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New tests show mercury in reservoirs still a concern
By Gail Binkly
Don’t eat too much of certain types of fish pulled from the waters of McPhee and Narraguinnep reservoirs.
That advisory, issued 13 years ago, will continue indefinitely into the future, based on the most recent tests of fish in those bodies of water. Testing of fish conducted at McPhee and Narraguinnep Reservoir more than two years ago shows that mercury advisories continue to be needed for certain species of predatory fish.
A report has yet to be issued by the Colorado Department of Public Health and Environment’s Water Quality Division, but a scientist with the department says the advisories will continue.
“The advisories will be revised, but they will continue. I cannot rescind them,” said Lucia Machado, physical research scientist with the department.
The current advisories were based on tests done in 1993. In the summer of 2004, Machado, with help from the Colorado Division of Wildlife, took new samplings at the reservoirs.
“The early word is that there’s not a lot that’s changed from the earlier testing” in 1993, said Mike Japhet, senior aquatic biologist with the Colorado Division of Wildlife in Durango, who helped with the sampling.
Japhet collected smallmouth bass, rainbow trout, yellow perch, Kokanee salmon, white suckers, flannelmouth suckers and “cut-bow,” a cutthroat-rainbow trout hybrid, and turned them over to the state health department. As before, the findings show that warmwater, predatory fish including smallmouth bass, northern pike and walleyes have elevated levels of mercury in their tissues. Coldwater fish such as trout and salmon don’t have enough of the toxic element to pose a health risk, Japhet said.
“We have now sampled 56 bodies of water around the state, and generally what they’re finding is the only fish that have elevated levels sufficient to cause public health advisories are the warmwater predatory fish,” he said. Machado agreed. “I have not found any trout to be of concern, which is good news for the anglers.”
McPhee has bass but no northern pike or walleye. Those fish do live in Narraguinnep.
Advisories for northern pike and walleye were posted for the first time at Vallecito Reservoir east of Durango this summer. Navajo Reservoir near the New Mexico border is also under advisory; so are portions of the San Juan River; Lake Farmington , N.M.; and a handful of lakes in northern Arizona.
Colorado’s old advisories, which had a complicated system ranking each type of fish, are being replaced by a simpler system, Japhet said.
But the basic message will be the same: Pregnant or nursing women, women who plan to become pregnant, and children 6 or younger should not eat too much of certain types of fish. For instance, the Vallecito advisory says people in those groups should not eat any walleye larger than 18 inches, period.
“It’s mostly a matter of people using common sense,” Japhet said. “People should heed the advisories, but I don’t know of too many people subsisting on the fish they catch from McPhee.”
Mercury is a naturally occurring element, but too much can cause serious damage to the body, particularly the nervous system and kidneys. Fetuses, infants and young children are at special risk; exposure can cause learning deficits and developmental disorders.
A 2004 study by the Environmental Protection Agency estimated that more than 630,000 babies are born in the U.S. each year with elevated mercury levels, and as many as 1 in every 6 women may have enough mercury in their blood to harm a fetus.
Where does the mercury come from? Mercury is not being created or destroyed, but it can be released into the environment through different processes. The largest source is coalfired power plants. When coal is burned, mercury is released. This airborne, inorganic mercury is essentially inert, and breathing it is believed to do little harm.
However, when the mercury lands in still water, bacteria change it into an organic form that can be absorbed by living things and is highly toxic. It’s consumed by micro-organisms in the water, which are then eaten by fish. Fish that eat other fish can accumulate high concentrations of mercury, particularly as they grow older and larger. The most common way for humans to be exposed to mercury is by eating contaminated fish, either freshwater or saltwater.
It’s difficult to say where the mercury in local reservoirs originated, Machado said. “Mercury comes from many sources,” she said. “Air deposition is definitely one source.” Leaching from old mines and contaminated soils upriver is another source.
Airborne mercury may drift hundreds or thousands of miles in the atmosphere, so it’s unclear how much regional power plants are to blame for local contamination.
But mercury pollution has become an issue in considering new power plants such as the proposed 1,500- megawatt Desert Rock plant on the Navajo reservation.
U.S. Rep. John Salazar (D-Colo.) has sent comments to the EPA regarding Desert Rock. In them, he expresses concern about mercury.
“Specifically how will the new plant affect existing problems with mercury contamination of reservoirs and lakes, especially those that serve as domestic water supplies?” Salazar stated.
“Recent studies by the United States Geological Survey have confirmed that the most likely source of mercury contamination of water bodies in Colorado is from coal fired plants in New Mexico. Given this fact, the release of more mercury into our air where it will then get into our water supplies is of grave concern to me.”
On March 15, 2005, EPA issued a federal rule to cap and reduce mercury emissions from coal-fired power plants. This “cap-and-trade” rule, when implemented, will cap total mercury, allowing dirtier power plants to buy the right to emit more mercury from plants that don’t pollute as much.