UN Enviroment Programme

Chapter 9. Status of soil pollution in Latin America and the Caribbean

Sources of soil pollution in Latin America and the Caribbean

The main sources of soil pollution in the region are: agriculture, waste management, mining, quarrying and smelting activities, and transport infrastructure and emissions. Energy production, other industrial activities, and livestock activities also contribute to a lesser extent to soil pollution. Military sites (shooting tests, weapons tests areas and areas impacted by armed conflicts) can be considered as minor sources of soil pollution. FAO and ITPS (2015) summarized the main driving factors of soil pollution for the region as follows: various human activities can lead to the pollution of soils and adjacent water bodies from fertilizers and agrochemicals used in high-input agriculture, as well as from mining and oil spills.

It is important to point out that the differences in the intensity of the main polluting activities in the countries of the Caribbean, Central America and South America cause considerable variation in the existence and extent of soil pollution in each sub-region.

9.2.1. Agricultural practices

Agriculture is the most common and widespread activity causing soil pollution in Latin America and the Caribbean, due to three main factors: overuse of agrochemicals, crop irrigation with polluted surface and groundwater water or untreated wastewater, and the use of uncomposted manure and slurry (which may contain contaminants) as fertilizers.

The area of land in the region used for irrigated crop production has increased since 2000, and the livestock and aquaculture industries are growing as well (ECLAC, 2010c). Indeed, during the last decades of the 20th Century, these industries have increased by about 20 percent (Hernández-Rodríguez et al., 2001), leading to major impacts on ecosystems. The expansion in these activities has an impact on land-use change and influences deforestation, soil degradation, loss of biodiversity, and greenhouse gas emissions (Figure 2). However, after the global economic crisis, the LAC’s rate of growth slowed significantly but the agricultural sector continued to raise, relying on a more intensive use of resources in the majority of the countries (ECLAC, FAO and IICA, 2015).

Figure 2. Aerial image of an area prepared for monoculture or ranching, near Porto Velho. 07 August 2020. ©Bruno Kelly/Amazônia Real (via Wikimedia Commons, CC BY 2.0).

Latin America and the Caribbean has the highest average of pesticide use per area of cropland in the world, with Saint Lucia (14.52 kg/ha) ranking first, followed by Brazil, Argentina, Belize and Colombia (Figure 3) (FAOSTAT, 2019c). Between 1990 and 2017 the annual amount of pesticides used or sold to the region’s agricultural sector has increased more than fourfold, from 182 000 tonnes to 830 000 tonnes (FAOSTAT, 2018). While in Central America the amount of pesticides doubled and in the Caribbean it increased by 33 percent, the most significant increase was in South America, with a 500 percent rise between 1990 and 2017. It is however important to note that some countries do not report to global agencies on their consumption. According to ECLAC (2012), the region’s poor pesticide use and management practices can lead to cross border impacts of pesticide-laden runoff into rivers and the ocean.

Figure 3. Average pesticide use per area of cropland (kg/ha) between 1990 and 2017.

Note: The map has been prepared for illustrative purposes only, the boundaries shown on this map do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.

Source: UN, 2020 modified with data from FAOSTAT, 2019a.

According to data reported by the World Bank (2019b) on fertilizer consumption in the region, there was a 50 percent increase from 2002 to 2016 (Figure 4), from 89.5 kg/ha to 140.2 kg/ha. According to FAO (2015a), the region’s use of fertilizers is expected to increase at an annual rate of 3.3 percent. Reyes (2017) determined the intensity of fertilizer use in region over the period 2006-2012. Brazil, Argentina and Colombia were the main consumers of fertilizers in South America (Tovar, 2007), while smaller Caribbean countries are also intensive users of fertilizers (Reyes, 2017).

Figure 4. Fertilizer consumption in Latin American and the Caribbean Region from 2002 to 2016.

Source: adapted from World Bank, 2019b.

