| Polychlorinated dibenzothiophenes（PCDTs）are sulfur analogues of polychlorinated dibenzofurans（PCDFs）with prevalent occurrence in aquatic environments and potential ecological risks.However,data on the levels and distribution of PCDTs in freshwater lakes in China,bioaccumulation,biotransformation and toxicity in aquatic organisms remain scarce.In this paper,three aspects of work were carried out.The concentrations of fourteen PCDTs in Chaohu Lake and its eight main rivers were determined,the possible sources and spatial distribution characteristics were identified.The bioaccumulation,transformation,and the effect on the antioxidation defense system of a typical PCDTs（4-mono-CDT）in freshwater mussel（Hyriopsis cumingii）were investigated.The adsorption behavior of 4-mono-CDT in the sediments of Chaohu Lake and paddy soils were studied by laboratory experiments.The main research contents and results are as follows:（1）The occurrence of 14 congeners of PCDTs in different matrices（i.e.,sediment,suspended particulate matter（SPM）,and water）of Chaohu Lake were investigated.It was determined that the concentrations of 14 PCDTs（ΣPCDTs）in the sediment,SPM,and surface water were 0.40-3.55 ng/g,0.38-2.95 ng/g,and 0.34-2.61 ng/L,respectively.The dominant congener found in sediments was 1,2,3,4,7-penta-CDT（19.54%）,and 1,3,9-tri-CDT was the predominant congener in SPM（19.13%）and water（20.08%）.Medium-and high-chlorinated PCDTs were detected as the major compounds in sediments and SPM.The low-chlorinated PCDTs（e.g.,mono-CDTs）have higher relative percentages in the water than those detected in the sediment samples.The annualΣPCDTs input of the eight main tributaries to Chaohu Lake was 19.90 kg.A strong linear correlation between theΣPCDTs levels and the organic carbon（OC）content demonstrated that OC had an important influence on the PCDT redistribution in Chaohu Lake.In addition,the organic carbon normalized partitioning coefficient(log KOC)of PCDTs in the SPM-water system in Chaohu Lake was 1.95-2.49 m L/g,and correlations between log KOCand other typical environment related properties of PCDTs were established.（2）The bioaccumulation,metabolism,and oxidative damage of 4-mono-CDT in Hyriopsis cumingii were investigated after exposure to 4-mono-CDT in semi-static water.The uptake rates（k1）,depuration rates（k2）,half-lives(t1/2),and bioconcentration factors（BCFs）of 4-mono-CDT in hepatopancreas,gill,and muscle tissues ranged from 0.492-1.652 L·d-1·g-1·d.w.,0.117-0.308d-1,2.250-5.924 d,and 2.903-8.045 L·g-1·d.w.,respectively.A dechlorinated metabolite（dibenzothiophene）was detected in hepatopancreas tissue,indicating that dechlorination was the main metabolic pathway of 4-mono-CDT.As the exposure time increased,the activities of superoxide dismutase（SOD）,catalase（CAT）,and glutathione peroxidase（GPx）were induced by low-dose group-inhibited by medium-and high-dose groups.The malondialdehyde（MDA）content increased with increasing 4-mono-CDT dose and exposure time.The antioxidant enzymes in hepatopancreas were more sensitive to 4-mono-CDT than those in gill.（3）The experimental results of adsorption kinetics showed that the adsorption equilibrium time of the four samples was 12 h,and the saturated adsorption content of 4-mono-CDT was between 70%and 80%.The results of batch equilibrium experiments showed that the adsorption behavior of 4-mono-CDT in the four samples conformed to the Freundlich equation.In addition,the adsorption parameter（n）in the east of Chaohu Lake is more than 1.4,showed a high nonlinear characteristic.The nonlinear characteristics may be related to the higher levels of organic carbon content,total nitrogen content and clay content in sediment in the east of Chaohu Lake.Besides,the study also showed that the maximum adsorption capacity appeared at acidic p H（p H=4）.The adsorption of 4-mono-CDT was promoted at 5 mg/L and inhibited at 100 mg/L by DOM. |
