Effects And Mechanisms Of Chlorinated Polyfluorinated Ether Sulfonate On Green Algae And Rare Minnow

Chlorinated polyfluorinated ether sulfonate(Cl-PFESA),with trade name F-53 B,is an alternative of perfluorooctane sulfonate(PFOS),which is used as a mist suppressant in the electrolytic process of metal plating.After the usage of PFOS was restricted,the application area,as well as the production and usage volume of Cl-PFESA,would be further expanded.Although Cl-PFESA has similar chemical structure and physiochemical properties with PFOS,the toxic mechanisms of Cl-PFESA is still unknown.Presently,Cl-PFESA has been found in many environemtal medium of China(surface water,influent and effulent of industrial and municipal waste water treatment,sludge)and in fish,even in liver of polar bear and other animals from Greenland.Aquatic enviroument is the important sink of Cl-PFESA in the ecosystem.Therefore,it is crucial to study the toxic effects and mechanisms of Cl-PFESA on freshwater organisms.The present study evaluated bioaccumulation of Cl-PFESA on green alga Scenedesmus obliquus and Chinese native species,rare minnows(Gobiocypris rarus).Furthermore,the toxic effects and mechanism were also studied.The main results include,(1)The bioaccumulation potentials of Cl-PFESA in Scenedesmus obliquus at environmentally relevant concentrions were analyzed.The results showed that log BAF of Cl-PFESA on Scenedesmus obliquus at environmentally relevant concentrations was 4.66,which was higher than that of PFOS.The 72 h-EC50 of Cl-PFESA for algal growth inhibition was 40.3 mg/L.In addition,Cl-PFESA exposure increased the total contents of chlorophylls by 1.24 times at 13.4 mg/L,indicating the normal photosynthesis process was disrupted.Significant change in membrane permeability was observed at 5.42 mg/L,with a54% increase compared with the control.The mitochondrial potential increased with increasing concentration of Cl-PFESA.Significant changes in mitochondrial potentials were observed at 1.49-5.42 mg/L,increasing by 35% to 137%.Reactive oxidative species(ROS)were induced by Cl-PFESA,and malondialdehyde(MDA)contents were also enhanced significantly,which demonstrated that Cl-PFESA exposure broke the balance of antioxidative defense.The presently available data of Cl-PFESA in the aquatic environmentsuggested its existence in surface water was much lower than the effective concentration.However,Cl-PFESA could therefore potentially increase the accessibility and toxicity of other coexisting pollutants in the environment to algae cells by interfering with the integrity of cell membranes.The bioaccumulation of Cl-PFESA in algae could also cause adverse effects to organisms at higher trophic levels in the aquatic food chain.(2)The effects and mechanisms of Cl-PFESA for thyroid disrupting on rare minnows adults were analyzed.Five-month old rare minnows were exposed to Cl-PFESA for 21 d.Results showed that Cl-PFESA interfered the thyroid hormones,which showed gender differences.T4 contents didn't change in neither male nor female.Slight changes of T3 concentrations were observed in female fishes treated by 12.2 ?g/L Cl-PFESA,decreasing by 25% compared with the control.fT3 of female fish did not change significantly.The levels of fT3/T3 increased by 35% and 53%,in male fishes treated by 12.2 and 244 ?g/L of Cl-PFESA,respectively.Cl-PFESA exposure disrupted genes related to the transportion,metabolism of thyroid hormones and the feedback regulation of HPT axis.The expression levels of TTR and TSH were down-regulated in both sex.The downregulation of DIO 2 was observed in liver tissue of female.(3)The developmental toxicity effects and mechanisms of Cl-PFESA on rare minnows were studied.After 28 d exposure to Cl-PFESA in 2-month old rare minnows,log BAF of C8 Cl-PFESA was 4.12±0.09.Log BAF of C10 Cl-PFESA was much higher than C8Cl-PFESA,suggesting the higher bioaccumulation potential of C10 Cl-PFESA.The results of RNA-sequencing showed that the amount of differential expressed genes(DEGs)was3313.Among the DEGs,1921 genes were up-regulated and 1392 genes were down-regulated.The enrichment analyis of GO found that in biolgical processes involved mainly included cholesterol and lipid metabolism.KEGG pathway enrichment analysis showed pathways related to ovarian development(ovarian steroidogenesis,oocyte meiosis,estrogen signaling pathway and cholesterol metabolism)were affected.After 12 weeks of depuration period,the body weight,body length and condition factors of the rare minnows did not change significantly.However,the GSI of females decreased significantly by 58.1%.The histopathological results indicated that the development of gonad was irreversibly delayed.The proportion of immature oocytes increased with increasing concentrations.However,there was no significant change in histopathology of male gonads.The results of the present study indicated that the bioaccumulation potentials of Cl-PFESA in algae and fish were relatively high.Moreover,Cl-PFESA damage cellmembrane of algae,disrupted thyroid hormone and gonad development.Therefore,it is warranted to further assess its ecological risk.