A Study On Microplastics Pollution In Lakes Of Central China And The Sorptive Behavior Of Phenanthrene And Pyrene Onto Microplastics

Microplastics have been considered as an emerging pollutant which are ubiquitously present in various media of aquatic environment.Marked by their diverse sources,long existence in the environment,easiness of migration,capabilities in concentrating and transporting toxic pollutants,and potential to be ingested by auqatic biota due to their microscopic size,the presence and associated environmental risks of microplastics have aroused increasing concern.Up to date,most of studies regarding microplastics pollution have been conducted in the marine environments.Although freshwaters are potential sources and transport pathways of plastic debris to the oceans,the pollution status of microplastics in freshwater systems does not attract enough attention.In particular,China is the largest producer of plastics all over the world,knowledge about presence of microplastics in its inland freshwaters is extremely insufficient.Due to the large surface-to-volume ratio,microplastics can sorb and concentrate hydrophobic organic contaminants from the ambient water,which may exert a toxic effect to the biota that ingest plastics.Conducting studies on the interaction mechanisms between microplastics and hydrophobic organic contaminants is meaningful for better uderstanding the environmental risks associated with microplastics.Based on this underground,we investigated the presence of microplastics quantitatively and qualitatively in waters of Wuhan urban lakes,Dongting Lake and Hong Lake,which are important lakes in the middle reaches of the Yangtze River.In addition,a series of laboratory experiments were conducted to explore the interactions between microplastics and hydrophobic organic contaminants and their potential mechanisms.Results of these studies are as follows:Microplastic concentrations ranged from 1660.0±639.1 to 8925±1591 n/m~3 in the Wuhan urban surface waters.The abundance of microplastics in the studied lakes was negatively correlated with the distance from the city center(p<0.001).Urban reaches of the Hanjiang River and Yangtze River were found to have relatively lower levels of microplastics than most of the studied lakes.Among the detected microplastics,fiber was the most frequent shape,occupying 52.9 to 95.6%in number,while colored particles accounted for 50.4 to 86.9%.More than 80%of microplastics in number had a size of<2 mm.Identification results of subsamples showed polyethylene terephthalate and polypropylene were the dominant components of microplastics analyzed.The concentration ranges of microplastics in Dongting Lake and Hong Lake were 900 to 2800 and 1250 to 4650 n/m~3,respectively.For the microplastics detected in both lakes,fibers occupied more than 60%in proportion.More than 70%of plastics were colored items.Particles with a size of<330?m comprised more than 20%of total microplastics.Identification results of subsamples by Raman spectroscopy showed polyethylene and polypropylene were the major components for microplastics in both lakes.The sorption kinetics of phenanthrene onto polyethylene,polystyrene,polyvinylchloride and natural sediment particles were successfully described by the pseudo-second-order model(R~2>0.992),while the equilibrium data were best-fitted to the Langmuir isotherm(R~2>0.995).Compared with natural sediment,microplastics exhibited higher capacities for phenanthrene which followed an order of polyethylene>polystyrene>polyvinylchloride.As the aqueous concentration of pyrene increased,both uptakes and distribution coefficients(K_d)of Phe within the solids decreased,with natural sediment giving the largest decline.Although proportions of phenanthrene desorbed from the contaminated microplastics were low,due to the high phenanthrene uptake,microplastics released larger amounts of the sorbed phenanthrene to water than the natural sediment during the desorption process.By comparative analysis of different sorption models,the pseudo-second-order kinetics model was found to be more appropriate in describing the entire sorption process of pyrene onto the polyethylene,polystyrene,polyvinylchloride particles(R~2>0.99).Sorption rates of pyrene onto microplastics were mainly controlled by intraparticle diffusion.Polyethylene exhibited the highest affinity for pyrene,followed by polystyrene and polyvinylchloride.The sorption equilibrium data of pyrene onto microplastics were best fitted to the Langmuir isotherm model(R~2>0.99).