Distribution And Migration Of Microplastics In Multiple Environmental Media From Inland To Estuarine Areas

Microplastic has become a hot topic in environmental science because of its ubiquity,persistence and potential eco-toxicity.The abundance,spatial patterns and accumulation of microplastic in different environmental media are critical to understand its behavior,transportation pathways and risks providing practical approach in pollution management and control.In comparison with open ocean,the freshwater-estuary system is more close to pollution sources which are originated from anthropogenic activities.Several typical lakes,rivers,estuaries,wetlands and urban streets from two similar catchments,i.e.,Lower Yangtze River and Port Phillip Bay catchment were henceforth selected as research cases.The abundance,shape and chemical composition of microplastics from roadsid dust,water,sediment and several kinds of aquatic organism were determined by applying microscopic and spectroscopy measurements.Accordingly,the following issues were expected to be addressed by mutiple analysis: 1)To characterize the microplastic pollution in multiple environmental media from different catchments;2)To establish the association between environmental stress and microplastic pollution;3)To describe the transportation and fate of microplastics in mutiple environmental media(mainly in aquatic systems);4)To propose practical microplastic pollution patterns and biomonitoring tools.The first case study was conducted at roadside dusts which represent part of the deposited air contaminants and diffuse pollution.It didn't receive enough attention as potential microplastic sources although roadside dusts are highly impacted by anthropogenic activities and weather condition.Roadside dust samples were collected from Port Phillip Bay and its upper catchment,Australia,over two seasons.The average microplastic abundance over two seasons ranged from 20.6 to 529.3 items/kg,with a predominant portion of fibers(70.8%)and items less than 1 mm(41.9%).Polyester and polypropylene(26.3%)were the dominant polymer types.Sampling sites displayed consistent microplastic abundances over time and shared similar patterns in size,shape and polymer composition.Multiple correlation and principal component analysis suggest that urbanization and rainfall are important influences to roadside microplastic accumulation.Microplastics accumulated on roads and road verges during periods of dry weather and were flushed away during heavy storms while the corresponding trigger value was unknown.Monitoring roadside dust can be considered as an initial and cost-effective screening of microplastic pollution in urban areas,roadside dust also contribute high amounts of microplastic via diffuse pollution pathway.In order to describe its spatial and accumulation pattern,the case studies targeted at floating microplastic collected from lakes and rivers in Lower Yangtze River catchment which including a typical polluted lake.The abundance ranged from 0.5-25.8 items/L and the peak value was found at northern-east part of Taihu Lake where high levels of nutrient were detected in water.Such a peak represent the highest microplastic pollution level in global freshwater lakes.The floating microplastic accumulated downstream at catchment scale while the concentration diffused offshore.Fibers(86.0%)and items less than 1 mm(69.4%)were dominant in floating microplastic,polyester and semi-synthetic material(60.3%)were the most commonly detected compound.Given that floating microplastic will end up in the progress of deposition,the sediment samples were then analyzed.Microplastics in sediment from Lower Yangtze River catchment ranged from 5.0-234.6 items/kg which represent moderate pollution in global background.The lowest abundance was detected at Poyanghu Lake and the highest one were found at northern-east part of Taihu Lake with a similar spatial trend to water samples.The distribution of sediment grain size had no relationship with microplastic spatial trend.Microplastics in sediment were characterized by polyester,polypropylene and semi-synthetic material(54.3%).Fiber(75.2%)and items less than 1 mm(79.9%)were commonly found while the portion of fibers and average microplastic size in sediment samples were lower than those in water.In consideration of regional background information,the accumulation of floating and deposited microplastic were mainly contributed by pollution input and meteorology conditions such as local wind dynamics.In order to quantify and categorize the influences that governed microplastic transportation and accumulation from inland area to estuary,a mirror study were conducted at Port Phillip Bay catchment,spanning