environment is observed around production sites of chlorinated paraffins which have substituted PCBs in many uses (Guida, Capella and Weber, 2020; UNEP, 2019c). Pharmaceutical industries are responsible for pollution due to releases into the environment of substances containing active pharmaceutical ingredients (APIs) and other related chemical substances via atmospheric emissions, effluents and solid wastes. The release of antimicrobials and by-products of antimicrobial production into the environment are a major concern for the development of antimicrobial resistance (Yakubu, 2017) which has been discussed in detail in section 3.3.4 . China and India are the countries where most of the APIs are manufactured and are reported to have extensive point-source pollution with APIs and the development of drug resistance (Arshad and Eid, 2018; Lübbert et al. , 2017; Maghear and Milkowska, 2018).

PFASs manufacture

Perfluoroalkyl Substances (PFASs) have been widely used in industrial and consumer goods to make heat-resistant, oil and water-repelling, and stain-resistant products since the 1940s (National Academies of Sciences, Engineering, and Medicine; Division on Earth and Life Studies; Environmental Health Matters Initiative, 2020). PFASs are highly persistent in the environment and can bio-accumulate (McCarthy, Kappleman and DiGuiseppi, 2017) and a range of negative health effects have been reported worldwide (Sunderland et al. , 2019). Due to the hazard they pose to environmental and human health, global phase-out initiatives of the original long-chain compounds, such as perfluoroalkyl sulphonic acids (PFSAs) and perfluoroalkyl carboxylic acids (PFCAs), which include PFOS and PFOA (Land et al. , 2018), has caused a shift toward the manufacture of new shorter-chain fluorinated compounds and non-fluorinated compounds, although the information on the risk of these compounds is still limited (ITRC, 2020; Wang et al. , 2013b).

The main sources of PFAS in the environment from manufacturing are spills, air emissions and inadequate disposal of manufacturing waste and wastewater, which have left widespread environmental contamination and pollution, not only in the water and soil around manufacturing industries, but also in remote areas, with significant concentrations of PFAS found even in remote areas of the Arctic (Boisvert, 2016; Skaar et al. , 2019). Brusseau, Anderson and Guo (2020) have reviewed data from around 1 400 locations around the globe, where PFAS concentrations have been measured, noting that PFAS concentrations ranged from 0.001 to 237 µg/kg in soils not directly affected by PFASs sources, so these can be considered as background values for global soils. In polluted areas consisting mainly in PFAS manufacturing areas and airports, the levels increase to a range from 0.4 to 460 000 μg/kg, with a median value of 8 722 μg/kg only for PFOS. In a study of a single PFAS manufacturing area in China, Jin and co-workers observed PFSAs and PFCAs concentrations in soils ranging from 0.10 − 2.34 µg/kg and 1.89 − 32.6 µg/kg, respectively (Jin et al. , 2015). Recent estimates of global loads of some PFAS in soils range from 1 500 to 9 000 tonnes, showing that soils constitute a global reservoir of these long-lived contaminants (Washington et al. , 2019), and that primary source sites, such as manufacturing areas, pose a serious risk to the environment and human health because concentrations are several orders of magnitude higher than background values (Brusseau, Anderson and Guo, 2020).

Food manufacturing

Even though food waste is generated over the whole food life cycle, from farm to fork, waste generated by food manufacturing represents a high percentage of the total waste. Examples of food waste generated during food manufacturing and processing are: milk spills during pasteurization and processing, edible fruit or grains classified as unsuitable for processing, or trimming of livestock during slaughter and industrial processing (Lipinski et al. , 2013), but also include those products that are contaminated and cannot be processed (Girotto, Alibardi and Cossu, 2015). To date, no overall estimates have been made of the value of food waste production by manufacturing industry (Mirabella, Castellani and Sala, 2014); attempts were made to estimate food waste at different stages of the life cycle for the EU27, where food waste from manufacturing and processing accounted for 39 percent (EC and BioIntelligence Services, 2010). Nevertheless, it seems to be widely accepted that food waste from the later stages of the food life cycle are higher in middle- and high-income countries than in low-income countries. Despite its potential role as source of energy, organic fertilizer or biosorbents to decontaminate wastewater (El-Sayed and El-Sayed, 2014), food waste can create environmental problems if improperly managed. The main soil contaminants associated with food residues are biological contaminants such as mycotoxins and pathogens (Rundberget, Skaar and Flåøyen, 2004), but other contaminants derived from processing can also be found, such as acrylamide, a neurotoxic and carcinogenic compound produced from sugar-rich foods cooked at high temperatures, PCDDs and PCDFs, or ethyl-carbamate in fermented food (Jha, 2015). Zhang et al. (2018) also reported the transfer of trace elements from machinery to tea during processing.

Food packaging and processing have been recognized as a localized pollution source of pesticides and biocides through the discharge of wastewater (Campos-Mañas et al. , 2019). Pesticide pollution of wastewater has two main origins: in fruit packaging plants, the rinsing of fruit to which fungicides had been applied to control infestations during storage; and rinsing fruits and vegetables that may retain residues of pesticides that were applied before harvesting (Karas et al. , 2016a, 2016b; Ponce-Robles et al. , 2017). Although in developed countries many agro-food industries include an on-site wastewater treatment plants or rely on neighbouring municipal wastewater treatment plants to remove the pesticides contaminants from the effluents, it has been observed that wastewater still contains high concentration of pesticides (Campos-Mañas et al. , 2019; Karas et al. , 2016b; Sutton et al. , 2019). In developing countries, where wastewater treatment plants are less efficient in removing contaminants due to less technological innovation, and which have weak regulatory frameworks that do not force the control of polluted effluent emissions, the environmental pollution situation caused by the agro-food industry is expected to be even more acute (Alemayehu, Asfaw and Tirfie, 2020; Faour-Klingbeil et al. , 2016; Trang, Jr and Song, 2019). Subsequent use of this water for irrigation provides a pathway for pollution of the soil with pesticides. In addition to the risk from the presence of the pesticides in the wastewater from agri-food industries, it is important to consider their transformation or breakdown products (Campos-Mañas et al. , 2019) because in some cases the transformation products are more toxic than the original pesticide (Lushchak et al. , 2018). The need to tackle the issue of point source pesticides pollution from agro-food industries is an urgent matter considering the expected growth of this market in the upcoming years.

