Assessing Microplastic Contamination Within Karst Groundwater Basins in Kentucky

The input and abrasion of plastic waste in the environment has long been known to form microplastics (MPs). These ubiquitous contaminants are easily mobilized into hydrologic systems. MPs are now being found in karst aquifers around the world, including several across Kentucky, USA. Due to their size (< 5 mm in diameter), chemical properties, abundance, and wide distribution, MPs pose numerous ecological hazards, including uptake by organisms and as substrates for contaminant sorption. Karst groundwater is especially vulnerable to surface contaminants; however, knowledge of the extent of karst MP contamination is limited, with most studies focused on individual sites or small areas. In this study, we created a MP contamination dataset for 30 karst springs and 10 locations where cave sediments were characterized across Kentucky. MP concentrations in groundwater samples ranged from 0 to 41.1 items/L and yielded an average of 4.9 ± 8.7 items/L. Sediment MP concentrations ranged from 0 to 306 items/kg. We performed statistical analyses and linear regressions to examine whether groundwater MP concentrations could be explained by factors including land use, population density, basin area, numbers of sinkholes, and sinking streams. Our models revealed that population density, agrarian land use, sinking stream density, and basin area were related to MP concentrations. All factors except basin area trended positively with MP concentration, while basin area trended negatively. These relations are generally corroborated by existing literature, however they indicate that further studies with considerably larger sample sizes are needed to determine mechanistic relationships.