Microplastic ingestion is ubiquitous in threatened stingrays from the Amazon estuary

Microplastic pollution has become pervasive across freshwater ecosystems worldwide, including the Amazon Basin, where increasing levels of plastic contamination have been reported. Despite growing evidence of microplastic (MP) ingestion in aquatic organisms, studies focusing on threatened species remain extremely scarce, particularly for estuarine elasmobranchs. Rays present high extinction risk among vertebrates and in majority are apex predators, which enhance direct interaction with MPs. The present study investigated, for the first time, MPs ingestion by threatened stingray species from the Amazon Estuary, assessing particles' occurrence and characteristics. Twelve individuals belonging to four elasmobranch species, incidentally caught by artisanal fisheries in Marajó Bay, were examined. Microplastics were detected in all specimens, totaling 181 particles. Fibers predominated (97%), followed by fragments (3%), with black (30.9%) and blue (30.4%) being the most frequent colors. Raman spectroscopy identified Polyester and Polyamide (Nylon) as the dominant polymers (25% each), followed by Polyethylene, Polypropylene, and Polyurethane (16.7% each), a polymer composition consistent with the major anthropogenic plastic previously reported in the Amazon Basin. Although ingestion levels varied considerably among individuals and species, contamination was ubiquitous. This study provides the first record of microplastic occurrence for the stingray species investigated, expanding current knowledge of plastic exposure in threatened Amazonian elasmobranchs. By establishing a baseline for future monitoring, our findings support the incorporation of plastic pollution into conservation assessments of threatened freshwater and estuarine rays.