This is a matter of some concern, since the use of excessive amounts of fertilizers, which exceed plants’ needs, contributes to the pollution and acidification of soils. Nitrogen, in its nitrate form, is highly soluble and weakly retained in the soil, resulting in groundwater contamination through nutrient leaching, which leads to a nitrification process (Dong et al., 2005; López, 2002). Liu et al. (2012) mapped the level of nitrogen pollution of water by river basins in Latin America, indicating that Mexico, Argentina and Chile are the countries with the largest areas of land polluted with nitrogen.

The use of phosphate fertilizers has also increased in the region during the 21st Century, being especially relevant in South American countries (Figure 5). Besides the high eutrophication risk posed by phosphates leached or transported by runoff to neighbouring water bodies and groundwater, phosphate fertilizers constitutes a source of trace elements, in particular cadmium (Marrugo-Negrete, Pinedo-Hernández and Díez, 2017; Silva et al., 2018; Vieira da Silva, Araújo do Nascimento and Muniz Araújo, 2017). As observed in Brazilian fertilizers, cadmium can exceed twice the concentration in fertilizers from other regions (Vieira da Silva, Araújo do Nascimento and Muniz Araújo, 2017), and although the potential risk to the environment and human health is considered low, close attention should be paid to cadmium levels in soils over time due to intensive and persistent application.

Figure 5. Use of fertilizers by nutrient (phosphate and nitrogen fertilizers) in croplands in the Latin American region.

Source: adapted from FAOSTAT, 2020a.

Livestock production is also an important activity, mainly in South America, and manure is frequently applied to the soil as an organic fertilizer (FAOSTAT, 2019b). However, manure can be a source of soil pollution by antimicrobials, antimicrobial resistant bacteria, pharmaceuticals and other contaminants such as trace elements, specially copper and zinc (Mantovi et al., 2003). The excess of nitrogen and phosphorous can leach into groundwater and pollute it. Figure 6 shows the amount of manure applied as fertilizer in the three sub-regions. Brazil, Argentina and Mexico are among the top 10 countries in the world for livestock production (ranking 2, 7, and 8 respectively) (Actualitix, 2016). The excess of nitrogen in the soil can also lead to poor root systems, soft tissues, weak plants, production delays, poor quality yields and increased susceptibility to diseases and pests (SMART, 2020).

Figure 6. Amount of manure applied to soils in the three sub-regions and estimated amount of manure leached and volatilized.

Source: adapted from FAOSTAT, 2019b.

According to CEPALSTAT (2019), the proportion of land under irrigation to total agricultural land has not varied significantly since 1990, with an average value of 3.7 percent in 2017 for the region. However this proportion varies significantly between countries. Suriname, for example, has almost 70 percent of its agricultural area under irrigation (Figure 7), mainly devoted to rice paddies, followed by Barbados, Saint Lucia, Ecuador and Grenada, all with irrigated areas exceeding 25 percent of their total area under agriculture (FAO, 2019). Monitoring systems for irrigation water quality should be established in these countries to prevent leaching of contaminants to groundwater or by runoff affecting surface water.

Figure 7. Percentage of irrigated area in relation to total agricultural area in Latin-America and Caribbean countries in 2017.

Source: adapted from CEPALSTAT, 2019; FAO, 2019.

Unsustainable and intensive agricultural practices for the production of crops, such as sugar cane, coffee, tobacco and cotton in the Caribbean, have led to soil erosion and increased soil pollution loads, as has occurred in Barbados and Cuba. Erosion has reached levels of up to 15 percent in some countries and could reach 60 percent by 2100 if no action is taken to halt current levels of land and soil degradation (ECLAC, 2010a; Justicia, 2007; Organización Panamericana de la Salud, 2012).

In Central America, agriculture is the largest contributor to soil pollution. Belize uses large quantities of pesticides which have not only polluted water and soil, but have also affected local populations’ health (Regeneration International, 2019). Guatemala’s economy is based largely on agricultural, forestry and livestock activities, which are directly dependent on the quality of soil, water and forests. However, there are serious soil pollution problems due to a relatively large area of the territory dedicated to agricultural production with techniques that involve significant damage to soil quality and increased contaminant loads. Some of these issues arise from a lack of environmental awareness amongst farmers (Ministerio de Ambiente y Recursos Naturales, 2016). In Panama, one of the most prominent impacts on soil and water is pollution due to the indiscriminate use of agrochemicals, particularly fertilizers in both crop production and pastoral areas (Autoridad Nacional del Ambiente, 2014).

