Occurrence Characteristics And Source-sink Analysis Of Microplastics In Typical Coastal Waters Of Shandong Peninsula

Microplastics(MPs)are plastic fragments,particles or fibers with a diameter of less than 5 mm.MPs,as a new pollutant,have attracted worldwide attention in recent years.The particle size of MPs is small,and they are widely distributing in the marine environment and they pose serious threats to the marine ecosystem by themselves or by combining with other pollutants.The coastal sedimentary environment is the main enrichment area of MPs pollution.Evaluating the pollution characteristics of MPs pollution in this area and analyzing the source and fate of MPs distribution in sediments will provide a basis for exploring the migration law of offshore MPs and its ecological risks,and also provide a scientific basis for our country to better protect the marine ecological environment.In this study,different types of typical sea areas in Shandong Peninsula are selected as research areas,including the island reef system(Changshan Islands),semi-closed bays(Laizhou Bay and Jinghai Bay)and open sea areas(Lancelet Reserve and Solen grandis Reserve).The abundance,type(size,shape,color)and polymer composition of sediments,organisms in Changshan Islands,Laizhou Bay,Jinghai Bay,Lancelet Reserve and Solen grandis Reserve are surveyed.It clarifys the pollution status of MPs in typical coast of Shandong Peninsula.Shannon index was used to evaluate the diversity of MPs sources,analyze the influence of sediment size on the distribution of MPs in semi-closed bays and open sea areas,and clarify the source and sink of MPs in sediments of different types of typical sea areas.The main conclusions are as follows:(1)The abundance of MPs in The Changshan Islands ranges from 133.14 to 499.82items/kg,with an average abundance of 252.59 items/kg.The size of MPs is less than500 μm,accounting for more than 70% of the total MPs.The shape of MPs is mainly granular,followed by fragment and fiber.The color of MPs is mainly transparent.The main polymer types of MPs in sediment are cellophane,polyethylene and polyethylene terephthalate.(2)The abundance of MPs in organisms in the Changshan Islands is 0.19 to 3.79items/individual,the abundance of MPs in fish is higher than that in cultured scallop;The shape of MPs in organisms is mainly fiber,followed by fragments and particles;MPs in organisms Most of the colors are transparent,and the least abundant color is black;The smallest size MPs(<300 μm)are most common(85.91%)in organisms;The types of polymers detected in organisms are cellophane,cellulose and polyethylene,among which cellophane is one of the most common polymers in living organisms,while polyethylene was only detected in scallops.(3)The pollution status of microplastics in sediments of two semi-closed bays(Laizhou Bay and Jinghai Bay)and two open sea areas(Lancelet Reserve and Solen grandis Reserve)in Shandong Peninsula was investigated.The results shows that the abundance of MPs in sediments at all sites ranged from 56.6 to 855.4 items/kg,with an average abundance of 427.6±218.2 items/kg.The average abundance of MPs in sediments of the four regions was 603.5±217.6 items/kg in Jinghai Bay,404.1±128.3items/kg in Laizhou bay,395.4±259.5 items/kg in Lancelet Reserve and 319.0±308.0items/kg in Solen grandis Reserve.In the sediments of Laizhou Bay,fiber is the main shape;In Jinghai Bay,fragments are the main shape;In Solen grandis Reserve,particles are the main shape,and in the sediments of Lancelet Reserve,particles and fibers are the main MPs forms.MPs in the smallest size category(53-300 μm)were the most abundant at all four survey points,accounting for more than 80% of the total MPs.A total of 16 polymer types were detected in all samples.The percentage of polymer components in sediments varied from region to region,with polyethylene being the most common polymer component in all sites.(4)According to the analysis of the diversity index results,the diversity index of MPs in Laizhou Bay was the highest,and that in Changshan Islands was the lowest,indicating that the sources of MPs in Laizhou Bay were the most complex.There is a significant negative correlation between MPs abundance and sediment grain size in the semi-enclosed bay(p<0.05),but no correlation between MPs abundance and sediment grain size in the open coastal zone(p>0.05),indicating that the smaller the sediment particle size,the higher the accumulation of MPs in the sediments of semi-enclosed sea areas.In the correlation analysis between sediment particle size and large-sized MPs,it is found that there is only a significant relationship in Jinghai Bay,which may be due to the fact that Jinghai Bay is a low-energy marine environment,and the marine hydrodynamic conditions and sedimentary environment are relatively stable.Ocean currents and other factors have less of an influence,leading to a large accumulation of MPs in its area.Therefore,different transport modes of MPs may exist in different marine sediment environments.