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Ebook An introduction to environmental chemistry and pollution (3E): Part 2

(BQ) Part 1 book "An introduction to environmental chemistry and pollution" has contents: Land contamination and reclamation, environmental cycling of pollutants, environmental monitoring strategies, ecological and health effects of chemical pollution, managing environmental quality. | CHAPTER 5 Land Contamination and Reclamation B. J. ALLOWAY 1 INTRODUCTION In many parts of the world, especially in the more technologically developed countries, soil, which forms the surface layer of the land, has been exposed to varying degrees of contamination from a wide variety of chemicals for many years, especially since the Second World War. Soil constitutes one of the three key environmental media, the other two being air and water, but the soil differs significantly from these two media because it is predominantly solid and has the capacity to retain many types of pollutants. These retention (sorption) mechanisms cause soil to function as sinks for contaminants. In this way soil acts as a filter, which reduces or prevents contaminants reaching the groundwater. Furthermore, the diverse populations of micro-organisms make soils powerful bioreactors which can degrade many hazardous organic chemical contaminants in addition to the normal biogeochemical cycles which are a vital component of terrestrial ecosystems. Some contaminants which are sorbed and not degraded will gradually accumulate and could reach concentrations that are potentially harmful to the functioning of the soil-plant system or to consumers of crops which take up these chemicals from contaminated soils. In contrast, pollutant concentrations in water and air become diluted through dispersion in these fluid media and, although larger volumes of these media can be affected by pollution, the effect is usually of limited duration. The range of chemicals found contaminating soils is vast and can include, for example: heavy metals, such as lead from paints and motor vehicle exhausts, polycyclic aromatic hydrocarbons (PAHs) formed during the incomplete combustion of organic materials such as wood and coal, synthesized organic chemicals such as chlorinated solvents or pesticides from leakages or direct application, radionuclides in fallout from the testing of nuclear weapons or accidents at .