Distribution, Settlement And Bioaccumulation Of Microplastic In The Estuary

Estuarine and coastal areas generally occupy with high density of human popoluation and economic developments.More than 44% of the world's population lives in the estuarine and coastal areas.Human activities greatly impact on the environemtnal conditions in the estuarine and coastal areas.Estuarine and coastal areas act as the sink of nutrients and pollutants.It is of great significance to study pollutants in estuarine and coastal areas and to assess the environmental effects of these pollutants.Microplastics is plastics which has a particle size less than 5 mm.Recently,microplastics has rasied world's concern as an emerging and persistent environmental pollutant.Microplastics would influence water quality as part of the suspended particles.Toxic substances from microplastics would be potentially released to the associated environment.Microplastics could be easily ingested by marine life and induce damages in these marine organisms.In addition,microplastics may act as a carrier of the pollutants which may biomagnify the effects of the pollutants to the organisms living in the environment.In this study,the composition of microplastics in the mudflat sediment and marine organism in the estuary environment were examined.The seasonal distribution pattern and settlement characteristics of microplastics in estuarine sediment were further investigated.The biological uptake and bioaccumulation of microplastics and several persistant pollutants in the esturine organisms were studied to understand its biological and ecological impact and associated risks in the environment.Surface sediments from 6 sampling sites(Wusongkou,Shidongkou,Liuhekou,Qiyakou,Xupu and Dongwangsha)in Yangtze estuary were collected to study the accumulation and distribution of microplastics in the estuary environment.The results showed that average microplastics concentration in Yangtze estuarine sediments was 3.42 ± 1.31 items/g,d.w.The relative higher concentrations of microplastics in the estuary environment were detected in Wusongkou,Shidongkou and Qiyakou.Microplastics found in Yangtze esturine surface sediments were mainly composed of fibers and fragments.Fibers had relatively higher abundance,size and size range in the studied esturine surface sediment.Seasonal pattern and settlement characteristic of microplastics were investigated to understand its environmental distribution dynamics.Concentration of microplastics in rainy season(3.16 ± 0.90 items/g,d.w.)was significantly lower than that of dry season(4.36 ± 1.66 items/g,d.w.),suggesting rain washing,tides and salinity could affect the accumulation of microplastics in the estuarine sediments.In a re-suspension simulation experiment conducted in the laboratory,sediments were divided into three layers: liquid,top sediment layer and bottom sediment layer.The settlement experiment results showed that microplastics tended to stay in top sediment layer which has a smaller particle size.Oysters,a filter feeding mollusk,were chosen to study the biological uptake,accumulation and the associated impacts of pollutants to marine organism.The in vivo content of microplastics in the oyster was 4.53 items/g,w.w.(35.6 items/g,d.w.).Half of microplastics were detected in the gill and mantle of studied oysters.Fibers and fragments were the major forms detected in the studied oysters.And fibers had relatively higher abundance,size and size range in the studied oysters.Result of microfourier transform infrared spectroscopy showed microplastics detected in vivo were mainly composed of polyester,aromatic hydrocarbon resin,polyethylene,polyethylene terephthalate and cellophane.And cellophane accounted for the highest proportion of microplastics detected in vivo.Moreover,polychlorinated biphenyls and organochloride pesticides(including dichlorodiphenyltrichloroethane and hexachlorocyclohexane)were examined in the studied oysters using gas chromatography-mass spectrometry.The detected concentration of dichlorodiphenyltrichloroethane(1.414 ng/g,d.w.)in the studied oyster were higher than the safe standard established in the China safety standard GB18406.4-2001,while the detected concentrations of polychlorinated biphenyls(2.083 ng/g,d.w.)and hexachlorocyclohexane(362.4 ng/g,d.w.)were in the safe range.No significant correlation was found between the concentration of microplastics and persistent organic pollutants.Concentrations of trace metal in the studied oysters were detected using inductively coupled plasma mass spectrometry and the results showed that the concentrations were: Cu: 181.0 ?g/g,d.w.;Cr: 30.48 ?g/g,d.w.;Cd: 4.415 ?g/g,d.w.;Pb: 395.1 ng/g,d.w..The detected concentrations of Cu,Cr and Cd were higher than the safety standard GB18406.4-2001.Significant correlation was found between the in vivo concentration of microplastics and Cu,Cd,Cr,Pb.The results of scanning electron microscope and energy dispersive X-ray spectroscopy confirmed that trace metals could be absorbed on the surface of microplastics in vivo.These results suggested that microplastics may have a combined toxicologcail effects with other trace metals in vivo to the biological organisms.This study investigated the seasonal composition and distribution patterns,and settlement charateristic of microplastics in Yangtze estuarine sediments,which provids fundamental data on the study of environmental impact of microplastics in estuarine and coastal areas.The bioaccumulation of microplastics in filter-feeding organism and joint toxicological impact of microplastics and other traditional pollutants were examined,which could be a reference to the assessment of health risks of pollutants in estuary and coast areas,especially on the safety assessment of the estuarine cultures.