Distribution, Composition And Ecological Risks Of Microplastics Pollution In The Watershed Water Of Dianshan Lake And Taipu River

Microplastics（MPs,plastic particles less than 5 mm in size）are a new type of pollutants with high hydrophobicity,large specific surface area and difficult to be degraded.Due to their small size and large quantity,they are widely distributed in oceans,lakes,rivers,soils,sediments and organisms,and have attracted domestic and international attention in recent years.The microplastics issue has been ranked as the second most urgent scientific problem in the field of environmental and ecological sciences in 2015.Although more than 96%of the current microplastics research is focused on marine ecosystems,however,about 80%of marine microplastics are thought to originate from terrestrial systems.As important"sources"and"sinks"of primary and secondary microplastics,rivers and lakes are important channels for microplastic transport and transfer to the sea,and are important areas affected by human activities and material transport.At present,there are very limited data for the investigation of microplastics in the surface water environment,especially for the contamination of drinking water source areas and ecological evaluation.Therefore,the abundance,particle size,color and morphology of MPs in the freshwater environment were investigated by H₂O₂ ablation filtration-microscope picking using Dianshan Lake and Taipu River as the study objects.Micro Fourier Transform Infrared Spectrometer（μ-FTIR）was applied to characterize the polymers.The pollution load,spatial distribution,compositional characteristics and ecological risk of microplastics in the watershed were investigated.The methodological and basic data provide scientific references for the environmental behavior and ecological risk evaluation of microplastics.The results are as follows:（1）Dianshan Lake,the largest natural freshwater lake in Shanghai and an important drinking water source protection area in the region,is connected to Taihu Lake in the west and Huangpu River in the east.Based on the"source-sink"design,this study investigated the surface water of Dianshan Lake at 18 sampling sites.The results showed that 100%of microplastics were detected,and the abundance of microplastics in surface water ranged from 0.58-5.38 items/L with a mean value of 1.96±1.08 items/L.MPs from sites near the living areas exhibited significantly higher concentrations than those from scenic spots and farming areas.Significant abundance discrepancies were also found that ordered:outlet>inlet>other sites.Riverine runoff was considered a vector factor for transporting MPs.Fibers attributed 88.04%of the total population in shape,and black-colored and small-sized（<0.5 mm）MPs presented major proportions in morphological distributions.The predominant polymer identified was given to polyethylene terephthalate（PET,72.9%）,followed by polyethylene（PE,11.9%）,and polypropylene（PP,3.81%）.The polymer-shape-size-color configurations indicated different potential sources（textile washing,aquaculture activity and plastic mulching film）.Although the pollution load index indicated a slight pollution level of MPs risk in the surface water compared with other studies in the Yangtze Estuary,the flux of MPs reaching the Huangpu River deserves long-term monitoring at the tidal limit of rivers.The results estimated the MPs contamination in the lake and served as a significant step towards filling the literature gap on MPs potential risks in freshwater ecosystems.（2）The Taipu River flows through Jiangsu,Zhejiang and Shanghai in turn,and is an important part of the water quality and ecological assessment of the Taihu Lake basin because it has unique industrial structure characteristics and gathers many textile printing and dyeing enterprises.Based on the migration characteristics of microplastics,this study monitored surface water（0-15 cm below the water surface）and bottom water（0-15 cm above the riverbed）samples from 13 sampling sites in the Taipu River and analyzed them for microplastic abundance,morphology,particle size,color and polymer type.The results showed that microplastic particles were widely present in surface and bottom waters with 100%detection rate.Their abundance ranged from0.65-6.07 items/L and 0.30-3.63items/L,respectively.A clear decreasing trend of MPs abundance was observed with the increased water depth（t=5.42,p=0.0240^*）.The ANOVA test revealed that the highest abundance of microplastics（4.87±1.08 items/L）was found in the waters of the textile industrial zone,which was significantly higher than that of the residential zone（2.68±1.40 items/L）,and the scenic zone（1.99±0.51items/L）and the drinking water source zone（1.65±0.64 items/L）（F=14.6,p<0.001*）,showing significant differences in the spatial assignment.Fibers were the most common microplastic form,with 87.2%and 81.4%of the surface and bottom layers,respectively.In addition,0.1-0.5 mm microplastics（46.7%and 45.8%of the surface and bottom layers,respectively）and transparent microplastics（50.0%and 47.4%of the surface and bottom layers,respectively）dominated.Polyethylene terephthalate（PET）,which is widely cited in the textile industry as a textile material,accounted for 71.4%and 59.7%of microplastics in the surface and bottom waters of the Taipu River,respectively,and was predominantly presented in the shape of"fibers",further reflecting that textile wastewater was the main source of microplastic pollution in the Taipu River.In addition,polyvinyl acetate（PVAC）,which is commonly used as a fabric coating and resin matrix in the manufacture of nonwoven fabrics,was detected for the first time in the watershed context,with its share of 6.72%and 2.98%of different polymers in surface and bottom water,respectively.Compared to other studies in the Yangtze estuary,the microplastic risk index（H）for surface and bottom waters in the Taipu River was 94.2 and 263,respectively,and the pollution load index PLI for surface and bottom waters was 0.122and 0.071,respectively,indicating a mild to moderate level of microplastic pollution in the Taipu River basin.However,textile wastewater increases the environmental"grey water"footprint and raises the risk of microplastic pollution during the textile life cycle,requiring higher cleaner production policies and strategies.This study supports the identification of ecological and environmental risks of microplastics in watersheds and provides insights for cleaner production in the textile industry.Overall,this study conducted a survey on Dianshan Lake and Taipu River,which initially revealed the pollution residual characteristics of revealed microplastics.Based on the results of microplastic morphology,size,color,polymer characteristics and potential risk,the current status of microplastic pollution load and potential risk in the aquatic ecosystem in Dianshan Lake and Taipu River were clarified.This study is of great significance in terms of microplastic pollution in the freshwater environment,and provides a reference for the pollution control of microplastics and the safety and security of water quality in water sources.Continuous monitoring of microplastics in the textile production life cycle is needed in the future to supplement microplastic chemical footprint data.