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Boats and other motorized watercraft are likely to be the primary source of MTBE (methyl tert-butyl ether) contamination in lakes and reservoirs, according to researchers at the University of California, Davis. MTBE, a fuel oxygenate, and the subject of much controversy in recent years, is added to gasoline in many areas of the country to increase burning efficiency and reduce emission pollutants. It has been identified by the U.S. Environmental Protection Agency as a possible human carcinogen.
Results of a ten-month study examining MTBE in California's Donner Lake were published in the Oct. 10 Web edition of the peer-reviewed scientific journal Environmental Science & Technology, published by the American Chemical Society, the world's largest scientific society. The article also will appear in the journal's Dec. 1 print edition.
"Exhaust products were the primary source of MTBE to Donner Lake and, we hypothesize, for most lakes and reservoirs," claims the report's lead author John Reuter, Ph.D., of the university's Tahoe Research Group. Two-cycle engines, commonly found in personal watercraft and outboard motors, generally have exhaust ports at or below the water line. "The seasonal distribution of MTBE correlated almost perfectly with boat use," Reuter said. He notes that, "statewide in California, surface water bodies that allow boating generally show measurable MTBE, while it is uncommon that a lake or reservoir without boating would contain MTBE." "Neither highway runoff nor precipitation contributed significantly" to the Lake Donner levels, the article states.
While similar observations have been made in recent years about MTBE contamination in recreational waters from boat exhausts, this is the first time that such a comprehensive study has been published in a peer-reviewed journal, according to Reuter. "Despite the apparent link between the use of motorized watercraft and levels of MTBE, this source has not been widely acknowledged in the literature reviews on MTBE to date," the article claims. The U.S. Geological Survey, according to the article, has reported MTBE as the second most frequently detected chemical in shallow groundwater from urban areas. Other potential sources of MTBE into shallow groundwater, according to the article, include leaking storage tanks, stormwater flow and urban precipitation.
Reuter is quick to point out that once the Lake Donner boating season is over, the MTBE dissipates within weeks and there is no indication that it persists between seasons. This is due to the fact that water temperatures in the lake are stratified with warmer surface waters and cooler deeper waters, which keeps the MTBE near the surface where it can volatilize into the air. Although MTBE levels in Lake Donner at times exceeded anticipated standards for taste and odor in drinking water, they did not exceed the 14 parts per billion public health goal, said Reuter.
Lake Donner, a popular resort area located in the Sierra Nevada mountain range in northeastern California, provides drinking water to several locations, including nearby Reno, Nev. It is named for the legendary Donner Party, the ill-fated pioneer expedition that was stranded near the lake during the winter of 1846-47.
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