The power of Posidonia oceanica meadows to retain microplastics and the consequences on associated macrofaunal benthic communities.

In the coastal environment, a large amount of microplastics (MPs) can accumulate in the sediments of seagrass beds. However, the potential impact these pollutants have on seagrasses and associated organisms is currently unknown. In this study, we investigated the differences in MPs abundance and composition (i.e., shape, colour and polymer type) in marine sediments collected at different depths (-5 m, -15 m, -20 m) at two sites characterized by the presence of Posidonia oceanica meadows and at one unvegetated site. In the vegetated sites, sediment samples were collected respectively above and below the upper and lower limits of the meadow (-5 m and -20 m), out of the P. oceanica meadow, and in the central portion of the meadow (-15 m). By focusing on the central part of the meadow, we investigated if the structural features (i.e. shoots density and leaf surface) can affect the amount of MPs retained within the underlying sediment and if these, in turn, can affect the associated benthic communities. Results showed that the number of MPs retained by P. oceanica meadows was higher than that found at the unvegetated site, showing also a different composition. In particular, at vegetated sites, we observed that MPs particles were more abundant within the meadow (at - 15 m), compared to the other depths, on unvegetated sediment, with a dominance of transparent fragments of polypropylene (PP). We observed that MPs entrapment by P. oceanica was accentuated by the higher shoots density, while the seagrass leaf surface did not appear to have any effect. Both the abundance and richness of macrofauna associated with P. oceanica rhizomes appear to be negatively influenced by the MPs abundance in the sediment. Overall, this study increases knowledge of the potential risks of MPs accumulation in important coastal habitats such as the Posidonia oceanica meadows.

Bioaccumulation of heavy metals in fish, crustaceans, molluscs and echinoderms from the Tuscany coast.

The concentration of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn were analyzed in the edible part of several species of fish, crustaceans, molluscs and echinoderms collected in sensitive areas of the Tuscany coast (northern Italy). The concentration of As (0.39-78.1 µg g-1) and Hg (0.01-1.56 µg g-1) resulted in most cases higher than reference thresholds. Target hazard quotient (THQ) and lifetime cancer risk (TR) indexes were calculated to assess cancer and non-cancer risk due to oral exposure; the highest THQ values referred to As and Hg, with values ≥ 1 in 39% and 48% of cases, respectively. Total target hazard quotients (TTHQ) values suggested that the local population could experience adverse health effects due to consumption of local seafood, mainly of demersal and benthic species. Cancer risk was mainly associated with As exposure, and with Cd intake, especially through molluscs consumption. The NMDS model highlighted species specific bioaccumulation processes and specific sensitivity of species to different bioavailable heavy metals. Specifically, Mullus spp. and Scorpaena porcus preferentially accumulate Hg and Cr, Octopus vulgaris specimens were discriminated by the presence of Pb and Zn, while an evident preference for Cd and Cu was recorded in Squilla mantis. In addition, the distribution of heavy metals in organisms revealed sound differences between Follonica and Livorno sampling sites, demonstrating a highly heterogeneous anthropogenic impact in terms of heavy metals input from the industrial activity resting on land.