Characterization And Risk Assessment Of Microplastic Fugacity In The Fifteen Mile River And Wastewater Treatment Plant In The Watershed

The prevalence of plastic pollution in the environment is considered a challenging global problem,with a wide range of plastic debris sizes,less than 5 mm in size,defined as microplastics.Since microplastics are suspected to have ecotoxicological effects due to their small size and their tendency to adsorb pollutants from the environment,a large number of studies aimed at assessing the abundance of microplastics in sediments,biota or aquatic water bodies,generating potential ecological risks,have attracted widespread attention in the international community.Thus,this paper selects the fifteen-mile river,an inland river in the urban area of Hefei,and the wastewater treatment plant(WWTP1)in the watershed as the research objects to investigate and evaluate the transfer,deposition,and removal of microplastics,which is quite representative.The main lines of the study are as follows.(1)The occurrence characteristics of microplastics in surface water and sediments of rivers during flood season and non-flood season were analyzed.The results showed that the average abundance of microplastics in river surface water was8.4 ± 2.5 n/L and 5.8 ± 1.7 n/L,respectively.The abundance of microplastics in sediments was 78.9 ± 8.3 n/kg and 63.9 ± 7.1 n/kg,respectively.Among them,fibrous microplastics accounted for the highest proportion,in the range of 32.5%-34.0% and27.9%-31.6%,respectively.The size distribution is in the range of 0-500 μm.There are 11 kinds of microplastics,including acrylate copolymer(ACR),chlorinated polyethylene(CPE),ethylene-vinyl acetate copolymer(EVA),polyethylene(PE),polyethylene terephthalate(PET),polypropylene(PP),polystyrene(PS),polyurethane(PU),polyvinyl chloride(PVC),polyamide(PA)and silicone resin.Among them,PE,PP,PS,PA,PVC and PET are the main types.(2)The occurrence characteristics of microplastics in each typical process stage of WWTP1 and the removal efficiency of the three-stage treatment stage were compared and analyzed under the two weather conditions of rainwater and dry.The results showed that the average abundance of fibrous microplastics in sewage and sludge was the highest,which was 49.3% and 39.7% respectively in dry weather,and50.1% and 43.2% respectively in rainy weather.The microplastics with a size of0-500 μm had the highest average distribution proportion in sewage and sludge,which were 64.9% and 60.4% in dry weather,and 67.9% and 69.0% in rainy weather,respectively.There are eight types of microplastics,including PE,PP,PA,PVC,PS,PET,PU and PF.Among them,PA,PF and PE are the main types.The proportion of PA is the highest,which is 24.32% and 21.68% respectively,followed by PF,which is17.94% and 14.95% respectively,and PE,which is 11.30% and 15.89% respectively.After the final combination of three-stage treatment,the total removal rate reached87.7% and 83.5%.(3)According to the analysis of the pollution source of microplastics,referring to the EU classification,labelling and packaging(CLP)standard and pollution load index(PLI)pollution load index model,the migration pollution and risk assessment index of microplastics in sewage treatment plants in rivers and watersheds were analyzed,and the pollution risk index was introduced to show the potential harm of microplastics.The results showed that the pollution index of microplastics in surface water and sediment in flood season was 2.24 and 2.34,respectively,which belonged to severe pollution.In the non-flood season,the pollution index of microplastics in surface water and sediment was 1.66 and 1.91,respectively,which was moderate pollution.The pollution index of microplastics in the influent of WWTP1 was 2.40 and 2.46,respectively,which belonged to severe pollution.The pollution index of the effluent was 1.0 and 1.2,respectively,which were moderate pollution.The pollution indexes of microplastics in dewatered sludge were 3.5 and 3.4,respectively,which belonged to severe pollution.It is concluded that the pollution risk of microplastics is positively correlated with the proportion of polymers and their risk scores;the microplastic pollution index is more volatile in flood season and rainy weather.