Warning signal from the Dead Sea: Plastic pollution at the deepest hypersaline lake

Plastics are recognized as persistent pollutants, yet their accumulation and degradation remain poorly constrained in most environments. A key difficulty is that rivers transport plastics into waterbodies where they are dispersed, obscuring temporal patterns of deposition. Identifying archives that preserve plastics through time is therefore critical for understanding both the history and future trajectory of pollution. The Dead Sea provides such an archive: hypersaline, high-density waters and rapid lake-level decline trap floating plastics along retreating shorelines, offering a unique natural setting to study plastic accumulation and weathering. This study reconstructs a two-decade history of macro- and microplastic deposition along the Kidron Valley outlet, which drains urban Jerusalem into the Dead Sea. Macroplastic loads, microplastic abundance, and chemical weathering were quantified on sequential beach terraces using field surveys and infrared spectroscopy. Identifiable macroplastics (single-use items and toys) were abundant and well-preserved on lower, younger terraces but fragmented on older, higher ones. Microplastics of varied shapes and colors matched this pattern, with PP and PE dominating (>90 %) and local minerals in weathered plastics. Terraces formed before 2000 lacked plastics, highlighting waste mismanagement. Sun exposure under hyper-arid conditions promoted surface oxidation (R-OH, CO, C-O), accelerating fragmentation-each kilogram of macroplastics generated ∼4000 microplastics annually. Accumulations were patchy but significant, with Nahal Kidron projected to deliver ∼1 ton by 2030. Beyond documenting a local pollution source, this archive demonstrates how urban plastic generation translates into accumulation in hyper-arid environments, providing a model for quantifying plastic input, breakdown, and environmental impacts in similar regions globally.