Permissible concentrations of arsenic and lead in soils based on risk assessment

Establishing permissible concentrations for As and Pb in soils is of practi cal importance because of toxicity of these metals, their widespread contam ination, and limited resources available for remediation of contaminated so ils. The USEPA pathway approach to risk assessment was used to assess an en vironmental hazard related to As and Pb in soils and to evaluate safe conce ntrations of these metals in contaminated soil. The results from large-scal e field experiments with soil fly ash-biosolids blends were used as input d ata to analyze pathways of the most intense transfer of the contaminants to a target organism. A direct soil ingestion by children (the soil-human pat hway) was considered the most important exposure route to soil As and Pb. A conservative risk analysis shows that As concentrations in soil can reach 40 mu g g(-1) without a hazard to exposed organisms. A Pb concentration in soil up to 300 mu g g(-1) does not cause an excessive intake of Pb by human s as evaluated by a direct soil ingestion exposure model.