Microplastic Presence in the Río Bravo/Grande Along the Ciudad Juárez, Chihuahua, Mexico–El Paso, Texas, United States of America Metroplex

Microplastics (MPs) have been detected in aquatic environments worldwide; however, freshwater systems remain underexplored. MPs’ presence has not been reported yet in the Río Bravo/Grande at the Mexico–United States border. In 2022 and 2023, water (30 L) and sediment (~500 g) samples were collected at the river along the El Paso (U.S.)–Juárez (Mexico) municipalities. Water and sediment were digested using H2O2 or NaOH to isolate (CaCl2), dye (Nile Red), quantify, and classify MPs by fluorescence microscopy. The number of microparticles detected in water and sediment ranged from 0.4 to 17 particles/L and 2.8 × 103–1.0 × 104 particles/kg, respectively. Similar concentrations of microparticles were estimated in water among sampled sites (ANOVA) in 2022 (p = 0.432, α = 0.05) and 2023 (p = 0.255, α = 0.05), but there were differences in sediments (2022, p < 0.01; 2023, p = 0.032. α = 0.05). Fibres, fragments, and films, with sizes ranging from 12.62 to 4282.25 µm, were found in the samples. Fibres were the most abundant shape in water (71.94%) and sediments (91.07%). MP concentrations varied in water and sediments in both years. The data generated by this study provide new insights into feasible methods for MP detection and its presence in the Río Bravo/Grande.