Plastics manufacturing

The issues associated with post-use plastic waste have been addressed in the sections on agricultural plastics ( Section 3.3.5 ), rural waste ( Section 3.3.6 ) and municipal waste ( Section 3.4.6 ).

Plastics are widely used in practically all manufacturing industries as containers and packaging, and eventually end up as waste that needs to be managed in an environmentally sound manner. Although the contribution of plastic waste to the total amount of solid waste generated worldwide is only about 12 percent (data for the year 2016, (Kaza et al. , 2018)), it has a large impact on the environment and human health due to its chemical composition and virtually no biodegradation. Global plastic production has increased exponentially since the 1950s, but only about 30 percent of the total plastic produced in the early decades is still used. Of the plastic produced today, only 6 percent is recycled globally (Ritchie and Roser, 2018), so it is clear that plastic waste pose and will continue to pose a serious environmental risk. Plastics contain many additives to given them their resistance and flexible properties, such as plasticizers, flame retardants, foaming agents or thermal stabilizers among others (Hahladakis et al. , 2018), many of which are toxic to organisms (e.g. hexabromocyclododecane (HBCDD or HBCD), bisphenol A, phthalates, PCDDs and PCDFs and polybrominated diphenyl ether (PBDE)) (Bläsing and Amelung, 2018). Fuller and Gautam (2016) found that soil samples at a former chlorinated plastic factory in Sydney, Australia, contained about 6.7 percent chlorine-rich microplastics. Plastic waste management has a fundamental role in the release of contaminants into the environment, with special importance in LMIC, where improper dumping or open burning continue being the most widespread practices (Babayemi et al. , 2019; Kaza et al. , 2018). Ding et al. (2018) found that PCDD/Fs concentrations in soils where plastics had been burned were 97 times higher than the concentration in Shanghai agricultural soils, highlighting that this plastic waste management approach strongly contributes to soil pollution. Wan et al. (2016) also found high levels of flame retardants and plasticizers in soils in a plastic waste treatment site in Northern China, especially in areas where open dumping and burning of waste took place. In addition, plastics can retain other organic contaminants and trace elements (Velzeboer, Kwadijk and Koelmans, 2014), which increase in potential toxicity in terrestrial ecosystems.

3.5.3. Energy production industries

Global energy needs are mostly supplied by the combustion of fossil fuels (coal, natural gas and oil), which cover 65 percent of the world’s energy needs ( Figure 19 ).

Figure 19. Electricity production from different sources (percent of total).

Figure 20 shows the sources for electrical energy production between countries, grouped according to their economic development. High-income countries with long-established economies are reducing their reliance on coal and other fossil fuels and increasing use of renewable sources. Middle-income countries and countries with recently developed economies are still more reliant on fossil fuels. For example, China was highly dependent on coal consumption during its economic and social development (Li et al. , 2018a).

Figure 20. Contribution of different sources to total electricity production in 2015, aggregated by income groups.

Coal is by far the major source of energy. The World Coal Association reported that coal produces about 42 percent of the world’s electricity (WCA, 2017), with wide variations between countries, generally according to their economic development and how recently it took place.

Coal-based energy production generates a large volume of waste, including fly ash, bottom ash, boiler slag, and flue gas (Luther, 2010; US EPA, 1999). The coal industry has estimated that global coal waste amounted to 360 million tonnes in 2010 (Rowland, 2014). These wastes accumulate mainly in landfills and surface impoundment ponds, which often lack adequate containment measures, resulting in frequent leaching and exposure of materials to weathering and erosion (Harkness, Sulkin and Vengosh, 2016; Yenilmez et al. , 2011).

Coal fly ash, also called coal combustion residuals (CCRs), contains mostly silicon and aluminium, trace elements including arsenic, copper, mercury and selenium among others and organic contaminants, such as PAHs. The content of trace element contaminants varies depending on the type of coal, with high sulphur coal generally containing higher concentrations. The contaminants in piles of coal fly ash can migrate by leaching and erosion to pollute soil and groundwater. Examples of polluted soils around coal waste deposits have been reported worldwide (Alekseenko et al. , 2018; Askaer et al. , 2008; Bian et al. , 2009; Campos et al. , 2010; Liu et al. , 2012; Ribeiro et al. , 2013; Roe, Hopkins and Jackson, 2005; Tozsin, 2014; Yenilmez et al. , 2011). Concentrations of cadmium up to 43 times higher than background levels have been reported in soils surrounding a coal waste pile in central-eastern China. The pollution was predominantly in the direction of the prevailing winds through erosion and dispersal of particles of the fly ash (Bian et al. , 2009). Campos et al. (2010) observed high levels of trace elements in Brazilian soils, which had been mobilized by the acidic properties of the coal waste that led to a reduction in the microbial activity in soils. The release of trace elements from the waste into the soil, and their leaching into groundwater and absorption by plants has been observed even in cold environments, where microbial activity and chemical alteration of the wastes is expected to be limited (Askaer et al. , 2008).

