Terrestrial Metals Bioavailability: A Comprehensive Review and Literature-Derived Decision Rule for Ecological Risk Assessment

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. Accordingly, two datasets 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 = 1264). Experimental factors that affected toxicity and bioaccumulation independent of the effect of soil chemical/physical properties were statistically apportioned from the variation attributed to soil chemical/physical properties for both datasets using a linear mixed model. Residual bioaccumulation data were then used to develop a non-parametric regression tree whereby bootstrap and cross-validation techniques were used to internally validate the resulting decision rule. A similar approach was employed with the toxicity dataset as an independent external validation. A validated decision rule is presented as a quantitative assessment tool 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.