US EPA

Interstudy variation among bioavailability studies is a primary deterrent to a universal methodology to assess metals bioavailability to soil dwelling organisms and is largely the result of specific experimental conditions unique to independent studies. The primary objective of this review is to synthesize information in the open literature on the effects of soil chemical/physical properties on metals bioavailability independent of extraneous variation due to the specific attributes of individual studies. Accordingly, two data sets were established from relevant literature; one includes data from studies related to bioaccumulation (total obs = 520), while the other contains data from studies related to toxicity (total obs = 1,264). Experimental factors that affect bioavailability independent of the effect of soil chemical/physical properties were considered nuisance variables, i.e. variables not of direct interest in the context of this study, but that need to be considered in analyzing the data. Variation associated with significant nuisance variables was statistically apportioned from the variation attributed to soil chemical/physical properties for both data sets using a linear mixed model.

Residual bioaccumulation data were then used to develop a nonparametric regression tree whereby bootstrap and cross validation techniques were used to internally validate the resulting classification procedure. A similar approach was employed with the toxicity data set as an independent external validation. These analyses obviously emphasize bioaccumulation as the primary metric for assessing bioavailability but demonstrate concurrence with studies on toxicity. The validated classification procedure is proposed as a quantitative tool that broadly characterizes typical aerobic soils in terms of their potential to sequester common divalent cationic metal contaminants and mitigate their bioavailability to soil dwelling biota. This classification procedure is proposed to augment other ecological risk assessment (ERA) approaches.

The Purpose of this report is to address a question that was submitted to the ERASC Support Center. The ERAF specifically requested a product that characterizes typical aerobic soils in terms of their potential to sequester common divalent cationic metal contaminants and mitigate their bioavailability to soil-dwelling biota. An exhaustive literature search and corresponding meta-analysis of the empirical data was recommended and performed. The result is a quantitative tool that broadly accounts for metals bioavailability and is proposed to augment the ecologicial risk assessment (ERA) process and risk-based remediation of metals contaminated soils. The tool, or classification procedure, presented here is suggested to be used with other analyses such as direct toxicity testing of contaminated soils. The present document summarizes the derivation and potential use of this tool as described in the ERASC draft response and a peer-reviewed article (Anderson et al., 2013).

This is the final report.

U.S. EPA. Summary Report. Terrestrial Metals Bioavailability: A Literature-Derived Classification Procedure for Ecological Risk Assessment (2020, Final Report). U.S. Environmental Protection Agency, Ecological Risk Assessment Support Center, Cincinnati, OH, EPA/600/R-20/042, 2020.