Identification And Pollution Characteristics Of Microplastics In Drinking Water

Microplastics are plastic fragments,films,particles and fibers with an effective diameter less than 5 mm.Microplastics have been widely distributed in water,sediment,organism and other environmental media.Not only are they pollutants themselves,they can also serve as carriers for other pollutants.Because of their small particle sizes,they are easy to be ingested by organisms,then enter into the food chain,migrate and are enriched in the food chain,causing direct or indirect harm to organisms and ecological environment.In view of the difficulty in qualitative and quantitative analysis of microplastics and the blank data of microplastic pollution in drinking water in China,this study used Rhodamine B(Rh B)staining to assist the labeling of microplastics,and analyzed the pollution characteristics of microplastics in the effluent samples of each process of the drinking water treatment plant and tap water samples in consumer households in some parts of China.(1)In order to optimize the dyeing effect of Rh B on microplastics,five kinds of microplastics,polyethylene(PE),polypropylene(PP),polyvinyl chloride(PVC),polystyrene(PS)and polyurethane(PU),were selected to compare their dyeing effects in three solvents,ethanol,acetone and distilled water.The fluorescence of the dyed microplastics was observed under natural light,dark conditions,light time,saturated sodium chloride,potassium hydroxide,nitric acid and gut fluid mixture.The results showed that the Rhodamine B working solution prepared by ethanol had better dyeing effect on PE,PP,PVC,PS and PU than that prepared by other two solvents.Five kinds of microplastics staining by Rhodamine B had obvious fluorescence under the fluorescence microscope,and could maintain the fluorescence stability under the above experimental conditions.Furthermore,Rhodamine B staining has no significant impact on the Raman spectrum of microplastics.(2)The total removal rates of microplastics by the two water purification plants were 76.64%(DWTP1)and 51.83%(DWTP2),respectively.The abundance of microplastics in DWTP1's distribution well raw water,flocculation tank effluent,sedimentation tank effluent and clear water effluent were 548 n/L,651 n/L,326 n/L and 128 n/L,respectively.The abundance of microplastics in the effluent of DWTP2 corresponding to the above processes were 436 n/L,450 n/L,320 n/L and 210 n/L,respectively.The types of microplastics in DWTP1 and DWTP2 were mostly fragments,accounting for 68.75% and 72.55%,followed by fibers,28.13% and 21.57%,and the film was the least,only 3.12% and 5.88%.The microplastics shapes in th raw water of water distribution wells and the effluent from the flocculation tank are similar to the above results.However,the distribution of microplastics shapes in the water from sedimentation tank and clear water effluent was different.The particle size distribution of microplastics in DWTP1 and DWTP2 were mostly 1-50 ?m,accounting for 40.63% and 58.82%,followed by 100-500 ?m>50-100 ?m >500-5000 ?m.In addition,PP(13.80%),PPS(6.90%),PMS(3.45%),PS(3.45%)were detected in DWTP1,and Poly(4-vinylbiphenyl)(13.33%)and PS(6.67%)were detected in DWTP2.(3)The abundance range of microplastics in some tap water samples collected in China was 0-1247 n/L,with an average abundance of 440 n/L.Fragments were the main type,accounting for 91.11%,followed by fibers and spheres,accounting for 6.20% and 2.69%,respectively.The size range of microplastics was 3-4453 ?m,and the average particle size was 66 ?m.Particles smaller than 50 ?m significantly predominated in most of the tap water samples,accounting for 79.93%,followed by 50-100 ?m,100-300 ?m,500-5000 ?m and 300-500 ?m,accounting for 10.44%,6.28%,1.88% and 1.47%,respectively.In addition,PE(26.7%)and PP(24.4%)were the main materials of microplastics in tap water samples.