Does Microplastic Pollution in the Epikarst Environment Coincide with Rainfall Flushes and Copepod Population Dynamics?

Karst areas are characteristic landscapes formed by the dissolution of soluble rocks, whose hydrology is largely influenced by rapid infiltration through the karst massif. These areas are often hotspots of biodiversity, especially for epikarst and cave fauna. The epikarst, the uppermost layer of the unsaturated zone, plays a crucial role in regulating water flow in karst aquifers. The aim of this study was to investigate the extent of microplastic (MP) pollution, its relationship with precipitation and its correlation with copepod populations in karst areas. The study was conducted between April 2021 and October 2022 in the Postojna–Planina karst area in SW Slovenia at surface and underground sampling sites to determine the pathways of MP pollution from the surface to the depth of the karst massif. The results indicate that heavier rainfall flushes out more MP contaminants from the surface and epikarst environment. The transport dynamics of MP pollution are similar to the dynamics of copepods, which are the baseline organisms for the food chain in caves. One MP sample contained only polyamide particles, which could indicate clothing as a possible source of pollution, but the results are inconclusive. With this study, we provide the first insight into the transport of MP pollution from the surface environment to deeper karst massifs.