Friday, April 10, 1998 | 12:51 p.m.
The phototoxicity study by James Oris of Miami University in Ohio suggests that Lake Tahoe's high elevation and exceptional clarity combine to increase the toxic effect of combustion byproducts called polycyclic aromatic hydrocarbons, or PAHs.
Ultraviolet radiation, more intense at Lake Tahoe because of its 6,200-foot elevation, changes the chemical nature of PAHs and, in effect, makes organisms more sensitive to sunburn, Oris said.
Other scientists say research planned at Lake Tahoe this summer will complement Oris' study.
"As all good research does, this study will redirect other research," said Glenn Miller, an environmental scientist at the University of Nevada, Reno, who last summer looked for the presence of gasoline constituents at Lake Tahoe.
The presence of gasoline compounds in Lake Tahoe has become a serious issue, following a decision by the Tahoe Regional Planning Agency last year to phase out the current generation of two-stroke engines by next year.
Marine engine manufacturers, boat owners and rental companies have filed a legal challenge of the agency's action, which was the first such restriction of two-stroke engines in the United States.
This year, the UNR team will measure the concentration of engine emissions in the lake deposited by different kinds of engines. Miller said researchers will study emissions from two-stroke engines, including those in personal watercraft, large outboards and smaller outboards, as well as four-stroke engines.
The U.S. Geological Service will expand its study of contamination at Lake Tahoe this summer, including tests for a wide array of hydrocarbons, pesticides and other chemicals in the lake and its tributaries. The study will measure the PAHs that Oris found so toxic.
Carol Boughton, a senior researcher at USGS, said the agency's finding last year of the fuel additive MTBE 100 feet beneath Lake Tahoe's surface sparked concern.
The Tahoe Research Group already has started comprehensive tests in Lake Tahoe for MTBE, or methyl tertiary butyl ether, a highly dissolvable gasoline additive that was intended to reduce carbon monoxide emissions but has caused concern among water-quality regulators.
A division of the University of California at Davis, the Tahoe Research Group is fulfilling the mandate of a California law passed last year that required further study of MTBE at Lake Tahoe. Beginning in February, the center's scientists are sampling water as deep as 1,500 feet, greatly expanding the scope of previous tests.
Researchers also tested for MTBE and other gasoline compounds in samples of snow in February, but found that the deposition of the gasoline constituents from the air was insignificant.
By the end of this year, said the center's Brant Allen, the combined studies should give authorities a better understanding of the extent of gasoline contamination in Lake Tahoe.
"Last year's studies showed us where we need to go," Allen said. "If we can continue all the studies and get them completed, we will have a comprehensive look at motorized watercraft in the Tahoe Basin."
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