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A new study has uncovered the Levant Basin as one of the world's most concentrated graveyards for plastic packaging and the mechanisms that help the plastic sink down to the seafloor.

The study, led by the Ph.D. student Xing-Yu Li and Prof Revital Bookman from the University of Haifa, and Dr. Yael Segal from Israel Oceanographic and Limnological Research (IOLR), was recently published in and shows for the first time how the southeastern Mediterranean's Levant Basin hosts some of the highest recorded deep-sea densities of plastic litter.

"We used trawls to survey the seafloor and we mainly found plastic bags and packaging that dominate the debris," says Xing-Yu Li, the leading author of the paper. "We were then curious to understand how the lightweight material, the plastic debris, are transported offshore and sink to the seafloor. We kept asking, what information can each recovered item really tell us?" continues Xing-yu, "and to answer that we used a multi-marker analysis.

"In the multi-marker approach, anything that is found on a piece of plastic is evidence. We extracted as much evidence as possible from every piece of waste, more than many previous studies, to build a fuller, more detailed view of the bottom waste."

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The multi-marker approach is a new framework that can link items such as the size, color, integrity, shape of the collected debris, polymer/additives (e.g., CaCO₃), and surface attachments (for example biofilm, tar, minerals) to buoyancy behavior and depth patterns across a large dataset.

This novel integrative approach takes the so far "counting" approach (i.e. counting the number of collected plastic debris) to a whole new level of mechanism-oriented evidence for tracing the debris source, offshore export and deep deposition of thin-film plastic packaging. It is the first time that research evaluated the buoyancy of microplastic collected from the deep sea.

Research findings reveal that the Levant Basin in the southeastern Mediterranean is a major global hotspot for plastic pollution, with extremely high seafloor concentrations of plastic bags and packaging. Furthermore, a "hot belt" of accumulation was found at the edge of the continental shelf (200 m), while the bathyal plain (>1000 m) acts as a final sink due to high pressure and sedimentation.

Plastic bags and packaging were mostly polyethylene, some containing CaCO₃ additives that sink closer to shore, while deeper basin plastics lacked such ballast and showed limited biofilm growth due to oligotrophic conditions. Instead, adhesion of sediments, shells, and especially tar enhanced their sinking and stability on the seabed.

Although many PBPs could regain buoyancy if disturbed, resuspension is limited, making the deep basin a unique repository for this waste. Sources include land-based inputs (notably Egypt, Israel, and Turkey) and in the deep basin shipping disposals. Fisheries contribute, surprisingly, little probably due to strict Israeli regulations.

"It's fascinating in the worst possible way," says Prof Bookman, "The eastern Mediterranean is quietly turning into a deep-sea landfill. Plastics that we use for only a few minutes are ending up trapped for centuries, threatening deep marine ecosystems we barely understand."

Dr. Segal says, "As the head of the national monitoring program, I see firsthand how plastic pollution is impacting the entire sea environment: beaches, water, sea bottom, and even local turtle populations."

According to the monitoring findings, plastic debris at the sea bottom is known worldwide, yet the mechanism was not known.

"For years, in our monitoring reports, we have reported a high concentration of plastic debris in this area. It was an unsolved mystery as we know that plastic debris should remain floating on the sea surface. Now we have a deep understanding of how it happens. The eastern Mediterranean is the most polluted area in the world, and we must take action for the sake of the next generation," says Dr. Segal.

While plastic packaging constitutes the majority of global plastic usage, there are emerging evidence that plastic films are transported offshore and ultimately accumulate at depth. As a result, they carry significant implications for the health of benthic habitats and for establishing accurate regional plastic mass balances. Furthermore, the observed interaction between plastic debris and tar residues may prompt a reassessment of the fate and transformation pathways of marine pollutants.

"This previously overlooked dynamic necessitates a broader perspective on pollution processes in marine environments," says Prof Bookman.

"Without systematic deep-sea accounting, we risk underestimating the true environmental footprint of plastic pollution and misallocating mitigation efforts by neglecting offshore and deep-sea sinks. In this context, coordinated basin-wide monitoring and management across countries that share the sea, including Egypt and Turkey, are essential for designing integrated strategies that address transboundary pollution and improve mitigation efficiency."