Tissue-specific bioaccumulation, depuration and metabolism of 4,4'-dichlorodiphenyl sulfide in the freshwater mussel Anodonta woodiana.

Polychlorinated diphenyl sulfides (PCDPSs) are considered as a class of sulfur-containing dioxin-like pollutants with ubiquitous occurrence in natural waters and potential ecotoxicity to aquatic organisms. However, to date, no information is available regarding the bioaccumulation and biotransformation of PCDPSs in aquatic species. In this study, the uptake and depuration kinetics of 4,4'-dichlorodiphenyl sulfide (4,4'-di-CDPS) in the freshwater mussel Anodonta woodiana were investigated through semi-static exposure. The uptake rates (k1 ), depuration rates (k2 ), biological half-lives (t1/2 ) and tissue-specific bioconcentration factors (BCFs) of 4,4'-di-CDPS in the gill, liver and muscle were measured in the range of 0.509-21.734 L d-1  g-1 d.w., 0.083-0.221 d-1 , 3.14-8.35 d and 3.662 × 103 -124.979 × 103  L kg-1 l.w., respectively. With the increase in exposure dose, the values of k1 and BCFs were significantly reduced, indicating that low-dose exposure to 4,4'-di-CDPS could lead to more severe bioaccumulation. Based on the analysis of mass spectra of the extracted liver samples, the structures of four metabolites of 4,4'-di-CDPS were identified. Moreover, the levels of these metabolites were also quantitatively measured. The proposed metabolic pathways of 4,4'-di-CDPS in mussel liver included sulfur-oxidation, dechlorination and methoxylation. Comparatively, sulfur-oxidation was the predominant metabolic pathway of 4,4'-di-CDPS in the liver of A. woodiana. These results provide valuable data and fill the information gap on the bioaccumulation and metabolism of PCDPSs in freshwater species.