GROUNDWATER: AN ENDANGERED INVISIBLE RESOURCE. MICROPLASTIC POLLUTION IN UNDERGROUND KARST SYSTEMS FROM SURFACE WATERCOURSES TO CAVE WATERS

Microplastic pollution is a global problem, however, in karst systems is still poorly known [1], especially in underground environments and aquifers, despite groundwater in karst aquifers constitutes about a quarter of the global drinking water sources. We investigated different water samples from a karst area of NW Italy, considering connected surface and underground waters. Spot sampling were carried out in one superficial tributary, in the underground collector of the Bossea cave, and in the riverbed of the Corsaglia stream, where the waters of the collector emerge. Microplastics were extracted from water by filtration and subjected to organic matter removal [2]. Filters were observed with and without UV light under a microscope and microplastics were characterized according to shape, colour, and size, with visual identification. Finally, spectroscopic analysis were carried out on 10% of the microplastics observed on each filter. The observed concentration of microplastics in the water of the tributary is of 23 items/L, in cave water varied from 12 to 54 items/L, while in the Corsaglia stream is of 29 items/L. Fibres represented the most abundant shape (95.1%) and most of microplastics were smaller than 1 mm (82.9%). The highest microplastic abundance was fluorescent under UV light (77.4%). Most fluorescent particles were transparent (46%), whereas black microplastics (68%) were more common for the nonfluorescent ones. Polyethylene (51.7%) and Polyvinyl alcohol (37.9%) are the main types of microplastics found. Our results highlight the presence of microplastics in karst water systems, from superficial waters to underground one, and provide useful information for evaluating the environmental risks posed by microplastics in karst waters. It must be considered that karst aquifers are open systems, even susceptible to contamination by surface pollutants, and therefore, the superficial areas must be monitored too. Karst areas conservation should become a priority for the management of water resources.