ISSUES IN SETTING HEALTH-BASED CLEANUP LEVELS FOR ARSENIC IN SOIL

Health risk assessments often do not take into account the unique aspe cts of evaluating exposures to arsenic in soil. For example, risks fro m ingestion of arsenic in soil are often based on toxicity factors der ived from studies of arsenic (soluble arsenate or arsenite) in drinkin g water. However, the toxicity of arsenic in drinking water cannot be directly extrapolated to toxicity of soil arsenic because of differenc es in chemical form, bioavailability, and excretion kinetics. Because of the differences between soil arsenic and water arsenic, we conclude that risks from arsenic in soil are lower than what would be calculat ed using default toxicity values for arsenic in drinking water. Site-s pecific risk assessments for arsenic in soil can be improved by charac terizing the form of arsenic in soil, by conducting animal feeding or in vitro bioavailability studies using site soils, and by conducting s tudies to evaluate the relationship between urinary arsenic and soil a rsenic levels. Such data could be used to more accurately measure the contribution that soil arsenic makes to total intake of arsenic. Avail able data suggest that arsenic usually makes a small contribution to t his total. (C) 1997 Academic Press.