In South America, the situation varies greatly from one country to another. In Uruguay and Paraguay, soil erosion is the most important environmental problem associated with agricultural activity. Erosion can contribute to the migration of dust from eroded bare soil that could lead to the dispersion of contaminated soil particles. Such dispersion affects surface and groundwater bodies and distant agricultural areas (MGAP, 2019b). In Peru, most of the pesticides used are synthetic organic compounds. They include fungicides such as Propamocarb and Cymoxanil to control blight (Phytophthora infestans) and insecticides, such as carbofuran, to control Andean weevil and potato moth (Gomero Osorio and Lizárraga Travaglini, 2010).

Additionally, there is a pressing need to deal with hazardous stockpiles of obsolete pesticides in the region. Leakage from abandoned pesticides, empty pesticide containers and buried stockpiles presents a pollution risk to surrounding soils and groundwater. Pesticide applications can also leach through soils and pollute underlying groundwater, which then threaten drinking water and water used for irrigation. Water erosion and run-off can also disperse soil pollution through the transport soil particles with associated pesticide contaminants. Such pollution can impact other crops, contaminating foodstuffs, representing a potential risk to public health (ECLAC, 2010b). Even ten years after the ECLAC report, the situation is almost the same and urgent action is needed.

In Nicaragua, toxaphene, dichlorodiphenyl trichloroethane (DDT), dieldrin, eldrin, lindane and endosulfan were used intensively in the 1980’s and 1990’s, and even at the beginning of the 2000s, leaving residues in the soil (Carvalho et al., 2003; Cruz-Granja, Dorea and Romero, 2001; UNEP, 2002). In Colombia it is estimated that there are approximately 500 tonnes of obsolete pesticides in several locations throughout the country either in warehouses or illegally buried (Sanchez, Rodriguez and Sarria, 2006). In El Salvador, the Ministry of Environment and Natural Resources (MARN) found more than 62 tonnes of pesticide wastes, in addition to contaminated solvents and equipment (MARN, 2016a).

The use, disposal and management of highly toxic pesticides is now being tackled by the Chemical programme of UNEP financed by the GEF, under the POPs Global Monitoring Plan in the Latin American and Caribbean Region programme. The second phase, implemented between 2016 and 2019, aimed at increasing national capacities to phase out and reduce releases of POPs, controlling the levels of POPs in breast milk and air, although with certain limitations in its implementation (Rauert et al., 2018). However, residues of POPs in soil from hazardous stockpiles of obsolete pesticides still represent a major problem in the region (GEF, 2019).

9.2.2. Urban waste management

The poor management of solid waste and sewage has led to serious soil pollution problems in the region (Kaza et al., 2018). Direct discharge into the nearest waterway without prior treatment is a very frequent practice that has a direct impact on soils. More specific information is provided below.

The region generated 231 million tonnes of municipal solid waste (MSW) in 2016, the daily equivalent of 0.6 kg/person in Latin America and 1 kg/person in the Caribbean (Kaza et al., 2018). Grau et al. (2015) reviewed data on MSW arising and its management across the countries in the region. Two key statistics were drawn from this analysis. First, on average, only 55 percent of MSW was deemed to be adequately managed and second, only 4.5 percent of MSW was recycled (Error! Not a valid bookmark self-reference.). However, there were great differences among countries. In Haiti, only 11 percent of MSW was collected and deposited in open landfills without any management treatment, while Trinidad & Tobago, Venezuela (Bolivarian Republic of), Argentina or Colombia had collection rates close to 100 percent but proper management rates varied from 0, 13, 64, and 93, percent, respectively.

Table 1. Status of Solid Waste Management in Latin America and the Caribbean.

Source: IDB, 2015.

