A Study On The Pollution Characteristics Of Microplastic-loaded Pcbs In Mangrove Sediments

Microplastics are characterized by small particle size,light mass and large specific surface area,and their surfaces are easily loaded with heavy metals and organic pollutants,which can adsorb microorganisms in the environment and also serve as carriers for the migration and dissemination of toxic pollutants in the environment.Therefore,the study of microplastics and their organic pollutant loadings has received much attention in the field of environmental science.Mangrove ecosystems serve as a common "sink" for microplastics and POPs(Polychlorinated Biphenyls,PCBs),and microplastics in the sediment can interact with PCBs as an environmental mediator,but the factors that shape such interactions are until the recent study.However,the factors of such interaction have not been elucidated until the current time.To address this scientific issue,this paper selects the most widely distributed and unique mangrove ecosystems in the subtropical(Leizhou Peninsula)and tropical(Hainan Island)coastlines as the research object,aiming to reveal the pollution characteristics of microplastic-loaded PCBs in mangrove sediments.In this paper,the distribution characteristics of PCBs,microplastics and their loaded PCBs in 17 mangrove sediment samples from the region were investigated by using GC-MS to determine the distribution characteristics of PCBs in sediments and the distribution characteristics of PCBs loaded on microplastics,and Raman to identify the categories of microplastic species.The sources of PCBs and their ecological risks were analyzed by principal component analysis and correlation analysis based on the composition structure of congeners;the main sources of microplastics were judged based on the environmental influences near the sampling sites;the amount of PCBs in sediments proved that microplastics in mangrove sediments were important carriers of loaded PCBs,which provided a new perspective for the subsequent migration of PCBs in mangroves by microplastic-sediment.The main conclusions are as follows:(1)The abundances of microplastics measured in mangrove sediments of Leizhou Peninsula and Hainan Island ranged from 135.00±15.00-738.00±83.00items/kg(dry weight,dw),and the abundance range of microplastics collected in mangrove sediments on their west coast(mean abundance 550±65.00 items/kg)was higher than that on the east coast(mean abundance 239± 35.00 items/kg,dw).Based on Raman spectroscopy analysis,polypropylene(PP)had the highest percentage,followed by polyethylene(PE)and polystyrene(PS).The microplastics at each sampling site were characterized as follows: fibrous microplastics were the main shape;1-5 mm microplastics were the main size;and transparent and white colors were the main colors of microplastics.The analysis revealed that the higher the total organic carbon in the mangrove sediment,the greater the abundance of microplastics.(2)Eight major PCBs congeners were detected in the mangrove sediments of Leizhou Peninsula and Hainan Island,with contents ranging from 9.80-13.91ng/g(dw)and an average content of 12.17±10.14 ng/g.Among all congeners,the contribution of tetrachlorobiphenyl to all PCBs was relatively high(26.59%).the PCBs content was consistent with China’s marine sediment quality standards of Class I.The results of ecological risk evaluation based on the sediment quality benchmark method showed that there was almost no ecological risk of PCBs pollution in mangrove sediments in this study area.(3)This study demonstrates for the first time that microplastics in mangrove sediments are important carriers for loading PCBs,and their loading is much higher than the amount of PCBs in sediments,so the sorption capacity of PCBs by microplastics in mangrove sediments may be underestimated;the amount of PCBs loaded by microplastics in sediments is significantly positively correlated with the morphology of microplastics(fibers and foams)and the type of microplastics(PP and PE)significant positive correlation(p < 0.05).Cluster analysis revealed that the PCB-loaded microplastic morphology(fragments and fibers)may be derived from domestic sewage as well as from fishing activities;cluster analysis also revealed a correlation between PCBs-loaded microplastic morphology(films and foams)and higher and lower chlorinated PCBs congeners.