How do you like your fish seasoned? A little mercury, perhaps some DDT? That's what you might get if you eat fish caught in national parks in the American West. From Alaska to the U.S.-Mexico border, fish being pulled from national park waters are showing alarming concentrations of heavy metals and pesticides.

Results of the six-year study were quietly made available Tuesday, when a release was published without fanfare on the National Park Service's website, as opposed to being distributed via email to media, a practice the agency turned to Tuesday to announce 2007 park visitation numbers.

The study of airborne contaminants in national parks across the western United States would seem to demonstrate that there's virtually no place in the Northern Hemisphere that can avoid contamination from pesticides and heavy metals. In some cases, mercury levels in fish were found to be far above human-health standards set by the U.S. Environmental Protection Agency, according to the Park Service.

Indeed, at one point, according to someone familiar with the study, Park Service officials considered advising backcountry rangers in Sequoia and Kings Canyon national parks not to eat trout they pulled from high country lakes. At the park, though, officials said Tuesday that that wasn't the case -- "That's not what the science says," said park spokeswoman Alex Picavet. -- and that they were planning to advise the backcountry personnel of the potential risks.

"We're going to work really hard with that staff, to talk to them about their risks, or at least their potential exposure, especially if they're supplementing their supplies with (fish)," said Ranger Picavet. "A majority of our backcountry rangers and trail crews are returnees, they've been here for years, and if we give them the information, the actual science that is in this report, they'll be able to make their own decisions.

"Obviously, they're supplied food, so the trout are not a necessary part of their diet. I think it's more of a recreational activity to do on their day off."

As for park visitors, she said officials were thinking of placing health advisories in wilderness permit materials.

"The people who are going to be most likely to eat enough fish or to have the opportunity to eat enough fish in our backcountry to be affected would be our own staff and researchers who spend months out there," said Ranger Picavet.

According to the study, some of the depositions were from local and regional sources, both past and present, while others were carried from Europe and Asia across the Pacific by trade winds.

Parks involved in the study were Glacier, Mount Rainier, Olympic, Rocky Mountain, Sequoia & Kings Canyon, Denali, Gates of the Arctic, and Noatak.

The research was funded primarily by the Park Service to evaluate the potential threats to park ecosystems and likely sources of these contaminants. The bottom line, the agency said, was that overall human risk from these contaminants is low for folks who don't rely heavily on caught fish for subsistence. For some wildlife, though, the concentrations could be toxic, it added.

While the extent of the effects on wildlife depending upon fish for survival is unknown, the risk to people is considered low and varies given location, frequency and type of fish consumption. How scientific data are used to make recommendations for people’s diets varies between states, as health risks associated with exposure to contaminants in select fish may be outweighed by the benefits of continued consumption of traditional foods. Most people are not likely to eat enough of the contaminated fish to be at risk.

The study found that out of more than 100 organic contaminants tested, "70 were found at detectable levels in snow, water, vegetation, lake sediment, and fish. While concentrations of most of these contaminants were below levels of concern, others appear to be accumulating in sensitive resources such as fish. For some contaminants, high concentrations in fish have exceeded fish-eating wildlife and/or human health consumption thresholds in many of the eight core parks studied."

The three contaminants of highest concern for human and wildlife health included: 1) Mercury – a heavy metal emitted through processes such as burning coal for electricity that causes neurological and reproductive impairment; 2) Dieldrin – an acutely toxic insecticide banned from use in the U.S. since 1987 that decreases the effectiveness of the immune system; and 3) DDT – an insecticide banned in the U.S. since 1972 that reduces reproductive success.

Average mercury concentrations in fish from Alaska’s Noatak National Preserve were above the EPA human-health threshold for consumption (i.e., adults eating 2.3 meals of these fish per month), while mercury concentrations in some fish exceeded the threshold at Gates of the Arctic, Olympic, Mount Rainier, and Sequoia & Kings Canyon national parks. Dieldrin concentrations in fish from Rocky Mountain, Sequoia & Kings Canyon, and Glacier national parks exceeded the health threshold for recreational fishermen (i.e., adults eating 2.3 meals of these fish per month). Dieldrin concentrations also exceeded health thresholds for subsistence fish consumption (i.e., adults eating 19 meals of these fish per month) at all national parks, except Olympic. Average DDT concentrations in fish exceeded the human risk threshold for subsistence fishers at Sequoia & Kings Canyon and in Oldman Lake at Glacier National Park.

At Rocky Mountain and Glacier national parks, researchers found trout that contained both male and female reproductive structures. "This condition is commonly associated with exposure to certain contaminants (e.g., dieldrin and DDT) that mimic the hormone estrogen," the study's authors said. "Because the sample size was small, however, the extent of the problem and correlation between fish reproductive effects and contaminant concentrations has not been established for parks in the study."

The study also noted that "mercury concentrations in fish at all eight parks exceeded health thresholds suggested for birds, and were above mammal health thresholds at some parks. DDT concentrations in fish exceeded the fish-eating bird health threshold in Glacier and Sequoia & Kings Canyon national parks."

At the National Parks Conservation Association, Clean Air Program Director Mark Wenzler said the findings were "troubling, but not surprising."

"Unfortunately, our national parks are not isolated islands of protection. They too, are suffering from the effects of global warming, air pollution, and chemical use outside of park boundaries," said Mr. Wenzler. "The same dirty air that travels across our schoolyards, backyards, and farmyards is toxic to the national parks and the wildlife, plants, and cultural and historic treasures the parks were established to protect.

"Air pollution and airborne contaminants harm what Americans value most about their national parks: it destroys habitat for park animals and plants, risks the health of park visitors and staff, damages the historic symbols of our heritage, and clouds the majestic views found in our national parks," he added.

While the study found that a portion of the contaminants came from overseas, NPCA officials nevertheless believe the "United States must lead by example" and work both to eliminate mercury emissions from domestic coal-fired power plants and to "ensure that the chemicals and pesticides used here are safe for humans, wildlife, and our national parks."

Here's a list of fish species sampled in lakes at the eight core parks: lake trout from Noatak, Gates of the Arctic, and Wonder Lake at Denali; burbot and whitefish from McLeod Lake at Denali; cutthroat trout from Glacier; brook trout from Olympic, Mount Rainier, Sequoia, and Lone Pine Lake at Rocky Mountain; and rainbow trout from Mills Lake at Rocky Mountain. Nevertheless, any one fish species, or lake, excluded from the above list is not necessarily exempt from contaminant concentrations of concern.

Agencies that participated with the Park Service on the study were the EPA, the U.S. Geological Survey, the U.S. Forest Service, Oregon State University and the University of Washington.