Fate of pharmaceuticals in a spray-irrigation system: From wastewater to groundwater

Land application of wastewater effluent is beneficial for recharging groundwater aquifers and avoiding direct pollutant discharges to surface waters. However, the fate of non-regulated organic wastewater pollutants, such as pharmaceuticals and personal care products (PPCPs), in such wastewater reuse systems is understudied. Here, a 14-month study (October 2016 through December 2017) was conducted to evaluate the fate and potential risks of seven commonly used PPCPs in a local wastewater treatment plant (WWTP) and from 13 groundwater monitoring wells at a spray-irrigation site where effluent has been spray-irrigated since the early 1980s. Acetaminophen and trimethoprim were the most frequently detected (93%) PPCPs in WWTP influent, while in the effluent, caffeine and trimethoprim were detected most frequently (70%). Wastewater treatment generally reduced concentrations of acetaminophen and caffeine by >88%; however, some compounds had low removal or were present at higher concentrations in the effluent compared with influent (e.g. naproxen, sulfamethoxazole, trimethoprim and ofloxacin). Seasonal trends were observed, with higher PPCP concentrations in the WWTP influent and effluent in the winter. Risk calculations conducted on the wastewater effluent suggest that the risk posed by PPCPs that persisted in the effluent are medium to high to aquatic organisms. Detection frequencies of PPCPs were lower in groundwater samples compared to the effluent, with sulfamethoxazole (40%) and caffeine (32%) as the most frequently detected compounds. Similarly, average concentrations of PPCPs in groundwater were found to be nearly two orders of magnitude lower than concentrations in the effluent. Minimal seasonal influence was observed for groundwater samples. Human health risk assessments indicate that concentrations in groundwater, which is used as a drinking water source, appear to pose minimal risk.