Species-dependent effects of earthworms on the fates and bioavailability of tetrabromobisphenol A and cadmium coexisted in soils

Abstract

The activity of e-waste recycling often causes the combined pollution of tetrabromobisphenol A (TBBPA) and cadmium (Cd) in soils. In this study, the effects of their co-existence on each other's fate, further reflecting the bioavailability, were analyzed in the presence of two ecologically different earthworm species, endogeic Metaphire guillelmi and epigeic Eisenia fetida. Mineralization of 14C-TBBPA combined with 10 mg Cd kg−1 was suppressed by the presence of M. guillelmi, whereas a facilitating effect was produced by the combination of 1 mg Cd kg−1 in the soil-E. fetida system after a 14-day exposure. The uptake of 14C-TBBPA by M. guillelmi (17% of initial amount) and by E. fetida (10%) dominantly contributed to significant (P < 0.05) decrease of extractable (more bioavailable) 14C residues in soils both with and without Cd spiked, while the mineralization of 14C-TBBPA in the soils was negligible (<0.4%). Meanwhile the amendments of the two earthworm species exerted different impact on 14C distribution in bound residues. In general, co-exposure to Cd did not significantly (P > 0.05) influence the accumulation and metabolism of TBBPA in the earthworms. Both earthworms accumulated only ~7% of Cd in soil, however, the bioavailable Cd determined by the diffusive gradients in thin films technique declined by ~46% in the presence of M. guillelmi, and a much smaller decrease was determined in the presence of E. fetida. Amendment of TBBPA at environmental levels did not alter the accumulation and subcellular distribution of Cd in both earthworms unless that at high doses. The results highlighted the importance of considering the difference of the earthworm species and the interaction of pollutants in soil-risk assessments of such combined contamination. CapsuleM. guillelmi displayed greater effect on the fate of TBBPA and Cd co-existed in soils than E. fetida, while the accumulation, metabolism, or distribution of the two pollutants in earthworms did not significantly alter due to interactions between the two pollutants.