Distribution Characteristics Of Polychlorinated Diphenyl Ethers In Chaohu Lake And Their Toxicity,Bioaccumulation And Biotransformation In Daphnia Magna

Polychlorinated diphenyl ethers?PCDEs?are typical persistent organic pollutants?POPs?,which have obvious biological toxicity and are widely distributed in water environment.However,the contamination status of PCDEs in the fresh water lakes of China and their toxicity effect on aquatic organisms remain poorly researched,as well as their accumulation and transformation in aquatic organisms.In this study,the levels of 15 congeners of PCDEs in Chaohu Lake and its main tributaries were determined.Then,the acute toxicity effect and bioaccumulation of PCDEs with different number of chlorine atoms in Daphnia magna were evaluated.Finally,the biotransformation of 4,4'-di-CDE with typical structure in Daphnia magna were studied.The main results and conclusions are as follows:?1?The total concentrations of 15 congeners of PCDEs in surface sediments,SPM and surface water of Chaohu Lake were 0.279 ng/g dry weight?d.w.?².474 ng/g d.w.,0.331ng/g d.w.².013 ng/g d.w.and 0.351 ng/L².021 ng/L,respectively.In general,the contamination by PCDEs in the western area of Chaohu Lake was much more serious than those in the middle and eastern areas.The medium and higher chlorinated PCDEs?e.g.,penta-and deca-CDEs?were the dominant congeners in sediments and SPM,and the proportions of lower chlorinated PCDEs?e.g.,tri-CDEs?in the water were significantly higher than those in the sediments and SPM.The combined input of?PCDEs from the eight main tributaries to Chaohu Lake was estimated at 6.94 kg/y,and the results of source analysis indicated that wastewater from chemical industry may be the main source of PCDEs.The results of correlation analysis showed that the organic carbon content?TOC?could influence the distribution of PCDEs in Chaohu Lake significantly.In addition,as the number of chlorine atoms increased,the calculated average organic carbon normalized partition coefficients(logK_oc)of the 15 congeners of PCDEs increased from 4.55 mL/g to 5.45 mL/g gradually.?2?With the increase of exposure concentration or exposure time,the acute toxicity effect of PCDEs on Daphnia magna enhanced obiviously.DE was highly toxic(1 mg/L<EC₅₀<10 mg/L),while 4-mono-CDE,4,4'-di-CDE,3,4,4'-tri-CDE and 3,3',4,4'-tetra-CDE showed extremely high toxicity(EC₅₀<1 mg/L)on Daphnia magna.With the increase of the number of chlorine atom,the toxicity of 5 congeners of PCDEs on Daphnia magna increased gradually.When the value of logK_ow is between 3 and 6.5,the acute toxicity of PCDEs on Daphnia magna showed a significantly positive correlationship with logK_ow.?3?Under the exposure concentration of 0.01 mg/L,PCDEs could strongly accumulate in Daphnia magna and the BCFs ranged from 1.93×10³ to 9.73×10³ L/kg lipid.With the the number of chlorine atom increased from 0 to 5,the bioaccumulation capicity of PCDEs enhanced gradually.When the value of logK_ow is between 3 and 7,the logBCF of PCDEs is positively correlated with logK_ow.Due to the too high logK_ow value?8.16?of deca-CDE,its bioaccumulation capacity in Daphnia magna decreased instead.The biotransformation experimental results showed that the 4,4'-di-CDE in Daphnia magna may be only transformed into 4-mono-CDE by dechlorination.