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 40K, 232Th, 235U, and 238U (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 (Al2O3) 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 SO2 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
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
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 CH4 and NH3 (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 (134Cs) and radiocaesium-137 (137Cs) isotopes, with a decrease in time of 134Cs compared to 137Cs. In a study on the behaviour of 134Cs and 137Cs, 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 137Cs accumulation in the rice grains was suggested, since a negative correlation was found between soil K concentration and 137Cs concentration taken up by the plants. Crop type is differently affected with soybean seeds accumulating more 134Cs and 137Cs isotopes than rice seeds (Nakanishi, 2018). In fruit trees, 134Cs and 137Cs 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/m2 and 200 kBq/m2 (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/m2 (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.
