Gonad Impairment And Parental Transfer Of Long-term Exposure To Tris(2-butoxyethyl) Phosphate At Environmentally Relevant Concentrations In Zebrafish

Tris(2-butoxyethyl)phosphate(TBOEP)is a common organic phosphorus flame retardant and plasticizer.It was detected in air,water,soil and organisms,and became a ubiquitous environmental contaminant.Previous studies showed that short-term exposure to TBOEP caused reproductive toxicity and endocrine disrupting effects.However,the study of long-term TBOEP exposure was limited.Therefore,this study investigated the reproductive toxicity and parental transfer effects caused by long-term exposure to environmentally relevant concentrations of TBOEP.In this study,zebrafish larvae at 20 days post fertilization(20 dpf)were exposed to environmentally relevant concentrations of TBOEP(0,0.1,1,10,and 100 ?g/L)for 120 d.First generation(F1)was hatched in the fresh water to 120 hours post-fertilization(120 hpf).We examined the effects of TBOEP on reproductive system in initial generation(F0)zebrafish by histological examination,detecting the alteration of the gene transcriptions in the hypothalamic-pituitary-gonadal(HPG)axis,the alteration of 17?-estradiol(E2)and testosterone(T)level in serum,and the bioaccumulation of TBOEP in gonad.We also evaluated the parental transfer effects after exposure to TBOEP by the heart rates,survival rates,malformation rates,and body length of F1 larvae and the bioaccumulation of TBOEP in offspring.The results are as followed:1.Exposure to TBOEP resulted in significantly less growth as measured by body length,body weight and gonadosomatic index(GSI)in F0 females but not F0 males.Observation of gonadal histopathological sections revealed that the proportion of oogonia(Oo)and spermatogonia(SPG)were significantly increased after exposure to 10 and 100 ?g/L TBOEP.And the proportion of pre-ovulatory oocytes(Pre O)was significantly decreased after exposure to 10 and 100 ?g/L TBOEP.Meanwhile,a significant decrease in the proportion of spermatid(SPD)was observed in 100 ?g/L TBOEP-treated group.2.The bioaccumulation of TBOEP in gonad was demonstrated.After 120 d exposure,mean concentrations of TBOEP were 2.14 ± 1.03,2.01 ± 0.62,2.07 ± 0.86,and 3.49 ± 0.75 ng/g wet weight(ww)in ovaries of female fish exposed to TBOEP at 0.1,1,10,and 100 ?g/L,respectively.While mean concentrations of TBOEP were 33.70 ± 8.70,53.6 ± 11.15,55.70 ± 1.87 and 83.20 ± 26.42 ng/g ww in testis of male fish exposed to TBOEP at 0.1,1,10,and 100 ?g/L,respectively.3.In female fish,significant increase of E2 levels were observed in 10 and 100 ?g/L TBOEP exposure groups,and T/E2 ratio was significantly decreased in various concentrations of TBOEP-treated groups.In male fish,T levels and T/E2 ratio were significantly increased in treatment groups exposed to 1,10 and 100 ?g/L TBOEP.We also detected that the transcriptions of genes in the hypothalamic-pituitary-gonadal(HPG)axis were changed,such as the upstream genes(gnrh3,cyp19b)in brain,steroid synthesis genes(cyp19a,cyp17,cyp11 a,cyp11b,17?hsd)and receptor genes(fshr,lhr,er?)in gonad.In conclusion,these results indicated that long-term exposure to environmentally relevant concentrations of TBOEP could disturb sex hormone balance by disturbing the gene transcriptions in the HPG axis.4.Lower survival,shorter body length,and faster heart rate were observed in various concentrations of TBOEP-treated groups.And the bioaccumulation of TBOEP in F1 embryos(0.283 ± 0.005 ng/g ww in 10 ?g/L TBOEP-treated group;1.304 ± 0.017 ng/g ww in 100?g/L TBOEP-treated group)might derive from parents.