Occurrence, sources, and ecological risk of microplastics in groundwater: Impacts by agricultural activities and atmospheric deposition

Although microplastic (MP) pollution in groundwater is a serious issue, its potential sources and environmental risks are poorly understood. This study identified the sources of MPs in groundwater from a megacity in China. It estimated the environmental risks of MPs using a combination of the pollution load index (PLI), the polymer hazard index (PHI), and the potential ecological risk index (PERI). The groundwater in Shanghai showed high MP abundances, ranging from 3 ± 3 particles/L to 99 ± 19 particles/L. A total of 43 polymer types were detected, of which polypropylene (PP) and polyethylene (PE) were the main polymer types. Groundwater in agricultural areas has the highest level of MP pollution, with >50 % of MPs being identified as PP. Plastic woven bags used in agricultural activities were the primary sources. Similar characteristics of MPs in groundwater from open wells and atmospheric deposition samples suggested that atmospheric deposition was a significant source of MPs in groundwater from open wells. Landfills and construction activities were also recognized as potential MP pollution sources in groundwater. Based on PLI, PHI and PERI analysis, the groundwater in Shanghai exhibited a high MP pollution load, a middle polymer hazard, and a high potential ecological risk level, respectively. The PERI analysis, a comprehensive assessment compared to the PLI and PHI analyses, indicated an overall high ecological risk of MPs in agricultural groundwater. This study advances the knowledge of MP sources and their ecological risks in groundwater, allowing for better MP pollution control in areas with high MP abundance and high risk levels.