Until the 1990s, human health risks of metal contaminated soils were based on total metal concentrations; derived from toxicity values of metals in water and not accounting for the role of the soil matrix and, more importantly, the impact of contaminant speciation on bioavailability. Over the past couple of decades, a concerted global effort has investigated the bioavailability of soil metal contaminants relative to human health risks utilizing in-vivo animal feeding studies and corresponding in-vitro bioassays to mimic in-vivo results for validation. Complementary to these efforts has been attempts to determine metal speciation to understand the complexity of soil metal bioavailability related to the form of the metal contaminant. By demonstrating that the speciation of the metal plays a driving role in the bioavailability of the contaminant, risk assessors have been able to make site-specific adjustments to clean up levels that are protective of human health while reducing the cost of remediation.

This presentation will discuss past and current efforts on soil metal bioavailability. In particular, research on in-situ immobilization that attempts to manipulate soil chemistry to alter metal speciation into less toxic forms will highlight before and after measures of biological risk resulting from amending agents.