Ecological Risk Assessment of Diffuse and Local Soil Contamination Using Species Sensitivity Distributions

Abstract

Ecological Risk Assessment related to soil contamination requires a conceptual framework and practical tools to support Risk Management. The conceptual framework is provided by the Risk Assessment paradigm, which means that risks are assessed based on an Exposure Assessment and an Effect Assessment step. Current practical tools to appraise soil quality by Ecological Risk Assessment are: (1) comparison of soil contaminant concentrations to ecological Soil Quality Standards; (2) quantification of ecological risks by modeling; (3) quantification of impacts in bioassays or in field monitoring; and (4) quantification of ecological risks by weight-of-evidence approaches. The present chapter concerns the theory and practices of Effect Assessment and risk modeling using Species Sensitivity Distributions (SSDs), and similar Functional Sensitivity Distributions (FSDs). SSD- and FSD-based Risk Assessment outputs are used for the appraisal of soil quality, soil protection and the management of (slightly and highly) contaminated sites, for both the upper soil and the groundwater. For the appraisal of soil and soil protection, one can derive Hazardous Concentrations (HCs) for individual contaminants, which are estimates of the concentration of a chemical that would affect a defined fraction of species. Likewise, one can derive Hazard Potentials (HPs) for contaminated soil samples, which represent effects levels for a certain fraction of the tested soil species when exposed in such a soil. This chapter introduces the theory of SSDs and illustrates the types of practical applications of SSD-based effect and risk models in all four of the aforementioned types of tools. Since Risk Assessment requires assessments of exposure as well as effects, the chapter also discusses Exposure Assessments for SSDs. Practical software models and database tools are described, to support easy application of SSDs in practice. Through the examples, the reader is informed on a multitude of useful options for SSD-based assessment. SSD-modeling is versatile, and can be of use to a range of soil contamination problems, from diffuse contamination in large areas to local contamination hot spots.