| In recent years,with the increasing prominence of environmental problems,the government and the public continue to pay attention to environmental protection.It has become very important and urgent to evaluate the toxicity of chemicals in the environment and determine the environmental safety concentration and health risk of chemicals.Zebrafish,a small fish,has the advantages of short sexual maturation time and low breeding cost,and has become one of the options for screening and evaluating potential endocrine disruptors in the environment.Triclocarban(TCC)is an antimicrobial agent added to everyday products that is effective against a variety of bacteria and fungi and is inexpensive to produce.As its use increases,it has been detected in water,soil and organisms.However,current studies on TCC mainly focus on short-term acute exposure and embryonic exposure tests,and there are few studies on long-term exposure to TCC.This paper selected zebrafish as the research object to study the effects of long-term exposure to TCC on the growth and reproduction of zebrafish,as well as the effects of long-term exposure to TCC on the offspring of parents.In this study,zebrafish embryos 2 hours post-fertilization(2 hpf)were exposed to environmental-related concentrations of TCC(0 μg/L,0.25 μg/L,1.25 μg/L,6.25 μg/L)for 120 days to reach sexual maturity.called F0 generation.F0 generation spawn in clear water,collected embryos were called F1 generation,and incubated in clear water for 120 hours.The body length,fatness,survival rate,sex ratio,brain index(BSI),liver index(HIS),and gonadal index(GSI)of zebrafish at different post-fertilization time(45dpf,60 dpf,120 dpf)of F0 generation were calculated to evaluate the effects of environmental related concentration TCC on the growth of zebrafish.By detecting the expression of endocrine-related genes(cyp19a1a,vtg1,erα,ar)on the 45 days postfertilization,and the changes of gene expression on the hypothalamic-pituitary-gonad(HPG)axis on the 120 days post-fertilization(120 dpf),The changes of estradiol(E2)and testosterone(T)in serum,the changes of related gene expression in sperm and ovule,and the changes of vitellogenin in liver were analyzed.The effects of environment-related concentration TCC on the reproductive endocrine system of zebrafish were analyzed.The body length,malformation rate,cumulative hatchability,the expression of endocrine-related genes(vtg1,erα,ar),malondialdehyde(MDA),catalase(CAT),total superoxide dismutase(T-SOD),glutathione peroxidase(GSH-Px),and other changes of F1 generation were evaluated under long-term exposure of TCC to the environment related concentration.The results are as follows:(1)TCC had different effects on the body length and fatness of zebrafish at different time post fertilization.Female brood fishs of F0 generation: in the growth process,compared with the control group,the body length and fatness of all exposed groups were not significant difference;Male brood fishes of F0 generation: at 60 days post-fertilization(60 dpf),the body length of 6.25μg /L exposure group was significantly increased and the fatness was significantly decreased;at 120 days post-fertilization(120 dpf),the body length of 6.25μg /L exposure group was significantly shortened.At sexual maturation,there were no significant difference in sex ratio and survival rates in all exposure groups compared with the control group.Female brood fishs of F0 generation: GSI was significantly decreased in 1.25 μg/L and 6.25μg/L exposure group;Male brood fishes of F0 generation: Compared with the control group,there was no significant difference in the body mass constants in all exposure group.These results suggest that TCC may affect male fish body length and female fish ovary development(2)Compared with the control group,45 days post-fertilization(45 dpf),the expression of endocrine-related gene vtg1 was significantly down-regulated in all exposure groups.At 120 dpf,at sexual maturity,in Female brood fishs of F0 generation :the transcription of genes(cyp19b,fshβ)in the HPG axis and genes(3βhsd,17βhsd,cyp17,cyp19a1 a,cyp11b)in the gonads were significantly affected.The transcription of erα and vtg1 in liver was significantly affected.The serum estradiol(E2)content was significantly increased.Male brood fishes of F0 generation: transcription of steroid biosynthesis related genes(17βhsd,cyp17,cyp19a1a)and receptor gene(erα)in HPG axial gonads was significantly affected;The serum testosterone(T)content was significantly decreased.Spermatogenesis related genes srd5a2,cgtr and prgs2 were down-regulated in gonads Compared with the control group,the cumulative spawning amount of zebrafish in exposure groups of 1.25μg/L and 6.25μg/L was significantly decreased.These results suggest that long-term exposure to TCC may disrupt the normal synthesis and secretion of sex hormones by disrupting the expression of genes related to the HPG axis,thus affecting the reproductive endocrine system of zebrafish and leading to a decline in reproductive capacity.(3)Compared with the control group,the body length of F1 generation in 6.25μg/L exposure group was significantly shortened;The cumulative hatching rate of F1 generation in 1.25μg/L and 6.25μg/L exposure groups decreased significantly.The expression of vtg1 in F1 generation was significantly up-regulated in 0.25 μg/L exposure group,and significantly down-regulated in 1.25μg/L and 6.25μg/L exposure groups by detecting endocrine-related genes.The expression of erα in F1 generation was significantly down-regulated in 1.25μg/L and 6.25μg/L exposure groups.The detection of antioxidant system in F1 generation showed that MDA significantly increased in 1.25 μg/L and 6.25 μg/L exposure groups in F1 generation,while GSH-Px significantly decreased in 0.25 μg /L and 1.25 μg/L exposure groups in F1 generation,and significantly increased in 6.25 μg/L exposure group in F1 generation.All the above results show that long-term exposure of blood fish to TCC will affect the growth and development of their offspring,and this phenomenon is more significant at high concentrations.In conclusion,TCC may affect the reproductive ability of zebrafish by affecting the development of ovary,interfering with the expression of genes related to HPG axis,interfering with the secretion of sex hormones,and affecting the expression of genes related to gamete formation.Toxicity of TCC can be transmitted from parent to offspring. |
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