Microplastic and microfibre pollution in unexplored caves

Microplastic and microfibre contamination has emerged as a pressing global issue, however, karst systems remain largely overlooked. Due to their properties, these microparticles of anthropogenic origin are highly mobile and environmentally persistent, allowing them to reach even the most remote ecosystems. Subterranean environments - the so-called “dark continent” - represent one of the least explored frontiers of terrestrial science, with vast areas still inaccessible. In such hypogean systems, the distribution of pollutants is tightly regulated by the interplay between surface–subsurface connectivity, aquifer hydrodynamics, geological context, and local environmental factors. In this study, the first evidence of microplastic and microfibre pollution in unexplored caves was presented, revealing how human activity could indirectly impact even the uncontaminated environments of the dark continent. Working together with speleologists, sediment samples from unexplored caves of the Abruzzo Region, Italy, were collected and investigated. Examined microparticles were counted and characterized by composition, size, shape, fluorescence, and color, via microscopy and spectroscopy. Our findings show that microplastic concentrations were generally low or absent, whereas natural and regenerated microfibres were more frequent, with fibres representing the dominant morphological category. Most particles were transparent and exhibited fluorescence under UV light. Likely sources of contamination in the study area include atmospheric deposition, local anthropogenic activities, road networks, and waste dispersal. These results provide clear evidence that anthropogenic microparticles are present even in remote karstic caves, posing potential risks to subterranean biota and groundwater resources. Given the intrinsic connectivity of karst systems, there is an urgent need for systematic monitoring and protection. We also emphasize the key role of speleologists in contributing to data collection during explorations, as such rarely studied habitats can provide critical insights into pollutant pathways, ecosystem vulnerability, and conservation priorities. Future long-term research will be essential to elucidate sources, transport mechanisms, and ecological impacts of these contaminants.