The introduction of drug residues into the food chain and their presence in drinking water has been recently investigated. The aim of this work was to monitor the presence of 19 active drugs in water samples collected from milking parlors of dairy farms located in Galicia (northwest Spain), one of the main Spanish milking areas. Overall, 65% of the samples tested positive for at least one of the compounds analyzed. A total of 12 drugs were measured, with concentrations ranging between 17 and 3,941 ng/L. Considering that a mixture of compounds may contribute to the overall effect of each compound and might increase or reduce its toxicity, it should be noted that 29% of the samples tested contained more than one pharmaceutical. To date, the effects of the continuous consumption of these mixtures of drugs in water or milk are unknown; however, antimicrobials may affect the human gut microbiota or have toxic effects in sensitive individuals.

Human urine is an abundant, renewable resource that can be used as a valuable source of fertilizer because it is rich in nitrogen, phosphorus and potassium. As fertilizers derived from urine become more widely used, it is important to understand how excreted pharmaceuticals are transported from urine to the environment. Many pharmaceuticals are excreted from the human body in their native form; therefore, when urine is used as a fertilizer, biologically active pharmaceuticals can be released into the environment. The goal of this study was to develop sensitive methods for the analysis of pharmaceuticals in urine, struvite, lysimeter water, soil, and food crops using liquid chromatography with tandem mass spectrometry (LC-MS/MS). The ability to detect low levels of pharmaceutical residues in various environmental matrices will aid in assessing the potential risks associated with the field application of urine that is used to fertilize croplands. The optimized method reported in this paper, which utilizes solid phase extraction for sample clean-up and pre-concentration, offers analyte recoveries ranging from 29 to 112 percent, and detection limits ranging from 0.89 ng L⁻¹ to 0.0047 μg g⁻¹. The optimized extraction method provides intra-day and inter-day reproducibility of less than 10% for all analytes in all matrices investigated, with the exception for ciprofloxacin in urine. The use of isotope dilution for quantification proved necessary to compensate for matrix effects, especially in urine where matrix effects can range from about 21% to 79%. Overall, the method described here is robust and widely applicable to various types of environmental samples.