Wednesday, July 25, 2012 - The reuse of treated wastewater can be a valuable resource in arid regions around the world, with water being reclaimed for irrigation, surface release, and groundwater recharge. But some contaminants in wastewater are being identified as health problems--especially pharmaceutically active compounds (PhACs). Now, new research offers a better understanding of the conditions under which these potentially harmful compounds accumulate and degrade over time in the soil.

Two USDA-ARS scientists from the U.S. Arid-Land Agricultural Research Center (ALARC) studied soils from a groundwater recharge basin in Gilbert, Arizona. American Society of Agronomy and Soil Science Society of America Member, Clinton Williams, and American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America Member, J.E.T. McLain, targeted their research on ibuprofen, caffeine, carbamazepine, and lincomycin.

One of the consequences discovered from exposure to these compounds is antibiotic resistance. Colonies of bacteria exposed to PhACs in nature can develop into resistant strains over time, leading possibly to infections in people that requiring more expensive and toxic medication. PhACs have also been linked to endocrine disruption in humans, affecting hormone glands regulating reproductive growth, metabolism, and other essential body functions. And while several past studies focused on PhACs in streams, rivers, and irrigated systems, there's little research regarding their accumulation in the soil of groundwater recharge systems.

This study, which is set to appear in the September-October issue of the Journal of Environmental Quality, tracks three years of soil samples taken from a Gilbert, Arizona recharge basin that uses a recharge method known as soil aquifer treatment (SAT). Williams and McLain examined the accumulation rates of PhACs to determine the long-term sustainability of the SAT system for removing contaminants.

The anti-inflammatory compound ibuprofen was measured as below detection limits in all samples. Lincomycin, an antibiotic, showed no net accumulation over the three-year study, but had significantly higher concentrations closest to the surface. And the stimulant caffeine exhibited net accumulation throughout the study, with its greatest concentrations also near the surface.

Finally, carbamazepine is a drug used to treat epilepsy and bipolar disorders. It showed accumulation over the course of the study similar to caffeine, yet had the lowest concentration of the four compounds at a depth of 0 to 5 cm. “You can look, and you can find these compounds everywhere at very low concentrations. But I’m mostly interested in what we saw happen with carbamazepine,” says Williams. “There’s something going on at the surface and that’s what I want to figure out.”

Understanding the low carbamazepine concentrations at the soil surface holds the answers to processes responsible for degrading PhACs leftover from wastewater. This could allow scientists to further increase the sustainability of wastewater reuse for groundwater recharge purposes, a crucial development for meeting future water demands, while at the same time, protecting human health.