Distribution Characteristics And Risk Assessment Of Microplastics In Nanming River Basin,Guiyang

Microplastics as an emerging pollutant in the environment,and its research is in the period of ascendant.Microplastics continue to accumulate in the natural environment with small size and large specific surface area,which can be combined with typical pollutants in the environment such as antibiotics,heavy metals and pesticides to increase their toxicity.Microplastics enter the food chain directly or indirectly,enrich in the food chain and transfer to a higher nutritional level,which poses a serious threat to organisms and their habitats.At present,studies on the occurrence characteristics,source apportionment and risk assessment of microplastics in urban rivers in southwest karst areas are relatively limited.River as the main medium of micro plastic transmission,carrying the important role of micro plastic in space.In this study,surface water,sediments,sewage treatment plants and waterworks samples were collected from the Nanming River Basin.The abundance,shape,size and color of microplastics were classified and counted by Leica stereo microscope,Raman spectrometer and scanning electron microscope.The composition and morphology of microplastics were detected.On this basis,the distribution characteristics and potential sources of microplastics in the Nanming River area were characterized,and the potential control factors of microplastics were further revealed by combining social development indicators reflecting human activities and water physical and chemical parameters.The potential risks of microplastics to the Nanming River were evaluated by risk index method and Nemerow pollution index method.The results showed that the average abundance of microplastics in surface water was 750 n/m~3(dry season)and 693 n/m~3(wet season),and the average abundance of microplastics in sediments was 1600 n/kg.There was a correlation between the abundance of microplastics in surface water and sediments,indicating that microplastics in sediments were mainly derived from surface water.The particle sizes of microplastics in surface water and sediments are mainly distributed at<500μm.The color of microplastics in water is mainly transparent.The morphology of microplastics is mainly fiber.The sediments are mainly green and fragmentary microplastics.The materials are mainly polyethylene and polypropylene.By scanning electron microscope observation,there are a variety of metal elements on the surface of microplastics,which will increase the risk of microplastics.There are many factors affecting the distribution of microplastics.In this study,the abundance of microplastics in Nanming River during dry season is consistent with the changes of socio-economic development indicators(population,urban land use and per capita GDP),and the microplastic color and shape diversity index was associated with a significant population density,indicating that microplastics in water during dry season are mainly affected by human activities.During the rainy season,the microplastics in the Nanming River migrated longitudinally along the river direction in the surface water,which was significantly positively correlated with the total nitrogen in the traditional pollution index,indicating that the increase of surface runoff and the increase of downstream catchment area led to the increase of the mass concentration of microplastics in soil,ground and wastewater into the river and total nitrogen.Ecological risk index method,polymer risk index method,pollution load index method and Nemero pollution index method were used to evaluate the risk of microplastics in Nanming River.The results showed that the potential ecological risk level of XZ sampling point was the highest,followed by SXH and SKS sampling points,and the sampling points were at a low level.It points out that sewage treatment plant is an important link to control microplastic pollution.