Toxic Effects Of Mixed Exposure Of Microplastics With Different Particle Sizes And Typical POPs On Scenedesmus Obliquus

Increasing plastic production leads to the accumulation of microplastic particles in the aquatic environment,and microplastics often co-exist with other pollutants in the actual aquatic environment.Existing studies have found persistent organic pollutants attached to the surfaces of microplastics.In recent years,due to the abuse of brominated flame retardants and organophosphorus insecticides,their potential hazards,toxic effects and persistence have become a special concern of the environment.Microalgae are primary producers of aquatic ecosystems and are one of the most common organisms tested in toxicology.Hormesis effect refers to the phenomenon of biphasic dose effect of low dose stimulation and high dose inhibition of tested organisms exposed to different doses of compounds.However,there have been few reports on whether exposure to microplastics,brominated flame retardants and insecticides can produce Hormesis effect on microalgae,and on the harm to aquatic ecosystems caused by combined exposure to microplastics,brominated flame retardants and insecticides.Therefore,it is necessary to further study the toxic mechanism of microalgae growth under the single and combined stress of microplastics,brominated flame retardants and insecticides.CAT activity,Malondialdehyde(MDA)content and cell membrane hydrophobicity were implicated in promoting toxicity of PS,TBBPA and CPF alone and in combination.The research results are as follows:1)Exposure to PS of different particle sizes caused Hormesis effect,and the stimulating effect of Hormesis effect first decreased and then increased,and the inhibitory effect first increased and then decreased with the increase of particle size.The reason may be that with the increase of PS particle size,the surface area of microplastics increases,the shading effect of algal cells is enhanced,and the physical damage and inhibition effect of microalgae are enhanced.From 0 ～ 20 days of experiment,the growth of Scenedesmus Obliquus was significantly stimulated and was in logarithmic growth phase.From 20 ～ 28 days after the experiment,the growth of Scenedesmus Obliquus gradually recovered and remained stable,which may be due to the adaptation of microalgae to the external environment in the later period.Similar changes were also observed in various indexes of Scenedesmus Obliquus.During 0 ～ 20 d of the experiment,Scenedesmus Obliquus content decreased,ROS level increased,antioxidant enzyme activity increased,MDA content increased,and cell membrane hydrophobicity decreased.After 20 to 30 days of experiment,there was no significant difference between the control group and the control group.2)Hormesis effect was observed on both TBBPA and CPF.Under the stimulation of high concentration of TBBPA and CPF,chlorophyll a content was decreased,which had a negative effect on the photosynthetic system of microalgae.Hormesis effect was correlated with the change of intracellular ROS levels in algae,that is,the moderate increase of intracellular ROS levels in the experimental group promoted growth,while the significant increase inhibited growth.Under the stimulation of high concentrations of TBBPA and CPF,the alga claviculata produced excessive ROS,putting the microalga in a state of oxidative stress,which was also demonstrated by increased SOD and CAT activities.At this time,the cell membrane is easily attacked by ROS,resulting in damage to the cell membrane,increased MDA content and decreased hydrophobicity of the cell membrane.Therefore,the growth of Scenedesmus Obliquus is significantly inhibited.3)By comparing the adsorption capacity of PS on TBBPA and CPF,the smaller the particle size of microplastics,the stronger the adsorption capacity.The adsorption capacity of PS on TBBPA is greater than that of CPF.High concentrations of PS combined with TBBPA or CPF mostly antagonistic mode,low concentrations of PS combined with TBBPA or CPF mostly synergistic mode.The combined exposure of PS and TBBPA and PS and CPF also affected the indexes of Scenedesmus Obliquus,and the changes of indexes were similar to that of single results.