Microplastic Contamination in the Eurasian Otter (Lutra lutra) as a sentinel of land use impacts in Central Italy.

Microplastic (MP) pollution poses a widespread threat to freshwater biodiversity. The Eurasian otter (Lutra lutra), an apex predator in freshwater ecosystems, is highly sensitive to anthropogenic pressures, such as pollution and habitat alteration and may be exposed to MPs through trophic transfer from contaminated preys. This study uses the Eurasian otter as a sentinel species to investigate MPs in their spraint within its recolonization area in Central Italy, where the species is currently expanding. We aimed to 1) explore the influence of land use variables, such as urbanization and agricultural activity on MP concentration and particle composition; and 2) compare MP concentration between main rivers and their tributaries to identify potential areas of increased exposure relevant to otter conservation. Suspected MPs were detected in 92.6% of the sampling stations, with a mean concentration of 14.91 suspected MPs g-1 of fecal dry weight. Blue and black fibers were dominant, while polystyrene and polyethylene were the most frequently identified polymers. Generalized Linear Mixed Models (GLMMs) indicated that higher suspected MP concentrations were associated with greater urban influence, and was higher in tributaries compared to main rivers, suggesting that smaller watercourses, which are often used by otters for nursery and feeding, may represent areas of increased MP of exposure for otters. Our results support the potential use of the Eurasian otter as a sentinel species for biomonitoring freshwater plastic pollution at the catchment scale. The occurrence of potentially hazardous polymers highlights the need for further ecotoxicological studies to determine whether MP exposure and associated contaminants may have implication for otter health.