Ecotoxicological effects of 2,4,5,4′-tetrachlorodiphenyl sulfone on Danio rerio embryos

Objective This study aimed to investigate the ecotoxicological effects of 2,4,5,4′-tetrachlorodiphenyl sulfone （TDN） on zebrafish embryos， and to provide data support for revealing the TDN toxicity mechanism on aquatic organisms and environmental and ecological risks assessment of organochlorine pesticides.Method Zebrafish embryos were exposed to 0， 6， 9， 12， 15， and 18 mg/L TDN solutions to record effects of TDN exposure on embryo survival rate， yolk sac area， heart rate， and body length. Activities of superoxide dismutase （SOD） and catalase （CAT）， along with malondialdehyde （MDA） content， were determined using their respective assay kits. Real-time fluorescence quantitative PCR was used to determine the relative expression of genes related to apoptosis， inflammation， and immunity in zebrafish embryos. Acridine orange and Sudan black staining were used to assess the apoptosis level and neutrophil counts.Result With increasing TDN concentration and exposure time， the survival rate of zebrafish embryos gradually decreased. After 72 h exposure to 0-15 mg/L TDN， the yolk sac area of zebrafish embryos increased significantly （P<0.05， the same below） or highly significantly （P<0.01， the same below）， the heart rate decreased significantly or highly significantly， and the body length decreased. Zebrafish embryos in the 15 mg/L TDN treatment group showed pericardial edemas. Under exposure to 6， 9， 12， and 15 mg/L TDN， the CAT activity of zebrafish embryos exhibited a highly significant increase， MDA content of zebrafish embryos showed some increase for all the embryos， and SOD activities of embryos in 9， 12， and 15 mg/L TDN treatment groups showed a highly significant increase compared with the 0 mg/L TDN treatment group. In the 6， 9， 12， and 15 mg/L TDN treatment groups， compared with the 0 mg/L TDN treatment group， the relative expression of the pro-apoptotic genes Bax and P53 in zebrafish embryos were all increased； the relative expression of the anti-apoptotic gene Bcl-2 was generally decreased； the relative expression of the inflammatory genes IL-6， IL-8， CXCL-C1C， TNF-α， Myd88， and P65 were generally increased； the relative expression of the immune-related genes Ifnγ， Mxa， and Mxb were generally increased. Acridine orange staining and Sudan black staining results showed that compared with the 0 mg/L treatment group， the apoptosis levels in the other groups were generally increased， and the neutrophil count was decreased.Conclusion Toxic effects of TDN on zebrafish embryos manifest as impaired growth and development， induction of oxidative stress， apoptosis， inflammation， and immune suppression through an “oxidative stress-apoptosis-immune disorder” pathway. Chlorinated pesticides share common mechanisms of harm， and their long-term effects on body homeostasis should be noticed in environmental risk assessments.