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Boat emissions harmful to aquatic life

Patrick McCartney

Low levels of motorized boat emissions are toxic to Lake Tahoe’s plankton and fish larvae, according to a university study scheduled to be released today.

The study was conducted last summer by James T. Oris of the Center for Environmental Toxicology and Statistics at Miami University in Ohio, and was funded by marine engine manufacturers.

While other scientists found evidence of gasoline contamination at Lake Tahoe, the new study demonstrates that engine emissions may pose a special risk to aquatic life at Lake Tahoe. Enhanced ultraviolet radiation because of the lake’s 6,200-foot elevation and lack of organic matter and turbidity may contribute to the toxic effect of gasoline compounds.

“The study may show the first direct link between a biological impact and motorized watercraft,” said Gordon “Gabby” Barrett, who oversees the Tahoe Regional Planning Agency technical advisory committee on watercraft.

While additional studies are needed before the significance of the findings are understood, evidence of a toxic effect by engine emissions could give the TRPA some ammunition in defending the restrictions on current-technology two-stroke engines the agency’s board approved last June.

The National Marine Manufacturers Association, which funded the toxicology study, was one of several parties to sue the TRPA over the ordinance that phases out carbureted two-stroke engines by June, 1999.

John Fagan, an attorney representing the engine manufacturers, declined comment on the study Wednesday, as did the association’s lead scientist.

“I would like to comment, but with pending litigation and the volatility of the subject, it’s appropriate not to try a case like this in the press,” Fagan said. He added, however, that the lawsuit challenges the evidence that existed last June when the agency’s board approved the restrictions, not on scientific findings since then.

Scientists who have reviewed a summary of Oris’ study say the next step is to see how widespread the toxic effect is.

“It could have an effect on the entire food chain, if further research shows it is significant in the whole ecosystem,” said John Reuter of the University of California at Davis’ Tahoe Research Group. “The study confirms some of the concerns people have had about (boat emissions) from the beginning. Some people were quick to say that there was no effect. Well, there is an effect.”

But Reuter added that the mortality of Lake Tahoe’s plankton is unlikely to have played a significant role in the lake’s dramatic loss of clarity, since plankton do not consume a large amount of algae.

In a two-week period last summer, Oris found an association between peak boating activity and concentrations of hydrocarbons in Lake Tahoe, and determined that ultraviolet radiation increased the toxic effect. The compounds studied, polycyclic aromatic hydrocarbons or PAHs, are a combustion byproduct of gasoline, and have been found to have a subtle effect on biological system.

Oris sampled water from North Shore sites with high boating activity, as well as from two miles offshore where boating is less common. He found a good correlation between boating activity and PAH concentrations, which ranged from 5 to 70 parts per trillion.

Although the concentrations seem remarkably low, the PAH contamination was enough to kill zooplankton even without ultraviolet exposure. Exposure to ultraviolet radiation enhanced the toxic effect, in a process called phototoxicity.

With ultraviolet exposure, the PAHs were toxic to both zooplankton and to the larvae of minnows, Oris found.

The findings corroborate research by Michigan State fisheries professor John Giesy, who in testimony at a TRPA hearing last year said that concentrations of PAHs of 53 ppt would kill 100 percent of zooplankton in 30 minutes when exposed to ultraviolet radiation.

Next summer, the U.S. Geological Service will look for PAHs throughout Lake Tahoe as part of the TRPA’s continuing research on the impact of motorized watercraft at Lake Tahoe.

Executive Director Russell Long of the Bluewater Network, which sued the U.S. Environmental Protection Agency over its two-stroke engine regulations, said marine engine manufacturers may have made a mistake in suing the TRPA over its restrictions on two-stroke engines, which emits a portion of its fuel unburned.

“The industry may have opened a Pandora’s box by fighting the TRPA in court over the pollution effects,” said Long, who spoke to Oris about his study Wednesday. “The studies may show that four-stroke engines may also be implicated in the pollution. Then you’d have a bigger problem.”

Tahoe Daily Tribune E-mail: tribune@tahoe.com

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