Sources of soil pollution in the region include those related to geogenic processes as well as anthropogenic activities. Geogenic contaminants are of natural origin, while anthropogenic sources include industrial activities, mining, agriculture and livestock, and consumer lifestyles. All are key drivers of soil pollution. Consumer lifestyles have also led to the expansion of energy production, transport and an increase in solid waste generation (UNEP, 2018).
There are debates and uncertainties about the origin of soil contaminants from geogenic sources and those from anthropogenic sources due to human intervention of the geogenic elements/compounds; the elevation of arsenic from ground to surface soil is one of these examples (Barbieri, Sappa and Nigro, 2018). Major soil contaminants, especially trace elements (arsenic, cadmium, chromium, lead, mercury and nickel) and hydrocarbons, are important in this regard because of their toxicity to humans and the environment. Three examples of geogenic sources of soil pollution are presented below.
Among trace elements, arsenic is considered the most serious mobile contaminant from geogenic sources in this region. Exposure to arsenic can cause human disease, including cancers of the skin, lungs and other internal organs (IPCS, 2001).
Although arsenic has been detected in groundwater worldwide as a consequence of natural processes, South Asian countries are one of the region’s most vulnerable to arsenic pollution of groundwater (Rahman, Naidu and Bhattacharya, 2009). The source of arsenic in groundwater/aquifer is derived from arsenic-bearing sediments, mainly from the reductive dissolution of iron oxyhydroxides where organic matter and microbes play a crucial role in the mobilization of arsenic. Heavy groundwater withdrawals for irrigation are thought to be the main reason for such pollution (Naidu et al., 2006).
Naturally, the range of arsenic concentrations in rock minerals is 1 – 10 mg/kg, but it can reach up to 10 000 mg/kg in some mining areas. High concentrations of arsenic can also found in loess, glacial tills, and peats, and can be further enriched in acid sulphate soils (up to 50 mg/kg), and shales (up to 200 mg/kg) (Polya and Lawson, 2015). South Asia, particularly the Bengal delta region, is a major hotspot for arsenic pollution from geogenic sources.
Several active volcanoes are located in the Asia–Pacific region, in the “Ring of fire”. Volcanic eruptions can emit varying masses of elements, such as arsenic, fluorine, gallium, mercury, sodium, tin, titanium, and zinc (Ma et al., 2019). Of these, arsenic, fluorine and mercury, are important, given their toxicological priority. For example, a moderately sized eruption of Mount Ruapehu, New Zealand, could emit mercury at 100-200 kg/day with potentially much higher emissions when large eruptions occur (Gustin, Lindberg and Weisberg, 2008; Nriagu and Becker, 2003). However, the very few studies on the subject are not sufficient to determine the extent of mercury soil pollution from volcanoes (Gustin, Lindberg and Weisberg, 2008; Varekamp and Buseck, 1986). Gotoh, Otsuka and Koga (1979) reported that mercury releases from volcanic activity slightly increased mercury in soils in Kagoshima, Southern Kyushu, Japan. However this direct input to agricultural soils might represent only a very small part of the total amount of possible sources from atmospheric deposition and anthropogenic activities (Gotoh et al., 1979). A report prepared for The Ministry for the Environment of New Zealand indicated that soils in volcanic areas could contain higher mercury concentrations than those in non-volcanic areas (Chrystall and Rumsby, 2009). A regional study revealed that soils affected by volcanic eruptions from Auckland and Waikato respectively contained mercury concentrations of <0.03-0.45 mg/kg, and ~0.19 mg/kg (with a median of 0.10 mg/kg). Volcanic ash contributing to the parent soil could be responsible for this mercury input. In contrast, soils in Canterbury, where the volcanic impact was not noticed, had lower mercury concentrations than those in Auckland and Waikato (Chrystall and Rumsby, 2009). Robinson et al. (2004) reported that soils from the Taupo volcanic zone in New Zealand’s North Island had arsenic concentrations ranging from 33 mg/kg to 79 mg/kg. Although there are surrounding human activities such as timber treatment with arsenical pesticides, the natural concentration of arsenic in soil was higher there than in other non-volcanic regions due to the volcanic contributions. Eruptions of volcanic ash from the Ruapehu volcano in New Zealand contain excessive amounts of fluoride compounds that could contaminate soil and water through leaching of fluoride compounds from the ash. It has also been reported that grazing animals have bioaccumulated fluorine- and suffered from fluorosis (Cronin et al., 2003).