Without appropriate abatement technology, mercury emissions to atmosphere, in its volatile form or associated with particles of fly ash ( Figure 21 ), are a major point source for soil and environmental pollution (Li et al. , 2017a). China is the largest mercury emitter in the world, with coal combustion being the major contributor (Zhang et al. , 2012c). Yang and Wang (2008) reported that soil, vegetable, and grain samples collected from field locations within 10 km distance from two Chinese coal-fired power plants had significantly higher mercury concentrations than controls and samples purchased from a grocery store away from any power plant. The upper limit of allowable mercury level in food was exceeded by 79 percent of vegetable samples and 67 percent of grain samples (Maximum Levels of Contaminants in Foods, GB 2762-2012). Mercury emissions from coal burning also represent a major source of global diffuse pollution due to the high mobility of mercury species, with South Africa, Mexico, India and Europe being the major emitters (Steenhuisen and Wilson, 2019).

Figure 21. Coal-fired power plants are important emitters of mercury, especially in East and South Asia, North America and EU28 (UNEP, 2019a). ©Benita Welter, from Pixabay.

Coal combustion is also responsible for releasing radioactive trace elements including uranium-238, the thorium-232 radionuclides decay series and potassium-40 in fly ash (Roper et al. , 2013). Overall, the radioactivity of coal fly ash depends on the type of coal used and the burning regime of the power stations (Temuujin et al. , 2019). Many studies have found that the leaching potential of trace elements and radionuclides from coal fly ash depends on the oxidizing conditions of the environment in which coal fly ash is stored and the containment measures put into place for its disposal. As coal combustion produces the largest waste in the world within the energy sector and energy production still mostly relies on it, precautions in handling coal fly ash waste are essential in order to avoid extensive soil and groundwater pollution (Schwartz et al. , 2018; Seki, Ogawa and Inoue, 2019; Temuujin et al. , 2019; Vengosh et al. , 2019; Verma, Madan and Hussain, 2016). The disposal of ash on lands and in ponds causes the dispersion of trace elements though leachates and erosion (Tiwari et al. , 2015), causing pollution not only of soil, but also of the surrounding surface and groundwater (Kim, Kazonich and Dahlberg, 2003; Lokeshappa and Dirkshit, 2012).

Oil and Gas

Petroleum hydrocarbon pollution of soil is a widespread global environmental concern. Crude oil and petroleum products including gasoline, diesel or lubricants can be released into the environment through accidents, managed spills, or as unintended by-products of industrial, commercial or private actions; causing local and diffuse pollution to the environment (Pinedo et al. , 2013). A 2006 study conducted by the European Environment Agency (EEA) showed that mineral oil was the main contaminant found in European contaminated sites, responsible for 34 percent of soil pollution. When the mineral oil group was extended to PAH and volatile aromatic hydrocarbons: benzene, toluene, ethylbenzene and xylenes (BTEX) the percentage increased to 53 percent (EEA, 2011). As a consequence of petroleum hydrocarbon spills, a series of changes occur with the chemical properties of the soil. Many of the components of petroleum, such as PAHs, are both phytotoxic and toxic to soil micro- and meso-organisms. They also have a range of biological effects including acute toxicity, carcinogenicity, mutagenicity, teratogenicity (Albers, 1995; Kennish, 1997), and endocrine disrupting activity (Clemons et al. , 1998). Petroleum spills can render soils hydrophobic, thus interfering with water movement in soil.

Oil and gas extraction through hydraulic fracturing (HF, fracking) has increased the potential for oil and gas resource extraction from low permeability rock. Water injected at high pressure contains approximately 1000 different chemicals used to facilitate the extraction. Following the injection, two types of wastewater are produced, called “flow-back” and “produced water” and both contain naturally occurring salts, radioactive materials, trace elements, other dissolved compounds, and oil components from the rock formation. The release of this wastewater through accidental spills onto the neighbouring environment exposes the soil to hundreds of heterogeneous chemicals some of which can potentially have detrimental effects on human health and the environment (Pichtel, 2016).

Nuclear power is considered a clean and affordable alternative to fossil fuels (IAEA, 2016) especially as a means to reduce greenhouse gas emissions (IAEA, 2019a; World Energy Council, 2016). However, nuclear energy accounted for only about 8 percent of total electricity production in 2015 worldwide (OECD and IEA, 2014), although nuclear power capacity is expected to grow by 10 to 30 percent by 2030 (IAEA, 2019b). In 2019, there were 53 reactors under construction, mostly in China, India and the Russian Federation. The countries that historically pioneered the development of nuclear power now tend towards other energy sources, especially renewables, for new power generation projects. The accident in 2011 at the Fukushima nuclear power plant triggered a halt on nuclear development for some countries.

The International Atomic Energy Agency (IAEA) has developed safety standards to mitigate the risks that nuclear power generation and radioactive waste pose to the environment and human health (IAEA, 2019c). Radioactive waste includes any gas, liquid or solid component that has acquired radioactivity during nuclear energy production due to its exposure to ionizing radiation, such as water used for cooling, metal containers, pipes, vents, etc. (US DOE, 1949). Nuclear wastes are enriched in uranium, thorium, cobalt-60, strontium-90, caesium-135, and technetium-99 and several trace elements, such as barium, cadmium, chromium, copper, nickel, lead, and zinc (Francis and Dodge, 1998).

