Unveiling the levant basin as a unique sink for plastic bags and packaging through comprehensive multi-marker analysis

Plastic litter is ubiquitously distributed across the seafloor, yet the transport trajectories and settling mechanisms of such debris remain poorly defined. In this study, we conducted a comprehensive analysis of seabed litter collected via bottom trawls at depths ranging from 80 to 1300 m in the southeastern Mediterranean Sea, an oligotrophic marine system. Our results revealed one of the highest global concentrations of deep-sea plastic litter (up to 3321 ± 12 items/km²), with plastic bags and packaging (PBPs) comprising over 91 % of total items. In contrast, near-shore areas exhibited lower plastic densities (222 ± 73 items/km²) and a reduced PBPs proportion (76.6 ± 8.2 %). The PBPs displayed heterogeneous distributions between the continental shelf and deep basin in the composition, shape, polymer type, and surface attachment. Additionally, calcium carbonate additives, found in nearly one-third of shelf polyethylene bags, were largely absent in the bathyal plain, suggesting their role as ballast impacting trajectory. Although 86.5 % of the PBPs exhibited relatively low levels of surface attachment (<3 μg/mm²), both organic and inorganic adhesion (e.g., biofouling, tar, sediments, shells) appeared play a pivotal role in their settlement and distribution. Notably, biofilm accumulation appeared to facilitate further inorganic adhesion, particularly at greater depths. By integrating physical, chemical, and biological characteristics, this study provides novel insights into the compositional variability and dispersal dynamics of plastic litter in deep-sea environments, offering a framework to better understand plastic accumulation in oligotrophic marine systems like the southeastern Mediterranean Sea.