Fate and O-methylating detoxification of Tetrabromobisphenol A (TBBPA) in two earthworms (Metaphire guillelmi and Eisenia fetida)

Tetrabromobisphenol A (TBBPA) is the world's most widely used brominated flame retardant but there is growing concern about its fate and toxicity in terrestrial organisms. In this study, two ecologically different earthworms, Metaphire guillelmi and Eisenia fetida, were exposed to soil spiked with 14C-labeled TBBPA for 21 days. M. guillelmi accumulated more TBBPA than E. fetida, evidenced by a 2.7-fold higher 14C-uptake rate and a 1.3-fold higher biota-soil accumulation factor. Considerable amounts of bound residues (up to 40% for M. guillelmi and 18% for E. fetida) formed rapidly in the bodies of both earthworms. 14C accumulated mostly in the gut of M. guillemi and in the skin of E. fetida, suggesting that its uptake by M. guillelmi was mainly via gut processes whereas in E. fetida epidermal adsorption predominated. The TBBPA transformation potential was greater in M. guillelmi than in E. fetida, since only 5% vs. 34% of extractable 14C remained as the parent compound after 21 days of exposure. Besides polar metabolites, the major metabolites in both earthworms were TBBPA mono- and dimethyl ethers (O-methylation products of TBBPA). Acute toxicity assessments using filter paper and natural soil tests showed that the methylation metabolites were much less toxic than the parent TBBPA to both earthworms. It indicated that earthworms used O-methylation to detoxify TBBPA, and M. guillelmi exhibited the higher detoxification ability than E. fetida. These results imply that if only the free parent compound TBBPA is measured, not only bioaccumulation may be underestimated but also its difference between earthworm species may be misestimated. The species-dependent fate of TBBPA may provide a better indicator of the differing sensitivities of earthworms to this environmental contaminant.