The main soil pollution risks are associated with nuclear power come from aging and deterioration of the reactors and associated failures that may occur since most of the reactors are over 40 years old (Cooper, 2013), or from major accidents. Although the likelihood of an incident is low, its impact can be severe and widespread. Major radioactive pollution of the environment as a result of nuclear accidents are discussed in Section 3.5.6 : the most significant being the Fukushima Daiichi nuclear plant in Japan after an earthquake and tsunami in 2011 (Chino et al. , 2011) and the Chernobyl nuclear disaster in Ukraine (former USSR) in 1986. Volatile radionuclides of noble gases, krypton and xenon, as well as iodine, caesium and tellurium were released from both accidents causing the pollution of all environmental compartments, including soil (Nieder, Benbi and Reichl, 2018; Steinhauser, Brandl and Johnson, 2014). There are also risks of release during incidents with transport of ore concentrates, refining, transport of new and spent fuel rods and the storage of spent fuel rods and other radioactive wastes.

Renewables – non combustion technologies

Energy production from renewable technologies has been driven mostly by hydropower, however lately wind and solar photovoltaic (PV) have contributed to the increase in renewable energy production (EIA, 2016). Solar PV and other renewables depend on rare earth elements, and so their production and use may have environmental risks and constraints from the acquisition of those constituents. Solar powered electricity has seen an increase in use over time, especially in Europe and China, reaching one percent of electricity produced globally in 2015 (World Energy Council, 2016). An emerging concern, and under debate, is the potential pollution of soils from thin film photovoltaic modules. Leaching of modules containing lead, cadmium sulphide/cadmium telluride and copper in the form of copper indium gallium diselenide can occur where the glass is broken or from open edges. The quantities of trace elements leaching from the broken photovoltaic glass mostly depends on the pH of the water solution and time of exposure of the water with PV modules. Leaching of cadmium and lead occurs in neutral to acidic conditions, for example with rainwater, whereas tellurium leaching is not influenced by pH (Zapf-Gottwick et al. , 2015). Weckend, Wade and Heath (2016) , noted that considering that the average lifespan of PV panels is 30 years, and the global expansion in the use of this energy source, the amount of waste from these panels is expected to increase exponentially, from 8 million tonnes in 2030 to 78 million tonnes in 2050. Renewable energy production based on the non-combustion technologies of hydropower, wind turbines, geothermal and solar have minimal risk of soil pollution through their routine operations.

Renewables – combustion technologies

Power can also be generated through combustion of renewable rather than fossil fuels. The fuels include biosolids, biomass, landfill gas, anaerobic digestion gas, organic wastes and refuse. Power generation from these sources should be undertaken in accordance with Best Available Techniques to minimize dispersal of contaminants in the emissions to atmosphere, aqueous discharges and solid wastes. For example, without appropriate abatement systems, power generation using biomass that has originated from phytoremediation projects could be a mechanism to re-disperse the hyperaccumulated trace elements. However the sector is gaining importance and constantly improving technologies, leading to greater efficiency and lower environmental impact. There is no doubt that in the next decade these will represent a relevant alternative to fossil fuels given the growing interest and commitment of countries to reduce emissions. However, attention must be paid to the waste generated by these sources of energy and find the best way to process and recycle them (Xu et al. , 2018). Potential emissions from incineration plants have been discussed under the municipal wastes in Section 3.4.6 .

Organic waste from urban, agricultural and industrial sources can be converted into useful forms of energy such as hydrogen (biohydrogen), biogas, bio-alcohol, to refuse-derived fuel through waste-to-energy technologies. This has economic and environmental benefits by extracting value from waste and reducing the amount of waste going to landfills (Uçkun Kiran et al. , 2014). However, plants can have accidental emissions of CH 4 and NH 3 (Cheng and Hu, 2010; Dri et al. , 2018), which contribute to climate change, and sulphur dioxide and oxides of nitrogen that contribute to acidification of rain and hence soils. The digestate generated during the processing of organic waste to produce energy has an important value as a fertilizer, however it can produce eutrophication and acidification if not applied to agricultural soil correctly, reducing its potential commercial and environmental value (Dri et al. , 2018).

3.5.4. Construction industry

Cement manufacturing plants, if not properly controlled, can be a large source of contaminants through atmospheric emissions that include oxides of nitrogen, sulphur dioxide, carbon dioxide, organic compounds, PAHs and trace elements that adhere to airborne dust particles (Addo et al. , 2012; Mandal and Voutchkov, 2011; Ogunkunle and Fatoba, 2014; Schuhmacher, Domingo and Garreta, 2004). Raw materials represent the most important source of trace elements in cement production, potentially releasing significant amounts of cadmium, copper and zinc (Achternbosch et al. , 2003). Many cases of trace element pollution of soil from dust emissions from cement factories are reported in the literature. For instance, an analysis of soils near the Douroud cement factory in the Islamic Republic of Iran showed that the concentrations of trace elements were higher than the US EPA standards and the dominant wind direction was where the highest concentration of trace elements in topsoil occurred (Jafari et al. , 2019). Contamination of agricultural soils by trace element pollution in the vicinity of a cement factory ( Figure 22 ), and the transfer of the toxic elements into the food chain, was observed in a cassava cultivation close a cement factory in Nigeria (Adejoh, 2016).

Figure 22. Karaganda Cement Plant in Aktau village, Kazakhstan. ©Nikolay Olkhovoy (via Wikimedia Commons, CC BY 3.0)

The cement industry utilizes wastes as secondary fuels and raw materials to improve the economics of their operations. The use of these materials has to be managed and controlled careful to avoid impacting the quality of the cement and the emissions of the plant. In a case in Austria, the use of hexachlorobenzene (HCB) contaminated waste (for destruction) in a cement plant resulted in the release of HCB, and the pollution of approximately 320 farms in the vicinity with transference of contaminants to cattle, meat, milk and humans (Weber et al. , 2015). China is the main cement producer worldwide on the basis of installed capacity and production, with 2 331 mega tonnes of cement produced in 2017, followed by India and the United States of America (DBS HK, 2018; Edwards, 2017). Chapter 13 includes a case study where a cement kiln was used to remediate 400 000 tonnes of soil polluted with DDT in the space of 2 years.

