Issue Date: May 3, 2011
Rock Slime Harbors Endocrine Disrupters
Pollutants that act like hormones flush into lakes and streams worldwide from farm runoff and treated sewage. Scientists worry about these compounds' presence in aquatic food webs because studies have connected them to feminized fish. Now, researchers report that endocrine-disrupting chemicals could accumulate in the brownish-green slimes called biofilms that coat stream and lake bottoms (Environ. Sci. Technol., DOI: 10.1021/es2000134). Their buildup there could make them a convenient meal for aquatic wildlife.
Endocrine-disrupting compounds (EDCs), such as pesticides, plasticizers, and synthetic hormones, mimic the action of natural hormones and can alter the development and behavior of wildlife. "Previous studies have looked for EDCs in the sediment and the water column but no one else has tracked them into biofilms," says Monika Jürgens, an environmental scientist at the U.K.'s Centre for Ecology & Hydrology, a government research lab.
Biofilms consist of 10% algae and 1% bacteria swimming in a rich matrix of polysaccharides, says Jeff Writer, an environmental engineer at the U.S. Geological Survey. Fish and aquatic insects dine on biofilms. Because biofilms play a central role in stream food webs, Writer and colleagues wanted to determine whether endocrine disrupters accumulated in the slimes.
The researchers harvested samples of biofilm, water, and sediment from a stream in Boulder, Colo. The researchers dunked the biofilm and sediment samples in a water-filled jar containing the most common endocrine disrupters in the environment, including the hormones found in birth control pills and the degradation products of surfactants used in industrial detergents.
After 185 days, the scientists measured compound levels using gas chromatography/mass spectrometry. They found that the stream biofilm absorbed roughly 10 times more endocrine disrupters than the sediments did. Writer says that endocrine-disrupting chemicals, which are hydrophobic, prefer biofilms to sediments or water because the slimes are the less polar environment.
Although the chemicals flocked to the biofilm, they degraded faster in the sediment. After 7 days, less than 10% of the compounds had broken down in the slime, while 20 to 30% degraded in the sediments. As a result, "these compounds could build up in stream biofilms," says Emma Rosi-Marshall, an aquatic ecologist at the Cary Institute of Ecosystem Studies, a non-profit research organization in Millbrook, N.Y. This endocrine-disrupter accumulation could serve as a pathway for the compounds to enter stream food webs, she says.
The findings also suggest that biofilms could attract other hydrophobic emerging contaminants, such as pharmaceuticals and personal care products, says David Sedlak, an environmental chemist at the University of California, Berkeley.
The results also could help engineers reduce the amount of endocrine-disrupting chemicals entering the environment, Writer says: Wastewater treatment plants could use biofilms to remove the pollutants from sewage before discharging the water into the environment.
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