In addition to trace elements, polycyclic aromatic hydrocarbons (PAHs) are another significant contributor to soil pollution as a result of natural causes. PAHs can come from the incomplete combustion of petroleum substances and reside in the soil. Although atmospheric deposition is a natural phenomenon, the extent of soil pollution from the deposition of toxic substances from the air depends largely on the anthropogenic contribution of those contaminants to the atmosphere. Following a forest fire in the Republic of Korea, Choi (2014) studied PAH concentrations in soil and reported an increase in PAHs in fire-affected soil (mean 0.13 mg/kg) compared to unaffected soil (mean 0.026 mg/kg) measured in the month following the fire. Nguyen et al. (2014) evaluated the concentration and source-tracking of PAHs in environmental systems, including soil in Sydney, Australia and reported that particularly higher molecular weight PAHs were available (0.40–7.49 mg/kg) in surface soils. The authors concluded that their sources were mainly pyrogenic, resulting from the high-temperature combustion of wood materials. However, Choi (2014) found that the pollution decreased over time and that in one year, the soil in the burnt area was similar to that in the unaffected area. It was assumed that rainfall dispersed PAHs, along with natural attenuation processes such as microbial degradation and volatilization (Simon, Choi and Park, 2016) A similar source of PAHs and a recovery trend was reported in the Republic of Korea by Kim, Choi and Chang (2011).
The Asia–Pacific region includes High Income Countries, Middle Income Countries and Low Income Countries, so the range of industrial activities is wide. Specific regional aspects of soil pollution caused by industrial activities are discussed in section 6.3. In general, the most common industries responsible for soil pollution in this region are: petrochemical processing; oil exploration; chemical processing; metal extraction, processing and smelting; electroplating; tanning and dyeing; and cement and brick kilns (Figure 2).
It is difficult to trace the causes of pollution in industrial complexes and the surrounding soils. However, discharges, poorly managed stockpiles and the diffusion of priority chemicals into the environment are the main sources of soil pollution, while the legacy of industrial sites often poses serious sources of pollution (Douglass and Ling, 2000; Pan et al., 2018; Pichtel, 2016; Tiller, 1992; Wang et al., 2019). Both the prevention of further dispersal of contaminants that are widely diffused, and their clean-up are costly and time-consuming.
In general, most priority contaminants, including trace elements (e.g. arsenic, cadmium, chromium (VI), lead, mercury), persistent organic pollutants (POPs) and other hydrocarbon compounds resulting from industrial activities, contaminate soils (Yang et al., 2018). The secondary metals industry releases many trace elements and unintentional POPs like polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/PCDF) that contaminate surrounding soils (Hu, Jin and Kavan, 2014; Weber et al., 2018). Theses releases result in pollution of soils with trace elements and PCDD/PCDF over time, with an associated risk of exposure of human and livestock (Weber et al., 2018). For example, eggs from free-range chickens raised around secondary metal industries and incinerators in China and Thailand had high levels of PCDD/PCDF (Mach et al., 2017; Petrlik, 2016).
Some chemical industries have a high pollution release potential, such as industries generating POPs or releasing unintentional POPs like PCDD/PCDF. Soils around production sites of hexabromocyclododecane (HBCD) (Li et al., 2012; Zhang et al., 2018) and short-chain chlorinated paraffin (Wang et al., 2018; Xu et al., 2016), listed as POPs, have been contaminated. Soils and sediments at chloralkali sites in Japan and China are contaminated with PCDD/PCDF and the full spectrum of other unintentional POPs (Takasuga et al., 2020; Wu et al., 2001; Yamamoto et al., 2018).
