InNorth America andEurope the extent ofcontaminated land is best known for as many of the countries in these areas have a legal framework to identify and deal with this environmental problem.[14][15][16] Other countries tend to be less tightly regulated despite some of them have undergone significantindustrialization and are searching for more regulation.[17][18]
E-waste processing inAgbogbloshie, Ghana. Improper disposal of manufactured goods and industrial wastes, often means that communities in the global south have to process goods. Especially without proper protections, heavy metals and other contaminates can seep into the soil, and createwater pollution andair pollution.
Historical deposition ofcoal ash used for residential, commercial, and industrial heating, as well as for industrial processes such asore smelting, were a common source of contamination in areas that wereindustrialized before about 1960.[21] Coal naturally concentratesarsenic,cadmiumlead andzinc during its formation, as well as otherheavy metals to a lesser degree.[22] When the coal is burned, most of these metals become concentrated in the ash (the principal exception beingmercury, whichevaporates).[23] Coal ash andslag may contain sufficient lead to qualify as a "characteristichazardous waste",[24] defined in the US as containing more than 5 mg/L, further revised to 1.5 mg/L of extractable lead using theTCLP procedure.[25] In addition to lead, coal ash typically contains variable but significant concentrations ofpolynuclear aromatic hydrocarbons (PAHs; e.g.,benzo(a)anthracene,benzo(b)fluoranthene,benzo(k)fluoranthene,benzo(a)pyrene,indeno(1,2,3-cd)pyrene,phenanthrene,anthracene, and others).[26] These PAHs are known humancarcinogens[27] and the acceptable concentrations of them in soil are typically from 0.1 mg/kg to 10 mg/kg, with a strong variation from a PAH to another.[28] Coal ash and slag can be recognised by the presence of off-white grains in soil, gray heterogeneous soil, or (coal slag) bubbly, vesicular pebble-sized grains.[29]
Herbicides are used to killweeds, especially onpavements[43] andrailways,[44] but also inagricultural crops either for destructing the total vegetation (e.g.glyphosate) or only a class of undesired plants (e.g.2,4-D). The so-called auxin herbicides are similar toauxins and are selective todicots.[45]Glyphosate is a non-selective (broad-spectrum) systemic herbicide which competes withenzymes used in the synthesis of key plantamino acids.[46] Most herbicides arebiodegradable bysoil bacteria.[47] However, one group derived fromtrinitrotoluene (2,4-D and2,4,5-T) have the impuritydioxin, which is very toxic and causes fatality even in low concentrations.[48] Another common herbicide isParaquat, banned in the European Union but still frequently used in agricultural areas of the United States and Asia.[49] It is highly toxic to humans[50] and other animals[51] and cannot rapidly degrade in the soil where it isadsorbed and thus protected inclay lattices.[52] Glyphosate is rapidly transformed inAMPA by soil bacteria but itsresidues are detected in drinking water, agriculture, and food products and have major effects on the health ofreproductive systems.[53] Glyphosate is used ingenetically modified crops to kill all vegetation except the target crop, more especially indeveloping countries where it offers yield and profit gains despite growing concerns about environment and human health.[54]
Insecticides are used to rid farms of pests which damage crops. The insects damage not only standing crops but also stored ones and in the tropics it is reckoned that one third of the total production is lost during food storage.[55] As withfungicides, the first insecticides used in the nineteenth century were inorganic e.g.Paris Green and other compounds ofarsenic.[56] Nicotine has also been used since 1690.[57]Neonicotinoids, i.e. synthetic insecticides derived from nicotin are the last generation of insecticides. They have been scheduled to be highly selective to insect pests, although it appeared thatacetamiprid,IMI, andthiacloprid were toxic to birds, thiacloprid to fish, and several neonicotinoids were harmful tohoneybees, either by direct contact or ingestion.[58]
There are now three main groups of synthetic insecticides:
