Effects Of Combined Pollution Of Microplastics And Pesticides On Plant-Microbe-Soil System

As emerging pollutants,microplastics are widely distributed in the environment,and their potential risks have been concerned by the researchers around the world.Pesticides are commonly used in agricultural production in China,and their effects on environmental health and food safety have been a hot spot within the research area.The microplastics have been greatly accumulated in agricultural soil due to the utilization of agricultural films and sludge.Furthermore,the pesticides were remained in the soil during the use procedure,which makes it possible for both contaminants exist simultaneously in the agricultural environment.In this study,the soil adsorption characteristics to trifluralin were investigated after the low-density polyethylene(LDPE)of 1%present.The single and combined effects of LDPE and trifluralin on plant growth and soil health were explored after the addition of LDPE(0.5%、1%、3%w/w)and trifluralin(field reference dose and two times of field reference dose,1.28 and 2.56 mg/kg).The main research results and conclusions are as following:1.LDPE could improve the adsorption rates of trifluralin in the soil.The adsorption kinetics experiment showed that both the pseudo-first-order and pseudo-second-order kinetic models could well fit the adsorption of trifluralin on soil and LDPE-contained soil,but the fitting coefficient(R~2)of the pseudo-second-order adsorption kinetics was higher than the fitting coefficient(R~2)of the pseudo-first-order adsorption kinetics,which proved that the adsorption process of trifluralin on the two mediums was mainly chemical adsorption,accompanied by physical adsorption.The Langmuir adsorption coefficient decreased in the in the soil with LDPE,and the fit of Freundlich was better than the Langmuir model,indicating that the adsorption of trifluralin on soil and LDPE-contained soil was multilayer adsorption.2.The pot experiment showed that LDPE and trifluralin single treatment did not affect the dry weight of Chinese cabbage,but the combined treatment of LDPE and trifluralin reduced the dry weight and increased the sensitivity coefficient of roots,indicating that LDPE could affect the dry weight of Chinese cabbage by aggravating the effect of trifluralin on the roots of Chinese cabbage.Single LDPE and LDPE combined with trifluralin had no significant effect on chlorophyll of Chinese cabbage.The net photosynthetic rate,stomatal conductance and transpiration rate were stimulated by 0.5%and 1%LDPE while inhibited at a high dose,indicating the effects of LDPE on the growth depend on the levels of LDPE.Superoxide dismutase activity increased first and then decreased under single treatment of LDPE,and the activity increased by 144.4%and 131.4%under the single trifluralin treatment,respectively.The toxic effects of LDPE and trifluralin on Chinese cabbage may be antergic when they occur together.The peroxidase activity increased with the increase of LDPE concentration under the treatments of single LDPE or combined with trifluralin,indicating that the increase of superoxide dismutase activity was the main way to remove the oxidative stress caused by trifluralin,and the activation of peroxidase activity may be the main mechanism to reduce the microplastics-induced oxidative damage in Chinese cabbage.3.The single treatment of LDPE reduced soil p H.However,soil pH values were reduced under the combination treatment of LDPE and trifluralin except for the high dose of microplastic and trifluralin,which might be the change of exchangeable cations in soil caused the combined treatments.Both single and the combined treatment of LDPE and trifluralin increased soil organic matter,carbon to nitrogen ratio and nitrate nitrogen content.Compared with the control,LDPE single treatment and the combined treatment with trifluralin increased soil catalase and urease activities,implying that LDPE may increase the toxicity and effect the N transformation.Under the single LDPE treatment,soil sucrase and acid phosphatase activities increased and then decreased with increasing LDPE concentration,and increased by 24.4%and 11.9%under the0.5%,respectively.The combined treatment with LDPE and trifluralin increased soil sucrase activity and had little effect on acid phosphatase activity.LDPE and trifluralin were positively correlated with the residues of trifluralin,and indirectly affected the residues by affecting soil enzyme activities.The residues were negatively correlated with the biomass of Chinese cabbage.4.There was no significant effect of LDPE on bacterial community diversity,but LDPE reduced the Shannon index of fungal communities,indicating that fungi are more sensitive to the existence of LDPE than bacteria.The combined treatment of LDPE and trifluralin increased the Shannon and Chao1 indices of bacterial communities,especially the highest dose microplastic and trifluralin increased by 1.0%and 7.5%,respectively.While low doses of LDPE mitigated the effect of trifluralin on fungalαdiversity.The combined treatments altered the abundance of microbial functional genes by enriching specific taxa of microorganisms.Xenobiotics Biodegradation and Metabolism genes and Inorganic Nutrient Metabolism genes were of the most significance in bacterial and fungal communities,respectively,suggesting that these two genes are sensitive genes under the combined contamination conditions of microplastics and trifluralin.