Environmental Health - Toxic Substances Hydrology Program

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Endocrine Disrupting Chemicals in the Slick Scum that Covers Stones in Streams

USGS scientist, Jeffrey Writer, holding a stone that's covered with a biofilm
USGS scientist, Jeffrey Writer, holding a stone from Boulder Creek, Colo., that's covered with a biofilm. USGS scientists found that the biofilm that coats many of the stones on the bottom of the creek absorbs endocrine-disrupting compounds. Photo credit: Ronald C. Antweiler, USGS.

The slick scum or biofilm that covers most rocks in streams can accumulate contaminants that disrupt reproductive and other endocrine systems in fish. This is the finding of a team of U.S. Geological Survey (USGS) and University of Colorado Boulder scientists as described in a recent article in Environmental Science and Technology (Writer and others, 2011). Biofilms are a mixture of algae, microbes, and organic matter that grow on streambed material such as rocks and stones. The scientists determined that biofilms absorb endocrine disrupting chemicals faster than they can biodegrade them; therefore the chemicals accumulate. Since many fish and other aquatic animals feed on biofilms, the contaminants in biofilms have the potential to be transferred through the food web.

The study took place in Boulder Creek, Colorado. Boulder Creek is similar to many streams around the country in which wastewater contributes a substantial amount (10 to 80 percent) of the water to the stream. The scientists took samples of biofilms, streambed sediments, and water above and below the wastewater discharge outlet on Boulder Creek in hopes of defining the role of biofilms in controlling the movement of contaminants downstream. Previous studies have shown that wastewater contains a variety of contaminants including endocrine disrupting compounds, and that exposure to wastewater can cause endocrine disruption in fish. The scientists analyzed the samples for two classes of endocrine-disrupting chemicals—hormones (such as 17β-estradiol, estrone, and 17a-ethynylestradiol), and nonylphenols (detergent degradation products such as 4-nonylphenol, 4-nonylphenolmonoethoxylate, and 4-nonylphenoldiethoxylate). The scientists detected minimal levels of these compounds in biofilms in Boulder Creek upstream of the wastewater discharge. In contrast, many of the compounds downstream of the wastewater outlet were detected at much higher levels. It is interesting to note that many of the hormones were not detected in any of the water samples, both upstream and downstream, but were detected in the biofilms. This shows that the biofilms efficiently accumulate hormones from water and can play a major role in understanding the impact of these chemicals on aquatic organisms.

This study was funded by the USGS’s Toxic Substances Hydrology Program and National Research Program, and by the National Science Foundation (Grant No. CBET-0854527).


Writer, J.H., Barber, L.B., Ryan, J.N., and Bradley, P.M., 2011, Biodegradation and attenuation of steroidal hormones and alkylphenols by stream biofilms and sediments: Environmental Science and Technology, v. 45, no. 10, pp. 4370-4376, doi:10.1021/es2000134.

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