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Complex Mixture of Contaminants Persists in Streams Miles from the Source

USGS scientist collecting a water sample from Boulder Creek, Colardo
A USGS scientist collecting a water-quality sample from Boulder Creek, Colorado. The scientist is following a set of protocols to ensure the water sample is representative of all the water flowing down the creek at sampling station. Photo credit: Jennifer Beck, USGS.

The Complex Mixture

Overall, there were 73 organic chemicals detected in the effluent from the Boulder, Colorado, wastewater treatment plant (WWTP) and 56 chemicals detected in Boulder Creek stream water below the WWTP discharge point. There were 98 organic chemicals detected in the effluent from the Ankeny, Iowa, WWTP and 71 chemicals detected in Fourmile Creek below the WWTP discharge point.

The mixtures contained metal complexing agents, detergent degradation products, personal care products, pharmaceuticals, steroidal hormones, pesticides, and other compounds. The highest concentration compounds (greater than 100 micrograms per liter) detected in both WWTP effluents were ethylenediaminetetraacetic acid (EDTA – a metal complexing agent) and 4- nonylphenolethoxycarboxylate (a detergent degradation product).

Concentrations of pharmaceuticals were lower (less than 1 microgram per liter), and several compounds, including carbamazepine (a drug used to control seizures) and sulfamethoxazole (an antibiotic), were detected throughout sections of the two streams that were studied.

Natural processes in stream ecosystems such as dilution and microbial degradation are known to attenuate some contaminants to below levels that can cause harm to ecosystems. However, a team of U.S. Geological Survey (USGS) scientists has shown that many chemicals discharged from municipal wastewater treatment facilities persist for miles downstream at levels known, or suspected, to cause adverse health impacts to aquatic organisms—including endocrine disruption in fish. The study also showed that these persistent chemicals occur in complex mixtures with unknown ecological consequences.

The results, published in Environmental Science and Technology, are part of a long-term study of the fate, transport, and ecological effects of the wastewater discharged into two streams (Boulder Creek, Colorado, and Fourmile Creek, Iowa) from municipal wastewater treatment plants. In a unique field application, the scientists used a sampling approach that involved multiple locations along the streams (Lagrangian) to ensure water samples and chemistry were representative of a parcel of water as it flowed downstream from the point of wastewater discharge. Many of the contaminants from the complex mixture of multiple types of chemicals (see text box) showed little decrease in concentration, other than that due to dilution, as they flowed down the approximately 6- to 8-mile segments of the streams studied. Importantly, some of these contaminants persisted at concentrations that are known, or suspected, to cause sublethal health effects to exposed organisms. Furthermore, several chemicals in the complex mixtures identified in this study are steroidal hormones and/or other chemicals that mimic estrogen, which could have additive health effects. The ecological consequences of the complex contaminant mixtures the scientists identified are poorly understood.

This study was funded by the USGS Toxic Substances Hydrology Program and Hydrologic Research and Development Program. Additional support was received by the U.S. Environmental Protection Agency.


Barber, L.B., Keefe, S.H., Brown, G.K., Furlong, E.T., Gray, J.L., Kolpin, D.W., Meyer, M.T., Sandstrom, M.W., and Zaugg, S.D., 2013, Persistence and potential effects of complex organic contaminant mixtures in wastewater-impacted streams: Environmental Science and Technology, v. 47, no. 5, p. 2177-2188, doi:10.1021/es303720g.

Barber, L.B., Antweiler, R.C., Flynn, J.L., Keefe, S.H., Kolpin, D.W., Roth, D.A., Schnoebelen, D.J., Taylor, H.E., and Verplanck, P.L., 2011, Lagrangian mass-flow investigations of inorganic contaminants in wastewater-impacted streams: Environmental Science and Technology, v. 45, no. 7, p. 2575-2583, doi:10.1021/es104138y.

Barber, L.B., Keefe, S.H., Kolpin, D.W., Schnoebelen, D.J., Flynn, J.L., Brown, G.K., Furlong, E.T., Gray, J.L., Glassmeyer, S.T., Meyer, M.T., Sandstrom, M.W., Taylor, H.E., and Zaugg, S.D., 2011, Lagrangian sampling of wastewater treatment plant discharges into Boulder Creek, Colorado and Fourmile Creek, Iowa during the summer of 2003 and spring of 2005--Hydrological and water-quality data: U.S. Geological Survey Open-File Report 2011-1054, 84 p.

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