Microplastics are small particles that are found everywhere on earth. Groundwater is the largest source of liquid fresh water and globally 2.5 billion people exclusively depend on it to meet their freshwater needs. While initial surveys indicate microplastics presence in groundwater, the distribution, total quantity and impact of microplastics on groundwater ecosystems is completely unknown. In this 4-year research project funded by the Leverhulme Trust we will use an interdisciplinary approach incorporating ecohydrology, analytical chemistry, mathematical modelling and ecology to 1) establish the first global baseline of groundwater microplastic contamination, 2) investigate microplastic uptake by, and effects on, groundwater food webs, 3) model the global risks of microplastics to groundwater.