Concentrations and Mobility of Human Pharmaceuticals In the Worlds Largest Wastewater Irrigation System, Mexico City-Mezquital Valley

Knowledge of concentrations and retention of pharmaceutically active substances in environmental compartments is crucial for minimization of negative side-effects of medical treatment. We hypothesize that concentrations and retention of drugs in the Mexico City-Valle Mezquital wastewater irrigation system can be estimated using information on water consumption together with data of sales, excretion, and metabolic transformation of drugs. Thus, Environmental Introduction Concentrations (EICs) of Trimethoprim, Clarithromycin, Clindamycin, Erythromycin, Metoprolol, Naproxen, Ibuprofen, Diclofenac, Sulfasalazine, Bezafibrate, and Gemfibrozil were calculated and environmental concentrations were measured in wastewater, irrigation water, soil drainage, and springs by liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). EICs of Trimethoprim, Erythromycin, Naproxen, Ibuprofen, and Diclofenac equaled or exceeded the action limit of the U.S. Federal Drug Adminstration of 1 µg/L for detailed environmental risk assessment. Calculated EICs compared well to measured concentrations after refinement with excretion rates and metabolic transformation. Concentrations of basic compounds having positive or neutral charge were effectively reduced during reservoir storage and soil passage of wastewater. In contrast, acidic, anionic compounds were hardly retained in soils or reservoirs. However, none of the substances was detected in spring water, yet. Realistic environmental concentrations can be calculated for the Mexico City Metropolitan Area. Physicochemical data allow a prediction of drug mobility in the wastewater irrigation system.