A Study On The Adsorption Behaviors Of Micro/Nano-Plastics For Heavy Metals And Their Ecotoxicity Toward Two Typical Aquatic Organisms

As a new type of environmental pollutant,micro/nano-plastics have been widely distributed in different water environment media all over the world.Due to the characteristics of diverse sources,long existence in the environment,easiness of migration,capabilities in adsorbing other environmental pollutants,small particle size and mistaken ingested by aquatic organisms,the impacts and ecological risks of micro/nano-plastics on the aquatic environment have attracted increasing attention of scholars.Because of China is one of the largest producer of plastics in the world,the micro/nano-plastics pollution in China's water environment is particularly serious.Thus,it is urgent to study the environmental behavior and ecological toxicity of micro/nano-plastics.Due to its huge specific surface area,micro/nano-plastics can absorb many kinds of pollutants from the water environment,thus causing potential harm to aquatic organisms.At the same time,heavy metals pollution is also a key problem in water environment.However,the interaction between micro/nano-plastics and heavy metals has not been paid enough attention.In addition,most of the studies on the ecotoxicity of micro/nano-plastics were focused on marine organisms,and the data on the impacts of micro/nano-plastics on freshwater organisms are seriously inadequate.Study on the adsorption behaviors of micro/nano-plastics for heavy metals and their ecotoxicity to aquatic organisms can provide important information for further understanding the environmental risks of micro/nano-plastics in waters.Based on this underground,the adsorption kinetics,adsorption isotherms and competitive adsorption behaviors of various heavy metals on polystyrene micro/nano-plastics were analyzed in this study.Moreover,the chronic toxicity,acute toxicity and combined toxicity with heavy metals of micro/nano-plastics to typical aquatic organisms were studied by indoor exposure experiments.Main results of these studies are as follows:?1?The results showed that the adsorption kinetics of lead and cadmium on polystyrene nanoplastics?100 nm and 1000 nm?were suitable for the pseudo-second-order model,and the adsorption isotherms were in accordance with the Langmuir model.The adsorption capacity of nanoplastics for lead was stronger than that for cadmium,and the adsorption capacity of nanoplastics with smaller particle size was stronger.There was a competitive adsorption relationship between lead and cadmium on polystyrene nanoplastics.The competitive adsorption of lead on polystyrenenanoplastics was stronger than that of cadmium.The competitive adsorption relationship on 100 nm nanoplastics was weaker than that on 1000 nm nanoplastics,which might be due to the larger specific surface area of smaller nanoplastics could provide more adsorption sites for heavy metals.?2?The results of batch adsorption experiments showed that the adsorption affinity of polystyrene microplastics?10?m and 50?m?for four heavy metals was lead>cadmium>copper>nickel,and the adsorption capacity of smaller polystyrene microplastics was stronger.The pseudo-second-order model is suitable for describing the adsorption kinetics of heavy metals on polystyrene microplastics,and the Langmuir model is suitable for describing the adsorption isotherms of heavy metals on polystyrene microplastics.?3?The long-term exposure experiment of polystyrene nanoplastics?100 nm?toward the model aquatic plant Ceratopteris pteridoides showed that nanoplastics could rapidly and massively adsorb on the spore surface of C.pteridoides,inhibit the spore germination and gametophyte development.In addition,nanoplastics could enter the rhizoid of gametophytes.The highest concentration of nanoplastics?100?g/ml?could cause lesions on the gametophytes.These findings suggest that nanoplastics in the water environment may pose a potential threat to the population reproduction of Pteridophytes.?4?The acute exposure experiment of polystyrene micro/nano-plastics toward D.magna showed that the micro/nano-plastics could affect the feeding rate of D.magna and lead to the increase of mortality,thus constituting acute toxicity to D.magna.The24 h-EC₅₀ and 48 h-EC₅₀ of 100 nm,1000 nm,10?m,and 50?m micro/nano-plastics to D.magna were 0.845,1.201,16.790,and 76.401?g/mL as well as 0.282,0.495,6.293,and 50.268?g/mL,respectively.The 24-LC₅₀ and 48-LC₅₀ of 100 nm,1000 nm,10?m,and 50?m micro/nano-plastics were 10.96,12.12,351.95,and 396.97?g/mL as well as 8.90,9.99,215.64,and 274.86?g/mL,respectively.?5?The accumulation of heavy metals in D.magna was not significantly affected by low microplastics concentration,but significantly increased at high microplastics concentration.The accumulation of heavy metals in D.magna was related to the adsorption capacity of microplastics for heavy metals.The doses and particles sizes of microplastics were both important factors responsible for the distinct combined effects of microplastics and heavy metals toward D.magna.The combined effect of heavy metals and microplastics was trended to alter from antagonism to additive effect with increasing microplastics concentration.Heavy metals possessed stronger adsorption affinity on microplastics showed more antagonism when combined with microplastics.Smaller plastic particles may cause more severe potential hazard to aquatic organisms.