An integrating approach to optimal characterization and quantification of mesoplastics in aquatic ecosystems: the...

The first comprehensive assessment of mesoplastic (2-25 mm) pollution was conducted in the sediments of Sebkha Sijoumi, a crucial Tunisian ecosystem. Twenty surface sediment samples were collected and analyzed using an optimized rigorous protocol involving density separation and granulometric sieving. The optimized analytical protocol was a sequential, multi-stage process designed for maximal recovery and high-resolution characterization of mesoplastics. The recovered particles then underwent a rigorous, high-resolution granulometric analysis via a cascade of standardized sieves (2 to 25 mm), enabling precise particle size distribution profiling. The results revealed highly heterogeneous contamination, with concentrations ranging from 4 to 135 particles/100 g dry sediment. A severe pollution hotspot was identified (Sample S5), indicating intense point-source input, whereas the median concentration (11 particles/100 g) suggested a baseline level consistent with other Mediterranean transitional environments. Granulometric analysis showed a pronounced dominance of mid-sized fragments (4-10 mm), signaling an advanced stage of environmental aging and a "fragmentation bottleneck." Morphologically, fragments were dominant, followed by films and fibers, with a complete absence of industrial pellets. Chromatically, white particles were overwhelmingly dominant (66%), indicating photodegraded consumer plastics. Source apportionment identified paints (52%) and packaging (34%) as the primary contributors, with paint particles identified as a significant and underestimated source. This study underscores Sebkha Sijoumi's role as a reservoir for secondary mesoplastics generation and highlights the urgent need for targeted mitigation strategies focused on urban runoff and textile emissions. Analysis of the mesoplastics from Sebkha Sijoumi showed that they were primarily composed of acrylic resin and polyethylene (PE). These lightweight polymers degrade through photo-oxidation, releasing microplastics and toxic additives into sediments and water. This pollution is directly toxic to foundational species, while ingestion by birds and larger fauna causes internal damage and transfers pollutants up the food web, severely threatening the lagoon's already fragile ecosystem.