Edwards Aquifer Urban Hydrology Network

Pharmaceuticals in the San Antonio Segment of the Edwards Aquifer

Summary of findings from Opsahl and Musgrove, 2023

The occurrence of emerging contaminants such as pharmaceutical compounds is a topic of growing concern for water resources. Pharmaceuticals are widely used for human and animals and have the potential to enter the environment. The occurrence of pharmaceutical compounds in surface water that recharges the Edwards aquifer can potentially affect groundwater quality. This study evaluated the occurrence and possible sources of pharmaceuticals in south-central Texas and the Edwards aquifer. The study utilized a “source-to-sink" approach that included samples collected from streams that provide recharge to the aquifer, unconfined groundwater, confined groundwater, and a major discharging spring (Comal Spring #1, an orifice of the Comal Springs complex) during 2018-20. An assortment of pharmaceutical compounds was detected at low concentrations at some surface-water sites, whereas detections were less frequent in groundwater and spring discharge.

Some key findings are:

For surface water:

• The two most commonly detected pharmaceuticals were the antidiabetic medication metformin, and caffeine, a stimulant found in a variety of products.
• Numerous pharmaceutical detections in the Frio River (a rural part of the region) (Figure 1A) and Leon Creek (an urban part of the region) (Figure 1B) indicate that pharmaceutical sources occur in both rural areas and urban areas.

• The near absence of wastewater treatment plant discharges and Texas Land Application Permit facilities (that is, facilities that dispose of treated wastewater by spray irrigation) might contribute to lower detections of pharmaceuticals relative to pesticides (Opsahl and others, 2018) in surface-water streams that provide recharge to the Edwards aquifer.

• The permitted discharge of treated wastewater into contributing zone streams potentially leads to the recharge of the shallow Edwards aquifer as the wastewater flows across the recharge zone.

For groundwater:

• Pharmaceutical compounds currently do not appear to substantially impair water quality in the shallow unconfined part of the Edwards aquifer. In contrast to surface water, few detections of pharmaceutical compounds occurred in groundwater samples (there were detections of a single pharmaceutical compound, the analgesic acetaminophen, at two groundwater sites).
• a modern recharge component to the deeper confined part of the aquifer might provide a potential pathway for introduction of contaminants, including pharmaceuticals, into the deeper aquifer.

In summary:

• The occurrence of pharmaceutical compounds in this study is likely primarily associated with various forms of wastewater or, in the case of the Frio River, potentially the direct excretion of pharmaceuticals into the river by recreationists.
• Although reported pharmaceutical concentrations for the San Antonio segment of the Edwards aquifer are currently low and detections are uncommon, ongoing development in the region has the potential to increase contaminant loads, including for pharmaceuticals. The results of this study provide a baseline for assessing future changes in pharmaceutical compounds in the Edwards aquifer.

Hydrogeologic setting and study site locations in the San Antonio segment of the Edwards aquifer, south-central Texas. Study locations are also available on the interactive map.

Continuous discharge or stage data and cumulative (sum of individual pharmaceutical concentrations) pharmaceutical concentrations for A, the Frio River and D, Leon Creek, south-central Texas, June 2018-August 2020.