Microplastics in caves: A new threat in the most famous geo-heritage in the world. Analysis and comparison of Italian show caves deposits

Microplastic pollution represent a worldwide concern, however, in karst areas is still largely unknown, especially in underground environments. Caves are the most important geological heritage worldwide, rich in speleothems, unique ecosystems custodians of important drinking water reserves, and a significant economic resource. Thank to their relatively stable environmental conditions, they can preserve information for a long time such as paleontological/archaeological remains, however, these characteristics make caves vulnerable environments too, easily damaged by climate variations and pollution. To increase the current knowledge of microplastic pollution, the deposits of different Italian show caves were investigated, improving the method for microplastic separation. Microplastic were identified and characterised using MUPL automated software, observed with and without UV light under a microscope, and verified under μFTIR-ATR, highlighting the importance of combine different methods. Microplastics were present in sediments of all examined caves, and were always greater along the tourist route (an average of 4300 items/kg) than the speleological areas (an average of 2570 items/kg). Microplastics less than 1 mm dominated the samples and the amount increased with the decrease in the size considered. Fibre-shaped dominated the samples and 74% particles was fluorescent under UV light. Analysed sediment samples contained especially polyesters and polyolefins. Our results highlight the presence of microplastic pollution in show caves, giving useful information to assess risks posed by microplastics in show caves and emphasizing the importance of pollutants monitoring in underground environments to define strategies for the conservation and management of caves and natural resources.