Study On The Combined Toxicity Mechanism Of Polystyrene Nanoplastics With Copper Ions And Copper Oxide Nanoparticles On Platymonas Helgolandica Var.tsingtaoensis

In recent years,nanoplastics as a new type of pollutant have received a lot of attention from domestic and international researchers.Studies have shown that nanoplastics can interact with organic contaminants,heavy metals and engineered nanoparticles,thus making them become carriers of pollutants in the marine environment and changing the way pollutants acted on aquatic organisms,which in turn may lead to higher ecological and environmental risks.However,studies on the combined toxicity of nanoplastics with heavy metals and engineered nanoparticles are still in the initial stage,and no regular conclusions have been obtained from the limited studies.Therefore,it is necessary to continue the in-depth study on the combined toxicity of nanoplastics with heavy metals and engineered nanoparticles to aquatic organisms,especially the primary producer microalgae,to enrich the theory of their combined toxicity mechanisms.In this study,we investigated the combined toxicity of nanoplastics with heavy metals and engineered nanoparticles by using polystyrene nanoplastics(PS)and polystyrene modified by carboxyl groups(PS-COOH)as typical representatives of nanoplastics(PS-NPs),Cu(II)and copper oxide nanoparticles(nCuO)as typical representatives of heavy metals and engineered nanoparticles,and Platymonas helgolandica var.tsingtaoensis as test organisms.The toxicity of nanoplastics with heavy metals and engineered nanoparticles was investigated,and the mechanism of combined toxicity was explored.The main research contents and conclusions are·as follows:(1)High concentrations(≥75 mg/L)of PS-NPs significantly inhibited the growth of microalgae,which may be related to the membrane oxidative damage they induced.Microalgae were able to cope with the oxidative stress produced by low concentrations(<75 mg/L)of PS-NPs through the increase of reduced glutathione(GSH).The results of scanning electron microscopy(SEM)showed that both PS-NPs adsorbed on the surface of microalgae,which was the reason for the membrane damage.PS-NPs did not inhibit photosynthesis,and PS had a stronger shading effect on microalgae due to the formation of micron-sized aggregates,which led to an increase in chlorophyll content of algal cells.There was no significant difference in the toxicity of two kinds of PS-NPs,which was due to the negligible effect of-COOH on PS-COOH.(2)The growth inhibition effect of Cu(II)on microalgae increased with the increasing Cu(II)concentration,which was influenced by the oxidative damage of cell membrane and the decrease of chlorophyll content.The growth inhibition effect of PS-NPs and Cu(II)combined exposure was enhanced compared to their single exposure.A synergistic effect was obtained using the independent action(IA)model and Abbott model.Stronger oxidative stress and more severe membrane damage were induced by combined exposure.The presence of PS-NPs could promote the internalization of Cu(II)by the algal cells,which was the reason for the enhanced combined toxicity.(3)In the f/2 medium,nCuO was able to undergo rapid aggregation and sedimentation,resulting in a lower effective nCuO concentration and a weaker toxic effect.The toxicity of nCuO was mainly dependent on the heterogeneous aggregation of nanoparticles and algal cells,but was less affected by the released copper ions from nCuO.PS-NPs were able to alleviate the growth inhibition effect of nCuO on microalgae.The IA model and Abbott model showed that they had an antagonistic effect.PS-NPs could reduce the oxidative damage of nCuO on algal cells and the disruption of nCuO on membrane integrity,which was related to the reduction of interactions between nCuO and microalgae through the heterogeneous aggregation of PS-NPs and nCuO.