In the Asia–Pacific region, the predominant mining is for coal, copper, gold, and bauxite, while quarrying is mainly for sand, stone and limestone. There are different levels of effects in the form of soil pollution resulting from mining and quarrying, as discussed in the succeeding subsections.
Mining and associated operations contribute to a significant level of soil pollution. Pollution comes from both current mining activities and former sites. Tailings, by-product disposal, effluents and acid-drainage, and sediment runoff from mine sites are the main causes of soil pollution. Trace elements, cyanide, and PAHs are the most commonly reported contaminants found in soil in the vicinity of mine sites.
The Asia–Pacific region is the world’s largest coal mining region, accounting for 78 percent of global production (according to sales reports). Similarly iron ore, copper and gold mining in the region accounts for the largest share of global production (The Business Research Company, 2020). Australia. China, India and Indonesia are key contributors to the mining sectors (Figure 3). The regional extent of mining-related soil pollution is discussed in section 6.3 for several selected countries.
Monometallic minerals sources are most exploited by China, followed by India, Viet Nam, Indonesia, the Republic of Korea and Japan (Figure 4). Quarrying is notoriously known for causing the deterioration of air and water quality in the vicinity of quarrying activities (Ibrahim et al., 2018; Naz et al., 2016; Yi, 2017). However, there is no aggregated information on the effect of quarrying on soil pollution in the Asia–Pacific region. A few studies report that the exploitation of sand and stone quarries threatens to deteriorate soil quality, mainly due to soil erosion and deforestation, and trace elements pollution due to the deposition of quarry dust on surface soils and the dispersion of poorly managed tailing wastes (Pal and Mandal, 2019). In studying the spatial distribution of trace elements from mining and quarrying sites in Wulian, China, Lv et al. (2014) reported that the highest concentration among the distributions of cadmium (0.48 mg/kg), zinc (224 mg/kg), copper (320 mg/kg) and lead (362 mg/kg) was linked to mining and quarrying activities at nearby sites. Quarrying not only impacts soil pollution but soil-bound elements also leach into the aquifer, which then contaminates groundwater. For example, groundwater can be contaminated by excess fluoride and other salts as a result of sand and stone quarrying (Misra, 2013). Studying the sandstone quarrying area of the Agra district in India, Misra (2013) reported that fluoride-rich deposits have become widely available in adjacent aquifers as a result of quarrying activities. This study reported fluoride concentrations in shallow aquifers located in a quarrying village of 1.5–3.8 mg/litre, which were higher than those recorded at a distance of 1-1.5 km from quarrying sites. Another aspect of the impacts of sand quarrying on soils is the degradation and erosion of massive amounts of soil from shorelines, resulting in the subsequent release of many soil-bound contaminants (Beiser, 2017).
New Zealand’s Ministry of the Environment has stated that “while our land is precious, today’s deteriorated soil environment has been caused because of what we have removed from it and what we have built on it” (NZ-MOE, 2019). Excessive soil loss is occurring in the Asia–Pacific region due to deforestation, agricultural development and increased pressure on soil from the expansion of urban areas and industrial structures. Agriculture is the primary food production sector for humans and cattle, and its industrialization has been a growing trend to meet the food demands for the region’s growing population. However, there are few key soil pollution drivers associated with agriculture that are important for the sustainable management of this sector. These include irrigation, agroplastics, the use of agrochemicals (pesticides and fertilizers), and the use of antibiotics and drugs in livestock production.
