Groundwater microplastic (MP) pollution is an issue of growing concern, particularly for public drinking water supply. However, there are few published studies investigating microplastic contamination in groundwater. Field data on microplastic presence are sparse, with no direct comparison between aquifer lithologies or a comparison between the local borehole environment and wider aquifer settings. In England, despite growing pressure to understand, systematically sample and regulate groundwater microplastics, no assessment to date has been conducted.

This study, the first investigating microplastic presence in English groundwater, addresses this research gap by developing a protocol for sampling and extracting microplastics >25μm. It is applied to three field studies assessing i) microplastics presence in pumped principal aquifer sites of chalk, limestone and sandstone lithologies in England, with high and low risk sites in each lithology designated by existing drinking water safety plans (DWSPs), ii) microplastic presence in Environment Agency monitoring boreholes for comparison with pumped aquifer samples of the same chalk aquifer, and iii) microplastics presence in groundwater surrounding two legacy landfill sites, gaining insights on risks to groundwater from potential point sources of microplastics. The research provides recommendations for implementing a wider systematic sampling assessment of microplastics in groundwater in England and assesses the suitability of DWSPs in guiding this.

The study found that average microplastic concentrations in pumped aquifer samples were low (0.85 MP/L), and their presence was more ubiquitous than expected. Existing DWSPs are not suitable for predicting microplastic presence. Future wider systematic surveys of microplastic in English groundwater should focus on microplastic sampling from pumped sites. Microplastics detected in monitoring borehole samples were not representative of the underlying aquifer conditions, were influenced by local borehole scale contamination sources and were highly heterogeneous. Where microplastics were detected, concentrations could exceed average concentrations from pumped sites by a factor of 78:1.