First report of microplastic presence in marine sediments from a shallow-water mud volcano (Northern Tyrrhenian Sea)

Microplastic (MP) pollution represents a worldwide problem, with plastic particles being documented across different environmental matrices and settings. The present study investigated MPs presence in marine sediments on and around a shallow-water mud volcano located offshore Scoglio d'Affrica islet (Northern Tyrrhenian Sea), a geologically active area, characterized by low anthropogenic pressure and far from terrestrial source of plastic pollution. Grain size analyses on sediment samples were carried out to evaluate potential relationships between MPs accumulation and sediment texture. The samples varied from sandy mud to sandy gravel, showing on average 33.7 (±16.9 standard deviation) items/kg of dry sediment, with fibers being the predominant shape of plastics identified. No statistically relevant differences among sampling sites and no significant correlation with sediment texture were found, although the absence of particles <0.1 mm, likely resulting from limitations in analytical detection, might have influenced results. Conversely, a positive trend was observed between MPs content and sampling depth. The presence of MPs on the summit of active mud volcanoes suggests a rapid sequestration of this contaminant from the water surface and water column in the seafloor compartment. These findings highlight the pervasiveness of plastic pollution problem even in nearly pristine settings and show the need for assessing MPs contamination across different geological settings and depth ranges, in order to deepen our knowledge on MPs presence and distribution within marine sediments, providing novel insights and hints for future research challenges.