| "Microplastics"is the collective term to describe a heterogeneous mixture of plastic debris,of various shapes,colors and characteristics,with a maximum diameter of 5 mm.Due to their small size,surface morphology and wide distribution in the environment,microplastics are easily mistakenly ingested by a wide range of organisms.At present,microplastics have been widely studied in the world,but the concentration distribution and pollution characteristics of microplastics in the Bohai Bay area of China have not been known.Therefore,the occurrence,distribution of microplastics,as well as the interaction between microplastics and microbes were studied in coastal areas of Bohai Bay Coast.The specific conclusion were as follows:In the surface water of the two characteristic estuaries near the shore of Tianjin City,the average concentration of microplastics in Haihe Estuary and Yongdingxin Estuary were 1333.3±782.1 n/m~3and 788.0±464.2 n/m~3,respectively.In addition,the concentration in one sampling site in the Dagu Estuary was 2400.0 n/m~3.The concentrations of microplastics in sediments of two estuaries were 234.7±89.6 n/kg dw,85.0±35.1 n/kg dw in Haihe Estuary and Yongdingxin Estuary,respectively.The concentrations of microplastics in Dagu Estuary was 123.3±35.1 n/kg dw.Among the microplastics in the two estuaries,fiber occupies the dominant position in both surface water and sediment,with an average proportion of 66.9%and 53.2%,respectively.Microplastics of small size(<1 mm)are most abundant in surface water and sediments,with relative abundance of 65.7%and 61.1%,respectively.Colored microplastics were the dominant type among color classification.Through ATR-FTIR identification,PE and PP were found to be the main components of microplastics in Tianjin coastal estuaries.According to the 16S rRNA high-throughput sequencing result,the average OTUs number in microplastics,surface water and sediments were 2213,1091 and3419,respectively,indicating that microplastics could provide a good living environment and adequate nutrients.During the process of entering the sea from the river,the number of OTUs on the surface of the microplastics remained basically unchanged,while the number of OTUs in the surface water and sediments fluctuated greatly with the change of the environment parameters(salinity,temperature and et al.).It shows that microplastics could be used as protective carriers to make the bacteria community attached to them have stronger resistance and environmental adaptability.The bacterial communities on the structure of microplastic are significantly different from the natural environment.In addition,polymer types were found to have little effect on differences between bacterial communities.The function of bacterial communities in the three substrates was predicted by Bugbase online prediction software,and the results showed that bacterial communities on the surface of microplastics had higher pathogenicity and stress resistance.The average concentration of MPs in the coastal sediments of Bohai Bay was192.3±138.9 items/kg dw,which was at a moderate pollution level.In addition,flotation experiment showed that most of PE and PP had the higher density compared with seawater.The density increasing was influenced by the co-effects of biofouling and inorganic materials.Among them,the formation of biofilms on the surface of microplastics increases the stickiness of the surface of microplastics,which helps microplastics particles to capture denser environmental particles,thereby increasing their density.The density increasing rates of PE and PP in the natural environment were 7.4%-12.6%and 12.1%-17.5%,respectively.Finally,we also estimated that the total number of MPs in the sediments of Bohai Sea was 534 trillion,suggesting that the coastal sediments could be the sink of MPs. |
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