The construction and demolition (C&D) sector is responsible for producing large quantities of waste every year, especially in developing economies due to their rapid economic growth (Turkyilmaz et al. , 2019; Yu et al. , 2018). In developed regions, C&D waste accounts for about 30 percent of the total waste stream (EC, 2019a; US EPA, 2016a). A mix of materials are used for construction, from inert materials such as soil, concrete and bricks to non-inert ones, such as steel, wires, cables, plastics, sealants, and insulation material. The non-inert materials are a potential pollution threat due to the substances contained such as asbestos, PCBs, brominated or chlorinated flame retardants, mercury, lead paint, plasticizers, and metal- and POPs-containing wood preservatives (Li et al. , 2016b; Llatas, 2011; Ritzen et al. , 2016; UNEP, 2017; Zheng et al. , 2017). Waste from the construction sector therefore pose a potential risk to the environment and human health. Staunton et al. (2014), reported that trace elements present in C&D waste were bio-accumulated in the terrestrial slug, Deroceras reticulatum (Mollusca: Gastropoda) used as a bio-indicator. Cattle have been contaminated with PCBs from C&D waste used for landscaping (Weber et al. , 2018b).

The type of activity historically carried out in the demolished building will also contribute to the presence of contaminants, as shown by Huang et al. (2016) , who found high levels of pesticides in the C&W waste from an abandoned pesticide manufacturing plant.

Of particular interest in C&D waste is the potential presence of asbestos. The issues of naturally occurring asbestos and the soil pollution that it can cause are discussed in section 3.2.3 . Similar soil pollution can occur in cases where C&D waste with asbestos pollution is disposed of inappropriately.

3.5.5. Transport

Vehicular traffic is responsible for the release into the environment of particulates, trace elements such as arsenic, cadmium, chromium, copper, lead, nickel and zinc, PAHs and road salts (Werkenthin, Kluge and Wessolek, 2014). These contaminants arise from a variety of sources and processes including: incomplete fuel combustion, oil leaking from engine and hydraulic systems, fuel additives, road and tyre abrasion, brake dusts, road surface leaching, traffic control device corrosion, and in the case of road salts, direct application to roads (Hjortenkrans, Bergbäck and Häggerud, 2007; Kluge and Wessolek, 2011; Lindgren, 1996). For instance, large quantities of rubber and plastic dust arise from tyre wear and are a major source of zinc (Councell et al. , 2004; Davis, Shokouhian and Ni, 2001; Hjortenkrans, Bergbäck and Häggerud, 2007; Wik and Dave, 2009). Polycyclic aromatic hydrocarbons are present in vehicle emissions, and also arise from the tar and bitumen-based materials used in road surface construction (Markiewicz et al. , 2017). High sodium and chloride concentration from de-icing salt usage during winter affects the mobility of trace elements and can cause an ion imbalance in soils and in plants (Moťková et al. , 2014; Tromp et al. , 2012).

The World Energy Council (2016) reported that approximately 63 percent of global oil consumption was in the transport sector and that substitution by other fuel sources was not expected be more than 5 percent by 2021. In Europe, with its fuel economy standards and regulations to reduce particulate emissions, sales of electric vehicles are expected to reach between 27 percent and 41 percent of the market by 2030 (Fritz, Plötz and Funke, 2019). Oil combustion in the transport sector is a major source of carbon dioxide and oxides of nitrogen emissions worldwide, contributing to global warming. It also contributes to particulate matter and unburned hydrocarbons releases. Oxides of nitrogen formed during oil combustion can lead to the development of smog and acid rain (World Energy Council, 2016).

Soils adjacent to older (>30 years old) and more heavily used roads have higher concentrations of trace elements such as lead, zinc, and chromium than those adjacent to newer roads, lesser used roads (Carrero et al. , 2013; De Silva et al. , 2016). Roadside environments feature three different areas of pollution: (1) 0-2 m, dominated by runoff and spray water from the road; (2) 2-10 m, dominated by splash water and partly influenced by runoff water, depending on the inclination of the slope; and (3) 10-50 m, which is affected mainly by airborne contaminant transport (Werkenthin, Kluge and Wessolek, 2014, and references therein). Metals mobility along the roadside is strongly influenced by soil pH and organic matter content (Kluge and Wessolek, 2011; Turer and Maynard, 2003).

Soils and plants in the vicinity of railway lines are likewise polluted with PAHs and trace elements including cadmium, cobalt, chromium, copper, iron, lead, mercury, molybdenum and zinc (Liu et al. , 2017; Malawska and Wiołkomirski, 2001; Wiłkomirski et al. , 2011). There are many sources of PAHs that occur along railways such as machine grease, fuel and transformer oils and creosote wood treatments that reduce the decomposition of railway sleepers/ties (Brooks, 2004; Moret, Purcaro and Conte, 2007; Thierfelder and Sandström, 2008). As for trace elements, electric locomotives, although considered environmentally friendly, can also increase metal concentration in surrounding soils by abrasion from wheels, tracks and pantographs (Bukowiecki et al. , 2007; Zhang et al. , 2012b, 2013). High concentrations of chromium, copper, iron, lead, mercury, and zinc in soils were also found in cleaning bays and railway sidings (Malawska and Wiołkomirski, 2001).

