Distribution And Ecological Risk Assessment Of Plastics And Microplastics In Zhoushan Fishing Ground And Adjacent Sea Areas

Plastics and microplastic contaminants are omnipresent within various environmental mediums,and have been detected in remote places such as plateaus and deep seas.Plastics and microplastics have become a global pollution problem due to their environmental persistence and potential ecological risks,which has raised concern between scientists,policy-makers,and environmentalists,as well as common citizens.Zhoushan fishing ground,an important fishing ground in China,is significantly affected by human activities.However,a lack of in-depth research on microplastic pollution in this hotspot restricts the understanding of the source,fate,and ecotoxicity of such pollutants in this area.With increasing production of plastics and wastes,it has been urgent to provide a scientific basis for policies and measures related to microplastic pollution control and governance.Therefore,a field plastic and microplastic pollution investigation were carried out in this study.In the field investigation,the spatiotemporal distribution and morphological characteristics of plastics and microplastics in surface water,sea floor and organisms in Zhoushan fishing ground were determined using microscopy and infrared spectroscopy.Based on the above data,a microplastic pollution index system was constructed from three aspects,pressure index,state index,and response index,using the expert scoring method and the analytic hierarchy process to comprehensively evaluate the ecological risks of marine microplastics.The main conclusions of this thesis are as follows:(1)A seasonal investigation was conducted on microplastics from the surface seawater of typical sections of Zhoushan fishing ground.Microplastics were detected in water samples from all locations,with an average concentration of 56.86±54.15items/m~3.Fibrous microplastics were dominant in the surface water of Zhoushan fishing ground.Ten different types of microplastic polymers,mainly polyethylene and polyacrylonitrile,were identified using micro-infrared spectroscopy.The concentration of microplastics decreased with the increase of the offshore distance.While the seasonal changes of microplastic concentrations were not obvious,indicating that nearshore human activities caused microplastic pollution.And there were a wide range of sources of microplastics in the open seas,which were mainly clothing fibers,as evident from analysis of polymer composition.(2)We conducted the first systematic survey of plastic litter on the seafloor in the Zhoushan fishing ground and adjacent East China Sea.Plastic debris was found in 95.35%of all the bottom trawl nets.In total,222 items and 6.04 kg of marine litter were collected in 43 monitoring hauls from part of the study area.Fishing gear and plastic film were the dominant type of sea-based source and land-based source,respectrively.PE was themost abundant polymer typewhere it accounted for 42.83%by weight because it has a wide range of uses.(2)In order to further investigate the pollution level of microplastics in the Zhoushan fishing ground,a seasonal investigation of microplastic pollution in fish and crustaceans in Zhoushan fishing ground was carried out.Results showed that the average abundance of microplastics in the gastrointestinal tract and gills of fish ranged from 0.04-4.00 items/ind.and 0.03-2.00 items/ind.,respectively.For crustaceans,the abundances were 0.23±0.13 items/ind.and 0.26±0.06 items/ind.,respectively.The abundance levels of microplastics in fish gastrointestinal tract and gills in spring were significantly lower than those in autumn,which was associated with their reproductive and spawning cycles.Microplastics in fish and crustaceans were dominated by fibers and individuals smaller than 1 mm,most commonly polyesters.These two experiments provided baseline data for the following marine microplastic ecological risk assessment model and risk assessment system.(4)A comprehensive assessment system and an evaluation model were constructed from three aspects,pressure index,state index,and response index,to evaluate the ecological risks of marine microplastics in Zhoushan fishing ground by integration and statistical analysis of existing data in this thesis.According to the comprehensive assessment results,current ecological risk of microplastic pollution in Zhoushan fishing ground was low.Most of the index factors,especially pressure index,had low or moderate risk level,indicating that the impact of microplastic pollution on ecological risk in Zhoushan fishing ground was still within a controllable range.Compared with other sea areas around the world,the environmental risk level of marine microplastics in Zhoushan fishing ground was low.