UN Enviroment Programme

Chapter 3. Sources of soil pollution

Sources of soil pollution and major contaminants in areas affected by armed conflict

In 2015, FAO and ITPS (2015) stated that “modern warfare makes use of non-degradable weapons of destruction and of chemicals that can remain in the affected soils for centuries after the end of the conflict”. Armed conflict has strongly affected soil health especially with the use of mechanization and modern weapon technologies. This section presents some of the most commonly found soil contaminants and their sources (Table 7) that are a direct result of armed conflict.

Table 7. Summary (not exhaustive) of the main contaminants found in areas affected by armed conflicts

Conventional Explosives

Warfare activities alter soil not only during conflict, but also during peace times through firing facilities, military bases, manufacturing operations, open/burning and open detonation, and dumping of munition. Soil pollution mostly comes from the use of nitro aromatic explosive compounds (such as trinitrotoluene (TNT), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), for which the US EPA has recommended concentration restrictions because of their toxicity for the environment and human health (Chatterjee et al., 2017; Qasim et al., 2007). By nature they are recalcitrant to volatilization, hydrolysis, and biodegradation, and as a result, can be absorbed by plants or leach into the groundwater (Chatterjee et al., 2017; Price et al., 2002). Moreover, the transformation products of nitro aromatic compounds are toxic and have a higher persistence than the original molecules. TNT and its transformation products affect soil fauna at different concentrations. For instance, lethal concentration for the earthworms Eisenia andrei and E. fetida was less than 200 mg/kg (Lachance et al., 2004; Renoux et al., 2000; Robidoux et al., 1999; Schäfer and Achazi, 1999), whereas for Enchytraeus albidus and E. crypticus earthworms, it was over 400 mg/kg (Dodard et al., 2003; Schäfer and Achazi, 1999). Overall, TNT and other chemical munitions were observed to affect soil microbial activity and communities (Fuller and Manning, 1998; Gong et al., 2001). Nitro-aromatic compounds also affect plant growth, germination capacity and root elongation (Nehrenheim et al., 2013; Vila, Lorber-Pascal and Laurent, 2008).

Manufacturing and testing of weapons are also responsible for soil pollution. The manufacturing of TNT, which started in the United States of America at the beginning World War I, produces effluents that are toxic due to the high concentrations of nitro-aromatic compounds (Ludwichk et al., 2015; US EPA, 2014a). The United States of America Department of Energy (US DOE) reported that over 70 million cubic metres of soil and at least 1 800 million cubic metres of water were contaminated by radioactive waste from the production of weapons (Ewing, 2004).

The negative effects from the use of incendiary weapons containing white phosphorus comes from their co-contaminants and residues of combustion. Such weapons may result in soil polluted with trace elements, hydrocarbons, organic solvents, surfactants, synthetic phenols, cyanide, dioxins, and radionuclides (Certini, Scalenghe and Woods, 2013). The weathering of abandoned bullets and other metallic weapons residues primarily releases lead in soils (Jørgensen and Willems, 1987; Lin et al., 1995; Manninen and Tanskanen, 1993). To a lesser extent other trace elements are released including antimony, arsenic, cadmium, chromium, copper, mercury, nickel and zinc (Ghanbarizadeh and Nejad, 2012; Johnson, Schewel and Graedel, 2006; Vasarevičius and Greičiūte, 2004).

In the United States of America, following the closure of military bases after the Cold War, extensive pollution of groundwater and soil from solvents, oxidizers and energetic materials was detected (Weir, 2015). Former defence installations account for 10 percent of EPA’s National Priorities List for its Superfund program. Also overseas installations were found contaminated in South Korea, the Philippines (Tritten, 2010) and the Japanese island of Okinawa (Weir, 2015). Figure 25 shows the estimated distribution of explosive-polluted soils worldwide. The recovery of these soils can take from years to centuries depending on the extent of soil pollution (Certini, Scalenghe and Woods, 2013).

Figure 25. Global distribution of explosive-contaminated soils.

Source: UN, 2020 modified with data from Via, 2016.

The detonation of mines causes adverse effects on soil with metal and plastic fragments and explosives residues (Certini, Scalenghe and Woods, 2013). Africa has the highest number of landmines, about 37 million, distributed in 19 countries. Among these countries Angola alone has 15 million landmines (Kobayashi, 2013).

Nuclear explosions

In July 1945, the first atomic bomb test took place at Socorro, New Mexico, followed by the detonation of two warheads a month later in Japan, first in Hiroshima and then in Nagasaki (Figure 26). The amount of uranium-235 and plutonium-239 used can be compared to 10 kilotons and 22 kilotons of TNT, respectively (Charpak and Garwin, 2002). From 1945 until 2006, the total number of nuclear explosions that took place in the world were 2 053 (Fedchenko and Hellgren, 2007). The threat from radionuclide pollution is due to their persistence in soils that can reach millions or thousands of years as in the case for uranium-235 and plutonium-239, respectively (Marsh et al., 1978; Xiaolong and Baosong, 2009). Plutonium (239+240+241Pu) pollution of terrestrial ecosystem still persists in Montebello Islands, Western Australia, after sixty years of nuclear bomb tests, where soils contain radionuclides concentrations up to 100 000 times higher than natural background values in Australia and which affect wildlife populations (Johansen et al., 2019). Following a nuclear explosion, fine particles with radionuclide contaminants are transported in air currents before deposition on the soil. There is a potential for wide scale pollution over long distances.

Figure 26. Mushroom cloud over Hiroshima and Nagasaki (1945). ©George R. Caron and Charles Levy (public domain, via Wikimedia Commons).

