Literature-derived bioaccumulation models for earthworms: Development and validation

Estimation of contaminant concentrations in earthworms is a critical compon ent in many ecological risk assessments. Without site-specific data, litera ture-derived uptake factors or models are frequently used. Although conside rable research has been conducted on contaminant transfer from soil to eart hworms, most studies focus on only a single location. External validation o f transfer models has not been performed. We developed a database of soil a nd tissue concentrations for nine inorganic and two organic chemicals. Only studies that presented total concentrations in depurated earthworms were i ncluded. Uptake factors and simple and multiple regression models of natura l-log-transformed concentrations of each analyte in soil and earthworms wer e developed using data from 26 studies. These models were then applied to d ata from six additional studies. Estimated and observed earthworm concentra tions were compared using nonparametric Wilcoxon signed-rank tests. Relativ e accuracy and quality of different estimation methods were evaluated by ca lculating the proportional deviation ([measured - estimate]/measured) of th e estimate from the measured value. With the exception of Cr, significant, single-variable (e.g., soil concentration) regression models were fit for e ach analyte. Inclusion of soil Ca improved model fits for Cd and Pb. Soil p H only marginally improved model fits. The best general estimates of chemic al concentrations in earthworms were generated by simple In-in regression m odels for As, Cd, Cu, Hg, Mn, Pb, Zn, and polychlorinated biphenyls. No met hod accurately estimated Cr or Ni in earthworms. Although multiple regressi on models including pH generated better estimates for a few analytes, in ge neral, the predictive utility gained by incorporating environmental variabl es was marginal.