Falling from the ceiling: first evidence of microplastic and microfibre pollution in cave dripping waters

Microplastic (MP) pollution is a global environmental concern. Recent works highlighted the need to consider even natural and regenerated microfibres (MFs). Despite their ecological and hydrological importance, karst systems remain understudied. Being open systems, karst underground environments are particularly vulnerable to contamination through the connections with surface habitats. For the first time, this preliminary research investigated the presence of MPs and other anthropogenic microparticles (AMPs), such as MFs, in cave dripping waters, highlighting the indirect impact of surface human activity. AMPs were counted and characterized via microscopy and spectroscopy. The 80.5% of the analyzed AMPs were cellulosic and 81.6% fibres. MPs ranged from 0 to 23 MP/L, confirming the presence of polyethylene terephthalate (PET) and polyurethane (PU), and were all fragments, except for one PET fibre. Microparticles < 1 mm were the most abundant (89.3%), of which the most had size between 0.49 and 0.10 mm (51.5%). Pollution sources in cave dripping waters could be linked to landfills in sinkholes, garbage, nearby roads, railways, and human activities. These results highlight MPs and other AMP pollution exists in cave dripping waters, impacting water resources, habitats and species. More comprehensive and multidisciplinary monitoring are needed, taking into account surface and subterranean connections in karst areas, aiming at conservation purposes. Promoting collaborations with show caves and cavers can be instrumental in pilot studies, and acquiring new and valuable data.