Potential ecological risk from microplastics and additives in the environment and mangrove-associated oysters: The case of a Ramsar coastal lagoon in the Gulf of Mexico

Microplastic pollution is an emerging environmental concern. Microplastics (MPs), in addition to polymers, contain additives, intended to enhance plastic properties. Ecological risk assessments of MPs, usually consider only the polymers. In this study, we advance MPs' risk analysis by incorporating additives into ecological risk indices. Since some additives pose high hazard scores, their inclusion can increase the estimated values of the MPs-induced risk index (H) and the Potential Ecological Risk Index (PERI), thereby providing a more comprehensive and realistic evaluation of MPs' ecological risks. The Tampamachoco Estuarine-Lagoon System (Gulf of Mexico) faces multiple human-related stressors that contribute to plastic pollution. We evaluated the abundance, spatial distribution, and ecological risk indices of MPs in surface water, mid-water, sediment, and oysters (farmed and wild) during dry and rainy seasons. MPs and additives were extracted: from water by direct filtration; from sediments using ZnCl 2 (density suspension ρ ≈ 1.6 g/cm³) and filtration; and from oyster tissue by H 2 O 2 digestion and filtration. We used µFTIR analysis to identify the polymers and additives. The average MP concentration was oysters > sediment > mid-water > surface water in both seasons. In oysters, MP load was higher in the dry season (4.73 ± 1.08 MPs/gww) than in the rainy season (1.22 ± 0.31 MPs/gww) (p < 0.05). Eleven kinds of plastic were identified, including additives. The Pollution Load Index (PLI) across all seasons and matrices indicated a minor risk (<10). In contrast, the H index revealed extreme danger risks (>1000), while PERI ranged from minor to medium (oysters), high (sediment), to extreme danger (surface and mid-water).