Environmental implications of biofouling on plastic debris in the multifunction port of Genoa (Italy)

Port environments are significant accumulation zones for plastic debris, critical for understanding interactions among plastic and marine ecological processes. Biofouling, the growth of organisms on submerged surfaces, crucially influences the fate and ecological effects of plastic litter. Two seasonal field experiments (late spring-summer and late autumn-winter) investigated the initial biofouling accrual on polyethylene terephthalate (PET), surgical and FFP2 masks, representing common and emerging pollutants. Distinct seasonal and substrate-specific patterns were revealed: summer deployments showed a more accelerated and extensive process (weight maxima reached after ca. 2.5 months in summer vs progressive increases for 4 months in winter, reaching values 3–3.5 times lower). Micro- and macro-fouling exhibited complex interplay, linked by trophic, spatial and mechanical relationships. Among tested materials, FFP2 masks consistently accumulated the greatest net weight across both seasons (maximum 14 g item−1 vs 8 g item−1 for PET in summer, 4 g item−1 vs 2 g item−1 for PET in winter). Biofouling caused FFP2 masks to lose positive buoyancy (maximum sinking velocity 3.8 cm s−1) and increased sinking velocity of PET (maximum 3.5 cm s−1) and surgical masks (maximum 2.7 cm s−1). This effect was due to inorganic matter accumulation in summer, largely from calcareous macrofoulers, and to organic matter and microbial biomass in winter. Furthermore, observed fish consumption of biofouled surgical masks indicated a concerning pathway for trophic transfer of plastics. Taxonomic composition confirms the critical role of plastics as species vectors. These results underscored the complex nature of plastic pollution and the necessity for integrated mitigation efforts.