The Combined Toxic Effect Of Polystyrene Microplastics And Esfenvalerate On The Liver Of Zebrafish

The appearance of plastic has provided great convenience for human life and production,but plastic pollution has become one of the most urgent environmental problems facing human beings in the 21 st century.Especially when plastic fragments are released into aquatic environment,they will be further degraded into micron plastics(MPs)and nanoscale plastics(NPs),which are easy to be ingested by aquatic organisms and cause certain ecological risks.Esfenvalerate(FEN)is a type II pyrethroid insecticide that adversely affects mammalian liver tissue and is highly toxic to aquatic organisms.Previous studies have focused on neurodevelopmental toxicity,reproductive toxicity and immunotoxicity of FEN,but the toxic effects and mechanisms of the liver,as the main organ of aquatic vertebrates to metabolize and expel heterologous substances,are unclear.A large number of studies have shown that microplastics are easy to adsorb other hydrophobic pollutants in aquatic environment and have serious negative effects on aquatic organisms.With the increasing of FEN residues and MPs accumulation in the environment,the chances of co-existence in the water are greatly increased,which will greatly harm the water environment and destroy the health of aquatic animals and plants.Therefore,it is very important to explore the toxic effect and mechanism of the combined pollution on aquatic organisms.This study took adult zebrafish as the research object and selected green fluorescent polystyrene microplastics(PS MPs)with three particle sizes of1 μm,10 μm and 100 μm for a 7 days accumulation experiment.We selected 1μm original polystyrene microplastics PS MPs(200 μg/L)and FEN(1 μg/L)to conduct single and combined exposure toxicity experiments for 21 days,which explored the toxic effects and mechanism of PS MPs and FEN on the liver of adult zebrafish from the aspects of gene,enzymology,and histopathology.The main results were as follows:1.The accumulation experiments of three particle sizes showed that only 1 μm and 10 μm of PS MPs can accumulate in the liver and can not reach the liver,because the diameter of 100 μm PS MPs is too large.2.Fenvalerate group alone significantly induced the levels of ROS,antioxidant enzyme activity and the expression of cat,sod and gpx.The combination of PS MPs and FEN significantly induced the highest levels of ROS and inhibited SOD,CAT,GPx enzyme activity and the expression of cat,sod,gpx and triggered the highest level of MDA content,indicating that the combined action caused liver oxidative damage.3.PS MPs and FEN combined exposure significantly induced the highest levels of 8-deoxyguanosine content and caspase3,caspase8 and caspase9 expression,indicating that compound exposure induced apoptosis in zebrafish liver through Caspase pathways.4.Tissue sections showed that the PS MPs and FEN group caused the most serious liver tissue damage,such as chromatin staining,nuclear disappearance and cell lytic necrosis.Taken together,small size PS MPs can enter liver tissue of zebrafish.The presence of environmental-related concentration PS MPs reflects the toxic effects of the combined exposure on liver tissues through the changes of antioxidant biomarker activity,DNA injury,apoptosis and histopathology.This study can provide a basic reference for the comprehensive evaluation of the interaction effect of PS MPs and other pollutants.