Microplastic (plastic < 5 mm in size) contamination is ubiquitous and has been found in environments ranging from deep ocean floors to Artic Sea ice. Microplastics are concerning emerging contaminants because they degrade slowly, are highly mobile, and can be easily consumed by wildlife. Once ingested by organisms, microplastics can cause both physical tissue damage as well as toxicity due to adsorption of other contaminants (e.g., heavy metals, organic compounds) on their surfaces. Microplastic research has mainly focused on marine settings, but has more recently expanded to surface freshwater systems. However, only one previous study has quantified microplastic pollution in groundwater. Thus, the potential for microplastic contamination of groundwater systems is understudied, and the role of land use in microplastic sourcing and transport to aquifers is unknown. Understanding the origins and extent of microplastic pollution in groundwater systems is critical because these reservoirs are often used as drinking water resources. Microplastic surveys of groundwater resources are a necessary first step in understanding the possible negative consequences to human health. Furthermore, karst environments often host fragile ecosystems (e.g., cave wildlife) and aquifers can discharge groundwater to surface water systems. Organisms in both subsurface and surface environments may be impacted by deteriorating groundwater quality due to plastic pollution. The proposed study will assess microplastic loads in karst groundwater springs in Missouri across a range of land uses, including the highly urbanized St. Louis metropolitan area as well as agriculturally-dominated and rural landscapes in central and southern Missouri. The research will also provide novel information on how microplastic contamination is transported to and through groundwater systems, which will help inform land managers for debris mitigation strategies. The proposed study will constitute a novel and important contribution to our understanding of the distribution of microplastics in water resources, which is essential to ensure both human and ecosystem health.