GEOLOGIC AND LAND USE CONTROLS ON MICROPLASTIC CONTAMINATION IN MISSOURI KARST SPRINGS

Microplastics are pervasive, emerging contaminants that present both known and unknown human and ecological health risks. However, research on their distribution and transport in groundwater and other subsurface environments is lacking. Karst aquifers, in particular, feature highly vulnerable water resources due to the development of tertiary porosity (e.g., sinkholes, conduits) in soluble bedrock that leads to high connectivity between the surface and subsurface. Furthermore, caves in karst landscapes often host fragile ecosystems that may be threatened by contamination from the surface. Our research thus aims to: (1) describe the extent and characteristics of microplastic pollution in karst springs in Missouri, United States, (2) assess the influence of geology (e.g., karstification) on their distribution, and (3) investigate the role of land use and anthropogenic activities in the delivery of these contaminants to karst waters. Baseflow samples collected from 30 springs located across different land use types (i.e., urban, agricultural, forested) show that suspected microplastics are ubiquitously present in Missouri karst, with concentrations ranging 1.2-15.0 counts/L. The most common morphology is fibers (93.3 %), and the dominant color is clear (53.3 %). Akaike information criterion scores and principal component analyses show that recharge area-normalized microplastic concentrations in the springs are best predicted by sinkhole densities within the recharge basins and the presence of geochemical indicators of anthropogenic activities (e.g., Na, Cl, B). These results indicate that both high subsurface permeability and urbanization may enhance microplastic pollution in karst waters. Additionally, microplastics are more abundant in cave springs compared to phreatic springs, suggesting that higher flow turbulence may also increase microplastic debris in subsurface waters. Ongoing work includes material characterization for the suspected microplastics using Raman spectroscopy, which will aid in identifying potential pollutant sources. Understanding the distribution and transport of emerging contaminants, like microplastics, in karst systems is essential to protect these fragile water resources, assess ecological hazards, and develop future mitigation strategies.