Implementation of Bioavailability in Prospective and Retrospective Risk Assessment of Chemicals in Soils and Sediments

Abstract

The quality of soils and sediments is commonly evaluated on the basis of total contaminant concentrations within prospective as well as in retrospective risk assessment. From common practice, the perception has arisen that performing risk evaluation by measuring or modelling total concentrations often leads to either over- or underestimation of the risks: too often there is an indication of risk whereas in reality the ecosystem seems to be unaffected, whereas on the other hand, there are examples in which adverse effects are observed in realistic field settings at levels well below toxicity levels generated in a laboratory setting. This calls for properly accounting for the impact of the binding capacity of soils and sediments on the availability and risks of contaminants in soils and sediments. Building upon an analysis of common approaches in prospective and retrospective risk assessment, an overview is given of options for inclusion of the encompassing bioavailability assessment in risk assessment. The overview culminates in a recommendation of chemical and analytical methods suited to mimic bioavailability, and a regulatory-oriented framework for actual implementation of these methods in effect-oriented risk assessment is depicted. Given pragmatic considerations (including the obvious desire of continued use of the current set of toxicity data), the regulatory framework boils down to directly relating measured/modelled bioavailable concentrations to either toxicity data for soil or sediment organisms or to toxicity data for aquatic biota.