Copper chrome arsenate (CCA), a product that was used as a pesticide and wood preservative (ATSDR, 2007) is a source of arsenic, which is also prevalent along railway tracks (Smith, Smith and Naidu, 2006) (Fayiga, Ma and Zhou, 2007). Similarly pentachlorophenol, which since 2017 has been added to the list of POPs for elimination under the Stockholm convention, was used as a wood preservative for railway sleepers/ties. Christodoulatos et al. (1994) noted the potential for pentachlorophenol to leach into soils.

The runoff from highways is often alkaline, leading to an increase in local soil pH levels, and as a consequence, to locally lower mobility of trace elements (Kayhanian et al. , 2012; Kocher, Wessolek and Stoffregen, 2005). In regions with acidic sandy soils and a high groundwater table, trace elements are more mobile (Werkenthin, Kluge and Wessolek, 2014), and pose a threat to groundwater due to downward percolation, particularly in the roadside areas that have the highest trace element concentrations.

Food production often occurs on soils in urban and peri-urban zones that are exposed to highway pollution. Several studies have found that metal loads in plants decrease as their distance from the road increases (Modlingerova et al. , 2012; Zechmeister et al. , 2006). This is true also in roadside agricultural soils (Krailertrattanachai, Ketrot and Wisawapipat, 2019; Ogundele Dt, Adio Aa, and Oludele Oe, 2015). Pollution of soils along roadsides that are used for food production can increase the risk of contaminants entering the food chain, and cause adverse effects on biota and terrestrial environments (Kibblewhite, 2018).

3.5.6. Industrial accidents

In the context of this report, industrial accidents are any major release of pollution that is caused as a result of natural disasters; poor design, management and maintenance of industrial installations; intentional damage; military conflicts; and unintentional accidents. Industrial accidents can occur during the extraction of raw materials, transport and transfer by pipeline, storage, and processing. Industrial accidents can impact countries in all regions of world, regardless of their state of development.

Crude petroleum spills have immediate negative effects on soils due the toxicity of PHCs to soil dwelling organisms as well as, at very high concentrations, due to the formation of an impermeable surface, which prevents water and gas exchange into the soil, and between soil and air. In this new anaerobic condition, plant roots tend to suffocate, while the number of bacteria and their metabolic activity decreases (Clemons et al. , 1998; Streche et al. , 2018). Accidental oil spills or equipment failure at petroleum drilling sites can contaminate soils with the release of drilling fluids, crude petroleum and refined petroleum products used for the equipment (Pinedo et al. , 2013). The Nigerian federal government reported more than 7000 spills between 1970 and 2000 (FAO and ITPS, 2015b). The Niger Delta region of Nigeria has suffered from frequent pollution from oil spills because of its increasing oil and gas industrial activities. A study attempted to understand the main reasons of the oils spills from 2011 until 2016 and found that vandalism and crude oil theft was the most important cause at 74.4 percent, followed by corrosion, equipment failure and human error at 25.3 percent (Oriaku, Udo and Iwuala, 2017).

Most of the soil pollution from radionuclides following the Fukushima accident occurred northwest of the reactor, resulting in a contaminated strip 40 km in length (Hirose, 2012). Before the accident, the Fukushima prefecture was a flourishing agricultural region (rice, fruits, vegetables and livestock) and fourth largest producer of rice (Yamaguchi et al. , 2016). Many studies have followed up the incident in Fukushima and investigated the extent and type of radionuclides on the soil surface over time. Analysis of soil in 2017 identified that the most numerous radioactive nuclides were mostly radiocaesium-134 ( 134 Cs) and radiocaesium-137 ( 137 Cs) isotopes, with a decrease in time of 134 Cs compared to 137 Cs. In a study on the behaviour of 134 Cs and 137 Cs, the isotopes were mostly adsorbed to fine clay and organic matter, and had slow downward movement (1–2 mm/year). The addition of potassium to the soil to limit 137 Cs accumulation in the rice grains was suggested, since a negative correlation was found between soil K concentration and 137 Cs concentration taken up by the plants. Crop type is differently affected with soybean seeds accumulating more 134 Cs and 137 Cs isotopes than rice seeds (Nakanishi, 2018). In fruit trees, 134 Cs and 137 Cs were mobile, moving from the bark into the wood, and transferred to the fruits. The efforts to remove radio-caesium, through bark removal or with high-pressure washing did not reduce the concentration of radio-caesium found in peach and plum fruit (Nakanishi, 2018; Sato et al. , 2015; Takata, 2019).

In 1986, the nuclear reactor at Chernobyl, at the time in the U.S.S.R. and now in Ukraine suffered a catastrophic fire that released clouds of radioactive emissions into the atmosphere. Over the subsequent weeks the emissions continued to be released and were spread by air currents ( Figure 23 ) and deposited over three areas in the Soviet Union, in total 150 000 km with more than 5 million inhabitants. Outside the former Soviet Union about 45 000 km across wide areas of Europe were impacted with radiocaesium-137 between 37 kBq/m 2 and 200 kBq/m 2 (UNSCEAR, 2011). The radionuclides were generally deposited with rain, often at higher altitudes. In the first few weeks after the Chernobyl accident, an immediate exposure from iodine-131, which has a short radioactive half-life (eight days), caused high thyroid exposure doses among the population, especially in children, due to the drinking fresh milk contaminated with iodine -131 (UNSCEAR, 2011). The pathways for diffusion of the pollution are shown in Figure 24 . The fallout of particles close to the reactor caused a high level of pollution of the soil surface with radiocaesium-137 up to 106 Bq/m 2 (Hu, Weng and Wang, 2010). The deposition of radiocaesium-137, which has a half-life of 30 years, has led to long-term internal and external human exposure to radionuclides with several health implications (Brevik and Burgess, 2016; UNSCEAR, 2011).

