First Evidence of Pharmaceutical Residues in the Cerrón Grande Reservoir, El Salvador

This study presents a comprehensive evaluation and environmental risk assessment (ERA) of pharmaceutical residues in the Cerrón Grande Reservoir, one of the most important surface water bodies in El Salvador. Sampling campaigns were conducted over a one-year period, covering both the dry (January 2024) and rainy (July 2024) seasons. A total of 76 pharmaceutical compounds were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS), of which only five were not detected. During the dry season, the highest environmental concentrations were observed for mecamylamine (1710–6913 µg L−1), 1,7-dimethylxanthine (379–2829 µg L−1), chloroquine (2.29–362.7 µg L−1), and hydroxychloroquine (5.02–315.4 µg L−1). Concentrations generally decreased in the rainy season, with mecamylamine (1526–2198 µg L−1), 1,7-dimethylxanthine (0.018–0.55 µg L−1), and caffeine (0.2–0.474 µg L−1) remaining the most prevalent. Compounds exceeding 1 µg L−1 were assessed using predicted no-effect concentrations (PNEC) to calculate risk quotients (RQ). Chloroquine (RQ = 3346.3), mecamylamine (RQ = 1437.8), hydroxychloroquine (RQ = 1027.2), and manidipine (RQ = 271.0) posed the highest risks during the dry season, while only mecamylamine (RQ = 502.0) exceeded this threshold in the rainy season. To our knowledge, this represents the first in-depth study of pharmaceutical residues in Salvadoran surface waters, providing a foundational reference for future research and environmental policy in the region.