The Characteristics And Toxic Effects Of Maternal Transfer Of Fipronil And O,p'-DDD In Zebrafish

Maternal transfer of pollutants have been frequently reported,and the toxic effects that caused by maternal transfer has already received more and more attention.However,up to now,the toxic mechanism of pollutants underlying the process of maternal transfer has not yet been clarified.In this study,we selected fipronil and o,p'-DDD as targeted compounds,and systematically studied the functional mechanisms of their bioconcentration,development toxicity,behavior toxicity and thyroid toxicity during maternal transfer in zebrafish.The enrichment content in F0 fish and F1 offspring,and the change of biological enrichment(BCF)in maternal transfer were detected.We choosed body length,weight and growth factor for developmental index,and measured mortality,hatching rate and deformity rate to carry out the developmental toxicity study.By analyzing the locomotor behavior of 120 hpf(hours post fertilization)larvae,we studied the toxicity mechanism by maternal exposure in F1 offspring.Furthermore,polymerase chain reaction(PCR)was used to investigate the expressions of related genes in hypothalamic–pituitary–thyroid(HPT)axis,ELISA was used to measure the content of thyroid hormones(THs),and in further,the thyroid toxicity effect in maternal transfer was studied.The specific research contents and results are follows:(1)Zebrafish of sexual maturity were exposed to environmentally relevant concentrations(1,5 and 10 ?g/L)of fipronil for 28 days.We studied the transfer mechanism of long-term fipronil exposure on the bioconcentration,development toxicity,behaviror toxicity and thyroid toxicity in zebrafish maternal transfer following parental exposure to fipronil.Bioconcentration results showed,the content of fipronil in F0 fish and F1 offspring was at an order of magnitude,both had concentration-dependent effect.The values of BCF ranged between 2.662-9.118.Because of the enantiomeric fractions(EFs)between 0.448 and 0.493,F0 fish and F1 offspring both could selectively concentrate S-fipronil.Development toxicity results showed that the growth factors of each exposure group was similar to the blank group,and fipronil exposure had no influence in growth and development of F0 fish,but it could lead to larvae deformity rate significantly increased.Locomotor behavioural analyses showed that the locomotor activity of larvaes was lower at high concentration(10 ?g/L),and the larvaes were less sensitive than control at photoperiod stimulation test.With further testing,we found that the THs level of F0 fish and F1 offspring decreased significantly and showed concentration-effect relationship.Meanwhile,the gene expression of the HPT axis down-regulated remarkably in brain tissue at 1 ?g/L,while that were opposite at 5 and 10 ?g/L.In liver tissue,the gene expression of the HPT axis(except Nkx2.1)up-regulated remarkably at different concentrations.Besides,We observed the transcriptions of genes of Deio1,NIS,Nkx2.1 and TPO significantly up-regulated,but TR? mRNA expression were significantly down-regulated.Principal component analysis showed that the concentrations of fipronil exposure could affect some of gene expression of brain and live tissue in F0 fish,as well as that in F1 offspring.The gene expression of F0 fish didn't have concentration-effect relationship,but F1 offspring had.In summay,the results suggested that thyroid toxicity had a certain relationship with the above toxicities.(2)We evaluated the thyroid interference effect and enantioselective toxicity on F0 fish and F1 generation by environmentally relevant concentrations(5 and 50 ng/g)of o,p'-DDD food exposure.First,with Chiralcel OJ-H chiral column,HPLC was used for enantiomeric separating the o,p'-DDD to get the pure sample of R-o,p'-DDD and S-o,p'-DDD.Then zebrafish of sexual maturity were exposed to Rac,R-and S-o,p'-DDD for 28 days.The results showed that the content of o,p'-DDD in F1 offspring were much more than F0 fish.But the EFs of o,p'-DDD ranged between 0.496-0.507,which meaned no enantioselective bioconcentration in zebrafish.o,p'-DDD exposure could lead to malformation rate significantly increase,and showed enantioselectivity on growth and development of F1 larvae,While no effect were observed in F0 fish.Through measuring the gene expression in HPT axis in the brain tissue and live tissue of F0 fish and F1 offspring,some of gene expression were significantly altered after o,p'-DDD exprouse,and maternal transfer could enhance the enantioselectivity toxicity.Combined with principal component analysis,It was further proved that R-o,p'-DDD and S-o,p'-DDD had enantio-selectivity in expressions of related genes in HPT axis.The above results demonstrated that Rac-,R-and S-o,p'-DDD maternal food exposure had the thyroid interference effect on F0 fish and F1 offpring,and exhibiting enantioselectivity toxicity.