1.Organochlorines includeDDT,Aldrin,Dieldrin andbenzene hexachloride (BHC). They are cheap to produce, potent and persistent but have harmful effects on a lot of beneficial organisms, from microbes[59] to a wide range of plants and animals, humans included,[60] hence their banishment in many (but not all) countries,[61] inasmuch asresistance occurred in a lot of target insect pests.[62] DDT was used on a massive scale from the 1930s, with a peak of 72,000 tonnes used in 1970.[63] Then usage fell as the harmfulenvironmental effects were realized.[64] It was found worldwide in fish and birds[65] and was even discovered in the snow in theAntarctic.[66] It is only slightly soluble in water[67] but is very soluble in the bloodstream,[68] and infats. It affects the nervous[69] and endocrine systems[70] and causes the eggshells of birds to lack calcium causing them to be easily breakable.[71] It is thought to be responsible for the decline of numbers of birds of prey likeospreys andperegrine falcons in the 1950s, now recovering.[72] As well as increased concentration via thefood chain, it is known to enter viapermeable membranes, so fish get it through theirgills and then it accumulates in fatty organs.[73] As it has lowwater solubility and a high affinity to the air-water interface,[74] DDT tends to stay at the water surface, so organisms that live there are most affected, in particularmosquito larvae,[75] the target organisms ofmalaria control.[76] DDT and its breakdown productDDE found in fish that formed part of the human food chain caused concern, with levels found in humanliver,kidney andbrain tissues around 13 ppm in 1970,[77] with a general decrease since DDT was banished from developing countries but with still high levels in Asia and Africa where DDT is used against malaria.[78] DDT was banned by theStockholm convention in 2001 to stop its further buildup in thefood chain. However, theWorld Health Organization allowed its reintroduction only for control ofvector-borne diseases in sometropical countries in 2006.[79] U.S. manufacturers continued to sell DDT to developing countries, who could not afford the expensive replacement chemicals and who did not have such stringentregulations governing the use of pesticides.[80]
2.Organophosphates, e.g.parathion,methyl parathion and about 40 other insecticides are available nationally. Parathion is highly toxic, methyl-parathion less so[81] but health concerns have resulted in cancellation of the use of methyl-parathion in most food crops in the United States.[82] There is no evidence thatmalathion affects the ability of humans to reproduce. There is also no conclusive proof that malathion causes cancer in humans, although some studies have found increased incidence of some cancers in people who are regularly exposed to pesticides, such as farmers and pesticide applicators.[83] This group of insecticides works by preventing normal nerve transmission asacetylcholinesterase is prevented from breaking down the transmitter substanceacetylcholine, resulting in uncontrolled muscle movements.[84]
The disposal ofmunitions, and a lack of care in manufacture of munitions caused by the urgency of production, cancontaminate soil for extended periods.[93] There is little published evidence on this type of contamination largely because of restrictions placed by governments of many countries on the publication of material related to war effort, in particular under ongoing conflict scenarios.[94] However,mustard gas stored duringWorld War II has contaminated some sites for up to 50 years[95] and the testing ofAnthrax as a potentialbiological weapon contaminated the whole island ofGruinard, leaving it in quarantine for 48 years.[96] There are abandoned delaboration sites around the formerWorld War I front in Belgium and also in France which are still contaminated by arsenic and lead.[97]
Contaminated or polluted soil directly affectshuman health through direct contact with soil[98] or via inhalation of soil contaminants that have vaporized.[99] Potentially greater threats are posed by the infiltration of soilcontaminants intogroundwateraquifers used for irrigation[100] or direct human consumption,[101] sometimes in areas far from any apparent source of above-ground contamination (long-range diffuse soil contamination).[102] Toxic metals can also make their way up thefood chain through plants that reside in soils containing high concentrations of heavy metals.[103] This tends to result in the development ofpollution-related diseases.
Most exposure to soil contamination is accidental, and can happen through:[104]
Ingesting dust or soil directly
Ingesting food or vegetables grown in contaminated soil or with foods in contact with contaminants
Skin contact with dust or soil
Vapors from the soil
Inhaling clouds of dust while working in soils or windy environments
However, some studies estimate that 90% of human exposure is through eating contaminated food.[104]
Health consequences from exposure to soil contamination vary greatly depending on pollutant type, the pathway of attack, and the vulnerability of the exposed population.[105] Researchers suggest thatpesticides andheavy metals in soil may harmcardiovascular health, includinginflammation and change in the body'scircadian rhythm.[106]
This area is contaminated with stagnant water and refuse, making the environment unhygienic.
