Plastic pollution in the Red Sea: A comprehensive analysis from the air to the seafloor

Since the start of mass plastic production, plastic pollution of all shapes and sizes has become omnipresent across environmental compartments. Yet, its full scale, effect, and consequences have only recently begun to be addressed. Estimating plastic loads and revealing major sources are fundamental for implementing effective interventions and legally binding measures to reduce plastic pollution. The Red Sea, a semi-enclosed basin with distinctive geographical, oceanographic, and anthropogenic features, has previously shown a surprisingly low abundance of plastic in surface waters, and no correlation with coastal population. Recent findings suggest that the water column can store a substantial amount of microplastics, potentially creating a bias in global estimations derived from concentrations reported solely in surface waters. The first assessment of integrated water-column microplastic stocks (items m-2) in the eastern Red Sea highlighted the capacity of subsurface layers to act as a plastic reservoir rather than merely a transitional zone between “input” surface waters and ultimate sediment sink. Deep-sea sediments appeared to hold up to 80% of microplastic in the Red Sea, functioning as a major sink despite slow sedimentation rates. However, total microplastic loads estimated in the Red Sea remained relatively low, implying the presence of other sinks or distinctive distribution patterns across the basin. With the absence of rivers and a scattered coastal population, maritime traffic emerged as one of the major pollution sources, particularly along the central axis, as seafloor macrolitter densities increased with depth and distance from shore. The detection of paint flakes in the water column and sediment samples further implicated the significant influence of sea-based inputs in the region. By contrast, long-range atmospheric transport of airborne microplastics was found to be extremely low despite the large dust inputs in the region, however, its significance may differ in other, particularly northwestern, parts of the basin.