The World Bank (2013) highlighted that three quarters of sewage or wastewater returns to the rivers and other water sources, which are then used to irrigate crop soils. Wastewater may contain a diverse range of contaminants, from pathogenic microorganisms to organic contaminants and trace elements such as chromium, copper, mercury and zinc, potentially creating public health and environmental problems. This report shows that distribution pipelines have been built in many countries to control wastewater fluxes, but after 20 years with minimal maintenance, many have started to leak, causing pollution to soils and groundwater. This is a major problem in Latin American cities, where wastewater treatment plants depend on additional government investments since taxes and service charges do not cover actual maintenance and operating costs. IDB (2018a) indicated that water management requires funds, which are usually scarce and have to compete with other priorities in the region. It is imperative to significantly increase the funding levels for the sector. IDB (2018a) also indicated that in Latin America a great share of industrial wastewater was not treated prior to its discharge into the environment.

In the British Virgin Islands, outdoor burning, dumping and compaction of waste are common practices and there is no leachate treatment plant (Towle et al., 2015). As the Dominican Republic lacks other adequate treatment facilities, all wastes are disposed in over 350 open dumps across the island (Del Rosario, 2017; JICA and ADN, 2006). Finally, in Trinidad and Tobago, most waste is disposed of in landfills and the remainder in waterways. Hospital waste is disposed of with common urban wastes (Caribbean Agricultural Science and Technology Network, 2005; Circle, 1996).

The Economic Commission for Latin America and the Caribbean has reported that tourism is a very important source of job creation in many countries of the region, but it causes the generation of large amounts of waste (ECLAC, 2012). Tourism requires an increase in transport and energy infrastructure, and creates additional vehicular traffic, all of which can be potential sources of soil pollution. In the Caribbean in particular, tourism is the main economic activity. It is responsible for additional volumes of MSW and wastewater from that produced by the indigenous population and industries. Given the already inadequate capacity for the environmentally sound management of MSW and wastewater, the additional burden from tourism causes further soil pollution (Del Rosario, 2017; Rawlins et al., 1998). Open dumps, in addition to causing actual soil and groundwater pollution, can adversely influence tourism due to unsightly aesthetics and smells. Villaverde del Rio (2019) indicated that in Aruba, tourist infrastructures have generated serious ecological disorders such as the destruction of ecosystems, decrease in water quantity and quality, soil pollution, extinction of multiple species of fauna, severe affectation of flora, fishing predation and sea pollution. Similarly, soils in the Bahamas have been affected by the mismanagement of solid residues that arose as a result of the construction of several large resort-type hotels, houses, commercial complexes and streets due (Ministry of Agriculture and Fisheries, 2001).

The availability of managed sanitary systems is also irregularly distributed in the region (Figure 8) (WHO, 2017). In Antigua and Barbuda, only 4.2 percent of people use toilets that are connected to a sewage system (National Assessment Team of Antigua and Barbuda, 2007). In the Bahamas, less than 10 per cent of the population is connected to sewage collection and treatment (U.S. Army Corps of Engineers, 2004) and liquid waste is usually disposed of through septic tanks, which often leak into groundwater bodies (Ministry of Agriculture and Fisheries, 2001). The supply of water for drinking and irrigation in the Bahamas is mainly through groundwater wells, which poses a risk to the health of the local population and the environment (FAO, 2015b). In Grenada, only 8.2 percent of the population are covered by the public residential sewerage service, while 36.3 percent have pit latrines and 2.4 percent do not have access to any excreta disposal facility (Organización Panamericana de la Salud, 2012).

Figure 8. Population using safely managed sanitation services (percentage).

Note: The map has been prepared for illustrative purposes only, the boundaries shown on this map do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.

Source: UN, 2020 modified from WHO, 2017.

