Research on the Migration and Transformation Behavior of Microplastics in Groundwater Systems and Their Ecological Health Risks

A comprehensive approach integrating laboratory column experiments, field monitoring, and adsorption-desorption studies was employed to investigate the migration mechanisms of microplastics (MPs) in groundwater systems and their associated compound ecological risks. Polyethylene (PE) microplastics of different particle sizes (0.1 - 100 micrometers) exhibited distinct migration patterns, with their migration primarily governed by the porosity of the aquifer. Particles smaller than 50 micrometers were capable of penetrating clay barriers and achieving deep underground transport. Biological exposure tests revealed significant biological impacts: Branchiopoda individuals ingested 0.2 - 5 particles per day, and the feeding efficiency of rotifers decreased by 15 - 40% under an exposure condition of 100 particles per liter. Meanwhile, fork-mouthed fish and groundwater fish showed stress responses related to particle load. At the microbial level, microplastics altered the community composition, increasing the abundance of Actinobacteria by 12% and decreasing that of Proteobacteria by 8%. Additionally, the overall bioavailability of co - pollutants increased by 20 - 50%. Moreover, these microplastics served as effective carriers for hydrophobic pollutants (such as benzo[a]pyrene), enhancing toxicity through the adsorption - desorption process and exacerbating oxidative stress across multiple trophic levels. These combined effects disrupted metabolic pathways, impaired ecological functions, and damaged groundwater - dependent ecosystems by altering the biogeochemical cycles of nitrogen and carbon. These results indicate that microplastics act as both physical pollutants and chemical carriers, amplifying ecological risks through synergistic interactions with other pollutants. Overall, this study emphasizes the urgent need for groundwater risk management strategies based on particle size classification, co - migration of pollutants, and ecological health assessment, providing a theoretical basis for the development of sustainable methods to mitigate the impacts of microplastics in the groundwater environment.