In some parts of region, irrigation of soils with arsenic-contaminated water has resulted in the loading of considerable amounts of arsenic into the soil. As a result, crops, particularly paddy rice, grown on arsenic-contaminated soils accumulate relatively high concentrations of arsenic (Islam et al., 2017). By using many large-diameter shallow wells to extract groundwater for irrigation, the arsenic in the groundwater is deposited on agricultural soils. Since paddy rice is the main crop in this region and grows under submerged conditions, rice accumulates high levels of inorganic arsenic from groundwater, ultimately posing a risk to human health (Naidu et al., 2006). The bioavailability and toxicity of arsenic depends on the chemical state of this element. Inorganic forms of arsenic (e.g. various arsenic oxides) are identified as more toxic than its organic forms (e.g. compound with arsenic-carbon bonds). An example of soil pollution with arsenic is presented in section 6.3.1.
The use of agrochemicals is also increasing in rapidly developing countries, such as China, which is now by far the world’s largest user, with an estimated 36 percent and 25 percent of global use for chemical fertilizers and pesticides, respectively (Guo et al., 2010). The Asia–Pacific region, which is the largest part of the world in terms of land area and population, is the largest producer and consumer of agrochemicals among all the regions of the world (Medium, 2019). The market value of agrochemicals produced in the Asia–Pacific region amounted to USD 17 billion in 2018, the largest fraction of the USD 56 billion global market (Statista, 2020a). Pesticide use per hectare of agricultural land is above global averages in East Asia, Polynesia and South-East Asia according to data for 2017 (Figure 5), with the highest values in Maldives (45.9 kg/ha), China (Hong Kong and Taiwan about 13 kg/ha), the Republic of Korea (12.0 kg/ha), Japan (11.8 kg/ha) or Malaysia (7.8 kg/ha) (FAOSTAT, 2019c, 2020). The extensive use of agrochemicals is one of the main causes of agriculture-related soil pollution problems in the region (Delang, 2017; UNEP, 2017b; Yadav et al., 2015a). For example, it is claimed that in Sri Lanka, farmers apply nearly 40 percent more fertilizer than the recommended quantity based on soil tests. Due to the lack of appropriate guidance to farmers on fertilizer application rates, and the assumption that that applying more fertilizer will lead to a larger harvest, the pollution of surface and groundwater with nutrients nitrogen and phosphorus has been significant (Ariyapala and Nissanka, 2006). In addition to nutrient pollution, cadmium input to crop fields and nearby water bodies from imported triple phosphate fertilizers in Sri Lanka has led to significant diffuse pollution of land and water bodies (Bandara et al., 2008). An example of soil pollution by agrochemicals in Sri Lanka is presented in section 6.3.1.
The large-scale application of POPs pesticides, in particular pentachlorophenol (PCP), and pesticides contaminated with POPs such as quintozene and 2,4,5-T, has in the past contaminated large areas with PCDD/PCDFs (Camenzuli et al., 2015; Holt et al., 2008; Zheng et al., 2012). In Japan, rice fields throughout the country have been contaminated with more than 450 kg PCDD/PCDF toxic equivalent quotient from PCP use and PCDD/PCDF have been dispersed for decades in association with soil particles in rivers, lakes and ocean sediments (Masunaga et al., 2001, 2003; Weber and Masunaga, 2005). In Australia, more than 2 000 km2 of agricultural soils and sediments on the East Coast are affected by PCDD/PCDF from past use of PCPs in agriculture (Camenzuli et al., 2015; Holt et al., 2008). Similarly, the use of PCP in China for snail control has contaminated agricultural soils (Zheng et al., 2012). Likewise, the more recent use of pesticides containing PCDD/PCDF, such as quintozene and 2,4-D in agriculture or on golf courses, has resulted in the release of PCDD/PCDF (Holt et al., 2010, 2012). Polluted soils have also been identified in Viet Nam at former pesticide storage sites, where more than 1 000 sites had been assessed for POPs pollution; and the remediation of polluted sites has started (TAUW, 2014). Similarly, soil pollution by pesticide residues has been reported in India and neighbouring countries which is presented in section 6.3.1.
