Toxicological Study And Risk Assessment Of Polystyrene Micro(nano)plastics On Important Bait Microalgae In Fishery Waters

Micro(nano)plastic(MNP)pollution in marine environments has become a hot issue.Due to the frequent fishing activities of humans and the massive use of plastic fishing gear,MNP pollution in the marine fishery waters known as"marine pasture"is becoming more serious.Bait microalgae are important primary producers of aquatic food webs in fishery waters and are also the starting point of pollutant transmission within the aquatic food chain,which are ideal organisms for carrying out ecological risk assessments of MNPs in fishery waters.This study investigated the toxic effects and mechanisms of concentration-dependent polystyrene microplastic(PS-MP)and size-dependent PS-MNPs on five important marine bait microalgae species,i.e.,Platymonas helgolandica tsingtaoensis,Platymonas subcordiformis,Dunaliella salina,Cyclotella cryptica and Cyclotella meneghiniana.Integrating the results in the present study with the relevant research data,we built the species sensitivity distribution(SSD)curves of MNPs on bait algae and other aquatic organisms,and deduced the hazard risk threshold of MNPs,and assessed the ecological risks of MNPs in twenty fishery waters of the world.The main research results are as follows:1.Toxic effects of different concentrations of PS-MPs on the five bait microalgae.No significant effects on the growth and chlorophyll a content were observed of the five microalgae exposed for 24 to 72 h to PS-MPs at environmental concentrations(10,10~3 and 10~5particles/L).The most significant oxidative stress was observed at 24 h and72 h.In general,PS-MPs with high concentration caused the most significant synthesized effects on the bait microalgae.The result of the integrated biomarker response(IBR)method indicated that Platymonas helgolandica tsingtaoensis was the most sensitive algae species to PS-MP exposure among the five tested microalgae species.2.Toxic effects of different sizes of PS-MNPs on Platymonas helgolandica tsingtaoensis.The toxic experiment of environmentally relevant concentrations(10,10~3and 10~5 particles/L)of two sized(500 nm and 45μm)PS-MNPs on Platymonas helgolandica tsingtaoensis was performed,and the results showed that small-sized PS-NPs caused more toxic effects on cell density,photosynthesis,oxidative stress and metabolism of Platymonas helgolandica tsingtaoensis.The zeta potential of 500 nm PS-NPs was significantly lower than that of 45μm,which was liable to accumulate and be adsorbed around the cells because of stronger interparticle forces.The exposure of500 nm PS-NPs blocked photosynthetic light energy and caused oxidative stress of Platymonas helgolandica tsingtaoensis.Compared to the control,metabolomics results showed that the numbers of metabolites and metabolic pathways with significant differences(p<0.05)under the exposure of 10~3 particles/L PS-MNPs at 24 h were both much higher than those at 72 h.The PS-MNPs significantly inhibited the synthesis of antioxidant metabolites in the taurine,hypotaurine,and alpha-linolenic acid metabolism pathways.Detoxification was observed in the algal cells at the later exposure stage,manifested by activation of the carotenoid biosynthesis pathway and increased synthesis of antioxidant metabolites to maintain the normal redox function.3.Environmental levels of MNPs in the fishery waters and ecological risk assessments on aquatic organisms.We analyzed the acute toxicological data of 29species of common aquatic organisms(including the data of five microalgae in the present study)from 8 phyla through a bibliometric analysis.The half maximal effective concentration(EC50)was used to construct the SSD curves.The 5%hazard concentration(HC5)was predicted with which the values of risk characterization ratios and short-term water quality criteria for aquatic organisms could be calculated.Then combined with Lithner’s polymer hazard index,the evaluation results of ecological risks of MNPs in the 20 fishery waters around the world showed the ecological risks of Mumbai coast,India and the Gulf of Mexico were much higher.The abundance of MNPs in these two fishery waters exceeded the predicted value of SWQC(127.35particles/L)and the values of RCR were higher than 1,and there existed MNPs types of high hazard risk level(IV)(polymethyl methacrylate and polycarbonate)which need further monitoring.The MNP pollution in other fishery waters was at a risk-free level for aquatic organisms,because the concentrations of MNPs were all significantly lower than the value of SWQC.The present results provide important technical support for ecological risk assessment of MNP pollution in fishery waters.