Occurrence and concentration variability of pharmaceuticals, pesticides, and polyphenols in Nyabugogo River, Rwanda.

Pharmaceuticals, pesticides, and polyphenols are increasingly detected in aquatic environments, impacting water quality and aquatic life. This study screened these contaminants in Rwanda's Nyabugogo River, analysing 45 water samples from rural, peri-urban, and urban areas using solid-phase extraction and LC-MS/MS. Fifty-seven pharmaceuticals, five pesticides, and four polyphenols were quantified, with the highest average concentrations of albendazole (960 ng/L), metalaxyl (70 ng/L), and caffeic acid (49 ng/L). Pharmaceutical levels were significantly higher in urban areas, reflecting inadequate sanitation and wastewater management in Kigali, while pesticide and polyphenol concentrations varied across different types of land use, influenced by agricultural and urban discharges. Temporal sampling revealed significant within-day concentration fluctuations but consistent day-to-day levels, indicating persistent contamination sources. These findings provide essential baseline data for monitoring organic pollutants and informing strategies to mitigate contamination in urban river systems.