gradients of land-use from un-developed catchments in conservation areas to more heavily-developed areas.The microplastic abundances ranged from 0.06 to 2.5 items/L in water and 0.9 to 298.1 items/kg in sediment,which is lower than those one in Lower Yangtze River catchment.The variation of microplastic abundance in sediments was closely related to that of the overlying waters.The average microplastic size(1.3 mm)were larger than those found in Lower Yangtze River catchment(0.8 mm)but fiber(80.4%)and items less than 1 mm(44.5%)were still dominated in all samples.Polyester,polypropylene and polyethylene(47.8%)represented a majority part of polymer detected.The diversity(chemical and shape composition)and fragmentation of microplastics in sediments were greater than those in water indicating sediments acted as sink for floating microplastic.A spatial analysis of the data suggests that the abundance of microplastics increases downstream in rivers and accumulates in estuaries and the lentic reaches of these rivers.Correlation and redundancy analysis were used to explore the associations between microplastic pollution and different land-use types.More microplastics and polymer types were found at areas with large amounts of commercial,industrial and transport activities.Microplastic abundances were also correlated with mean particle size.Microplastic hotspots within a coastal metropolis might be caused by a combination of natural accumulation via hydrological dynamics and contribution from increasing anthropogenic influences.Our results strongly suggest that coastal metropolis superimposed on increasing microplastic levels in waterbodies from inland areas to the estuaries and open oceans.In comparison with abiotic fraction,organism could be a temporary vector for microplastic in environments and the body burden of microplastic is important to understand its fate and eco-toxicity.Again,the microplastics in bivalve(Corbicula fluminea)and fish(Gambusia holbrooki and several kinds of commercial fish)from Lower Yangtze River and Port Phillip Bay catchment were measured.In particular,organ specific analysis was also used in fish study.For Corbicula fluminea,the microplastic abundance ranged from 0.2-5.3 items/ind.(0.2-12.5 items/g).For Gambusia holbrooki,the microplastic abundance in body and head ranged from 0.2-1.1 items/ind.(0.5-4.4 items/g)and nil detected-0.3 items/ind.(nil detected-12.5 items/g)with a detection rate of 3.3%-38.3% and 0-13.3%,respectively.For commercial fishes,the microplastic abundance in gut and gill samples ranged from 0.3-5.3 items/ind.(0.1-8.8 items/g)and 0.3-2.6 items/ind.(0.1-5.2 items/g)with a detection rate of 22%-100% and 22-89%,respectively.No microplastics were detected in the liver or muscle tissue of L.maculatus.In terms of microplastic characteristic,fiber(74.5%-96.4%),items less than 1 mm(40.1%-87.1%)and polyester(25.8%-37.1%)were dominanted in all samples.Specimen collected from northern-east part of Taihu Lake,Yangtze Estuary and Melbourne urban areas contained high levels of microplastics suggesting the correlation between pollution input and microplastic uptake in aquatic organism.Microplastic uptake was related to organisms' size,weight,gender and ingestion pathway.I established the quantitative relationship between microplastic abundance in environments and those in organism's gut and soft tissues.The biomonitoring based on fish gut and Corbicula fluminea could be used to assess microplastic encounter rate and microplastic pollution in sediment.The association and difference between microplastic characteristics from multiple environmental media shed light in the concepts of microplastic "spatial transportation" and "vertical transportation".The major influences involving in the transportation were evaluated.The pattern for spatial transportation can be considered when microplastic accumulated downstream and concentrated in urban areas with intensive anthropogenic activities.The geological characteristic,weather conditions and continuous pollution input governed the principle pathways involved in spatial transportation,contributed to the accumulation of microplastics.The difference between microplastic abundance,shape and chemical composition from multiple environmental media indicated microplastic's vertical transportation.Microplastic's shape and chemical composition largely impact its bioavailability and the efficiency of deposition,which is critical in microplastic vertical transportation from source to sink.In future,it is important to quantify and categorize the factors involved in microplastic "spatial transportation" and "vertical transportation" when estimating microplastic emission from land to open ocean.