Figure 23. Formation of Plumes due to meteorological conditions during the period after the initial explosion at Chernobyl.

Figure 24. The main transfer pathways of radionuclides in the terrestrial environment.

Environment

Chennai’s soil, delhi’s air most contaminated due to high pcb concentration: study       .

Informal recycling of e-waste, open burning of solid waste, combustion of coal and ship-breaking activities cause PCB contamination

By Subhojit Goswami

Published: sunday 26 february 2017.

India is now reaping what it had sown decades ago. Prolonged use of toxic industrial chemicals in electrical equipment have contaminated the country’s soil, air and possibly water, finds a new study.

According to an analysis of soil samples from Goa and six cities, including New Delhi and Mumbai, the average concentration of polychlorinated biphenyls (PCBs) in Indian soil was almost twice the amount found globally—12 ng/g (nanogram per gram) dry weight as against 6ng/g. The study was carried out by the SRM University (Tamil Nadu) in collaboration with international institutes.

PCBs are synthetic organic chemicals used in electrical equipment, adhesives, paints and several other products. In April 2016, India said manufacturing and importing polychlorinated biphenyls (PCBs) will be banned after December 31, 2025.

Recently, a joint study by the researchers at the James Hutton Institute and University of Aberdeen found that even the bottom of the ocean is not safe from PCB contamination with “extraordinary” levels of contamination found in two of the deepest trenches in the ocean—Mariana Trench in the North Pacific and Kermadec Trench in the South Pacific. This polluting chemical persisted and found its way into the remotest corner of the earth even though the US had banned its use back in 1979.

PCB concentration in India cities

After studying air samples and 84 samples of surface soil up to 20 cm from New Delhi, Mumbai, Chennai, Bengaluru, Kolkata, Goa and Agra, it was revealed that heavier PCB compounds were prevalent in urban areas.

Chennai: the city was found to be most contaminated in terms of PCB concentration in soil, with an informal e-waste shredding site recording maximum concentration. Located close to the port, the city imports e-waste and also generates nearly 47,000 tonnes of e-waste annually.

Bengaluru: the second highest contamination was reported in a village in Bengaluru, which was home to an open solid waste dumping ground.

Delhi: while soil PCB concentration was less in New Delhi and Mumbai, these cities showed high levels of PCB in the air, primarily due to emission during informal e-waste recycling.

Eastern Delhi is home to several informal electronic waste recycling units. The city, alone, generates 15,000 tonnes of e-waste every year, in addition to the e-waste imported for recycling purpose. High levels of tetra and penta PCB congeners were found in soil samples from eastern Delhi.

READ: Delhi’s solid waste: a systemic failure

Mumbai: high level of PCB concentration in Mumbai could be due to ship-breaking and informal e-waste recycling, uncontrolled burning of municipal solid waste , which result in e-waste and biomedical waste finding their way in the pile. Highest level of penta PCBS, contributing about 69 per cent of total PCB concentration, was observed at Kurla.” Coastal cities were found to be influenced by port activities, particularly ship-breaking activities, impacting PCB loading in Mumbai and Goa,” says Paromita Chakraborty, lead investigator and also the assistant professor (Civil Engineering) at the SRM University.

Impact on health and scale of the problem

Long-term exposure to PCBs can cause certain cancers and birth defects. It can damage the central nervous system, immune and reproductive systems, and also affect the food chain.

According to researchers, informal recycling of e-waste, open burning of dumped solid waste, combustion of coal and industrial waste, ship-breaking activities act as a sink for heavy chlorine compounds.

While talking to Down To Earth, Chakraborty affirms that the issue of PCB concentration in India has been persisting for decades. “PCB isn’t a recent problem for India. Iwata et al reported high PCBs from west coast of India in 1994. Apart from our studies in Indian metropolitan cities, in 2008, Pozo et al reported very high atmospheric PCB level in an agricultural site of India. During early 2000, there were several papers reporting PCBs, especially dioxin-like PCBs in human milk from dumpsites of Kolkata and from major cities like Mumbai, Chennai and New Delhi. PCBs have been observed in the northeastern states as well. Initially, open burning of dumped wastes was a prime problem associated with elevated PCBs in most parts of India. Due to a long range of atmospheric transport, sites away from the sources were found to be contaminated.”

She further adds, “Owing to the influx of e-waste (from developed nations) and growth of informal e-waste recycling sectors, such hazardous compounds are emitted in the environment, thereby acting as an ongoing source.”

The problem of PCBs is waning in developed world, it continues to be a major problem in developing economies such as Ghana, China and India.

According to her, the existing PCB database in India is restricted to stockpiles present with power companies of government and private enterprises. PCB emissions from ship breaking, informal e-waste recycling and open burning of solid waste needs to be thoroughly accounted.

What actions can be taken?

What’s the solution we have in hand? “Informal e-waste recycling process is an emerging problem and it is growing. Still, it is one of the sources of PCBs in developing nations today. Besides proper waste disposal, open burning of dumped waste should be stopped. Not only PCBs, but several other organic pollutants can be released due to incomplete combustion of waste, particularly plastics, e-waste and biomedical waste,” says Chakraborty.

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A Study On Soil Pollution In & Around Guwahati – A Case Study of Pollution Caused By The River Bharalu

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Reetashree Bordoloi

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KULDEEP KAUSHIK

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International Journal of Research & Review (IJRR)

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Case study of New Delhi

Loudest city in india.