Due to the increase in livestock production, particularly in developing countries, the use of drugs (e.g. antimicrobials and hormones), nutrients, fertilizers, as well as the discharge of wastewater (e.g. abattoir waste and sewage) and sediments from eroded pastures into the soil have increased proportionally (FAIRR, 2020; FAO, 2013). According to FAOSTAT (2019b), the Asia–Pacific region has been a major producer of live cattle in the world. China alone produced 83.4 million heads in 2017, followed by Pakistan (44.4 million), Australia (26.2 million), Bangladesh (23.9 million), India (18.5 million) and Indonesia (16.6 million), with varying numbers in other parts of the Asia–Pacific region. The increasing industrialization of livestock production and its processing plants, such as abattoirs and tanneries, poses a significant risk to land use due to exposure to contaminants associated with these industrial activities.
Scientific research on animal burial sites and soil pollution is very scarce in this region. However, sudden and massive outbreaks of animal diseases influence the use of excessive amounts of antibiotics and drugs in affected cattle (Han et al., 2018). Disposal of infected corpses in the soil is a significant source of these pharmaceutical residues in the sub-surface soil. For example, since 2010, more than 6 000 burial sites have been established for livestock infected with foot-and-mouth disease and avian influenza in the Republic of Korea (MOE, 2017). In the past, several persistent pesticides listed as POPs in the Stockholm Convention (DDT, HCH, aldrin, dieldrin and heptachlor) as well as trace elements such as arsenic and copper have been used to treat cattle and sheep against ticks and other pests. These cattle treatments have resulted in the pollution of a large number of sites. For example, in New Zealand alone, there are approximately 50 000 “sheep dip” sites contaminated with POPs pesticides or arsenic from this practice, with an associated risk of exposure (MFE-NZ, 2006).
The main sources of soil pollution from energy production are coal-powered generators and oil-based operations, while end-of-life solar panels are an emerging source of soil pollution. In the majority of countries in the Asia–Pacific region, the coal-powered generator - the main type of electricity generating plant (approximately 60 percent of total generation) (BP, 2019) (Figure 6) - causes soil pollution mainly through the emission of trace elements, sulphide and other fly ash associated contaminants such as PAHs. Due to the weak infrastructure and lack of regulation in the region, a significant contribution to pollution also comes from coal and oil transportation, land and water use for energy production, and post-operation ash/sludge disposal (NRC, 2010).
Although emissions from fossil-fuelled power plants are a major contributor to greenhouse gases and atmospheric pollution (e.g. emission of carbon dioxide, particulate matter, black carbon, oxides of nitrogen, sulphur dioxide, non-methane volatile compounds, and ozone), the consequences of these emissions on soil quality have also been found to be serious (UNEP, 2020). Singh, Agrawal and Narayan (1995), reported that the concentration of sulphate, sulphur and calcium increased in the soil near a coal-powered plant while nitrogen was depleted in the same habitat. In fact, coal contains several trace elements, including highly toxic elements such as arsenic, chromium (VI), mercury, and cadmium. Although some countries have regulations that require pre-treatment of coal to remove contaminants prior to combustion, this is not the case for a large number of countries that use coal-powered plants. Even if coal is pre-treated, poorly managed coal stockpiles on soil, ash disposal, and leaching or accidental discharge of coal-treated wastewater and sludge cause soil pollution in the region (Linnik et al., 2019; Wang et al., 2016; Zaman et al., 2018). The use of oil-fuelled power plants in Asia-Pacific is comparatively low, accounting for only 1.5 percent of total electricity generation by fuel (BP, 2019); it also contributes to soil pollution through the emission of trace elements (e.g. sulphur, vanadium and nickel), hydrocarbons (e.g. PAHs and PCDD/PCDF). However, the main soil pollution risk from the use of oil in power generation relates to spills from accidents and mismanagement (Jones, 2016; NSW-EPA, undated; NTN, 2009).