In Central America, the situation is similar. The use of open-air dumps is common practice in Belize, where the waste of 85.2 percent of the population is disposed of in this way, compared with 69.8 percent in Guatemala and 59.3 percent in Nicaragua (IDB, 2015). Open burning of these materials or their release into water bodies is a concern in these three countries as well as in Honduras and Panama (Tello Espinoza et al., 2010). In Costa Rica, only 15.2 percent of wastewater is collected and treated, while the rest is simply collected in the sanitary sewer system and discharged directly into water bodies (Fallas, 2012). A study by USAID in El Salvador found that 93 percent of wastewater is discharged without treatment into rivers and streams, 83 percent of surface water is polluted, leading to soil pollution from irrigated systems (Magaña, 2010). In Panama, economic growth has been accompanied by the pollution of water sources and soils by improperly disposed solid waste and the discharge of wastewater into existing water bodies (Autoridad Nacional del Ambiente, 2014). In Mexico, only 40.2 percent of wastewater is treated and 83.93 percent of solid waste is collected, of which only 9.63 percent is recycled. Thus, an important part of the residues have a direct impact on the soil (Secretaría de Medio Ambiente y Recursos Naturales, 2017).

In South America, Colombia, Ecuador, Bolivia (Plurinational State of), Peru, Brazil and Venezuela (Bolivarian Republic of) dispose of most of their wastewater directly without treatment into surface water bodies, according to national experts’ views, and solid wastes are not properly disposed of (IDB, 2015). Such practices lead to the contamination of soils directly through contact and leaching of solid wastes, and indirectly through the contamination of water leading to soil pollution from irrigation systems (Fontaine, Quiñónez and Cisneros, 2008; Forno and Pauwels, 2010; Grupo RRP, 2018; Lopera and Campos, 2011; Stepping, 2016; Villalba, 2017). Conversely, in Chile, 94.2 percent of the total wastewater is treated (FAO, 2017b). In Argentina, most locations have selective collection and recovery plants for recycling and composting, which reduces the impact on soils (González, 2010) and in Uruguay, most solid waste arrives at recycling plants (SE, 2019).

In Barbuda, soil and groundwater pollution by pathogens and antimicrobial resistant bacteria from septic tanks is a concern (USACE, 2004). This situation is repeated in Aruba and generally throughout the Caribbean and in Central and South American countries such as Bolivia (Plurinational State of), Belize, Nicaragua, Honduras, Guyana and Panama, due to the large amount of residues generated by the tourism sector and large cities and the limited capacities to treat them properly (CARIBSAVE, 2012; Del Rosario, 2017; Index mundi, 2019; JICA and ADN, 2006; Lodos et al., 2000; Ministerio de Ambiente y Recursos Naturales de Guatemala, 2017; Ministry of Agriculture and Fisheries, 2001; OPS, 2012a; Tello Espinoza et al., 2010; Thomas-Hope, 1998). Wells in slums and shanty towns are often poorly constructed and dug near inadequate sewage systems, increasing the risks of pollution of water sources and subsequent soil pollution where the water is used for irrigation (DEHS, 2013).

In Barbados, waste disposal has serious limitations for the country’s sustainable development and waste management was a critical issue (ACDI, 2008). Similar issues impact Dominica (PAHO, 2012) and Haiti, where polluted waters and degradation of marine and river coastlines are closely related to soil pollution (UNEP, 2013).

A topic of particular interest in the last few years has been the amount of plastics and microplastics generated in the region. Figure 9 shows the total amount of uncollected household wastes and plastics in selected Caribbean countries (Diez et al., 2019). The data indicates that approximately 10 percent of the uncollected waste is plastic, indicating the extent of soil pollution by this waste. The Costa Rican Association of Soil Science indicated that plastic and electronic waste are a growing problem, with about 550 tonnes of plastic being discarded daily (Universidad de Costa Rica-URC, 2018). In Haiti, the same problem needs to be addressed, as only 11 percent of solid waste is collected and most of the post-consumer plastics are disposed of in the open, from where they can migrate directly into canals, sewers and bodies of water. Discarded plastics become a breeding ground for pests and are directly related to diseases such as malaria, dengue and Zika (BID, 2019).

Figure 9. Total uncollected household waste and plastic in some Caribbean Countries.

Source: adapted from Diez et al., 2019.

