Effects Of Humic Acid On The Toxicity Of ZnO NPs To Zebrafish Embryos

ZnO nanoparticles(ZnO NPs)is one of the most widely used metal nanomaterials,and its large-scale use also increases the risk of discharge in the aquatic environment.So it has the potential aquatic toxicity.Humic acid(HA),as one of the most widespread natural organic matters in water,its abundant groups are conducive to the adsorption of nanomaterials.HA would change the migration and transformation pathway of nanoparticles in water,so as to change the toxicity of nanoparticles to organisms.After discharge into water,nanomaterials nolonger exist alone as it always affected by various natural organic matters in water.Therefore,it is necessary to evaluate the toxic effect of HA on ZnO NPs.In this study,the ZnO NPs and HA were selected as the research objects,and the zebrafish embryos were selected as the biological subjects.Survival rate,hatching rate,heart beats rate,body length and antioxidant enzyme activity of zebrafish embryos were selected as indicators of toxicity test,to studied the ZnO NPs in zebrafish embryo developmental toxicity and HA on its toxicity,and to explore the toxicity mechanism of ZnO NPs on zebrafish embryos and role of HA.The results show that the stability of ZnO NPs suspension is extremely poor.With the concentration increases,the precipitation phenomenon of ZnO NPs will be more obvious,and the absolute value of the Zeta potential and its stability will decrease.1?20mg/L ZnO NPs have negative impact on the survival rate and hatching rate zebrafish,both of which decrease with the increase of the concentration of ZnO NPs,and show a concentration-effect relationship.ZnO NPs can also increase heart beats but decrease body length of Zebrafish,and it induce a series of malformations of zebrafish.5?40mg/L HA can increase the absolute value of zeta potential and stability of ZnO NPs,and reduce its precipitation phenomenon.HA can increase the survival rate and hatchability of zebrafish embryos exposed to ZnO NPs,and the higher the concentration of HA,the more obvious the mitigation effect on zebrafish toxicity caused by ZnO NPs.Three possible toxicity mechanism of ZnO NPs and the role of HA can be speculated as follows:(1)The release of Zn²⁺in the ZnO NPs suspension was not the main cause of embryo toxicity in zebrafish.HA will increase the release of Zn²⁺from ZnO NPs suspension,which cased the hatching delay of the zebrafish embryos.(2)The aggregation properties of nanoparticles make them adhere to the surface of zebrafish in large quantities,increasing the contact probability between zebrafish and ZnO NPs.HA will increase the stability of ZnO NPs suspension and reduce its adhesion on zebrafish.(3)ZnO NPs can damage the antioxidant system of zebrafish,and the enzymes activities of CAT and SOD in zebrafish.The presence of HA can restore CAT and SOD enzyme activities to normal levels and eliminate the negative effects of oxidative stress.