On the other hand, the number of currently operating nuclear power plants remained unchanged worldwide after 1988. However in recent years, many countries in the Asia–Pacific region have embraced or plan to exploit this technology. Bangladesh, for example, has been planning to embark on nuclear power generation since it signed an agreement with the Russian Federation. In 2017 it also expanded its cooperation with other countries, such as China and India, to build such plants in Rooppur and Pabna district (WNA, 2020b). China, India, Japan and the Republic of Korea have the largest number of nuclear power plants in the region (WNA, 2020b) (Table 1). Accidental spillage of radioactive substances from a nuclear power plant can result in severe soil pollution, as occurred in 2011 in Fukushima, Japan (Endo et al., 2012; Yoshida and Takahashi, 2012). Other radionuclide-related soil pollution is discussed in section 188.8.131.52.
Another emerging pollution risk associated with energy production is the generation of solid waste by end-of-life solar panels in this region. In particular, Australia is facing a crisis due to the accumulation of solar panels that pose a threat to landfill and the leaching of associated trace elements such as cadmium, copper, indium, lead, and zinc (Stewart, Salim and Sahin, 2019). A case example related to the solar panel waste is presented in Section 6.3.4.
While the transport sector is one of the biggest contributors to air pollution, there are few reports on transport-related soil pollution. The increasing demand in the region for transport facilities, with a growing number of vehicles but slow adoption of those powered by electricity, remain the main cause of roadside soil pollution. Reports suggest that two types of contaminants derived from these sources are trace elements, and petroleum hydrocarbons. These are often emitted as aerosols from vehicle engines, and spills during the transport of dangerous substances, and from the wear of tyres, brakes and road surfacing materials that end up being deposited on the roadside soil (Kibblewhite, 2018; Li, Poon and Liu, 2001).
Wang and Zhang (2018) reported that soil collected from the roadside in Hangzhou, China, where traffic is heavy, contained several trace elements (e.g. copper, lead and zinc) at concentrations higher than background geochemical values in similar soil. The degree of pollution was positively correlated with traffic density. Similar incidences were reported for a wide range of trace elements and hydrocarbons, including cadmium, copper, lead, manganese, mercury, palladium, platinum, rhodium, zinc, and PAHs in other studies in the region (Hwang et al., 2019; Khan et al., 2011; Li, Poon and Liu, 2001; Singh, Raju and Nazneen, 2015; Wawer et al., 2015). Elevated concentrations of trace elements from traffic are detected along roads (Trombulak and Frissell, 2000), with metals recently introduced in automotive technology (e.g. antimony and manganese) being higher along newer roads. Common trace elements (e.g. cadmium, copper, lead, or zinc) are higher along older roads, confirming the risk of significant trace element deposition and retention in roadside soils (De Silva et al., 2016).
In many European countries, increased levels of PCDD/PCDF and polychlorinated biphenyls (PCBs) have been detected in roadside soils, with a decreasing concentration after 2 m to background levels within 10 m from the edge of the road (Benfenati et al., 1992; Jartun et al., 2009; Šídlová et al., 2009). Unfortunately, no similar assessments were found for countries in the Asia–Pacific region. The source of PCDD/PCDF was the historical use of chlorinated scavengers in leaded fuel. Road marking paints were identified as the historic source of the PCB. The formulation of such paints changed, with the PCB component being replaced by chlorinated paraffin, which are now also partly listed as a POP under the Stockholm Convention (Jartun et al., 2009; UNEP, 2019; Weber et al., 2018).
