ENVIRONMENTAL GEOCHEMISTRY 21 Oneacre JW (1993) Subtitle D Regulations Impact on Ground Water Monitoring Geotechnical News 11(3): 49 52 Oneacre JW and Figueras D (1996) Ground Water Variabil ity at Sanitary Landfills: Causes and Solutions, Uncer tainty in the Geologic Environment Proceedings, ASCE, Madison, WI, pp 965 987 Ramawsamy JN (1970) Effects of Acid and Gas Production as Sanitary Landfills Ph.D Dissertation,West Virginia University Rank, et al (1992) Environmental Isotopes Study at the Breitenqu Experimental Landfill (Lower Austria) Tracer Hydrology In: Hotzl and Werner (eds.) Proceedings of the 6th International Symposium on Water Tracing, Karls ruhe, Germany, Sept 21 26, pp 173 177 Rotterdam: Balkema Whiticar MJ and Faber D (1985) Methane Oxidation in Sediment and Water Column Environments Isotope Evidence Advances in Organic Geochemistry 10: 759 768 ENVIRONMENTAL GEOCHEMISTRY W E Dubbin, The Natural History Museum, London, UK Copyright 2005, Natural History Museum All Rights Reserved Introduction Soils and sediments occupying the Earth’s surface lie at the interface of the lithosphere, atmosphere, biosphere, and hydrosphere Within the weathered, complex, and porous milieu of these Earth-surface materials, myriad biogeochemical processes govern the movement of both nutrients and pollutants from the lithosphere to biota, where they are incorporated into plant and animal tissues, or to groundwaters, where they may be transported great distances to streams, rivers, and oceans This chapter describes the most notable pollutants, both organic and inorganic, and the dominant processes governing their mobility and bioavailability in terrestrial and aquatic environments Trace Elements Trace elements are those that occur in the lithosphere at concentrations typically less than g kg (Table 1) Among the trace elements are the micronutrients (e.g., Cu, Ni, Zn), which are essential for the growth and development of micro-organisms, plants, and animals, and also the metalloids, which have characteristics of both metals and non-metals (e.g., As, B) (see Minerals: Arsenates) Heavy metals are defined as those trace elements with densities >5.0 g cm Virtually all trace elements, even the micronutrients, exhibit toxicity to animals and plants when present at excessive concentrations Radionuclides are a separate but important class of inorganic contaminant that may occur naturally (e.g., 222Rn, 226Ra, 238U) or as a consequence of nuclear fission related to atomic weapons testing and nuclear power generation (e.g., 90 Sr, 137Cs, 239Pu) Although trace elements occur naturally in all terrestrial environments, anthropogenic inputs may increase these concentrations considerably The principal anthropogenic sources of trace elements are mining and smelting activities, fossil fuel combustion, chemical and electronics industries, as well as the addition of fertilisers and biosolids arising from agricultural operations One notable example of severe trace metal pollution caused by smelting activities is found near Karabash, in the south Ural Mountains region of Russia, where for decades smelting operations have deposited metals on the surrounding landscape, destroying much of the vegetation and so contributing to widespread soil erosion (see Environmental Geology) Toxic levels of trace elements (e.g., Cr, Ni) may also occur naturally, as in soils derived from serpentinitic rocks, which can lead to phytotoxicity and the consequent lack of vegetation over large areas of the landscape where the serpentine soils occur (see Clay Minerals) Alternatively, these elevated trace element concentrations may induce metal tolerance among certain plant species (e.g., Thlaspi spp.) as biological communities adapt to these metal rich environments Trace Element Bioavailability and Speciation It is well established that total trace element content in soil or sediment is a poor indicator of toxicity A more reliable measure of ecotoxicity is trace element bioavailability A trace element is considered bioavailable if it can be utilized by biota Bioavailability is therefore broadly equated with solubility, although some plants and micro-organisms are able to extract metals from solid phases normally considered insoluble The solubility, and hence bioavailability, of a particular trace element is determined largely by its solid-phase speciation and mode of surface complexation The main parameters