Investigation On Toxic Effects And Corresponding Mechanisms Of Microplastics And Organophosphorus Flame Retardants On Microcystis Aeruginosa

Microplastics（MPs）are a new type of pollutant that has been detected in various water environments.The environmental behavior and potential environmental risks of MPs have become a research hotspot in recent years.Organophosphate flame retardants（OPFRs）,as substitutes for traditional flame retardants,have been widely used in various industries.However,their extensive production led to their entry into the aquatic environment.MPs and OPFRs have been confirmed to coexist in the aquatic environment.Whether the two will interact and whether the resulting composite pollution system will cause harm to the aquatic environment has become an urgent issue that needs to be addressed.Therefore,this study set Microcystin aeruginosa as the experimental model,use polystyrene microplastics（PS）,amino modified polystyrene microplastics（PS-NH₂）,carboxyl modified polystyrene microplastics（PS-COOH）,triethyl phosphate（TEP）,tris（2-chloroethyl）phosphate（TCEP）to investigate the toxic effects of single and mixed exposure of microplastics and organophosphorus flame retardants on Microcystis aeruginosa,and discussed its mechanism.The main research content and results are as follows:1)The single toxicity of MPs to Microcystis aeruginosa is:5μm PS-NH₂>0.1μm PS-NH₂>0.1μm PS>0.1μm PS-COOH>5μm PS-COOH>5μm PS;The changes of chlorophyll a,carotenoids,reactive oxygen species（ROS）,superoxide dismutase（SOD）,catalase（CAT）,malondialdehyde（MDA）and other physiological indicators indicate that MPs can inhibit the synthesis of chlorophyll a and carotenoids in algae cells,while subjecting algae cells to oxidative stress,leading to lipid peroxidation reactions and damaging the cell membrane by altering its hydrophobicity,ultimately inhibiting the growth of algae cells.2)Both TEP and TCEP have a hormetic effect that promotes the growth of Microcystis aeruginosa at low concentrations and inhibits it at high concentrations,the biological effects caused by TCEP are more pronounced;The variations of relevant physiological indicators induced by TEP and TECP indicate that low-dose OPFRs could promote the photosynthetic activity to provide more energy for algal cells and moderately increase the intercellular ROS amount to positively regulate the cellular life activities,thus stimulating the algal growth.On the contrary,high-dose OPFRs could hinder the synthesis of photosynthetic pigments to reduce the energy supply,induce excessive ROS production to cause oxidative damage on algae cells,and damage the cell membrane via changing the hydrophobicity,ultimately inhibiting the growth of Microcystis aeruginosa.3)0.1μm PS,0.1μm PS-NH₂,0.1μm PS-COOH has adsorption effect on both types of OPFRs;The presence of OPFRs reduces the toxicity of MPs.Overall,The interaction effect of MPs and OPFRs on Microcystis aeruginosa was antagonism;The adsorption of0.1μm MPs and OPFRs reduces the impact of microplastics on chlorophyll a and carotenoids,and reduces oxidative damage to algae cells;Overall the mixed system of 0.1μm MPs and TEP resulted increase on cell membrane hydrophobicity,while the mixed system of 0.1μm MPs and TCEP resulted in a significant decrease on cell membrane hydrophobicity.4)Both-NH₂ and-COOH enhance the adsorption capacity of 5μm MPs for TEP and TCEP;The mixed system of 5μm MPs and OPFRs has an inhibitory effect on the growth of Microcystis aeruginosa.The interaction between 5μm PS,5μm PS-COOH with OPFRs is additive and synergistic,and the interaction between PS-NH₂ and OPFRs is generally antagonism;The toxicity mechanism of the mixed system formed by 5μm MPs and OPFRs on Microcystis aeruginosa is also related to the mechanisms of photosynthesis and oxidative stress.The presence of-NH₂ and-COOH reduces the influence of the mixed system of 5μm MPs and OPFRs on the hydrophobicity of algal cell membranes,which is beneficial for the growth of algal cells.