Critical soil concentrations of cadmium, lead and mercury in view of health effects on humans and animals

To assess the impact of elevated concentrations of metals in terrestrial ecosystems, a major distinction should be made in risks/effects of heavy metals related to (i) the soil ecosystem (soil organisms/processes and plants) and (ii) human health or animal health resulting from bioaccumulation. The latter effect is related to the phenomenon that a chemical accumulates in species through different trophic levels in a food chain, or secondary poisoning. Heavy metal accumulation in the food chain is specifically considered important with respect to cadmium (Cd), mercury (Hg), and, to a lesser extent, lead (Pb). Accumulation ultimately causes toxic effects on (i) humans by affecting food quality of crops (Kawada and Suzuki 1998) and animal products, as well as drinking water quality, and (ii) animal health by affecting fodder quality and by direct intake of contaminated soil (Adriano 2001). For both humans and animals, health effects arise mainly through accumulation in target organs such as kidney and liver (Satarug et al. 2000). Apart from direct health effects related to intake of food and soil, elevated metal levels in soil also lead to an increase in leaching losses of metals to groundwater and surface water, which will, after a considerable delay time, affect both drinking water quality and aquatic organisms (Crommentuijn et al. 1997).