Cadmium toxicity threatens wildlife in Rocky Mountains

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, reports Nature Magazine.

Scientists that 46% 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.

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 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 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 le vels 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.

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.”

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