Trace elements have also been associated with waste in the region. Hernández-Colorado, Alvarado and Romero (2012) indicated that high concentrations of copper (ranging from 60 mg/kg to 307 mg/kg) were found in soils near polluted landfills, values higher than the average reported for European countries. Honduras reported mercury emissions of 66.95 kg/year in 2011 from the Managua landfill (Castillo and Rodríguez, 2011). Another environmental study on trace metals in soils found levels of lead between 15-214 mg/kg, chromium between 12-417 mg/kg, and copper between 156-1 057 mg/kg, in soils near a landfill in Nicaragua affecting the health of scavenger children (Cuadra, 2005).

Additionally, the mixing of household and hazardous industrial waste was a common practice in the Latin American and Caribbean region (Escobari and Malky, 2005). Hazardous and industrial wastes were discharged in open dumps with no containment or leachate management, and without previous treatment. Industrial activities release mixtures of organic and inorganic contaminants into the soil, as is the case in Trinidad and Tobago and Nicaragua, where most industries do not have effluent treatment systems or incentives to invest in cleaner technologies. Most industrial waste is disposed of in landfills and waterways, a situation that repeats also for medical waste (Barreto Cajina et al., 2004; Caribbean Agricultural Science and Technology Network, 2005; Circle, 1996). High levels of volatile organic contaminants, mainly BTEX compounds (benzene, toluene, ethylbenzene and xylenes) and chlorinated solvents (tetrachloroethene, 1,2-trichloroethene, 1,2-dichloroethene, vinyl chloride) and semi-volatile organic compounds were detected in the United States Virgin Islands (Rodriguez, 2018; US EPA, 2019a). In Puerto Rico, the US EPA determined that industrial operations and discharges from a landfill had polluted the soil with chemical products including tetrachlorethylene and trichlorethylene (US EPA, 2017) and 22 other areas with PCBs and volatile organic compounds (Rivera, 2013). Extensive areas polluted by processed oil hydrocarbons, mainly due to spills and oil industry activities, have been reported in Mexico (Navarro, 2009).

9.2.3. Mining and extractive activities

Mining is another of the main sources of soil pollution in the region. The principal mining activities focus on the extraction of gold, lead, nickel, silver (5 800 million tonnes only in Mexico), zinc, lithium, iron (480 billion tonnes), tin, bauxite and alumina, and copper (5.6 billion tonnes only in Chile) (Statista, 2020). ECLAC (2018) indicates that Latin America and the Caribbean has a significant share in the world’s reserves of the main metallic minerals, including 61 percent of lithium, 39 percent of copper, 32 percent of silver and nickel, 25 percent of molybdenum and tin, 23 percent of zinc, 18 percent of bauxite and aluminium, 15 percent of iron and lead and 11 percent of gold. The same report indicates that 37 percent of mining exports worldwide come from the region. Mining extraction has increased six-fold, from 659 million tonnes in 1970 to 4 billion tonnes in 2017. The main environmental challenges of mining that persist in the region are: water, air and soil pollution resulting from extraction, smelting and transportation; competition for the use of water resources (basins and reservoirs); destruction of habitat and protected areas; and the high-risk of informal and illegal gold mining, which use large amounts of mercury to extract the gold ((ECLAC, 2018). Mining and oil extraction pose other environmental problems, including deforestation, which leads to loss of plant cover, impacts climate change and increases soil erosion (UNEP, 2011).

According to Nolasco (2011), the principal metals extracted in Central America are gold, silver, lead, and zinc. The main contaminants from the mining processes are iron, lead, mercury, cadmium, arsenic and cyanide. Arsenic and mercury compounds present in mine tailings and the wastewater used for shale oil exploitation through fracking cause downstream pollution in soils and water bodies (FAO and ITPS, 2015; Lechtenböhmer et al., 2011).

The environmental problems usually associated with mining are related to the release of chemical used in the extraction process (such as cyanide and mercury), and the leaching of contaminants contained in the mineral. In Chile, copper deposits frequently contain compounds such as sulphates, arsenic and molybdenum, and generate the phenomenon of “acid drainage”, which leads to the acidification of soils and water. In this context, the main challenge facing the countries of Latin America and the Caribbean is the proper regulation of the mining industry, especially small and medium-sized enterprises (BID, 2018).

