The open-pit gold mines that populate parts of Nevada are producing more than just precious metal. The mines are polluting neighboring states in the West with dangerously high levels of mercury, which blows downwind into Utah and Idaho. Nevada’s mining industry is the nation’s leading mercury polluter, and has emitted over 100 tons of mercury since the early 1980s.

According to an extensive story in the Las Vegas Sun, the mercury contamination in at least one lake in Idaho is 150 times higher than in lakes in the Northeast that have caused concern over mercury emissions from power plants.

Only in the last decade have Nevada’s gold mines been required to report their mercury emissions, according to the article, and even today the only emissions reduction program is voluntary. This week, however, a state regulatory agency is considering implementing mandatory reductions.

In the open-pit mines, which are 1,000 feet deep, tons of rock are pulverized to get just a single ounce of gold. Mercury and gold co-exist in the ore, and mercury is released into the air when the ore is heated to extract the gold.

Photo credit: Great Basin Mine Watch