| Toxicity hazard of contaminant co-exposure to biological has become the focus issue of people concerning. Perfluorooctane sulfonate(PFOS, C8F17SO3) is a kind of persistent organic pollutants. PFOS can induce liver toxicity, neurotoxicity, reproductive toxicity, development toxicity and so on. PFOS is widely used in the production industrial and daily chemicals. PFOS is also widely detected in the soil, water and organism. PFOS can cause serious harm to human health. The toxic effect of PFOS has becomes a hotspot research in recent years. Nanometer zinc oxide(Nano-ZnO) is a kind of typical nanometer metal oxides. The application amount of Nano-ZnO is increasing due to its unique chemical characteristics. Nano-ZnO can enter into the biology through the skin and lead to bioaccumulation. The toxic effect of Nano-ZnO on biological also causes people’s attention. Because of their potential co-existence and increasing content in the water, it is necessary to explore the mechanisms of toxicity and interactions of mixtures chemicals. This paper has systematically studied the effects of developmental toxicity, thyroid gland toxicity, and reproductive toxicity in zebrafish after exposed to PFOS and Nano-ZnO. It also has discussed the possible mechanisms of toxicity. The paper provides the basic research for emergency treatment of compound pollutants, and it also provides the scientific basis for ecological risk analysis of pollution water. According to the results of acute toxicity test, the 96 h LC50 of PFOS and Nano-ZnO were 3.502 mg/L and 60 mg/L, respectively.(P 0.4+Z 12.5),(P 0.8+Z 25),(P 1.6+Z 50),(P 0.4+Z 50),(P 0.8+Z 50) and(P 1.6+Z 50) co- and single-exposure groups were designed to analyze embryonic developmental toxicity after exposure for 96 h.(P 0.2+Z 6.75),(P 0.4+Z 12.5),(P 0.8+Z 25),(P 0.2+Z 50),(P 0.4+Z 50) and(P 0.8+Z 50) co- and single-exposure groups were designed to analyze thyroid toxicity after exposure for 14 days. The type of joint toxicity and possible mechanism of toxicity were also analyzed in the paper.(P 0.05+Z 1.7),(P 0.1+Z 3.4) and(P 0.2+Z 6.75) exposure groups were designed to analyze reproductive toxicity. The toxicity effects of parents and offspring embryo after exposure to PFOS and Nano-ZnO were also analyzed in the paper. This paper discussed corresponding toxicity effect from hatch to sexual maturity of zebrafish after exposure to pollutants. The results showed the following conclusions.(1) PFOS and Nano-ZnO single-exposure could induce the acute toxicity of zebrafish embryo. PFOS and Nano-ZnO co-exposure could enhance the acute toxcity of zebrafish embryo. The co-exposure significantly increased mortality and malformation rate of larval, decreased hatching rate and heart rate of embryo compared with exposure to PFOS alone. The response of oxidative stress and cell apoptosis were enhanced in co-exposure groups. The activity of SOD, GPx, MDA, Caspase-3 and Caspase-9 were significantly increased in co-treatment groups. The expression level of cell apoptosis related genes(p53, Bax, Bcl-2, Caspase-3 and Caspase-9) were up-regulated in co-exposure groups. The expression levels of oxidative stress related genes(SOD1, Cat and GPx1a) were significantly downregulated in co-exposure groups. The toxicity was increased after co-exposure to PFOS and Nano-ZnO compared with exposure to PFOS alone. Based on the structural characteristics of PFOS and Nano-ZnO, the potential mechanism of toxicity is that the PFOS damaged the membranes by perturbing the lipid bilayers. Nano-ZnO penetrated through the cell membranes easier and caused more cell damage. This process affected the activity of important enzymes and the balance of hormones, and enhanced the development toxicity of zebrafish.(2) The deveolpment toxicity of zebrafish larval was enhanced after co-exposure to PFOS and Nano-ZnO for 14 days.(P 0.8+Z 25) and(P 0.8+Z 50) mg/L coexposure groups significant induced mortality and malformation rat e of larvae, inhibited the body length of larvae. The content of T3 was increased and the content of T4 was decreased in co-exposure groups, respectivley. The gene expression levels of TSHβ、TG、TTR and TRα and protein expression levels of TG and TTR were significantly down-regulated in co-exposure groups. The gene expression levels of TRβ, Deio1, Deio2, NIS and CRH were significantly up-regulated in co-exposure groups. But gene expression level of TPO was not affected in all exposure groups. The results showed that PFOS interacted with Nano-ZnO entering into the cell membrane and interfered with the function of thyroid gland axis. This process affected absorption, synthesis and transport of iodine. It also affected the binding process of nuclear receptors, destroied loci of HPT axis and destroied the balance of thyroid hormone. Finally, it caused a series of damage on the growth and development of zebrafish. This might be the reason that induced more serious thyroid toxicity in zebrafish larvae after co-exposure to PFOS and Nano-ZnO.(3) PFOS and Nano-ZnO co-exposure increased cumulative mortality rate and decreased the body weight and body length in the parental generation of zebrafish. The number of calculated spawning and the content of egg protein were decreased in zebrafish embryos after co-exposure to PFOS and Nano-ZnO. GSI gonad index was not changed, which meaned that co-exposure groups did not affect the weight of the ovary and testis of zebrafish. Co-exposure affected cells mature in the testis and the ovarian of the parental generation. Co-exposure also increased the pathological damage of liver and intestines. The OTM value and micronucleus rates of peripheral blood cells were increased with increasing the concentration in co-exposure groups. The resutls suggested that co-exposure groups had synergy effect on DNA damage of peripheral blood cells. The levels of T were decreased in male fish after exposure to(P 0.1+Z 3.4) and(P 0.2+Z 6.75) mg/L groups. The levels of E2 were also significantly decreased in female zebrafish after exposure to(P 0.1+Z 3.4) and(P 0.2+Z 6.75) mg/L groups. PFOS and Nano-ZnO co-exposure affected the secretion of sex hormones in the zebrafish body. The gene expression level of Vtg1 was not significantly affected in Nano-ZnO single-exposure groups. But gene expression level of Vtg1 was significantly down-regulated in liver tissue of zebrafish after coexposure to Nano-ZnO and PFOS. It turned out that Nano-ZnO and PFOS coexposure decreased the content of yolk protein in offspring embryo. PFOS and NanoZnO co-exposure increased mortality, decreased fertilization rate and hatching rate. But there were not significant affect on body length and malformation rate in offspring. The pollutants could affect the secretion of sex hormone, sexual maturity, secondary development and disturb sexual function. It might be the reason that coexposure groups enhanced the reproductive toxicity of zebrafish.In conclusion, PFOS and Nano-ZnO co-exposure enhanced the development toxicity, thyroid toxicity and reproductive toxicity of zebrafish. Therefore, in order to make reasonable risk assessment, the work should not only consider the single toxicity of pollutants, but also consider the interaction mechanism of mixed pollutants. It can better protect human life and health. |
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