13 Using a Multi-Scale Geostatistical Method for the Source Identification of Heavy Metals in Soils Nikos Nanos 1 and José Antonio Rodríguez Martín 2 1 School of Forest Engineering - Madrid Technical University Ciudad Universitaria s/n, Madrid 2 I.N.I.A. Department of the Environment, Madrid Spain 1. Introduction For quite a long time, soil has been considered a means with a practically unlimited capacity to accumulate pollutants without immediately producing harmful effects for the environment or for human health. Presently, however, we know that this is not true. Public awareness has been raised on the harmful potential of some soil trace elements –commonly known as heavy metals- that can accumulate in crops and may end up in human diet through the food chain. Many studies have confirmed that heavy metals may accumulate and damage crops or even mankind (Otte et al., 1993; Dudka et al., 1994; Söderström, 1998). Along these lines, the most dangerous metals owing to their toxicity for human beings are Cd, Hg and Pb (Chojnacka et al., 2005). Natural concentration of heavy metals in soil is generally very low and tends to remain within very narrow limits to ensure an optimum ecological equilibrium. Nonetheless, human activities that involve emitting large quantities of heavy metals into the environment have dramatically increased natural concentrations in the last century. Although soils are quite capable of cushioning anthropogenic inputs of toxic substances, there are times when this capacity is exceeded, which is when a pollution problem arises. The natural concentration of heavy metals in soils depends primarily on geological parent material composition (Tiller, 1989; Ross, 1994; Alloway, 1995; De Temmerman et al., 2003; Rodríguez Martín et al., 2006). The chemical composition of parent material and weathering processes naturally conditions the concentration of different heavy metals in soils (Tiller, 1989; Ross, 1994). In principle, these heavy metals constitute the trace elements found in the minerals of igneous rocks at the time they crystallize. In sedimentary rocks, formed by the compactation and compression of rocky fragments, primary or secondary minerals like clays or chemical precipitates like CaCO3, the quantity of these trace elements depends on the properties of the sedimented material, the matrix and the concentrations of metals in water when sediments were deposited. In general, concentrations of heavy metals are much higher in igneous rocks (Alloway, 1995; Ross, 1994). Nonetheless, these ranges vary widely, which implies that the natural concentration of heavy metals in soil will also vary widely. www.intechopen.com