Plastic abundance and seasonal variation on the shorelines of three volcanic lakes in Central Italy: can amphipods help detect contamination?

Despite the exponential increase of studies on plastic debris in recent years, there are still few works focusing on the problem as it relates to inland waters: little is known about the accumulation and dispersion dynamics on lake shores, and there are no standardized sampling methods for monitoring purposes. The accumulation of plastic litter in natural habitats also threatens the resident organisms. In this paper, we investigated the abundance and accumulation of plastic particles, ranging in size from 1 to 50 mm, from the beach sediment of three volcanic lakes in Central Italy: Albano, Bracciano, and Vico. The collection was designed to define the most important variables that one must consider in order to obtain a representative sample of plastic litter in a lake environment. In view of the high heterogeneity of sampling protocols used, comparison among the obtained results is limited and sometimes impossible. By using one of the proposed sampling methodologies, and critically analyzing the results, we aimed to highlight a possible monitoring criterion and to identify specific elements that can be meaningful and representative. The samples were collected in May and September 2017. For each lake, we sampled plastic items and sediments from two beaches. Albano contained the largest amount of plastic (in weight), while Bracciano had the largest number of particles. Our observations lead us to infer that the number of particles is the parameter most sensitive to environmental variations, as well as the more suitable for monitoring with greater definition the differences between sites. Moreover, sampling should be taken in different seasons, following a sampling pattern that includes at least two beaches placed in strategic positions with respect to wind and waves. In order to identify new indicators to evaluate the entry points of plastic into the food web, we collected, from the same sites analyzed, some specimens of the Talitrid Amphipod Cryptorchestia garbinii, a detritivorous species having a critical role in debris turnover of these environments. To investigate the microplastic (MP) ingestion in natural conditions, we analyzed their digestive tracts with both Nile red staining method and micro-FTIR spectroscopy. The analyses confirmed that C. garbinii was able to ingest plastics in natural conditions. Therefore, it can signify one of the entry points for microplastics (MPs) in the trophic chain. This observation constitutes the first evidence of MP ingestion in this species.