[Characterization， Sources and Risk Assessment of Microplastic Pollution in Surface Water and Groundwater of the Hetao Irrigation Area].

The Hetao Irrigation Area is an important commodity grain base in China. The irrigated area has already had a history of large-scale agricultural film use for more than 30 years， resulting in microplastic pollution that has aroused wide concern. This study collected surface water samples in the all-drainage channel and main drainage channel and groundwater samples in Wuyuan County， Bayannaoer City， Inner Mongolia Autonomous Region to investigate the pollution characteristics， sources， and risks of microplastics in surface water and groundwater in the Hetao Irrigation Area. The concentration of five types of microplastics， including polyvinyl chloride （PVC）， polyethylene （PE）， polyethylene terephthalate （PET）， polypropylene （PP）， and polystyrene （PS）， were determined by the tube furnace pyrolysis-thermal desorption-gas chromatography-mass spectrometry （Py-TD GC/MS） method. The results of the study showed that the concentration of microplastics in drained surface water ranged from ND to 317.1 μg·L-1， showing the concentration trend of PVC>PE>PET>PP>PS， of which PVC and PE were the dominant microplastic species， with concentrations significantly higher than those of PP and PS （P<0.05）. The concentration of microplastics in groundwater ranged from ND to 44.8 μg·L-1， showing a concentration trend of PE>PVC>PET>PP>PS， and the concentration of microplastics in drained surface water was significantly higher than that in groundwater （P<0.05）. Hierarchical clustering and Spearman's correlation coefficient methods were used to analyze the sources of microplastics in drained surface water and groundwater. The results showed that agricultural films were the main source of microplastics in water samples from the study area and that infiltration of microplastics carried by water flow from surface water was a potential source of microplastics in groundwater. The pollution load index （PLI） was used to evaluate the pollution level of microplastics， and the polymer hazard index （PHI） was used to evaluate the potential risk of microplastics in the water environment of the Hetao Irrigation Area. The PLI value indicated that the microplastics in the surface and groundwater in the study area were at a low level of contamination and that the increase in the amount of water discharged from the study area in the autumn irrigation period due to the flooding of the area diluted the microplastics in surface and groundwater. The PHI value indicated that PVC was the most potentially hazardous. The PHI value indicated that PVC had the highest potential risk. The results of this study can provide a research basis for the prevention， control， and management of microplastics in the Hetao Irrigation Area.