Geographical distribution of plastic items in the mountains of Lombardy region–Northern Italy

Mountain environments are becoming receptacles for plastic pollution due to the increasing use and improper disposal of plastic products. However, data on plastic occurrence in mountain ecosystems remains scarce. This study fills this gap by providing an assessment of plastic waste distribution in high-altitude landscapes. We collected plastic items (both mesoplastics and macroplastics) along 28 transects in the Alps and Prealps of Lombardy - Northern Italy. Items were classified by weight, size, original use, and polymer composition. GPS coordinates of plastic item positions were recorded along 21 of these transects. Plastic items (979 overall) were found along all the transects. On average (± standard error), 34.96 ± 5.10 plastic items per transect were found, corresponding to 24.30 ± 37.29 g km<sup>-1</sup>. Polypropylene (24.92 %), polyethylene (15.71 %), and polyvinyl chloride (10.83 %) were the most abundant polymers, while food packaging (31 %), mountain clothes (5 %), health care (5 %), and mountain equipment (4 %) were the most represented original uses. In-situ abandonment seems, therefore, the predominant source of plastic waste along mountain paths. Plastic distribution seems not related to the presence of mountain refuges (i.e., staffed mountain structures), altitude, geographical position, or frequentation of the transects (assessed using STRAVA tracks). However, the mean number of items decreased from the start to the end of the transects, with most items found in the first km. Straightforward policies, such as placing recycling bins at the start of mountain paths, promoting portable trash cans for backpackers, and conducting awareness campaigns against plastic abandonment, could effectively reduce plastic dispersion in mountain areas.