| The composition of chemical pollutants in natural water environment is complex,including various organic pollutants and inorganic pollutants.These pollutants will interact with each other to affect environmental behavior of the pollutants.Microplastics?with particle size of less than 5 mm?,as an emerging pollutant,have become a hot environmental issue concerned by scholars at home and abroad.Microplastics are widely present in various water environments,they can adsorb other organic pollutants,due to their small particle size,large specific surface area,and strong hydrophobicity,thereby,changing the environmental behavior and biological effects of microplastics and organic pollutants.At present,a lot of research work have been carried out on the mechanism of action and composite toxic effects of microplastics and organic pollutants,but most of them focus on the marine environment,and the research about the freshwater environment is still very limited.Nitro polycyclic aromatic hydrocarbons?NPAHs?are derivatives of polycyclic aromatic hydrocarbons.Because of their special structural characteristics,NPAHs have stronger carcinogenicity,bioaccumulation and biotoxicity than parent polycyclic aromatic hydrocarbons,which has attracted widely attention.Therefore,to study the interaction mechanism and composite biological effects of microplastics and NPAHs in fresh water environment,to grasp the impact of microplastics on the environmental behavior of NPAHs transport and fate,and to clarify the micromechanism of microplastics affecting the biological effects of NPAHs are the theoretical basis for comprehensive and effective evaluation of the environmental effects of microplastics and NPAHs,which can provide a scientific basis for the ecological risk assessment of environmental pollution in aquatic systems.In this study,polyethylene?PE?,polypropylene?PP?and polystyrene?PS?of three microplastics,widely found in water environment,and 2-nitrofluorene?2-NFlu?,9-nitroanthracene?9-NAnt?of two NPAHs,frequently detected in water environment were selected to act as target pollutants.Comprehensively considering environmental factors,including microplastic aging,p H value and ionic strength,the adsorption of microplastics and NPAHs were studied to clarify their adsorption characteristics and adsorption mechanism;PE with strong adsorption capacity for 9-NAnt was screened,using zebrafish?Danio rerio?as test organism,to explore the toxic effects and microscopic mechanism of molecular biology of microplastics-NPAHs on zebrafish under single or compound exposure conditions.The main findings are as follows:?1?Adsorption behavior and mechanism of microplastics with 2-NFlu and 9-NAnt.The adsorption capacities of three microplastics for 9-NAnt(680-735?g g-1)were greater than 2-NFlu(570-600?g g-1),which was due to the stronger hydrophobic action between 9-NAnt?Kow=4.78?and microplastics than that of 2-NFlu?Kow=3.37?.The adsorption kinetics and isothermal adsorption of 2-NFlu and 9-NAnt on three microplastics were consistent with quasi-second-order kinetics and linear isotherm equations,indicating that the adsorption of 2-NFlu and 9-NAnt on microplastics were heterogeneous multi-molecular layer adsorption,dominated by partitioning action and including physical?van der Waals force?and chemical action.In addition,given the significant impact of the type and structure of microplastics,the surface of PE and PP were relatively rough and contained cracks and pores,while the surface of PS was relatively smooth and granular,so intraparticle diffusion,dissolution and micropore filling may also be the important mechanism for the adsorption of 2-NFlu and 9-NAnt by microplastics.?2?Effects of environmental factors and microplastic particle size on the adsorption of 2-NFlu and 9-NAnt by microplastics.As the p H of the aqueous solution increased?3-11?,the negative potential on the surface of microplastic increased and electrostatic repulsion was formed between microplastics and 2-NFlu,which significantly reduced the adsorption amount of 2-NFlu on three microplastics;with same p H conditions,adsorption amount of 9-NAnt on PP and PS also decreased.Under the condition of low concentration ionic strength,the salting-out of Na Cl(0.1-0.5 mol L-1)and Ca Cl2(0.001-0.01 mol L-1)could improve the adsorption of 2-NFlu by three microplastics,while excessive concentration of Ca2+(0.01-0.1 mol L-1)formed competitive adsorption with 2-NFlu,resulting in the reduction of adsorption amount of2-NFlu.In contrast,with the increase of ionic strength,the adsorption of 9-NAnt on PP and PS decreased,while the adsorption of 9-NAnt on PE was almost unaffected by p H and ionic strength of aqueous solution,indicating that electrostatic and hydrophobic effects were one of the important adsorption mechanisms between microplastics and 2-NFlu and 9-NAnt.In addition,the adsorption capacity of microplastics for 2-NFlu and9-NAnt were negatively correlated with particle size of microplastics,and aging action of microplastics could enhance their surface polarity,thus reducing their adsorption properties for 2-NFlu and 9-NAnt.?3?Toxic effects of PE-NPAHs on zebrafish?Danio rerio?.Acute toxicity test results showed that 96-hour half lethal concentration of 9-NAnt was 3.20 mg L-1,indicating that 9-NAnt was a highly toxic chemical substance.Chronic toxicity test results displayed that PE could enter fish body as 9-NAnt carrier,and the bioaccumulation of 9-NAnt had concentration dose effect with PE-9-NAnt complex;PE significantly reduced the accumulation of 9-NAnt in zebrafish.After single exposure of low concentration PE?10 mg?for 4 days,the activity of P4501A,ACh E,SOD,CAT,LDH and content of MDA,LPO were significantly increased;the single exposure of 9-NAnt significantly improved the activity of P4501A,but had no significant effect on other biomarkers;under low-exposure of PE-9-NAnt?10 mg?complex,the activity of P4501A and LDH increased significantly.After 7 days,the toxic effect of PE or 9-NAnt single exposure on zebrafish was no longer significant;under PE-9-NAnt exposure condition,the P4501A activity increased significantly,and the activity of ACh E and LDH reduced significantly,showing certain neurotoxicity and disorders of energy metabolism in zebrafish.The analysis of integrated biomarker response index?IBR?showed that PE had the highest biotoxicity to zebrafish in all exposure groups after 4 days,and PE-9-NAnt complex showed larger biotoxicity effect after 7 days,while the presence of microplastics could alleviate the biotoxicity of 9-NAnt to a certain extent. |
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