Occurrence and concentrations of pharmaceutical compounds in private wells in Central Pennsylvania

Over-the-counter and prescription medications are routinely present at detectable levels in surface and groundwater bodies. The presence of these emerging contaminants has raised both environmental and public health concerns, particularly when these water supplies are used as drinking water sources. However, the frequency of occurrence, range of concentrations, and potential health risks are not yet well understood, especially for groundwater supplies. We partnered with the Pennsylvania Master Well Owner Network to collect raw water samples from 26 households with private wells in the West Branch of the Susquehanna River Basin. All samples were analyzed for seven over-the-counter and prescription pharmaceuticals: Acetaminophen, ampicillin, caffeine, naproxen, ofloxacin, sulfamethoxazole, and trimethoprim. At least one compound was detected at all sites, with ofloxacin detected in 100% of samples while naproxen was not detected in any samples collected. Samples collected from the groundwater wells were compared to surface water samples collected from the West Branch of the Susquehanna River and were found to be higher in the groundwater during the same sampling period. A simple modeling approach based on the pharmaceuticals’ physicochemical parameters (half-life and retardation factor) was employed to provide insight into the differences in frequency of detection for the target pharmaceuticals. Additionally, risk calculations revealed that none of the concentrations observed in the groundwater wells posed any significant human health risk, with risk quotients well below the minimal risk value. However, the risk assessment does not address the potential effect of exposure to mixtures of pharmaceuticals that are likely present in water simultaneously.