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.

QSPR modeling of the logKow and logKoc of polymethoxylated, polyhydroxylated diphenyl ethers and methoxylated-, hydroxylated-polychlorinated diphenyl ethers.

In the present study, the structural parameters of 209 types of polymethoxylated diphenyl ethers (PMeODEs), 209 types of polyhydroxylated diphenyl ethers (PHODEs), seven types of methoxylated-polychlorinated diphenyl ethers (MeO-PCDEs) and seven types of hydroxylated-polychlorinated diphenyl ethers (HO-PCDEs) were calculated using the Gaussian 09 program at the B3LYP/6-311G** level. Using structural and positional parameters as descriptors, quantitative structure-property relationships (QSPR) models for the prediction of n-octanol/water partition coefficient (logKow) and soil sorption coefficient normalized to organic carbon (logKoc) were established and verified. The position parameters N2(6), N3(5) and N4 were the main positional factors influencing logKow and logKoc of PMeODEs and PHODEs. The molecular polarizability α was entered into the QSPR models of the logKow and logKoc of PMeODEs, PHODEs and MeO/HO-PCDEs, indicating that the molecular volume could influence the two environment-related properties of DEs significantly. All of the established QSPR models showed good goodness-of-fit, robustness, and predictive ability. The two models for all of the tested DEs are slightly inferior compared with the models for only a class of compounds. In addition, application domain analysis indicated that the models reliably predicted the logKow and logKoc of the mon- to hexa-DEs.

Toxicity evaluation of 4,4'-di-CDPS and 4,4'-di-CDE on green algae Scenedesmus obliquus: growth inhibition, change in pigment content, and oxidative stress.

Polychlorinated diphenyl sulfides and polychlorinated diphenyl ethers are two types of dioxin-like pollutants, which are prevalent in aquatic environments. However, to date, limited information is available regarding their toxicity to green algae. In this study, growth inhibition, effect on pigment content, and oxidative stress potentials of 4,4'-di-CDPS and 4,4'-di-CDE on green algae Scenedesmus obliquus were investigated. The results indicate that the EC50 values of 4,4'-di-CDPS after 24, 48, 72, and 96 h of exposure were 1.736, 1.172, 0.994, and 0.820 mg/L, while the corresponding values for 4,4'-di-CDE were 0.697, 1.087, 0.833, and 0.327 mg/L. As compared to the control group, most of the measured pigment content in algal cells significantly decreased after 96-h exposure to these two chemicals, suggesting their suppressive capability on the photosynthesis process in algal cells. Additionally, oxidative stress occurred as demonstrated by the significantly inhibited activities of the antioxidant enzymes (total superoxide dismutase (T-SOD), catalase (CAT), and glutathione peroxidase (GPx)), and high increases in malondialdehyde (MDA) content in all 4,4'-di-CDE-treated groups and some moderate-dose and high-dose treatments with 4,4'-di-CDPS. Acute toxicity tests and biochemical analysis showed that 4,4'-di-CDE was more toxic than 4,4'-di-CDPS on S. obliquus.