Radionuclide pollution also occurs from inadequate storage or dismantling of nuclear weapons. Cases of radioactive waste releases were recorded during the Cold War in the Russian Federation for plutonium (Skipperud et al., 2005); uranium at a weapon deposit near Boston, United States of America (Skryness, Swenson and Pananos, 1994); strontium and caesium at a nuclear production complex in Washington, United States of America (Zachara et al., 2007).

Major concern is arising from the use in conflicts of depleted uranium (DU) armour piercing weapons and their long-term effect on the environment and human health. The risk of soil pollution arises from the fine radioactive dust released during the impact of DU projectiles into armour. DU is a dense by-product of the uranium enrichment process to create nuclear weapons and fuel for nuclear power reactors. It has a toxicity similar to lead and it is an alpha particle emitter, with a half-life of 4.5 billion years. DU has a higher radioactivity compared to natural uranium (Pearson, 2002; Todorov and Ilieva, 2006).

The corrosion of intact projectiles and abandoned DU munitions is also a source of pollution which was noted after the Gulf War, Iraq and Kosovo conflicts (Pearson, 2002; Schimmack et al., 2007; Todorov and Ilieva, 2006). The DU is subject to corrosion following weathering processes, the rate of which depends on soil composition and the local geophysical properties and environmental conditions (UNEP, 2003). The leaching rate of uranium from corroded DU was hypothesized to be dependent on the mineral composition of the corroded DU, where the prevalence of three uranium mineral species can decrease the solubility of uranium from the DU (Wang et al., 2016). Corrosion results in uranium dust that is soluble in water and is responsible for an extensive and slow pollution of soil from leaching of uranium-238, the major naturally occurring uranium isotope (Schimmack et al., 2007; Todorov and Ilieva, 2006). Field measurements conducted at 11 sites in Kosovo found more than 100 Bq/kg of uranium-238 in soils up to a few metres from the localized DU concentration points. The vertical distribution of DU along the soil profile was measured up to 20 cm (Sansone et al., 2001). In a three-year laboratory study, it was observed that leaching rates increased with the weathering process, resulting in a more than 100-fold increase in uranium-238 leachate compared to the first year (Schimmack et al., 2007).

Chemical warfare agents

Chemical warfare agents (CWA) are compounds that incapacitate an enemy, through death or injury (Shenoi, 2002). An example of CWA are nerve agents, which were originally produced as insecticides, but used for military purposes because of the extent of their toxicity (Newmark, 2004). Few studies have focused on the effects and impact of nerve agents in soil. To date, it is only expected that they may kill living biota (Certini, Scalenghe and Woods, 2013).

The use of organoarsenic-based CWAs is responsible for the arsenic pollution of wide areas in which the chemical was used. In Loecknitz, Germany, the site of a military store of CWA that was destroyed in 1945, the mean value of arsenic measured in soils was 923 mg/kg compared to the background values of 10 to 50 mg/kg. Samples of velvet grass (Holcus lanatus) harvested in the area contained arsenic (Pitten et al., 1999). Following the termination of the cold war, efforts were made to control and denature stockpiles of CWA to avoid their potential escape into the environment.

In the Viet Nam War (1955–1975), the CWA mostly used was the herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), which caused the deforestation of 2 million hectares. The chemical, more famously known as “Agent Orange”, is a plant growth hormone, which causes a premature shedding of the leaves (Cawthorne, 2003; Stellman et al., 2003).

In soil 2,4,5-T and other herbicides can adversely affect the microbial biomass, and as a consequence, the biodegradation of organic matter (Mitsevich et al., 2000). Studies have found that the 2,4,5-T used by the U.S. army contained residues of polychlorinated dibenzo-para-dioxins (PCDD), which is highly toxic and remained in soils after several decades (Mai et al., 2007; Wayne Dwernychuk, 2005). Soil polluted with PCDDs is a threat for human health because it can easily be transferred into the food chain (Dwernychuk et al., 2002). The spillage of “Agent Orange” during the loading of the spraying aircraft polluted the airfields, and a case study of the remediation of soil polluted with PCDD at Danang, Viet Nam is included in Chapter 13.

Metal residues

Battlefields, bombed cities and military training areas are all sites of high levels of pollution by trace elements and organic contaminants. The sources are shells, bullets and bombs, unexploded mines, cartridge cases, damaged vehicles, leaking fuel and burning buildings.

Battlefields and training areas where there has been intense use of weapons over extended periods are all sites of high levels of pollution by trace elements, and organic compounds. These areas remain polluted with lead, copper, zinc, nickel antimony, arsenic and bismuth (Alloway, 2013b). A 625 square kilometre area near Ypres in Belgium where there were three major battles during the first World War, mean copper levels in surface soils have been reported as 18 mg/kg compared to the mean for the Flanders region of 12 mg/kg (Van Meirvenne et al., 2008).

Buttstops at military ranges accumulate concentrated volumes of spent bullets, which usually comprise 95 percent lead, 2 percent antimony, 3 percent copper and 0.5 percent nickel (Alloway, 2013b).

Collateral damage

Strategic objectives in armed conflicts can include the incapacity of an enemy to fight through the destruction of their infrastructure and resources. Fuel manufacture and storage are often targeted with the consequence of leakage of large quantities hydrocarbons into the soil or their combustion with the release of hydrocarbon and other emissions to the atmosphere and subsequent deposition onto the soil. During Operation Desert Storm in Kuwait in 1991 as the Iraqi military retreated, they destroyed more than 800 oil wells, setting fire to many. Large areas were flooded with crude oil that gushed from the damaged wells and formed oil lakes, which together with the fumes and particulates from the fires polluted vast tracts of soil (Al-Sarawi, Massoud and Al-Abdali, 1998). In the southern oil lake the oil reached depths ranging from 50 cm to 150 cm. A total of more than 300 oil lakes covered a surface area of 49 km2 (Al‐Awadhi et al., 1996).