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

Assessment of the risk of elevated soil metal concentrations requires appropriate critical limits for metal concentrations in soil in view of ecological and human toxicological risks. This chapter presents an overview of methodologies to derive critical total metal concentrations in soils for Cd, Pb, and Hg as relevant to health effects on animals and humans, taking into account the effect of soil properties. The approach is based on the use of nonlinear relationships for metals in soil, soil solution, plants, and soil invertebrates, including soil properties that affect metal availability in soil. Results indicate that the impact of soil properties on critical soil metal concentrations is mainly relevant for Cd because of significant soil-plant, soil-solution, and soil-worm relationships. Critical Cd levels in soil thus derived are sometimes lower than those related to ecotoxicological impacts on soil organisms/processes and plants, which is especially true for critical soil Cd concentrations in view of food quality criteria for wheat, drinking water quality, and acceptable daily intakes of worm-eating birds and mammals. There are, however, large uncertainties involved in the derivation from assumptions made in the calculation and uncertainties in acceptable daily intakes and in relationships for Cd in soil, soil solution, plants, and soil invertebrates. Despite these uncertainties, the analyses indicate that present Cd concentrations in parts of the rural areas are in excess of the critical levels at which effects in both agricultural and nonagricultural systems can occur.