Muddy Creek is nondescript, a narrow stream trickling through the
sagebrush steppe of southern Wyoming. But like many Western waterways,
it carries selenium, a natural poison that seeps from rocks and dirt and
accumulates in the food chain much as mercury does.
Both humans and animals need tiny amounts for good health, but too
much is dangerous. In areas with a lot of selenium in the soil,
including Utah’s Middle Green River Basin and Nevada’s Stillwater
National Wildlife Refuge, activities that bring soil into contact with
water — irrigating, mining, drilling and road building — boost natural
concentrations, and can cause illness and deformities in people,
livestock and wildlife.
Now, researchers are studying the Muddy Creek watershed, trying to
determine how much of the element occurs naturally, and how much is
being released by human activity. Tracking selenium sources in this way
is tricky, but essential; few studies have examined where selenium comes
from and where it ends up.