Furthermore, the unregulated or superficially regulated disposal of end-of-life (EOL) vehicles and ships is a source of soil pollution. In this region, in addition to domestically disposed vehicles, the disposal of imported EOL vehicles and ships is also a growing market. These activities are commonly referred to as the “wreckage” or “scrap” industry. For example, Bangladesh has one of the largest ship-breaking industries in the world, where EOL ships come from many developed countries (Alam et al., 2019). The threat posed by EOL vehicles to soil and sediment health depends largely on management practices and regulation (Patwary and Bartlett, 2019). For example, EOL vehicles constitute a large source of aluminium for the recycling market (Gesing, 2004; Li, Yu and Gao, 2014). On the other hand, they are a significant source of priority contaminants that are harmful to humans and ecosystems. Such contaminants include trace elements (e.g. cadmium, chromium, copper, mercury, and lead), PCBs, other POPs and PAHs (Alam et al., 2019; Science-for-Environment-Policy, 2016; Siddiquee et al., 2012). Local atmospheric pollution from these substances can also lead to soil pollution through aerial deposition and fall-out (Science-for-Environment-Policy, 2016). Japan has followed a recycling process to collect the ferrous and non-ferrous metals fraction, which accounts for 50–55 percent of the total mass of vehicles, and only 1-2 percent of EOL vehicles end up in landfills (Sakai et al., 2014). However, it is unlikely that all countries in the Asia–Pacific region will match this recycling rate due to lack of regulation, management and infrastructural capacity.
The release of contaminants from solid waste depends on the types of waste and its management. Several types of solid wastes have the potential to pollute soil. These include municipal solid waste (MSW), industrial solid waste, agricultural solid waste and bio-medical solid waste.
MSW is the largest contributor to soil pollution. The World Bank has stated that “the world generates 2.01 billion tonnes of municipal solid waste annually, with at least 33 percent of that—extremely conservatively—is not managed in an environmentally safe manner” (Kaza et al., 2018). Figure 7 shows that the future is likely to be challenging, in particular for the Asia–Pacific region, as the generation of MSW is projected to increase by 23 percent by 2050, the largest increase in any of the regions of the world. Most of countries in Asia-Pacific face challenges with inadequate systems to manage MSW and its changing composition, and therefore open dumps and landfills remain the main waste management practices (Kaza et al., 2018). The World Bank has highlighted the danger to the region posed by solid waste at current rates of arising, and future projections, if no action is taken (World Bank, 2018). The region does have some success stories of environmentally-sound waste disposal, one example of which comes from Japan (Jones, 2018). Like Japan, many other countries in the region have instituted segregated collection of the various types of household waste, which helps to improve subsequent waste management processing. However, Japan has adopted strategies in which it has invested equal resources in disposal and collection management. This has enabled Japan to process the majority of its municipal waste, with only 1.2 percent going to landfill (Jones, 2018).
Open dumps, stockpiles and landfills can release trace elements into surface and sub-surface soils. Groundwater pollution may be a direct consequence of leaching from surface soils (Mor et al., 2006). Trace elements (e.g. chromium, copper, lead, zinc), ions (ammonium, chloride, nitrate, and sulphate), and phenols are among the most common contaminants, and, depending on the mobility and continuous percolation of polluted landfills, they can leach into groundwater (Mor et al., 2006; Naveen et al., 2017; Vongdala et al., 2018).
In addition to MSW, end-of-life electrical and electronic waste (e-waste) is another potential source of land and soil pollution and may well become another major crisis for the region (Keshav Parajuly and Josh Lepawsky, 2019). Until 2006, a significant amount of e-waste was exported to China for processing and recovery of the valuable metals and components. This generated a large volume of contaminated soils and sediments, polluted by trace elements, PCDD/PCDFs, PCBs and polybrominated diphenyl ethers (PBDE) (Cai et al., 2008; Wong et al., 2007). After China restricted e-waste imports in 2006 and other waste imports in 2018, e-waste and plastic wastes were diverted to other Asian countries. More recently, countries such as Thailand, India, and Viet Nam have started to struggle with their domestic e-waste and are becoming “dumping sites” for imported e-waste. An example of the dumping of household solid waste in Sri Lanka and an example of the e-waste crisis in Thailand are presented in section 6.3.3. Like MSW, e-waste also releases and emits various elements and substances, including trace elements (cadmium, chromium and lead), PCBs and bisphenol A. Stockpiling and landfilling are two major sources of soil pollution (SPREP, 2014). Polluted soils and sediments from e-waste recycling in China and Thailand have resulted in human exposure to PCDD/PCDF, PCB and PBDE. Livestock, such as chickens and cattle, that were grazing on the soil, have ingested the contaminants, which then transferred to meat, milk and eggs for human consumption (Labunska et al., 2014; Mach et al., 2017; Weber et al., 2018).