Not unexpectedly, soil contaminants can have significant deleterious consequences for ecosystems.[119] There are radicalsoil chemistry changes which can arise from the presence of manyhazardous chemicals even at low concentration of the contaminant species.[120] These changes can manifest in the alteration of themetabolism ofsoil microorganisms andsoil animals resident in a given soil environment.[121][122] The result can be virtual eradication of some of the primaryfood chain, which in turn could have major consequences forpredator or consumer species.[123] Even if the chemical effect on lower life forms is small, the lower pyramid levels of thefood chain may ingest alien chemicals, which then become more and more concentrated for each consuming rung of the food chain.[124] Many of these effects are now well known, such as the concentration of persistentDDT materials for avian consumers, leading to weakening ofegg shells, increased chickmortality and potentialextinction of species.[125]
Detrimental impacts of contaminants on soil food chains result in dramatic changes inhumus forms, mediated by the disappearance or reduced activity of key organisms, also called soilecosystem engineers, e.g. earthworms, which arez particularly sensitive to a wide range of soil contaminants.[126] Incontaminated land thetopsoil passes from a stage in whichorganic matter is decomposed and incorporated to mineral matter (mull humus, with a good granularsoil structure) to a stage in which organic matter accumulates undecayed above a compact mineral soil with poor structure (mor humus).[127]
Heavy metals and other soil contaminants can adversely affect the activity, species composition and abundance ofsoil microorganisms, thereby threateningsoil functions such as biochemical cycling ofcarbon andnitrogen.[131] However, soil contaminants can also become lessbioavailable by time (natural attenuation),[132] and microorganisms and ecosystems can adapt to altered conditions.[133] Soil properties such aspH,organic matter content andtexture are very important and modify mobility,bioavailability andtoxicity of pollutants in contaminated soils.[134] The same amount of contaminant can be toxic in one soil but totally harmless in another soil.[135] This stresses the need for soil-specificrisk assessment[136] andremediation measures.[137]
Excavate soil and take it to a disposal site away from ready pathways for human or sensitive ecosystem contact. This technique also applies todredging ofbay muds or navigablecanals containingtoxicants.[141]
Aeration of soils at the contaminated site,[142] with attendant risk of creatingair pollution.[143]
Various national standards for concentrations of particular contaminants include the United States EPA Region 9 Preliminary Remediation Goals (U.S. PRGs),[152] the United States EPA Region 3 Risk Based Concentrations (U.S. EPA RBCs),[153] and National Environment Protection Council of Australia Guideline on Investigation Levels for Soil and Groundwater.[154]
The immense and sustained growth of thePeople's Republic of China since the 1970s has exacted a price from the land in increased soil pollution.[155] TheMinistry of Ecology and Environment believes it to be a threat to the environment, to food safety and to sustainable agriculture. According to a scientific sampling, 150 millionmu (100,000 square kilometres) of China's cultivated land have been polluted, withcontaminated water being used to irrigate a further 32.5 million mu (21,670 square kilometres) and another 2 million mu (1,300 square kilometres) covered or destroyed by solid waste. In total, the area accounts for one-tenth of China's cultivatable land, and is mostly in economically developed areas. An estimated 12 million tonnes of grain are contaminated by heavy metals every year, causing direct losses of 20 billionyuan ($2.57 billionUSD).[156] Recent survey shows that 19% of the agricultural soils are contaminated which contains heavy metals and metalloids. And the rate of these heavy metals in the soil has been increased dramatically.[157]
According to the received data from Member states, in theEuropean Union the number of estimated potential contaminated sites is more than 2.5 million[158] and the identified contaminated sites around 342 thousand. Municipal and industrial wastes contribute most to soil contamination (38%), followed by the industrial/commercial sector (34%). Mineral oil and heavy metals are the main contaminants contributing around 60% to soil contamination. In terms of budget, the management of contaminated sites is estimated to cost around 6 billionEuros (€) annually.[158]
Generic guidance commonly used in theUnited Kingdom are the Soil Guideline Values published by theDepartment for Environment, Food and Rural Affairs (DEFRA) and theEnvironment Agency. These are screening values that demonstrate the minimal acceptable level of a substance. Above this there can be no assurances in terms of significant risk of harm to human health. These have been derived using the Contaminated Land Exposure Assessment Model (CLEA UK). Certain input parameters such as Health Criteria Values, age and land use are fed into CLEA UK to obtain a probabilistic output.[159]
Guidance by the Inter Departmental Committee for the Redevelopment of Contaminated Land (ICRCL)[160] has been formally withdrawn byDEFRA, for use as a prescriptive document to determine the potential need for remediation or further assessment.
