Effect Of 4,4’-dichlorodiphenyl Sulfide On Typical Aquatic Organisms:Toxicity,Bioaccumulation And Transformation

Polychlorinated diphenyl sulfides（PCDPSs）are a type of doxin-like pollutants,which have been widely detected in the aquatic environment.Because of their environmental persistence,PCDPSs exhibit potentially harmful to aquatic organisms.However,little report have studied on the toxicity,bioaccumulation and biotransformation of PCDPSs in aquatic organisms.In this study,a typical dichlorodiphenyl sulfide 4,4’-dichlorodiphenyl sulfide（4,4’-di-CDPS）was used to study the toxicity on green algae Scenedesmus obliquus,and the bioaccumulation and transformation effect on freshwater mussel Anodonta woodiana.The simulating lab test was setted up,and focused on the following two experiments.1)Toxicity evaluation of 4,4’-di-CDPS on green algae Scenedesmus obliquus:Growth inhibition,change in pigment content and oxidative stress;2)Study on the bioaccumulation,depuration and metabolism of 4,4’-di-CDPS in freshwater mussel Anodonta woodiana.The results present as follows:（1）In the acute toxicity-experiment of 4,4’-di-CDPS on Scenedesmus obliquus,algal cells growth showed a promoted-inhibited effect with the increase exposure concentration of 4,4’-di-CDPS.The low-dose treatment group showed hormesis,and the high dose group was close to the total inhibition concentration.The Logistic fitting curves was used to characterize the relationship of optical density（OD650）and the growth inhibition rate of algal cells.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.,indicating the EC50 value was decreased while the toxicity of 4,4’-di-CDPS to Scenedesmus obliquus was enhanced with the increase of exposure time.（2）The changes of pigment content and oxidative stress on Scenedesmus obliquus under different concentrations（10,50 and 100 μg/L）of 4,4’-di-CDPS were studied.The results showed that the content of the photosynthetic pigment（Chl a,Chl b,T Chl and Car）in Scenedesmus obliquus was generally decreased with the increase of 4,4’-di-CDPS concentration.The changes of Chi a and total chlorophyll content after exposure to 4,4’-di-CDPS are more sensitive than the other two parameters that were measured.It may be inferred that Chi a and total chlorophyll content can be used as more suitable biomarkers for assessing the adverse effects of 4,4’-di-CDPS on algal photosynthesis.The effect of 4,4’-di-CDPS on the antioxidant enzymes（T-SOD,CAT and GPx）of Scenedesmus obliquus showed that the low concentrations of 4,4’-di-CDPS can induce the three enzymes activity,while the medium and high concentrations of 4,4’-di-CDPS inhibit the enzymes activity.This suggests that antioxidant enzyme system can quickly response to the low concentration treatments to maintain intracellular oxidative balance,but fail to balance the oxidation under middle and high dose treatments and cause the cells oxidative damage.The MDA content of algal cells increased rapidly in the medium and high doses of 4,4’-di-CDPS,indicating that the presence of 4,4’-di-CDPS in medium and high doses resulted in lipid peroxidation in the algal cells.（3）According to the semi-static water exposure,the bioaccumulation effect of 4,4’-di-CDPS in different tissues（viscera,gill,mantle and foot tissues）of Anodonta woodiana was studied.The results showed that the enrichment capacity of 4,4’-di-CDPS in Anodonta woodiana characterized by viscera>gill>mantle>foot tissues.The enrichment capacity of 4,4’-di-CDPS in An.odonta woodiana was positively correlated with exposure time and concentrations.For the depuration process,the content of 4,4’-di-CDPS declined the fastest in gill,while and the lowest in foot tissues.Comparing different doses of 4,4’-di-CDPS exposure of k1 values can be seen,a low-dose of 4,4’-di-CDPS exposure can cause the mussel body very strong enrichment,and the lower the dose,the stronger the accumulation ability is.And different with k1,values,k2 values in each tissues shows no obvious correlation between exposure concentration.Comparing the BCFs of each tissues under different doses of 4,4’-di-CDPS,we found that 4,4’-di-CDPS has high bioaccumulation potential in Anodonta woodiana,the bioaccumulation ability of gill and viscera were much stronger than that of mantle and foot tissues.（4）The experiment of metabolic transformation 4,4’-di-CDPS in Anodonta woodian.a was established.According to the analysis of GC-MS,we found that 4-mono-CDPS,4,4’-di-CDPSO,4,4’-di-CDPSO₂ and 2-MeO-4,4,-di-CDPS were generated in the visceral of mussels.It is speculated that the predominant metabolic pathways of 4,4’-di-CDPS in mussel viscera are sulfur-oxidation,dechlorination and methoxylation,and sulfur-oxidation in Anodonta woodiana.