FOR RELEASE: 2 p.m. Eastern July 12, 2000
Contact: Roger Segelken
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| A white-tailed ptarmigan in winter when cadmium-bearing plants are the birds' main source of food. Photo courtesy of James Larison. A high-resolution copy of this photo (2388 x 1580 pixels, 2416K) is available here. |
Their study, which was funded by the National Geographic Society, focused on abandoned mining districts in Colorado and a little-known species of grouse called the white-tailed ptarmigan (Lagopus leucurus). According to the lead author of the report titled "Cadmium Toxicity Among Wildlife in the Colorado Rocky Mountains," the metal is affecting the ptarmigan in mining areas and may threaten some populations of the bird with extinction. Cadmium from abandoned mines may also affect other wildlife species in the area, including deer, elk, moose, rabbits, beaver and other birds, the researchers predict.
"Even humans in the region may not be immune to the effects of cadmium," said James R. Larison of Cornell and Oregon State universities.
Other authors of the Nature report are Gene E. Likens, director of the Institute of Ecosystem Studies in Millbrook, N.Y., and an adjunct professor of ecology and evolutionary biology at Cornell; John W. Fitzpatrick, professor of ecology and evolutionary biology and director of the Cornell Laboratory of Ornithology; and J.G. Crock, a chemist at the U.S. Geological Survey in Denver. Larison is a doctoral degree candidate at Cornell and a faculty member at Oregon State University in Corvallis.
While the extreme toxicity of cadmium has been established by short-term, lethal-dose experiments, the ptarmigan study in Colorado's Animas River watershed is the first to show the more subtle, but nonetheless important, result of chronic exposure to excess cadmium in a plant-based diet. Particularly susceptible are animals that forage on willow growing in cadmium-rich soils, say the researchers, who note that willows are especially adept at concentrating the toxic metal in their plant tissues. For the little grouse, cadmium damages kidneys and produces thin, brittle bones that may shorten its life span as well as fragile eggshells that reduce reproductive success.
Cadmium is the silver-white metal used to manufacture rechargeable batteries, produce alloys with other metals and electroplate chrome on auto parts and appliances. It has been mined in the Colorado Rockies for more than a century. Cadmium finds its way into the environment when rainwater washes through the piles of ore tailings at abandoned mine sites.
Most trees and other plants readily take up cadmium from the soil, but willows in particular act as biological pumps to biomagnify, or concentrate, the toxic metal in willow leaves and leaf buds to as much as 100 times the levels found in soil. Those same levels of cadmium were found by the researchers in the crop contents of birds that ate willows.
Once ingested, cadmium can become concentrated in kidney tissue. All the adult birds tested in the central and southwestern mountains of Colorado had elevated kidney-cadmium levels. Toxic levels of cadmium were documented in 44 percent of adult birds, whereas birds living outside the ore belt region of Colorado had near-normal cadmium levels in their bodies. High concentrations of cadmium damage kidney tissue and reduce the birds' ability to process calcium. Among adult birds tested in Colorado, 57 percent had damaged kidneys.
To make matters worse, the mining areas that are rich in cadmium also tend to be calcium poor -- in part because of the high acidity of the water and soils --- so birds have little chance of accumulating the mineral they need for strong bones and robust eggshells. According to Larison, birds with insufficient calcium in their diets are even more likely to accumulate toxic cadmium levels. He discovered the most profound cadmium problems among female grouse, which stay in the mining areas during the winter months when willows are their principal source of sustenance.
"Birds in the winter really get hammered," Larison said. "Their bones fracture easily so they die at a younger age and they don't have enough calcium to build normal eggshells." The average ptarmigan could accumulate toxic kidney-cadmium levels after just 600 days of eating cadmium-rich plants, the ecologists estimated for their Nature report.
"The reason that these cadmium-contaminated populations do not go extinct is that new recruits arrive each year from places with normal cadmium levels to replace those that die off," Larison explained.
In addition to the National Geographic Society, the cadmium study was funded by the Colorado Division of Wildlife, the American Museum of Natural History, the American Ornithologists' Union, Sigma Xi, Cornell University and the Cornell Laboratory of Ornithology.
Related World Wide Web sites: The following sites provide additional information on this news release. Some might not be part of the Cornell University community, and Cornell has no control over their content or availability.
-- National Geographic news: http://www.ngnews.com/
-- Ptarmigan photos: http://osu.orst.edu/dept/ncs/photos/index.html
-- Cornell Lab of Ornithology: http://www.ornith.cornell.edu/
Journal
Nature