The CLEA model published by DEFRA and theEnvironment Agency (EA) in March 2002 sets a framework for the appropriate assessment of risks to human health from contaminated land, as required by Part IIA of theEnvironmental Protection Act 1990. As part of this framework, genericSoil Guideline Values (SGVs) have currently been derived for ten contaminants to be used as "intervention values".[161] These values should not be considered as remedial targets but values above which further detailed assessment should be considered; seeDutch standards.
Three sets of CLEA SGVs have been produced for three different land uses, namely
residential (with and without plant uptake)
allotments
commercial/industrial
It is intended that the SGVs replace the former ICRCL values. The CLEA SGVs relate to assessing chronic (long term) risks to human health and do not apply to the protection of ground workers during construction, or other potential receptors such as groundwater, buildings, plants or other ecosystems. The CLEA SGVs are not directly applicable to a site completely covered in hardstanding, as there is no direct exposure route to contaminated soils.[162]
To date, the first ten of fifty-five contaminant SGVs have been published, for the following: arsenic,cadmium, chromium, lead, inorganic mercury, nickel, selenium ethyl benzene, phenol and toluene. Draft SGVs for benzene, naphthalene and xylene have been produced but their publication is on hold. Toxicological data (Tox) has been published for each of these contaminants as well as for benzo[a]pyrene, benzene, dioxins, furans and dioxin-like PCBs, naphthalene, vinyl chloride, 1,1,2,2 tetrachloroethane and 1,1,1,2 tetrachloroethane, 1,1,1 trichloroethane, tetrachloroethene, carbon tetrachloride, 1,2-dichloroethane, trichloroethene and xylene. The SGVs for ethyl benzene, phenol and toluene are dependent on thesoil organic matter (SOM) content (which can be calculated from the total organic carbon (TOC) content). As an initial screen the SGVs for 1% SOM are considered to be appropriate.[163]
As of February 2021, there are a total of 2,500 plus contaminated sites inCanada.[164] One infamous contaminated sited is located near a nickel-copper smelting site in Sudbury,Ontario. A study investigating the heavy metal pollution in the vicinity of the smelter reveals that elevated levels of nickel and copper were found in the soil; values going as high as 5,104ppmNi, and 2,892 ppmCu within a 1.1 km range of the smelter location. Other metals were also found in the soil; such metals include iron, cobalt, and silver. Furthermore, upon examining the different vegetation surrounding the smelter it was evident that they too had been affected; the results show that the plants contained nickel, copper and aluminium as a result of soil contamination.[165]
In March 2009, the issue ofuranium poisoning in Punjab attracted press coverage. It was alleged to be caused byfly ash ponds ofthermal power stations, which reportedly lead to severe birth defects in children in theFaridkot andBhatinda districts ofPunjab. The news reports claimed the uranium levels were more than 60 times the maximum safe limit.[166][167] In 2012, the Government of India confirmed[168] that the ground water in Malwa belt of Punjab has uranium metal that is 50% above the trace limits set by the United Nations'World Health Organization (WHO). Scientific studies, based on over 1000 samples from various sampling points, could not trace the source to fly ash and any sources from thermal power plants or industry as originally alleged. The study also revealed that the uranium concentration in ground water of Malwa district is not 60 times the WHO limits, but only 50% above the WHO limit in 3 locations. This highest concentration found in samples was less than those found naturally in ground waters currently used for human purposes elsewhere, such asFinland.[169] Research is underway to identify natural or other sources for the uranium.
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Portal for soil and water management in Europe Independent information gateway originally funded by the European Commission for topics related to soil and water, including contaminated land, soil and water management.
European Soil Portal: Soil Contamination At EU-level, the issue of contaminated sites (local contamination) and contaminated land (diffuse contamination) has been considered by: European Soil Data Centre (ESDAC).