Modelling polycyclic aromatic hydrocarbon bioavailability in historically contaminated soils with six in-vitro chemical extractions and three earthworm ecotypes.

Accurate prediction of organic contaminant bioavailability for risk assessment in ecological applications is hindered by limited validation on relevant bioassay species. Here, six in-vitro chemical extraction methods (butanol, non-buffered and buffered hydroxypropyl-β-cyclodextrin (HPCD, Buf-HPCD), Tenax, potassium persulfate oxidation, polyoxymethylene solid phase extraction (POM)) were tested for PAH bioaccumulation prediction in three earthworm ecotypes with dissimilar exposures, Amynthas sp., Eisenia fetida, and Lumbricus terrestris, in historically contaminated soils from manufactured gas plant (MGP) sites. Extractions were compared directly and modelled in a calculation approach using equilibrium partitioning theory (EqPT) with a novel combination of different organic carbon/octanol-water partitioning parameters (K and K). In the direct comparison approach Buf-HPCD showed the closest prediction of accumulation for burrowing Amynthas sp. and L. terrestris (within 1.5 and 3.1, respectively), but Tenax and POM showed the closest approximation for E. fetida (within 1.1 and 0.9, respectively). The optimum method for predicting PAH bioaccumulation in the calculation approach depended on earthworm species and the partitioning parameters used in equations of the four models, but overall POM, which was independent of K, showed the closest approximation of accumulation, within a factor of 2.5 across all species. This work effectively identifies the optimum in-vitro based approaches for PAH bioavailability prediction in earthworms as a model soil health indicator for ecological risk assessment within regulatory and remediation decision frameworks.