Biological Effects And Mechanisms Of Nanoplastics On Typical Aquatic Microorganisms

Globally,8.3 billion tons of plastics have been produced by 2015.However,only 6-26%of all produced plastics has been recycled,with the rest ending up in landfills or releasing into the environment.After entering the environment,plastics are degraded into microplastics(<5 mm)or nanoplastics(<100 nm)by different abiotic and biotic factors.Nanoplastics are also derived from directly industrial plastic nanoparticles.Nanoplastics have the propensity to penetrate cell membrane and accumulate in tissues and organs of exposed organisms,triggering physiological and metabolic disorders,growth impediments,diminished reproductive fitness,and even early mortality.In addition,nanoplastics can absorb and enrich organic contaminants from the aquatic environment.This effect has the potential to increase the chemical uptake and bioaccumulation rates of such co-contaminants.Meanwhile,nanoplastics can transfer these environmental contaminants to other environments through food webs and long-range transport of particles,posing a serious threat to the ecosystem.Therefore,the biological effects of nanoplastics in the aquatic environment have become a global concern.However,current research mainly focuses on the effects of nanoplastics on animals,especially marine animals.Based on this,according to the environmental behavior and fate of nanoplastics in the aquatic ecosystem,the biological effects and mechanisms of nanoplastics on typical aquatic microorganisms was investigated,which provided basic data for assessing ecological toxicity of nanoplastics and their possible environmental risks.The main conclusions are as following:(1)The interaction mechanism between nanoplastics and microbial aggregates in sewage treatment plants was analyzed.By measuring the endogenous respiration rate of activated sludge,it was found that the acute inhibition of activated sludge by nanoplastics was enhanced with increasing its concentration.Extracellular polymeric substances(EPS)played an important role in the interaction between activated sludge and nanoplastics.X-ray photoelectron spectroscopy(XPS)results indicated that the functional groups involved in the interaction between nanoplastics and EPS were carbonyl and amide groups and the side chains of lipids or amino acids.Furthermore.fourier transform infrared(FTIR)spectroscopy results showed that the combination of nanoplastics with EPS reduced the relative abundance of antiparallel ?-sheets and random coils,increased the relative abundance of aggregated strands,[3-sheets and a-helices,which lead to the bioflocculation of activated sludge.(2)The signal pathways for the acute toxicity of nanoplastics on Synechococcus elongatus were clarified.A novel method for assessing the environmental safety of nanoplastics at molecular level was expanded.S.elongatus as the main primary producer in the river and the model strain of cyanobacteria,was selected in this study Through the acute exposure of differently charged nanoplastics on S.elongatus,it was found that the positively charged amino-modified polystyrene nanoplastics(PS-NH2)could significantly inhibit the growth of S.elongatus(EC50=3.81 ?g/mL),while the effect on growth of negatively charged sulfonic acid-modified polystyrene nanoplastics(PS-SO3H)below 100 ?g/mL was negligible.Non-targeted metabolomics analysis showed that PS-NH2 altered the metabolites including alkylamines,amino acids,carbohydrates,fatty acids,lipids,nucleotides and organic acids.Combined with gene editing technology and metabolomics analysis,the disruption of glutathione metabolism and damage to membrane integrity were confirmed as the main causes of PS-NH2 toxicity(3)The effects and mechanisms of nanoplastics on Microcystis aeruginosa at the translation level was elucidated,and the top hub proteins for the synthesis and release of microcystin(MC)were screened.The effects of nanoplastics on the growth,MC synthesis and release from M.aeruginosa,a dominant species causing cyanobacterial blooms,were investigated.It was found that PS-NH2 significantly inhibited the growth of M.aeruginosa after short-term exposure,with the normally green M.aeruginosa turning yellow.This inhibition was significantly reduced upon long-term exposure,with M.aeruginosa regaining its green coloration,indicating that the interaction of nanoplastics and cyanobacteria was dynamic.Both short-term and long-term exposure of PS-NH2 significantly promoted MC synthesis and release.However,the acute exposure of PS-SO3H negligibly affected the extracellular release of MC.PS-NH2 inhibited photosystem ? efficiency,reduced organic substance synthesis,and induced oxidative stress.To protect the cell from oxidative stress and enhance the fitness of bloom populations,quotas of MC synthesis would increase,thereby promoting the synthesis of MC.Furthermore,PS-NH2 promotes the extracellular release of MC from M.aeruginosa via up-regulating the transporter and impairing cell membrane integrity.Through weighted gene correlation network analysis(WGCNA),the metabolism of organic substance was negatively correlated with the synthesis of MC,phospholipid synthesis was positively correlated with the release of MC,and the thylakoid membrane and light capture system were negatively correlated with the release of MC.(4)The sorption behavior of tetracycline by differently charged nanoplastics in the surface water of estuaries was analyzed,and joint toxicity of nanoplastics and tetracycline on Skeletonema costatum was evaluated.The salinity in estuaries exacerbated the aggregation of nanoplastics.The stability of nanoplastics depends not only on the surrounding environment,but also on the characteristics of nanoplastics,especially the functional groups.Because of the electrostatic repulsion,salting-out effect,and partition function,the sorption capacity of tetracycline by differently charged nanoplastics was enhanced with increasing salinity.The biological effects of tetracycline-saturated nanoplastics on S.costatum depends on the surface hydrophobicity and charges of this mixtures.