Scientists have found tiny amounts of agricultural pesticides in the otherwise pristine winter snow at several Western national parks.
Although the pesticide residue includes some products banned in the United States, researchers say there is no immediate risk for humans — even if they lick the snow. They are still studying the consequences for plants, fish and wildlife in the park.
"We thought these areas were pristine, and they're not," Barbara Samora, Mount Rainier National Park biologist, told The News Tribune of Tacoma.
Researchers also found pesticides in winter snow at national parks in Alaska, California, Colorado and Montana. They said the results mostly relate to regional pesticide use, but they did not rule out the influence of pollution from other parts of the world.
The pesticide analysis was based on seasonal snowfall samples collected three years ago. On Mount Rainier in Washington state, a team of researchers climbed to Alta Vista, a viewpoint 5,676 feet above sea level, between Paradise and Camp Muir, and collected snow samples. Two such treks took place in March 2003.
Clues about exposure elsewhere
Snow samples from all the parks showed tiny concentrations of pesticides, measured in fractions of nanograms. A nanogram equals 1 billionth of a gram.
"These may well be the cleanest snows anywhere in the U.S., so the exposure we receive in urban areas is probably higher," said Dan Jaffe, a University of Washington atmospheric chemist who read the report.
Lead scientist Kim Hageman, an Oregon State University chemist, analyzed snow samples from seven parks, including three in Alaska. She tested for 47 organic compounds. Of those, eight stood out, including four that are banned but persist in the environment.
To identify the source of the contaminants, Hageman compared data on agricultural activity within a radius of about 90 miles of each of the parks. She found the highest concentrations of pesticides in snow from parks near farmlands.
"Clearly, regional U.S. and Canadian agricultural practices, both past and present, play a significant role in contributing to the accumulation of pesticides in the seasonal snowpack," Hageman wrote.
Highest amounts at Sequoia
Because there's no farmland near Alaskan parks, scientists concluded that contamination in snow there originates elsewhere. Hageman detected the highest concentrations of pesticides in snow from Sequoia National Park in California, near the Central Valley, which is largely agricultural.
Mount Rainier is affected by both regional and long-range atmospheric transport of chemical contaminants, Hageman said. "The more cropland, the more concentration in a nearby national park," she said.
Bridget Moran, a state Department of Agriculture environmental toxicologist, read Hageman's paper and downplayed the regional influence. "Mount Rainier tracks closer to background levels in Alaska than it does to the other national parks," she said.
Besides Hageman, four other scientists contributed to the report, which appeared in a recent Web edition of Environmental Science & Technology, a scientific journal.