In Colombia, soil pollution has been caused by the development of unsustainable industrial, mining and urban activities (Ministerio de Ambiente y Desarrollo Sostenible, 2016). According to the Department of Plans and Environment of the Chilean Ministry of Environment, mining activities have generated the largest number of polluted sites (Ministerio del Medio Ambiente, Departamento de Planes and Ambiental, 2018). In Ecuador, the increase in artisanal and illegal mining has caused an increase in trace elements pollution, exceeding the limits set in Ecuadorian regulations (e.g. cadmium 0.5 mg/kg; chromium (VI) 2.5 mg/kg; and lead 25 mg/kg) (Oviedo-Anchundia et al., 2017). In Argentina, according to Carrere (2004), gold mining is one of the most destructive and polluting activities, as it uses sodium cyanide, which can be leached into the soil. Leaching of cyanide solutions from extraction processes into soils has also been observed in Brazil (Cesar et al., 2011). In Suriname, mercury levels downstream of artisanal and small-scale gold mining (ASM) operations are generally high, but its subsequent impact on fish, wildlife populations and people remains poorly known. Measures are being taken to regulate small-scale gold mining, to promote alternatives to mercury and raise awareness of artisanal miners and the public of the health issues (The Ministry of Labour Technological Development and Environment (ATM), 2013).

It is worth adding that the use of mercury in ASM also affects people who do not work in this type of activity. Indeed, as it evaporates to release gold, mercury vapours migrate, entering the river sediments, where they may be transformed by microorganisms into methylmercury, which is much more toxic than metallic mercury (US EPA, 2014). Through fish living in the river and absorbing the mercury, it enters the food chain of the populations living alongside the river.

In Jamaica, lead concentrations of 400 mg/kg were found up to a depth of nine metres in soils surrounding smelting furnaces (Gerald, Bryan and Vutchkov, 2007) (600 mg/kg NJDEP regulatory limit). Also in Jamaica, a study on trace element pollution indicated high concentrations of cobalt, aluminium, manganese, copper, cadmium and zinc in soils due to smelting furnaces (Brown Morrison, 2013; Mandal and Voutchkov, 2011).

The majority of closed uranium mines in Argentina continue to pollute the environment because they have not been properly closed and contained. As at 2008, more than 36 000 tonnes of low-activity radioactive uranium waste are not isolated (FUNAM and Montenegro, 2008). In Mexico, heavy metal pollution is a growing problem due to silver mining. The most important polluting metals for their abundance are mercury, arsenic, lead and chromium (Covarrubias and Peña Cabriales, 2017).

9.2.4. Other sources of soil pollution

The high natural content of metals such as chromium and nickel in some soils is due to parental material (i.e. geogenic). This is the case of Cuban soils developed from serpentine with very high contents of nickel (2 000 mg/kg), chromium and cobalt, fortunately in forms that are not available to plants (Alfaro et al., 2014).

The armed conflicts in El Salvador, Colombia and part of Panama have also left a legacy of polluted soils with various contaminants. In those areas, an unknown number of explosives contained in unexploded landmines, as well as explosive residues and metal components of exploded landmines have posed a serious threat to the environment and human health (Comité Internacional de la Cruz Roja, 1996; Escandon, 2006; Gonzalez and Sarmiento, 2018; IUCN, 2000).

Asbestos and synthetic dyes are frequently considered minor soil contaminants due to the ban on their use and production in many countries of the region, such as Argentina, Chile, Colombia, Honduras, and Uruguay (Archdaily, 2018; BCN, 2009; Hess, 2000; LaRed21, 2002; Ministerio de Salud, 2001; Portafolio, 2019). In June 2019 in Colombia, the House of Representatives approved the ban on the use of asbestos in the country, which will prohibit its production, commercialization, use or export in any activity in the national territory as of January 2021.