Mechanism Of Low Concentrations Of Polystyrene Microplastics Influence The Cytotoxicity Of Ag Ions To Escherichia Coli

Because microplastics have a wide range of sources,a long existence cycle,can absorb other environmental pollutants,are small in size and are easily ingested by aquatic organisms,the problem of microplastics pollution in the water environment has gradually attracted the attention of scholars around the world.At the same time,heavy metal pollution is also one of the problems of water environment pollution.However,at present,the toxic mechanism of microplastics combined with heavy metal pollution on freshwater organisms is not very clear,and most of the current studies focused on high concentration of microplastics,and its short-term toxic effects,which are seriously inconsistent with the actual situation.While,the toxic effects of microplastics in the photoaging process have not attracted enough attention.Our research studyed microplastics alone,the combined treatment of PSMPs and Ag⁺and its ecotoxicity to aquatic organisms in the aging process,providing important information for further understanding of the environmental risks of microplastics.Therefore,in this study,polystyrene microplastics(PSMPs)with different sizes,surface functional groups and aging conditions were used as models to analyze the toxicity of PSMPs alone,PSMPS with Ag⁺,and the initial stage of PSMPs to E.coli in the UV aging process(UV-315 irradiation 4 h).By detecting the survival rate of E.coli,ROS value,ATPase activity,and cell membrane permeability and other indicators,this helped us understand the cytotoxicity and toxicity mechanisms of PSMPs to E.coli.The main experimental results are as follows:(1)Through a single toxicity experiment of PSMPs on E.coli,it was found that PSMPs hardly affected the viability,membrane integrity,ROS production and ATPase activity of E.coli(p>0.05).This showed that low concentrations of PSMPs hadno significant effects on the growth of E.coli.This result was also consistent with the term"plastic circle".(2)When PSMPs and Ag⁺were exposed together,because of the different exposure time and the different nature of PSMPS,their effects on the viability of E.coli showed different trends.In the initial stage of exposure,low concentrations(1.0 mg/L)of PSMPs dynamically affected the cytotoxicity of Ag⁺to E.coli through a variety of toxic mechanisms.PSMPs probably maintainded the viability of E.coli by protecting the cell membrane,inhibiting the generation of ROS in cells,and/or restoring the activity of ATPase(P<0.05 or P<0.01).During the 48-hour co-exposure process,PS-NF(without functional group)reduced the cytotoxicity of Ag⁺by protecting the integrity of the cell membrane,while the aging PS-NF had less influence on the cytotoxicity.PS-NH₂ and PS-COOH significantly promoted the generation of ROS in E.coli and the inhibition of ATPase activity,thereby enhancing the cytotoxicity of Ag⁺.(3)In the experiment of ultraviolet aging microplastics,PSMPs under ultraviolet irradiation caused the increase of ROS in E.coli,the decrease of ATPase activity,and the increase of cell membrane permeability,which ultimately leaded to a significant drop in the survival rate of E.coli(P<0.05 or P<0.01).However,the toxicity of PSMPs with a large particle size(10?m)during irradiation was lower than that of microplastics with a smaller particle size(1?m),which possiblydue to the shielding effect of the microplastics with a larger particle size.The reason was that E.coli received less ultraviolet radiation,and the large-size microplastics themselves produced less superoxide free radicals.In general,low concentrations of PSMPs had less cytotoxicity to E.coli;PSMPs cooperated with Ag⁺changed the population level of E.coli,and even the structure of aquatic ecosystems;the aging process of microplastics in real situations is more complex.Therefore,the actual environmental and health risks of PSMPs need to be further investigated,and due to dynamic toxic effects and mechanisms,the actual toxic effects of PSMPs should be carefully considered.