Human pharmaceutical surface water pollution across urban gradients in the Buenos Aires Metropolitan Region,...

Human active pharmaceutical ingredients (HAPIs) are micropollutants of emerging concern for aquatic ecosystems. Adequate access to health systems combined with poor sewerage connectivity and inadequate wastewater treatment plants has placed developing countries among the most vulnerable scenarios regarding HAPI water pollution. However, field data to better understand this phenomenon is still insufficient for large metropolises of South America. This study aimed to evaluate, in two contrasting seasons of the year, the occurrence of 16 highly prescribed HAPIs in 26 sites distributed along urban gradients of seven watersheds of the Rio de la Plata estuary southern plain within the Buenos Aires Metropolitan Region. Owing to their average annual concentrations and frequencies, acetaminophen, ibuprofen, carbamazepine, atenolol, enalapril, metformin, and sildenafil were the dominant HAPIs. Total HAPI concentrations and numbers significantly increased as the watercourses ran into more intensely populated areas. Sampling sites within urban conglomerates receiving wastewater treatent plant discharge displayed higher HAPI concentrations and numbers, demonstrating the inefficacy of current plants in eliminating these substances. Sampling sites within urban conglomerates without official discharge also showed high HAPI concentrations and numbers, indicating "straight-piping" and septic tank leaks as significant pollution sources. Detecting some HAPIs in rural sites would indicate that other minor sources (e.g., veterinary uses or atmospheric deposition) are also contributing. Shifts in HAPI frequencies and concentrations around the overall medians were a better indicator of seasonal variations than the absolute values affected by hydrological conditions. This study enhances understanding of the relationship between urbanization and HAPI surface water pollution in a major metropolitan area of South America, offering valuable data for future HAPI aquatic ecological risk assessments in the region.