Pharmaceutical residues in the drinking water supply: Modeling residue concentrations in surface waters of drugs prescribed in the United States

Pharmaceutical residues and other organic wastewater contaminants (OWC) have been shown to survive conventional water-treatment processes and persist in drinking water supplies.

To estimate the geographical distribution of the Predicted Environmental Concentration (PEC) of selected drugs prescribed by office based physicians in the United States (US), after non-metabolized residues have been excreted and processed in wastewater treatment plants.

The geographical distribution of the PEC of pharmaceutical residues in surface waters was calculated, in four regions of the US. Prescription drug data was obtained from the National Ambulatory Medical Care Survey, a representative sample of office based physicians in the US. The PEC of Metformin, Cimetidine and Ranitidine prescribed by office based physicians in the US between 1998 and 2000 was compared to the concentrations of these pharmaceuticals estimated in a surface water characterization project conducted by the United States Geological Survey between 1999 and 2000.

There were 803,185,420 medications prescribed by office-based physicians in the US between 1998 and 2000. Relief of pain, hormonal, cardiovascular and antimicrobial medications were the top four drug classes prescribed, most of which prescribed in the Southern states where the largest concentrations of African Americans reside. The concentration of Metformin estimated by USGS in surface waters was correlated to the PEC of Metformin prescribed by office-based physicians, albeit not significantly.

The PEC may be a useful tool to predict the concentration of pharmaceutical residues in surface waters for those pharmaceuticals not characterized in surface waters. The geographic disparity in pharmaceutical prescriptions also merits further attention.