Adsorption Of Three Pesticides On Polyethylene Microplastics And Their Combined Toxicity Effects To Zebrafish

The widespread use of plastic products has led to an increasing number of plastic pollutants and the formation of microplastics（MPs）in the environment,resulting in serious ecological and environmental problems.However,microplastics are not existing single in the environment.Studies have shown that pollutants will be adsorbed by microplastics in the environment,changing the environmental performance and bioavailability of pollutants.Pesticides are common environmental pollutants,and their toxic effects on non-target organisms have been studied,but the toxic effects and mechanisms of combined exposure of microplastics and pesticides on non-target organisms are still unclear.Therefore,5μm virgin and aged polyethylene microplastics were selected to investigate the adsorption of three different types of pesticides（acetochlor,penthiopyrad,and lambda-cyhalothrin）on the polyethylene microplastics.Acetochlor(0.50 mg·L^-1)and penthiopyrad(0.03 mg·L^-1)with 5μm of virgin and aged polyethylene microplastics(1 mg·L^-1)were selected for the study in zebrafish for 35 d of exposure tests alone and in combination.The combined toxic effects of polyethylene microplastics and pesticides on the zebrafish were investigated in terms of acute toxicity,bioconcentration,histopathological tests,changes in intestinal flora,oxidative stress enzyme activity and immune-related genes and proteins（nf-κb pathway）.The results showed that:1、The adsorption capacities of polyethylene microplastics for the three pesticides were in the order of:lambda-cyhalothrin>penthiopyrad>acetochlor.The adsorption capacity of aged polyethylene microplastics（APE）for these three pesticides was 1.14-1.42 times higher than that of virgin polyethylene microplastics（VPE）.Polyethylene microplastics adsorption of acetochlor and lambda-cyhalothrin in accordance with the Langmuir model.The adsorption of penthiopyrad on polyethylene microplastics is consistent with the Freundlich model.Adsorption takes the form of spontaneous heat absorption.The effect of environmental factors（p H and natural organic matter）on the absorption tests is not significant.2、Polyethylene microplastics significantly increases the acute toxicity（1.62-1.79times）and bioaccumulation of acetochlor in zebrafish.After 21 days of exposure,compared with the control group,the individual exposure of polyethylene microplastics and acetochlor causes slight damage to the intestinal structure of zebrafish,and the richness and diversity of intestinal microbial communities are significantly increased.Moreover,the individual exposure of acetochlor reduces the intestinal CAT activity and MDA content,and promote the expression of intestinal immune-related genes and protein content.However,there is no significant difference in intestinal structural damage between combined exposure and single exposure.The abundance and diversity of intestinal microbial communities are significantly decreased,the activities of SOD and CAT are significantly decreased,the content of MDA is significantly increased,and the expression disorder of intestinal immune-related genes.It indicated that the combined exposure causes significant changes in the intestinal flora of zebrafish,resulting in higher oxidative damage and affecting the immune function of zebrafish..3、Polyethylene microplastics significantly increases the acute toxicity（1.38-1.53times）and bioaccumulation of penthiopyrad in zebrafish.After 21 days after exposure,compared with the control group,the individual exposure penthiopyrad combined exposure of penthiopyrad and aged polyethylene microplastics cause slight damage to the intestinal tissue structure of zebrafish,significantly increase the intestinal flora richness and species diversity,induce oxidative stress in the gut,and promote the expression and protein content of intestinal immune-related genes,thereby causing the immunotoxicity of penthiopyrad to zebrafish.After combined exposure,there is no significant difference in tissue injury compared with the single exposure group.The richness of intestinal flora is reduced,and the species diversity is increased.The activities of SOD and CAT and the content of MDA are decreased,and the expression of intestinal immune-related genes and the content of protein are inhibited.These results indicate that the combined exposure of virgin polyethylene microplastics and penthiopyrad affect the homeostasis of gut microbiota,leads to oxidative damage in the gut,changes the immune function of the gut.Combined exposure of penthiopyrad and aging microplastics exacerbates the immunotoxicity of penthiopyrad in zebrafishIn conclusion,the addition of polyethylene microplastics increases the bioaccumulation and acute toxicity of the two pesticides in zebrafish.The combined pollution of the microplastics and pesticides produces more severe oxidative stress and changes immune toxicity to zebrafish.Therefore,it is necessary to pay attention to the combined toxic effects of microplastics and pesticides on environmental organisms.This study can provide a basic reference for assessing the interaction effects of microplastics and other contaminants.