| As a type of emerging contaminant,microplastics have increasingly attracted international concerns.In detail,microplastics have been proven ubiquitous in almost all environmental media,accompanied by various degrees of potential risks to the ecoenvironment.Therefore,it’s indispensable to further elaborate on the distribution characteristics and detrimental impacts of microplastics in the aqueous environment.Many factors including the population density,and the habits of interpersonal activities,could significantly affect the environmental source,pathway,and fate of microplastics.In this study,several urban waterbodies with differentiated hydrological conditions in Hefei City were comprehensively surveyed,aiming to highlight the distinction between rivers and lakes in the same urban area.Moreover,the possible sources,sinks as well as biotoxic impacts of microplastics in surface water were discussed,based on field investigation and simulation experiments.The main findings are as follows:(1)As for spatial distribution,the Abundance of microplastics in urban rivers in Hefei was significantly different(P<0.05).Specifically,the concentration of microplastics in the Nanfei River was significantly higher than that in the Shiwuli River with ranges of 10.45 to80.25(ave: 33.51±22.78)items/L and 3.65 to 16.70(ave: 8.63±4.48)items/L,respectively.In terms of characteristics,The preponderance of type was microsphere(83.09%);the preponderance of particle size was 50～333 μm(89.55%);and the preponderance of color was white(53.29%)and transparent(35.55%).The results of the infrared analysis showed that there were 15 and 9 kinds of polymers in the surface water of the Nanfei River and Shiwuli River,respectively.Polypropylene(48.6%)was the main component,followed by polyethylene(14.33%)and polyamide(12.92%).Combined with the types of surrounding land,population density,and human activities,plastic microbeads from daily cosmetics were considered the conceivably essential cause of microplastics in urban rivers in Hefei,which indicates that the tailwater discharge is the main contributor of microplastics in urban rivers in Hefei.In addition,tributary inflow,rainwater runoff,shipping activities,and agricultural production would have made an unneglected contribution to the microplastics in urban rivers.Environmental management and ecological restoration measures such as interception facilities,sediment dredging,and constructed wetlands can inhibit the ecological and environmental hazards of microplastics.(2)The detection rate of microplastics in urban lakes in Hefei was 100%,and the abundance displayed a significant difference(P<0.05)with abundance ranges of 0.75 to4.8(ave: 3.07±1.29)items/L.The contamination level of urban lakes in Hefei was comparable to that of Wuhan,Changsha,and Yueyang.The shapes of microplastics in urban lakes were mainly debris(28.59%),film(22.75%),and microsphere(22.75%).The microplastics with small sizes(50～500 μm)accounted for the main part(61.25%),and the colors were mainly transparent and white accounting for 32.66% and 25.75% respectively.The results of the infrared analysis showed that there were 22 types of polymers in the urban lakes,in which polyethylene(38.75%)and polypropylene(15.31%)dominated.Compared with urban rivers,lakes have limited sources of microplastics due to their more closed hydrostatic condition with the main contributors of rainwater runoff and atmospheric deposition.In addition,the intensity of human intervention is also the main influencing factor that determines the overall level of microplastics in the lake.(3)Microplastics could inhibit the growth of Chlorella pyrenoidosa,and the inhibition effect shows a certain time dependence.In the early stage of the exposure experiment,the growth inhibition effect of polystyrene plastic microspheres on Chlorella pyrenoidosa was not remarkable.In the middle of the exposure experiment,polystyrene plastic microspheres showed a remarkable inhibition on the growth,chlorophyll a and chlorophyll b concentration,and protein content of Chlorella pyrenoidosa.The inhibition rate increased along with the concentration of polystyrene microspheres.At the same time,algal cells were subjected to a certain degree of lipid oxidation,malondialdehyde content increased,antioxidant enzyme activity decreased,and had a significant inhibitory effect.In the later stage of the exposure experiment,due to the enhancement of the adaptability of algal cells to the environment,the inhibitory effect of polystyrene plastic microspheres on the growth,chlorophyll a and chlorophyll b concentration,and protein content of Chlorella pyrenoidosa was gradually weakened.At the same time,the content of malondialdehyde decreased,the inhibition rate of antioxidant enzyme activity gradually decreased,and the structural morphology of algal cells was restored,but there was still a certain degree of lipid oxidation and structural damage.This study is expected to provide basic data and theoretical references for the ecoenvironmental risk assessment and pollution prevention of microplastics in freshwater environments within densely populated city. |
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