CORVALLIS, Ore. -- An alarming number of white-tailed ptarmigan in a large region of the southern Rocky Mountains are suffering from acute cadmium poisoning -- an exposure to high concentrations of the extremely toxic trace metal.
Scientists report Thursday in the journal Nature that 46 percent of the adult birds surveyed in a 10,000-square kilometer area in south-central Colorado were found with cadmium accumulations in their kidneys well above the toxic threshold of 100 parts per million.
Cadmium toxicity causes kidney and liver dysfunction, brittle bones, and adversely affects reproduction and survival.
Lead author James R. Larison, an Oregon State University professor and alpine ecologist, said the findings are not unlike those that linked the pesticide DDT to a problem of thin-eggshells in the peregrine falcon three decades ago. The implications of the toxicity go beyond a single species.
"What we found in our study was that a particular genus of plants -- willows -- were 'biomagnifying' or concentrating cadmium," Larison said. "They act as biological pumps, increasing the concentrations of cadmium by two orders of magnitude. Birds eat a lot of willow, especially in the winter when other foods are scarce.
"They aren't the only creatures to eat willow, though," he added. "The possibility exists that deer, elk, moose, snowshoe rabbits, beaver and other animals may face similar problems, just as it is possible that other plants -- including some vegetables -- may have the same abilities to biomagnify cadmium that willow does."
Larison said the human health risk from eating ptarmigan likely is small, unless the internal organs are consumed. But, he added, many people eat vegetables grown in the area and these could pose a risk to human health.
The former director of Sea Grant Communications at Oregon State University, Larison has spent the past four years at Cornell University pursuing his doctorate in ecology and evolutionary biology. His doctoral study was funded primarily by the National Geographic Society. Other authors in the Nature article include Gene Likens, director of the Institute for Ecosystem Studies in Millbrook, N.Y., John Fitzpatrick, director of the Cornell University Laboratory of Ornithology, and J.G. Crock, a chemist with the U.S. Geological Survey.
The study focused on an expansive section of Colorado stretching from Denver and Fort Collins to Durango known as an "ore belt." Larison, who has returned to the OSU faculty, said abandoned mines throughout this area have "exacerbated the problem."
Though cadmium is natural to the area, he pointed out, mining tends to mobilize potentially toxic metals.
"Cadmium poisoning originally was discovered in Japan, with rice acting as a biomagnifier," Larison said. "Elderly women in particular were affected with severe osteomalacia -- a condition not unlike osteoporosis. Trace amounts of cadmium can be found in almost all soils, surface waters and plants, but human activities tend to concentrate it. Mining is one obvious factor, but cadmium also is mobilized by certain industrial and agricultural practices."
Once ingested, cadmium cannot easily be excreted from the body and accumulates, usually in the kidneys and liver. The kidneys are responsible for calcium levels in the blood, Larison said, and when cadmium levels rise and kidneys tubules fail, calcium levels drop. To compensate, the body "borrows" calcium from bones. In Japan, elderly women eating a diet heavy in cadmium-contaminated rice suffered from severe bone decalcification.
In Larison's study, 57 percent of the adult ptarmigan had damaged kidneys and their bones contained 8 to 10 percent less calcium.
"We also found a number of birds with bone fractures," he said. "For every one we found, there may have been others that did not survive long enough for us to discover them."
Cadmium toxicity in predators eating ptarmigan is a concern, Larison pointed out, because they likely would eat the internal organs and the cadmium would then accumulate in their bodies as well. Ptarmigan predators include eagles and hawks, as well as foxes and coyotes.
Though the Nature article focuses on one area in the Rocky Mountains, cadmium poisoning potentially could occur elsewhere, Larison said.
"We happened to look at the effects just on white-tailed ptarmigan eating willows in Colorado," Larison said. "But there are some indications that the conditions for cadmium poisoning are widespread."
Note to Editors: Digital images of 1) a white-tailed ptarmigan and 2) an X-ray of the brittle bone structure of a cadmium-poisoned bird, are available on the News and Communication Services web site: http://osu.orst.edu/dept/ncs/photos/index.html
By Mark Floyd, 541-737-0788
Journal
Nature