Differential accumulation of polycyclic aromatic hydrocarbons (PAHs) in three earthworm ecotypes: Implications for exposure assessment on historically contaminated soils

Abstract

This study compared accumulation of the 16 US-EPA priority polycyclic aromatic hydrocarbons (PAHs) in three different earthworm ecotypes, <i>Amynthas</i> sp., <i>Eisenia fetida</i>, and <i>Lumbricus terrestris</i>, in four historically (> 50 years) contaminated manufactured gas plant (MGP) soils using bioassays. Epi-endogeic deep burrowing and soil ingesting <i>Amynthas</i> sp. accumulated significantly more ∑16 PAHs than any other species (upto 8.7 times more), and epigeic surface dwelling <i>E. fetida</i> showed the lowest ∑16 PAH accumulation. Results indicated the importance of earthworm habit and physiology on PAH partitioning into earthworm lipids. Exposure to soil borne PAHs via the gut, as compared with passive diffusion from pore water, was important in species tested, being most evident in burrowing species <i>Amynthas</i> sp. and <i>L. terrestris</i> and for the desorption-resistant higher molecular weight (HMW) PAHs. Biota-soil accumulation factors (BSAF) were low, as influenced by aging, sequestration and strong PAH sorption to secondary sorptive phases in the historically contaminated soils. Bioconcentration factors (BCFs) calculated from freely dissolved pore water PAH concentrations derived from polyoxymethylene solid-phase extractions (POM) were species specific, indicating stronger relationships with octanol-water partition coefficient (K_OW) for <i>Amynthas</i> sp. and <i>L. terrestris</i> than for <i>E. fetida</i>. Modelling demonstrated that K_OW values were not a reliable proxy for BCF in equilibrium partitioning theory (EqPT) to predict bioavailability for the range of earthworms tested, being less accurate for <i>E. fetida</i> compared to the burrowing species. The study showed that including burrowing and soil feeding earthworm species, such as <i>Amynthas</i> sp. and <i>L. terrestris</i>, in standard testing would benefit regulatory decisions for more accurate quantification of PAH bioavailability in ecological risk assessment on historically contaminated soils.