Toxicity Of Perfluorohexane Sulfonic Acidon Zebrafish

Per-and polyfluoroalkyl substances(PFASs)have good physicochemical properties and have been widely used in industrial and commercial consumer products since their development.Among them,perfluorohexane sulfonate(PFHxS),a short-chain congener substitute for perfluorooctane sulfonate(PFOS),has been detected in a variety of environmental media due to its increasing use and environmental emissions in recent years.Due to its good water solubility,water becomes the most widespread environmental medium for PFHxS.However,there is still a lack of comprehensive and systematic studies on the toxic effects of PFHxS on aquatic organisms.Therefore,based on the classic mode aquatic organisms,zebrafish as the research object,PFOS as positive control,this thesis has investigated the toxic effects and potential molecular mechanisms of PFHxS on zebrafish embryos and adult zebrafish of different genders.Details of the study are as follows.(1)The acute toxicity and developmental toxicity of PFHxS exposure to zebrafish embryos early in life were assessed.The LC50 of zebrafish exposed to PFHxS at 120 hpf is 508.11 μM,which is higher than the PFOS LC50 value of 45.11 μM.Further observation of the apparent morphological indices of zebrafish at 24-120 hpf revealed that high concentrations of PFHxS can cause malformed phenotypes such as pericardial edema,yolk sac edema,and spinal curvature in the developmental process of zebrafish.PFHxS exposure below 100μM(non-lethal dose)caused altered spin motility in zebrafish embryos,increased heart rate and blood flow speed in the larvae,and inhibited the normal motility of the larvae.Besides,PFHxS caused transgenic zebrafish Tg(fabp10a:ds Red;ela3l:EGFP),Tg(zp3:fsta,myl7:EGFP)Heart damage,abnormal liver and exocrine pancreas hyperplasia in larvae.To explore the underlying molecular mechanism,PFHxS exposure led to upregulation of cardiac development-related genes such as myh7,tbx20 and fgf8 a,induced downregulation of gonadal development genes such as cyp17a1,cyp11a1 and lhr,and caused significant changes in the relative expression of genes such as esr1,star and vtg.Experimental data based on cardiac and gonadal development and relevant signaling pathways indicated that PFHxS caused irreversible gonadal developmental toxicity and cardiovascular toxicity effects on zebrafish embryos.(2)The toxicity effects of PFHxS exposure on female zebrafish were systematically evaluated.Simulated environmental exposure doses(0.02 μM and 0.2 μM)PFHxS was used to exposure of adult female zebrafish,a tendency of disappearing hepatocyte membrane and abnormal enzyme concentration in the liver of female zebrafish was observed by paraffin section.Fewer mature oocytes,fewer and indistinct yolk granules,and reduced relative expression of cyp19a1 a,cyp11a1,fshr,and vtg genes in the ovary compared compared with the control group,indicating that PFHxS may have anti-estrogenic effects.The heart exhibited cardiac hypertrophy and thickened cardiomyocytes compared to the control,and gene expression showed down-regulation of myh7 and myh6 myocardial protein expression.In female zebrafish,apical damage of intestinal villi,loss of cup cells and intestinal epithelial cells were clearly seen in intestinal sections,and expression of pro-inflammatory factors tnfα was detected to be upregulated in the intestine.(3)The toxic effects of PFHxS exposure in male zebrafish were studied comparatively to assess the sex differences.Adult male zebrafish were observed at the same exposure concentration as females after 14 d.We found that the male zebrafish had edema and balloon-like degeneration of hepatocytes.The concentrations of GPT,T-CHO,TG and other enzymes in the liver were abnormal.The male fish had reduced spermatophore and enlarged void in the spermathecae,increased Ach E enzyme concentration in the brain,decreased expression of HPG axis-related genes such as cyp19a1 a,cyp11a1,fshr,lhr,and hsd17β3,and PFHxS caused anti-estrogenic effects in the male fish.After exposure,cardiac hypertrophy and thickening of cardiomyocytes in male fish were similar to those in females,and myh7 and myh6 expression was down-regulated to a degree comparable to the expression of positive controls.Observation of intestinal HE and AB-PAS pathological sections showed damaged intestinal villi,altered internal structure of the intestinal lumen,and increased expression of the pro-inflammatory factor il-1β compared to controls.In summary,PFHxS exhibited lower toxicity characteristics than PFOS,but still caused irreversible embryonic developmental toxicity,cardiovascular toxicity,reproductive toxicity and endocrine disrupting effects on zebrafish.The experimental results obtained in this thesis provide a scientific basis for the systematic assessment of the biosafety and human health effects of PFHxS,and help to scientifically control the production and use of PFHxS in the future.