Distribution Of Microplastics In Maowei Sea And Its Inflow River Qin River

Microplastics generally refer to plastic particles with particle size<5mm,which has attracted wide attention in recent years.Some studies have pointed out the widespread distribution of microplastic pollution in the oceans,but tracing the origins of microplastics in the environment remains a challenge.In addition,the results of different sampling methods may be different due to the sampling methods in the water have not formed a standard.Qin river basin and Maowei sea in Qinzhou,Guangxi province,were selected as the research area.In order to verify the influence of different sampling methods on microplastics in fresh water and to determine the main sources of microplastics in the water environment,the distribution characteristics of microplastics in water,sediment and living things in this area were investigated,and the influence of different sampling methods on fresh water sampling results was analyzed.Finally,the source of microplastic contamination in the area was traced.In the study of two major waste water treatment plants(HD,HX)in Qinzhou city,the results showed that the abundance of microplastics in HD and HX's inflow was1.80±0.35 n/L and 0.15±0.05 n/L,respectively,while the abundance in effluent was0.13±0.02 n/L and 0.04±0.02 n/L.The average removal rate of microplastics in HD and HX was 92.4%and 71.7%,respectively.The removal rate of microplastics by A~2/O process used by HD was significantly higher than that of HX's CAST process,and the difference was mainly reflected in the biochemical treatment stage.A large number of microplastics were also detected in the sludge.The abundance of microplastics in the sludge of HD and HX was 533.3±66.7 n/kg and 181.8±43.7 n/kg(dry weight),respectively.Although most of the microplastics were removed from the waste water treatment plants,the average daily microplastics emissions of HD and HX were(3.9±0.6)×10~6 n/L and(3.2±1.6)×10~6 n/L,respectively.This shows that the waste water treatment plants are still an important source of microplastics in the environment.A total of 12 sampling sites were set up in the Qin river basin.Water samples were collected using two plankton nets with different pore sizes(75?m and 300?m)and Teflon pumps.The results show that the abundance of the three sampling methods were:N-75:0.1-5.6 n/m~3;N-300:0.1-4.6 n/m~3 and pump:16.67-611.11 n/m~3,respectively.There was no significant difference in abundance,particle size and microplastic type between the two plankton nets(F=0.302,P=0.588).However,the abundance of microplastics collected by the Teflon pump was significantly higher than that of the two plankton nets(F=9.12,P=0.001),especially more fibers microplastics were collected by the Teflon pump(F=9.525,P=0.001).The sample size of the Teflon pump was smaller than the plankton nets,which may lead to a larger microplastic abundance in fresh water.The abundance of microplastics in sediments was 0-97 n/kg(dry weight).Polyethylene and polypropylene were the main types of microplastics in fresh water and sediment,accounting for 67.2%and 72.3%of microplastics respectively.Microplastics in fresh water and sediment were mainly large particle size(1-5mm).Waste water treatment plants and aquaculture were the main sources of microplastics in fresh of Qin river.About 22%of the microplastics in fresh water of Qin river were estimated to come from waste water treatment plants and about 35%from mariculture activities.In addition,the remaining part may come from the uncollected sewage discharged from the upper reaches of the Qin river and the input of surface runoff.The average abundance of microplastics in the water of Maowei sea was 0.85±0.13n/m~3,and foam(43.8%)was the main type.The abundance of microplastics in the sediment was 22.4±19.6 n/kg,with sheet(50-100%)accounting for the majority of the samples.The abundance of microplastics in oysters was 0.18±0.15-0.22±0.21 n/g(wet weight)and 1.7±1.6-2.0±1.9 n/ind.Fiber(99%)accounted for the majority in oysters.Microplastics of 1-5mm were the main components in the water,sediments and oysters in Maowei sea.PP was the main component in the water and sediments,accounting for37.3%and 28.8%respectively,while the fiber components in oysters were mainly PET(47.6%)and Cellophane(32.1%).The microplastics in the Maowei sea mainly come from the input of Qin river and mariculture,the fibers in the oysters may eventually come from the waste water treatment plants,fishing boats and coastal sewage discharges.