Forecasting the Transport and Fate of Pharmaceuticals in Coarse Grained Aquifers
The occurrence of trace quantities of pharmaceutically active compounds in both surface water and groundwater has been widely reported. Although these compounds are detected at low concentrations in the environment, information on the fate and transport of pharmaceuticals in natural systems is still limited. The long-term effects on organisms from exposure are not known. The recognition that human and veterinary pharmaceuticals present in waste streams persist in aquatic environments has raised human and ecosystem heath concerns. The over arching goals of this research are to describe and quantify key processes influencing the transport and fate of a selected group of pharmaceutical compounds in sediment and groundwater systems, and to evaluated the sorption and reaction process likely to impact specific compound behavior in coarse grained hydrogeologic settings. This research is a key component of an ongoing international effort to examine the fate and transport of a select group of pharmaceuticals identified as being persistent in groundwater. Laboratory and field evaluations are being conducted in a variety of groundwater settings: the Berlin sand and gravel aquifer, a Canadian sand rich aquifer, and a highly conductive fluvial sand, gravel, cobble and boulder aquifer of the Missoula Valley, in Montana, USA (the focus of this work). Six compounds commonly reported in groundwater were selected for evaluation: carbamazepine, caffeine, gemfibrozil, ibuprofen, naproxen and sulfamethoxazole. Within the course of the project additional compounds were added to the analyses: nicotine, cotinine, ecstasy, methylated ecstasy, and cocaine. Batch sorption experiments and column tests were used to compute aquifer material attenuation properties. River and groundwater samples were geochemically characterized using approaches developed by researchers at the University of Waterloo, Canada. Batch and column experiments provided retardation and degradation values for the Missoula sediments. Overall, two compounds, carbamazepine and sulfamethoxazole, had small retardation factors in the study site setting, supporting observed behavior in other systems. The polar negative compounds under investigation, ibuprofen, naproxen, and gemfibrozil, behaved similarly with low but recognizable retardation in the presence of fine sediment. The transport of caffeine was affected by degradation while MDA (ecstasy) and MDMA (methylated ecstasy) were observed to be largely retarded. Sampling of native Missoula aquifer groundwater near the water table identified the sporadic occurrence of sulfamethoxazole and carbamazepine. Sampling of large yield municipal well found very low concentrations of sulfamethoxazole and atrazine. The likely source is the municipal sewage system in the case of sulfamethoxazole and weed control in the case of atrazine. This work suggests that in coarse grained unconfined aquifers with rapid groundwater flow, low levels of some pharmaceutical compound can be present, especially carbamazepine and sulfamethoxazole. Other compounds are likely to degrade or sorb to sediments and are not anticipated to be present in underlying groundwater systems. Future research should include detailed numerical transport simulations and vadose zone lab work to determine how an unsaturated sediment environment impacts transport.
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