Occurrence Characteristics Of Microplastics In Aquatic Environments And Non-targeted Analysis For Typical Microplastic Leachates

Plastics play a crucial role in serving production with important social and economic significance.But at the same time,discarded plastics enter the ecological environment and have long-term negative effects.Among them,plastic particles less than 5 mm in diameter are defined as microplastics.With the development of microplastics research,academia calls for the scientific methods of microplastics sampling,analysis,and evaluation based on unified standards,and to further understand the environmental risks of microplastics in the future.In this study,the sampling and analysis of microplastics in different aquatic environments were carried out,and typical polymer types of microplastics with high detection frequency were identified.After that,leaching experiments were carried out on typical microplastics in the laboratory,and the organic composition of the leachates was analyzed by the non-targeted method.Besides,the combined toxicity of the typical microplastic leachates was evaluated according to the hazard classification data of the detected components.The sampling and analysis method of microplastics in surface water was optimized.A large volume of water is collected and filtered in-situ,and suspected particles in the water are intercepted by the metal filter.The sampling device relies on a high-power centrifugal pump to provide suction and is free of plastic materials in front of the metal filter.This method successfully improves the lower limit of freshwater sampling volume to 100 L,and the size of the filter is decreased to 100μm.Using this method to collect and analyze microplastics in the surface water of urban rivers,the results showed that the microplastic abundances in the Suzhou Creek range from 30.0—316.7 items m^-3,with the highest abundance in the downstream by the Zhejianglu Bridge.The diurnal variation of the microplastic abundances in the Xiqiu Creek range from 29.8—109.7 items m^-3,and the monthly variation range from 10.0—100.0 items m^-3;fiber is the predominant shape（96%）,and polypropylene is the predominant composition（59%）.The variation of microplastic abundances is closely related to the aeration equipment in the river.The migration characteristics of microplastics were investigated.This study reports the occurrence and distribution of microplastics in the surface water and sediment along the Yangtze River and rivers of Chongming Island.The results showed that the microplastic abundances in surface water and sediments ranged from 0.0—258.9 items m^-3 and 10.0—60.0 items kg^-1 d.w.,respectively,and the abundance in surface water along the Yangtze River was significantly higher（p<0.01）than that in rivers of Chongming Island.In the surface water and sediment,the shape of fiber accounted for 33%and 67%,respectively;more than 72%of microplastics had the longest dimension of less than 1 mm;11 polymer types were identified in which polyethylene,polypropylene,andα-cellulose were abundant in number.The density of microplastics in the two phases inside and outside the island is significantly different（p<0.01）,indicating that the migration process in aquatic environments is dominated by different driving forces.The Yangtze Estuary is an important gateway for microplastics to enter the marine environment from the freshwater environment.Because of the violent vertical disturbance in estuarine water,high-density microplastics in sediments can re-enter the water through a resuspension process.However,the rivers in Chongming Island lack water hydrodynamics,and high-density microplastics in the water tend to settle naturally into the sediments.A non-targeted analysis workflow was integrated to identify organic components in typical microplastic leachates.In the leaching experiment,there were three leaching media,simulated gastric fluid（SGF）,river water,and seawater,and the leaching objects were polyethylene,polypropylene,polyvinyl chloride,polyethylene terephthalate,and polyester fibers comprising both raw and recycled materials.Totals of 111.0±26.7,98.5±20.3,and 53.5±4.7 different features were tentatively identified as compounds in SGF,freshwater,and seawater leachates,respectively,of which 5 compounds（bisphenol A,1,2-benzoisothiazole-3（2H）-one,decanoic acid,octanoic acid,and palmitic amide）were confirmed by reference standards.The leaching capacities of the media were compared,and the clusters of structurally related features leached in the same medium were studied.For leachates generated from raw and recycled plastics,volcano plots and Pearson’s Chi-squared tests were used to identify characteristic features.More characteristic features（3—20）had an average intensity across all recycled plastics that was significantly higher（p<0.05）than that（1—3）of raw plastics under different conditions.The results indicate that gastric solution is more likely to leach components from microplastics,and there exists a difference in leachate’s organic composition between raw and recycled materials.Four models based on machine learning algorithms were constructed to quantitatively predict the organic components in typical microplastic leachates.The model was constructed by using artificial neural network（ANN）and random forest（RF）algorithms.The mixed standard measured dataset was used as the training set,and two molecular descriptors were used as parameters.Then it was used to predict the relative response factors（RRF）of compounds under electrospray ionization test conditions.The abundance of the compound was divided by the relative response factor to obtain the predicted concentration.Combined with the ion evaporation mechanism,the movement of the solute in the ion source can be represented by the Abraham molecular descriptor（physical and chemical properties related to the solute transfer process）and the Chem Mine R molecular descriptor（structure information）.By using 5-fold cross-validation and Y-randomization to evaluate the predictive ability of the model,the results showed that the RF model using both Abraham and Chem Mine R molecular descriptors has a better predictive ability.The mean absolute error of the training set was 0.13,and the coefficient of determination was 0.90.The predicted concentrations of compounds in typical microplastic leachates were calculated then,and the compound with the highest concentrations in the three media was bisphenol A(0.19 ngμL^-1).An evaluation system for the combined toxicity was proposed.The combined toxicity of five polymers with raw and recycled materials was evaluated based on hazard data.The hazard classification standards for compounds are based on the latest version of the Globally Harmonized System of Classification and Labeling of Chemicals,and five orders of magnitude of hazard scores are assigned according to the hazard level.The total hazard score was obtained by summing all the compound hazard scores in each microplastic leachate,and the base 10 logarithm was taken to obtain the final hazard rating.This study found carcinogenic and reproductive toxic compounds,such as bisphenol A and catechol,in microplastic leachates.After the calculation of the combined toxicity evaluation method,recycled PVC leachate,recycled PE leachate,and raw PET fiber leachate were found to have high hazard scores,and thus considered a very high level of environmental risk.