A new study from researchers at the University of Nevada, Reno, finds elevated mercury levels in wood ducks along the Carson River, downstream from Nevada’s historic Comstock Lode.
In the 1800s, miners used mercury to extract gold and silver from crushed rock. Much of that toxic metal washed into nearby waterways, where it settled into sediments along riverbanks and floodplains.
Researchers analyzed 15 years of feather samples from wood ducks living year-round along the Carson River. They found that some ducklings carried mercury concentrations far above federal safety thresholds for human consumption.
Co-author Perry Williams said the contamination has not simply stayed buried.
“Mercury is not just in the water or in the banks,” Williams said. “It's continuously being taken up by the invertebrates and the fish and the things that eat the fish, and everything in the food web. And we're part of that food web as well.”
That movement through the food web is significant. Mercury can convert into methylmercury, a highly toxic form that accumulates in organisms and increases in concentration as it moves up the food chain.
The study also found that wet years play an important role. Heavy snowpack and strong spring runoff can churn up river sediments, reintroducing mercury that had been relatively stable during drier periods.
Co-author Mae Gustin said high flows increase exposure for wildlife.
“Mercury forms in the banks, and then when you have high flows, it gets washed out into the river so the ducks are exposed to it,” Gustin said.
Nevada does not currently have a statewide advisory for eating wild waterfowl, even though some ducklings in the study showed mercury levels that exceed federal consumption guidelines.
While the research focused on the Carson River watershed, the implications extend beyond northern Nevada.
Historic mining shaped watersheds across the Mountain West, including parts of Colorado, Idaho and Montana. Many of those rivers still contain legacy contamination from gold and silver extraction.
As climate change brings sharper swings between drought and intense runoff in the region, researchers say similar patterns could emerge elsewhere.
This story was produced by the Mountain West News Bureau, a collaboration between KUNR, Wyoming Public Media, Nevada Public Radio, Boise State Public Radio in Idaho, KUNC in Northern Colorado, KANW in New Mexico, Colorado Public Radio, KJZZ in Arizona and NPR, with additional support from affiliate newsrooms across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting and Eric and Wendy Schmidt.