Many developed countries (e.g. Canada, Europe, Japan, and the United States of America) exported low-grade plastic wastes to China for recycling. Due to high levels of contamination from other materials, much of this “recyclable plastic” waste had to be disposed of. Due to the mounting environmental problems that it was causing, China banned its import in 2018. Some of this trade has now transferred to other Asian countries and has led to the pollution of areas and soils in Indonesia, Malaysia and the Philippines (Azoulay et al., 2019; GAIA, 2019; GreenPeace, 2019a). For a single site in Indonesia where waste plastic was used as fuel for Tofu production boilers, the contaminated surrounding environment resulted in high PCDD/PCDFs contamination of chicken eggs, which were 70 times higher than regulatory limits (Petrlik et al., 2019).
Other sources of soil pollution in the Asia–Pacific region include brick kilns, dust storms, military weapons tests and burial sites.
The brick kiln market in the Asia–Pacific region is the largest in the world, accounting for about 87 percent of total world production (HZZK, 2020). The greatest environmental threat of large-scale brick production is its dependence on coal-burning. There are many cases of unregulated emissions of contaminants in this region, particularly in South Asia where most operators have not implemented modern automated kiln technologies (HZZK, 2020). Brick kilns are considered to be one of the most air-polluting industries, while the aerial deposition of contaminants emitted from burning tyres in the kilns causes soil pollution in the surrounding areas. The unregulated or poorly regulated disposal of residues generated from coal and tyre combustion introduces additional pollution risks to the local soil system (Bisht and Neupane, 2015). An example highlighting this aspect in Bangladesh is presented in section 6.3.1.
Extreme drought conditions on the surface soil and the intensification of mining activities have doubled the risk of transporting soil dust. In some cases, toxicologically priority elements such as lead are carried by dust from some distance and could have adverse effects on exposed populations (Dong et al., 2015). Health hazards highlighting this aspect in Australia are presented in section 6.4.1.
Defence operations, military weapons testing and the legacy of nuclear bomb testing remained a key issue in the Asia–Pacific region. However, information on the effect and extent of these operations on soil pollution is often limited. The legacy of nuclear tests in the Marshall Islands and some atolls in the Pacific Ocean by the United States of America between 1946 and 1962 still includes soil pollution (Kaiku, 2019). Approximately 85 000 m3 of radioactive waste, with an estimated decay time of 24 000 years, was buried on Runit Island. An example of the adverse health effects of nuclear waste in the Marshall Islands is presented in section 6.4.3 (Figure 8).
Other military activities are also responsible for soil pollution. For example, soil contaminated with per- and poly-fluoroalkyl substances (PFAS) by defence operations in Australia have been identified. The pollution is being continuously monitored but, due to the lack of available and appropriate management strategies, no remedial actions have been initiated (AUS-DoD, 2020).
It is important to mention the use by the United States of America of the defoliant, “Agent Orange” during the war in Viet Nam between 1962 and 1971. Soils in Viet Nam and other neighbouring countries affected by the spraying of Agent Orange (mixture of herbicides chemically known as 2,4,5-Trichlorophenoxyacetic acid and 2,4-Dichlorophenoxyacetic acid) during the Viet Nam war were contaminated with large amounts of PCDD/PCDFs (Stellman et al., 2003). Soils are still heavily contaminated at hot spot sites and around airports (Van Thuong et al., 2015) and high levels are still found in eggs from free-range chickens in the area where Agent Orange has been used (Kudryavtseva, Shelepchikov and Brodsky, 2020). With the support of the United States of America and international organizations, the Government of Viet Nam has undertaken remediation activities at the most polluted sites such as at Danang using thermal desorption and catalytic oxidation (Fuller, 2012).