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Assessing Environmental Chemical Mixtures in United States Streams

USGS Scientist collecting water samples in a stream
USGS scientist collects water samples and measures stream-water field parameters at North Sylamore Creek, Arkansas, on January 7, 2014. About 60 sample bottles are filled and shipped to USGS and U.S. Environmental Protection Agency laboratories across the Nation for chemical and biological analysis. Photograph taken by John Tyler Mays, USGS.

The U.S. Geological Survey (USGS) and the U.S. Environmental Protection Agency (EPA) are collaborating on a field-based study of chemical mixture composition and environmental effects in stream waters affected by a wide range of human activities and contaminant sources.

Scientists sampled 38 streams spanning 24 States and Puerto Rico. Thirty-four of the sites were located in watersheds impacted by multiple contaminant sources, including industrial and municipal wastewater discharges, crop and animal agricultural runoff, urban runoff, and other point and nonpoint contaminant sources. The remaining sites were minimally developed reference watersheds.

Collected samples are undergoing comprehensive chemical and biological characterization, including sensitive and specific direct analysis for over 700 dissolved organic and inorganic chemicals and field parameters, identification of unknown contaminants (environmental forensics), and a variety of screening bioassays to evaluate biological activity and toxicity.

Assessment and management of the risks of exposure to complex chemical mixtures in streams are priorities for human and environmental health organizations around the world. The current lack of information on the composition and variability of environmental mixtures and a limited understanding of their combined effects are fundamental obstacles to timely identification and prevention of adverse human and ecological impacts of exposure to chemical mixtures.

When complete, the results of this collaborative study will help to address these issues. The results of the study will (1) document mixtures and concentrations of chemicals present in the environment, (2) help identify potential human and ecological exposures, (3) guide prioritization of toxicological studies of chemical mixtures, (4) provide insight into potential biological effects of multiple contaminants, (5) help relate biaoassay screening approaches to environmental chemical characterization in support of new monitoring strategies, and (6) provide data for models to predict chemical mixtures in watersheds affected by diverse land- and chemical-use patterns.

This study is supported by the USGS Toxic Substances Hydrology Program and the EPA Office of Research and Development.


Buxton, H.T., Reilly, T.J., Kuivila, K.M., Kolpin, D.W., Bradley, P.M., Villeneuve, D.L., and Mills, M.A., 2015, Chemical mixtures and environmental effects--A pilot study to assess ecological exposure and effects in streams: U.S. Geological Survey Open-File Report 2015-1113.

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