Back in 2011, a study by the Centre of Science and Environment (CSE) has confirmed that New Delhi is the loudest city in India. The level of noise in the streets can go above 100 decibels, which is several times louder than Singapore. The noise level has reached dangerous levels, beyond the recommended guidelines of 50-55 decibels for residential zones. Prolonged exposure to this level of noise has resulted in the increase of risk in hearing loss for the citizens. According to studies, the average age of citizens in New Delhi are 10 years older in terms of hearing, which means they are at greater risk of losing their hearing in their 50s or early 60s.

A picture of a rush-hour traffic jam in the city of Delhi

The loud noise is often generated by the honking of cars, which means changes in attitude and behavior can reduce the main source of the noise. However, this is a hurdle as the habit of honking is ingrained into their daily routine. The streets of New Dehli are shared by vehicles, people, cyclists and more. Traffic is very heavy and the use of honk is essential to alert people walking on the street of an oncoming vehicle. As this concerns personal safety, the honking behavior will be a strong internal barrier as the drivers cannot simply stop honking.

High levels of soil calcium and clay facilitate the recovery and stability of organic carbon: Insights from different land uses in the karst of China

• Research Article
• Published: 03 May 2024

Cite this article

• Xiai Zhu 1 ,
• Youxin Shen 1 ,
• Xia Yuan 1 , 2 ,
• Chuang Yuan 1 ,
• Liya Jin 1 , 2 ,
• Zhimeng Zhao 3 ,
• Fajun Chen 1 , 4 ,
• Bin Yang 1 ,
• Xiaojin Jiang 1 &
• Wenjie Liu 1  

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Soil organic carbon (SOC) is a crucial medium of the global carbon cycle and is profoundly affected by multiple factors, such as climate and management practices. However, interactions between different SOC fractions and land-use change have remained largely unexplored in karst ecosystems with widespread rock outcrops. Owing to the inherent heterogeneity and divergent response of SOC to land-use change, soil samples with close depth were collected from four typical land-use types (cropland, grassland, shrubland, and forestland) in the karst rocky desertification area of China. The aim of this study was to explore the responses of SOC dynamics to land-use types and underlying mechanism. The results showed that land-use type significantly affected SOC contents and its fractions. Compared with cropland, the other three land uses increased the total organic carbon (TOC), microbial biomass carbon (MBC), and non-labile organic carbon (NLOC) contents by 6.11–129.44%, 32.58–173.73%, and 90.98–347.00%, respectively; this demonstrated that a decrease in both labile and recalcitrant carbon resulted in SOC depletion under agricultural land use. Readily oxidized organic carbon (ROC) ranged from 42 to 69%, accounting for almost half of the TOC in the 0–40-cm soil layer. Cropland soil showed significantly higher ROC:TOC ratios than other land-use types. These results indicated that long-term vegetation restoration decreased SOC activity and improved SOC stability. Greater levels of soil exchangeable calcium (ECa) and clay contents were likely responsible for higher stabilization and then accumulation of SOC after vegetation restoration. The carbon pool index (CPI) rather than the carbon pool management index (CPMI) exhibited consistent variation trend with soil TOC contents among land-use types. Thus, further study is needed to validate the CPMI in evaluating land use effects on soil quality in karst ecosystems. Our findings suggest that land-use patterns characterized by grass or forest could be an effective approach for SOC-sequestration potential and ensure the sustainable use of soil resources in the karst area.

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Effects of vegetation succession on soil organic carbon fractions and stability in a karst valley area, Southwest China

Dynamics and fractions of soil organic carbon in response to 35 years of afforestation in subtropical China

Soil organic carbon accumulation during post-agricultural succession in a karst area, southwest China

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Acknowledgements

We would like to express the gratitude to the Xishuangbanna Station for Tropical Rainforest Ecosystem Studies. We also thank the Institutional Center for Shared Technologies and Facilities of Xishuangbanna Tropical Botanical Garden, CAS for their help in chemical determination.

This work was supported by the National Natural Science Foundation of China (32101380; 32371608; 32271648; 32171557), Yunnan Fundamental Research Projects (202301AT070354; 202101AT070056; 202101AS070010; 202201AT070216), Youth Innovation Promotion Association CAS (2021397), Postgraduate Research and Innovation Foundation of Yunnan University (KC-23233905), and Yunnan Provincial Department of Education Science Research Fund Project (CY22624109).

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CAS Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Mengla, 666303, Yunnan, China

Xiai Zhu, Youxin Shen, Xia Yuan, Chuang Yuan, Liya Jin, Fajun Chen, Bin Yang, Xiaojin Jiang & Wenjie Liu

College of Ecology and Environmental Science, Yunnan University, Kunming, 650500, China

Xia Yuan & Liya Jin

Guizhou Provincial Key Laboratory of Geographic State Monitoring of Watershed, School of Geography and Resources, Guizhou Education University, Guiyang, 550018, China

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Neijiang Normal University, Neijiang, 641100, Si Chuan Province, China

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Xiai Zhu: Conceptualization, Data curation, Formal analysis, Writing—original draft. Youxin Shen: Writing—review & editing, Resources. Xia Yuan and Chuang Yuan: Investigation, Methodology, Formal analysis. Liya Jin, Zhimeng Zhao, and Fajun Chen: Software, Validation, Formal analysis. Bin Yang, Wenjie Liu and Xiaojin Jiang: Resources, Supervision, Foundation.

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Zhu, X., Shen, Y., Yuan, X. et al. High levels of soil calcium and clay facilitate the recovery and stability of organic carbon: Insights from different land uses in the karst of China. Environ Sci Pollut Res (2024). https://doi.org/10.1007/s11356-024-33552-y

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Received : 12 December 2023

Accepted : 29 April 2024

Published : 03 May 2024

DOI : https://doi.org/10.1007/s11356-024-33552-y

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