John Wiley & Sons, Ltd.

Deriving site‐specific soil clean‐up values for metals and metalloids: Rationale for including protection of soil microbial processes

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Although it is widely recognized that microorganisms are essential for sustaining soil fertility, structure, nutrient cycling, groundwater purification and other soil functions, soil microbial toxicity data were excluded from the derivation of Ecological Soil Screening Levels (Eco‐SSL) in the United States. Among the reasons for such exclusion were claims that microbial toxicity tests were too difficult to interpret because of the high variability of microbial responses, uncertainty regarding the relevance of the various endpoints, and functional redundancy. Since the release of the first draft of the Eco‐SSL Guidance document by the U.S. Environmental Protection Agency in 2003, soil microbial toxicity testing and its use in ecological risk assessments have substantially improved. A wide range of standardized and non‐standardized methods became available for testing chemical toxicity to microbial functions in soil. Regulatory frameworks in the European Union and Australia have successfully incorporated microbial toxicity data into the derivation of soil threshold concentrations for ecological risk assessments. This paper provides the three‐part rationale for including soil microbial processes in the development of soil clean‐up values (SCVs): 1) presenting a brief overview of relevant test methods for assessing microbial functions in soil, 2) examining datasets for Cu, Ni, Zn, and Mo that incorporated soil microbial toxicity data into regulatory frameworks, and 3) offering recommendations on how to integrate the best available science into the method development for deriving site‐specific SCVs that account for bioavailability of metals and metalloids in soil. While the primary focus of this paper is on the development of the approach for deriving SCVs for metals and metalloids in the United States, the recommendations provided in this paper may also be applicable in other jurisdictions that aim at developing ecological soil threshold values for protection of microbial processes in contaminated soils. Integr Environ Assess Manag © 2013 SETAC

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