| With the rapid development of the global economy,plastics are widely used in packaging materials,construction,automobile manufacturing,electronic products,clothing,agriculture and medicine due to their lightness,good insulation and economic durability.A large number of plastic garbage are flooding into both freshwater and marine ecosystems each year.Plastic waste has caused serious environmental pollution in the whole world.Plastic particles less than 5 mm in diameter are called microplastics.In recent years,after the rise of research on microplastics pollution in marine environment,some researchers began to pay attention to microplastic pollution in inland freshwater environment.In addition,researchers have explored the toxicological effects between microplastics and aquatic organisms,and the adsorption rules between microplastics and various pollutants through laboratory experiments.Dams fragment rivers and offer society many benefits but also cause multilevel effects throughout the aquatic ecosystem.As a result of impoundment,reservoirs may be a potential area for the accumulation of microplastics.The Three Gorges Reservoir(TGR)is by far the largest reservoir in China.Many anthropogenic pollutant sources have developed since the impoundment of the Three Gorges Dam such as industrial and household sewage,garbage dumping,and agricultural pollution.Thus,many environmental and ecological problems have emerged in the TGR such as heavy metals and organic pollutants.Danjiangkou Reservoir(DJKR)is located at the confluence of the Danjiang and Hanjiang Rivers,which together form the largest tributary of the Yangtze River.DJKR is a water source area in the Middle Route of the South-to-North Water Transfer Project in China.The water quality of the DJKR is a necessary prerequisite for the success of the project Detailed studies on microplastic pollution in these two typical reservoirs have not yet been carried out.Therefore,this study investigated the microplastic pollution in the TGR and the DJKR.We investigated microplastic pollution levels in surface waters and sediments from the TGR.The TGR is the largest reservoir in China and is located across the Chongqing municipality and Hubei Province.Microplastic abundance in the surface water ranged from 1597 to 12,611 n/m3 and in the sediments was 25 to 300 n/kg.In the surface waters,the contamination was more serious in urban areas,and in the sediments,countrysides were the most heavily polluted areas.Fibers were the most abundant microplastics,the dominant color was transparent,and small-sized particles were predominant.Of all the microplastics identified by micro-Raman spectroscopy,polystyrene(PS)was the most common type(38.5%)followed by polypropylene(PP,29.4%)and polyethylene(PE,21%).Compared with low-density microplastics,the high-density ones were more likely to be deposited from the water into the sediment.Several contaminants adsorbed by microplastics,such as organic solvents and pharmaceutical intermediates,were observed and qualitatively analyzed by Raman spectroscopy.Microplastics in surface water and sediment samples of the DJKR were investigated in this study.Microplastics were observed in all water and sediment samples with abundances varying from 467 to 15,017 n/m3 and 15 to 40 n/kg,respectively.Microplastics were rich in colour and dominated by fibrous items.Small-sized particles(<2 mm)were more frequently observed than other sizes.Analysis by micro-Raman spectroscopy showed that PP was the major polymer type.Previous studies have shown that microplastics have strong adsorbability to pollutants such as polycyclic aromatic hydrocarbons,polychlorinated biphenyls and antibiotics.Estradiol(E2)was selected as the adsorbent to study its adsorption on microplastics(PE,PP and PS).The effects of external temperature and volume of microplastics on the adsorption were evaluated.The results showed that the adsorption experimental values of E2 on three kinds of microplastics conform to the pseudo-second-order model.The adsorption capacity of E2 is PE>PP>PS,and the adsorption capacity of E2 decreases with the increase of adsorption temperature.As the volume of microplastics decreases,the specific surface area of microplastics increases gradually,so the adsorption effect increases gradually.This study investigated microplastic pollution levels in surface waters and sediments from the TGR and DJKR,provided valuable references for further understanding the microplastics pollution in river-style reservoirs,and discussed the potential impact of the microplastic-pollutant complexes in the reservoir ecosystems.Through indoor simulation experiments,the adsorption characteristics of microplastics and E2 have been studied.This study enriches the data of microplastic pollution in inland freshwater systems(especially in drinking water reservoirs),and is helpful to the study of water quality improvement and ecological protection of drinking water sources.The risk assessment and management of microplastics in the TGR and DJKR should be paid more attention based on their potential threats to the aquatic organisms and residents impacted by the drinking water source pollution. |
