The Joint Toxicity And Adsorption Behavior Between Typical Microplastics And PPCPs In Aquatic Environment

The global production and consumption of plastics are increasing gradually,and the recycling ratio of plastics is small.Therefore,a large amount ofplastic waste entered the ecological environment.Due to the refractory and long-lasting nature of plastic wastes,the impact of plastic debris on the ecological environment cannot be ignored.Microplastics,in the natural environment,usually coexist with other pollutants,and studies have shown that microplastics can adsorb organic pollutants.However,the effects of this complex system on their environmental behaviors and biological toxicity are complex and irregular,and the mechanisms of adsorption behavior and joint toxicity are important for the assessment of potential risk of the joint system.In this study,the typical kinds of microplastics were selected:polyethylene(PE 74?m),polystyrene(PS 74 ?m),polyvinyl chloride(PVC,74 ?m),and PVC800(1 ?m).The Skeletonema costatum was used as a test organism to explore the joint toxicity between microplastics and PPCPs(Triclosan,TCS).Moreover,for better explaining the mechanism of joint toxicity,we conducted the adsorption experiments between microplastics and TCS.In addition,considering the ageing process of microplastics in real environment,we deeply studied the adsorption behavior between ciprofloxacin(CIP)and aged microplastics produced by ultraviolet radiation(UV).The main contents and conclusion are as follows:(1)We found that TCS had obvious inhibition effect on microalgae growth within the test concentrations,and single microplastics also had significant inhibition effect which followed the order of PVC800>PVC>PS>PE.However,the joint toxicity of PVC and PVC800 in combination with TCS decreased more than that of PE and PS,and the higher adsorption capacity of TCS on PVC and PVC800 was one possible reason for the greater reduction of their toxicity.The joint toxicity of PVC800 was still most significant(PE<PVC<PS<PVC800)because of the minimum particle size.According to the independent action model,the joint toxicity systems were all antagonism.Moreover,the reduction of SOD was higher than MDA which revealed that the physical damage was more serious than intracellular damage.Scanning electron microscopy(SEM)images revealed that the aggregation of microplastics and physical damage on algae was obvious.(2)we further investigated the interaction between microplastics and TCS,and found that the adsorption ability of PVC and PVC800 was significant with the sorption capacity 8.64 mg/g and 12.53 mg/g respectively.According to the adsorption isotherm,the adsorption behavior of two kinds microplastics was neither Langmuir nor Freundlich,but the combination of both.The results of adsorption isotherms demonstrated that both microplastics have homogeneity and heterogeneous surface,and are combined with monolayer and multilayer adsorption.Moreover,according to the results of Fourier transform infrared spectrum(FTIR),no new functional groups were detected in the process of adsorption,which indicated that the main adsorption mechanism was physical process.Combining with the results of salinity and pH,we concluded that the main adsorption mechanisms between microplastics and TCS were partition-diffusion and electrostatic interactions.(3)We obtained the aged microplastics by UV acceleration ageing process,and then studied the interaction between the aged microplastics and CIP.The results of FTIR and SEM showed significant surface oxidation and localized microcracks on the aged microplastics.The sorption kinetics and isotherms models indicated that the sorption capacity of aged microplastics was higher than that of virgin microplastics.and their physical interactions including partitioning,electrostatic interactions,and intermolecular hydrogen bonding,were the dominant mechanisms,as demonstrated by FTIR analysis.Moreover,the sorption capacity of the virgin microplastics decreased as the degree of crystallinity increased,whereas the opposite trend was observed with aged microplastics,which indicated that the crystallinity was not the controlling factor.In addition,salinity suppressed CIP adsorption on all the tested microplastics.The pH influences the electrostatic attraction between the microplastics and CIP because CIP has different charge at different pH values.