Many metals and organic substances have an affinity for organic matter or mineral particles. Soils thus provide a suitable medium for the accumulation of contaminants from aqueous sources and atmospheric deposition. Land pollution by toxic chemicals from agriculture and industry arises from the dumping on land of ever-increasing amounts of domestic and industrial solid wastes, and leads to contamination of soil, food and water. As the world population and the degree of urbanization increase, this may prove to be a significant health hazard.
Major areas of concern in soil pollution include agricultural land pollution from chemical fertilizers, pesticides, or nutrients, solid wastes from industry and urban populations, and radioactive pollution from either nuclear explosions, release of liquid or solid radioactive wastes produced by industrial or research establishments, or radioactive fallout from the emissions of smoke-stacks of chemical works.
Compounding the problem of agricultural land pollution is the persistence of the degraded chemical products of soil additives, whose toxicity may, in fact, be more pronounced than that of the original additive. Slurry – the effluent of cattle and hogs – and the liquor from grass silage used as cattle feed are extremely polluting to land and water. Slurry can be 100 times and silage 200 times as polluting as untreated domestic sewage.
Regarding contamination from urban areas, the land available for waste disposal is diminishing, thus concentrating waste and its disagreeable effects, producing feeding grounds for insects and rodents and causing odours created from slowly smoldering fire or from organic decay. This creates a severe nuisance and public health hazard.
Industrialization has constantly increased the amount of waste being dumped on the soil. It has been estimated that 50% or more of the raw materials used by industry ultimately become waste products, of which about 15% can be considered deleterious or toxic. In addition, inorganic contaminants such as fluorides, emitted from smoke stacks, can contaminate nearby farmland.
At a 1999 ECE-sponsored seminar on contaminated soils, it was estimated that European areas containing remains of old chemical plants, spills of toxic metals, and other contaminants number more than 6000 sites.
The US multi-billion Superfund campaign was launched in 1980 to clean up contaminated land. The legislation was passed in response to a nationwide outcry over illnesses caused by toxic waste that had ben covered by housing at a New Jersey site known as Love Canal. The Superfund law was set up to ensure that businesses assumed the liability for cleaning up thousands of sites where hazardous substances were dumped. It was the largest programme administered by the Environmental Protection Agency. In 1993, it was considered to have failed to achieve many of its goals, with slightly more than 200 out of thousands of sites cleaned up and with years lost to costly litigation over who should pay for the work. There is to be a major revision of the law in 1994, easing standards of "cleanness" depending on how the land would be used in the future. For example, less restoration would be needed if the site was to be used for commercial or industrial development than residential development, since the risk of exposure would be less.
In the northern hemisphere, levels of radiation from fission products deposited in the soil by fallout are about 10 to 30% of those due to natural radioactive substances in the soil. In time, this increased radioactivity could affect soil fauna or their predators. In 1992, it was reported that fifteen percent of Russia's territory, or an area of one million square miles, had become unsafe for human habitation due to the effects of toxic waste dumping.
It was reported in 1993 that many polluted city sites in the UK, such as old tanneries, gas works, smelting and heavy industrial plants and rubbish dumps, some abandoned in Victorian times, were now not likely to be registered as contaminated due to protest from property owners and developers at the consequent loss of value of such lands. It is estimated that one tenth of UK land is polluted to some extent, but only 2% of all polluted sites urgently require treatment. The cost of totally restoring all affected land in the UK has been estimated at between £20 billion and £60 billion (1993). The lack of agreement on how to define contamination and appropriate decontamination is impeding clean-up.
It was reported in 1995 that an estimated 27,000 to 50,000 hectares of land in the UK was contaminated. Common sources of contamination are landfill sites which have been capped but which generate methane gas liable to cause explosions.
Currently in Australia there are over 80,000 contaminated sites in the urban environment and Australian industry spends millions of dollars per year for containment of sites. Techniques for the assessment and decontamination of these sites are often imported from the USA and Europe, and invariably these are inadequate for Australian soil environments, which differ significantly from those in the rest of the world.
A serious potential consequence of land contamination is the poisoning of ground water.