| Microplastics(MPs)are defined as plastic particles with a particle size of less than 5mm.As a new type of environmental pollutants.MPs contamination has been caused a public concern recently.Because of its light weight,small particle size,difficult degradation,long distance migration,and high absorptivity of toxic and harmful substances,MPs widely exist in the environment and have potential threats to the organisms and human health,as well natural ecosystems.Most MPs pollution comes from plastics wastes by human activities and urban sewage discharge,and the pollutants were largely accumulated in the estuary and the coastal areas due to hydraulic transportation.Although a number of studies have been conducted to investigate the amount and distribution of MPs on marine ecosystems,some freshwater bodies and sediments,less is known about the distribution characteristics of MPs in urban wetlands.Urban wetland ecosystem is an important filter of urban pollutants and plays an important role on the improvement of the urban environment and the healthy life of urban residents.In this project,the abundance,particle size,shape,color and polymer composition of MPs were investigated in the urban wetland soils in Changsha City,by using a combinative approach of the field investigation,sampling and laboratory analysis,and employing the measurement techniques of density separation,FT-IR,correlation analysis and linear regression analysis.The relationships between MPs abundance and environmental factor(the contents of soil carbon,nitrogen,phosphate,heavy metals etc.)were developed.The impact of social economic factors on MPs pollution was examined.The results from this study provided scientific basis and practical guidance not only for the control and prevention of MPs pollution in Changsha City,but also for the construction and management of an ecologically civilized city.The main findings are as follows:(1)The abundance of soil MPs ranged from 47 to 1369 n·kg-1,with an average abundance of 379 n·kg-1 in the wetlands of Changsha.Among the sampling sites,KF-E3 site(Kaifu District River Estuary)had the highest soil MPs abundance,which was significantly higher than that in other wetlands sites(P<0.05),while YH-L site(Yuhua District Tongsheng Lake)had the lowest MPs abundance.The particle size of most MPs was less than 0.1 mm(59.13%)and 0.1-0.5 mm(28.18%);the shape of MPs mainly belonged to fiber(39.04%)and fragments(36.61%);the black,green and transparent colors were found as the common MPs colors in the study area,accounting for 68.0%of the total numbers;the polypropylene,polyethylene and polyamide were the main polymer types,with an average proportion of 30.4%,19.0%and 19.0%of the total MPs numbers,respectively,while the proportion of the polyvinyl chloride was the smallest,accounting for 3.8%of the total MPs numbers.(2)All sampling sites were classified into five wetland types.The average abundance of soil MPs ranges from 254 to 578 n·kg-1 in the five wetland types in Changsha City.The highest abundance of MPs was found in the estuary,which was significantly higher than that in other wetland types(P<0.05).Correlation analysis showed that the correlation between the physical and chemical properties of soil and the abundance of MPs was not significant.However,the abundance of MPs was significantly negatively correlated with the Cr concentration(P<0.05),and was significantly positive correlated with the Ni concentration(P<0.05),and the zinc(Zn)adsorbed by MPs were significantly correlated with the background value of Zn in soil(P<0.01).In addition,the abundance of MPs was significantly positively correlated with the concentration of PM10(P<0.01).(3)There were obvious differences of the MPs pollutants in the wetlands among 7 Administrative Districts within the Changsha City.Kaifu District had the highest soil MPs abundance(614 n·kg-1)and Changsha County had the lowest value(205 n·kg-1).The differences of MPs abundance was significant between the two Districts(P<0.05).Regression analysis showed that the increase in the level of urbanization(R2=0.245,P<0.05)may aggravate the MPs pollution in the wetlands.The total population(R2=0.289,P<0.05),and the total value of the primary industry(R=0.316,P<0.05)had negatively significant effects on the abundance of MPs pollutants.In general,the R2 value is small and the fit is low.(4)Spatial analysis showed that the abundance distribution of soil MPs in Changsha wetlands varied greatly,showing a decreasing trend from the mainstream of Xiangjiang River to the east and west.The particle size and shape composition of soil MPs in wetlands had an obvious spatial convergence.In addition,the spatial distribution characteristics of heavy metal concentration were similar with that ofthe MPs abundance.The abundance of soil MPs was relatively high in areas with high urbanization level and PM10 concentration.(5)Compared with data published in different regions at home and abroad,the abundance of MPs pollutants of wetland soils was in the middle levels in Changsha City.Strengthening the treatment of microplastics in domestic sewage and the recycling of plastic waste in industrial production will alleviate the microplastic pollution of wetland soil in Changsha City. |
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