Occurence of microplastics in water, sediment, and fish in high-mountain lakes from Alps

Microplastics (MPs) have been found in remote ecosystems such as the Arctic polar regions, high-mountain lakes, and glaciers via atmospheric transport and deposition. Due to their low density, MPs are lifted by wind currents into the upper layers of the atmosphere and then deposited by snowfall or rainfall in high-mountain ecosystems. Recently, it was proposed the use of high-mountain lakes as indicators of MPs pollution. With this study we wanted to determine whether MPs can be found only in abiotic compartments (water and sediment) or also in aquatic organisms such fish (Salvelinus fontinalis). The study site was two high mountain lakes (Upper and Lower Lake Balma) located in the western Alps (Italy). No MPs were found in water samples, whereas the mean MPs in sediment samples was 1.33 ± 0.67 items/m3 and 1.75 ± 0.62 items/m3 in Lower and Upper Lake Balma, respectively. The mean number of MPs items found in the gastrointestinal tract (GIT) of fish was considerably higher in specimens from the Lower (0.45 items/g GIT) than in those from the Upper Lake (0.20 items/g GIT). There was a negative relationship between fish size (weight and age) and MPs abundance in the GIT of fish, indicating that young fish accumulated more MP items probably due to the high prey ingestion rate compared to adults. The same MPs color (blue, white, black), shape (fibers and fragments), and chemical type (polypropylene and polyethylene) were found in both sediment and fish of both lakes. Our findings suggest the use of S. fontinalis as an indicator of MP pollution in high-mountain lakes. Further studies are needed to better understand the sources and the effects of MPs in these remote ecosystems.