Pharmaceutical Residuals as Tracers to Distinguish Septic- from Fertilizer-Derived Nutrients in Groundwater

In any given developed, non-agricultural, unsewered area, septic systems and fertilizer application (to lawns and gardens) represent two major sources of nutrients to groundwater. We propose to distinguish between these two possible sources by analyzing groundwater samples for pharmaceutical residuals (e.g., relatively persistent ones such as bupropion, clofibric acid, carbamazepine, citalopram, diclofenac, primidone, venlafaxine, etc.) since fertilizers do not contain any of these pharmaceuticals but domestic wastewater could. Groundwater samples were taken through piezometers at an unsewered area in Northport Bay and a sewered area in Manhasset Bay, both in western Long Island Sound where excessive nitrogen loading has led to reduced dissolved oxygen concentrations, and where the groundwater contribution to the nitrogen budget is very poorly constrained. Groundwater samples were filtered through GF/F filters, extracted with C-18 solid phase extraction discs, and analyzed using liquid chromatography-tandem mass spectrometry. Preliminary results from a small set of the samples indicated the presence of trace amount of pharmaceutical residuals (e.g., clofibric acid and diclofenac) in the groundwater of the unsewered area but not in the groundwater of the sewered area. More analyses are being done to further assess the utility of pharmaceutical residuals as tracers for different nutrient sources.