The Combined Toxic Effects Of Microplastic And Triphenyl Phosphate On Zebrafish (Danio Rerio)

Toxicity effect of combined contaminants has become the focus of people concerning.As an emerging pollutant,microplastics have been detected frequently in marine water and surface water in recent years.Microplastics have some harmful effects on the aquatic organisms,even further pass through in the food chain,and eventually enter the human body,thus more and more attention has been paid to their toxic effects.Triphenyl phosphate(TPP)is a representative compound of organophosphate flame retardants(OPFRs).TPP has been detected in a variety of environmental media,and its presence in the environment can cause a variety of toxic effects such as neurotoxicity,reproductive toxicity,developmental toxicity,and endocrine disruption effects.The high ratio of surface area to volume of microplastics enables the chemicals to adsorb the plastic surface,leading to the accumulation of contaminants on the surface and form a complex mixture of contaminants.Because of their ubiquity and increasing amount in the water,it is necessary to explore the mechanisms of toxicity and interactions of mixtures chemicals.However,there are few studies on the toxicity of microplastics,especially their combined toxicity with chemicals.Zebrafish(Danio rerio)are a suitable model organism to study the bioaccumulation and toxicity of contaminants in aquatic environment.This study selected 46 nm polystyrene(NPS)and 5.8 ?m polystyrene(MPS)as typical microplastics,and TPP as the model compounds.We systematically studied the developmental toxicity for zebrafish embryo,the endocrine disruption effect and the reproductive toxicity for adult zebrafish of PS and TPP,and further described the possible toxicity mechanism,and explored the effects of different particle sizes of PS on the combined toxicity.Taking zebrafish embryos as the model organism,we found that microplastics can enter the embryos and have cumulative effects in the intestines of larves.Individual microplastics have toxic effects on zebrafish embryos,and the toxicity of NPS is stronger than that of MPS.The developmental toxicity of zebrafish embryos is sensitive after exposed to PS and TPP.The study indicated that the mortality and malformation rate increased and the hatching rate decreased after combined exposure.Compared with the individual TPP,in the the combined exposure of PS and TPP,the expression levels of related genes varied greatly on the HPG axis(hypothalamus-pituitary-gonad axis)and HPT axis(hypothalamus-pituitary-thyroid axis),and thyroid and reproductive toxicity significantly enhanced.Exposed to(TPP + NPS)treatment group has a stronger developmental toxicity for zebrafish embryo than that of(TPP + MPS)treatment group.Short-term growth and reproduction experiments were performed to explore the endocrine system and reproductive properties of zebrafish exposed to the mixture system.The results showed that the endocrine system of adult zebrafish was disturbed in a sex-dependent way after exposed to PS and TPP.Specifically,compared with the individual TPP exposure,the development of ovary and testis was greatly inhibited after combined exposure,and the reproductive development level was affected.Additionally,the GSI(gonadosomatic index)and HSI(hepaticosomatic index)were also affected,and the vitellogenin(VTG)level,sex hormone(E2 concentration,T concentration,and E2/T value)also showed different levels of change(increased or decreased).In the composite system,the presence of PS affected the endocrine system,which further affected the reproductive capacity and embryo quality.Egg production,spawning events,fertilization and hatching rates were all inhibited after combined exposure.In particular,the(TPP + MPS)treatment group had the strongest reproductive toxicity,and the embryo quality was also the worst.Overall,compared with the individual TPP,the combined toxicity of(TPP + NPS)and(TPP + MPS)composite systems are both enhanced,and the(TPP + MPS)system seems to have a stronger ability to disrupt the endocrine system and reproduction system of adult zebrafish.In conclusion,whether in the embryonic stage or the adult stage,PS and TPP co-exposure in the environment enhanced the developmental toxicity,the disruption of endocrine system and reproductive toxicity of zebrafish.Usually,the effects of pollutants on the endocrine system can cause hormonal disorders,slow the development of sexual organs,and thus leading to the changes of reproductive behavior.Through the investigation of this study,it is of great significance to understand the trend of interaction between microplastics and environmental pollutants.