U.S. Food and Drug Administration tests have shown that it is safe to drink milk from dairies located near wells where a radioactive isotope was discovered, Nevada Gov. Jim Gibbons said Monday.

A study released Friday by the U.S. Geological Survey had shown that drinking water wells around Fallon, 60 miles east of Reno, contained radioactive polonium-210. That prompted officials from nearby Sorensen's Dairy and Oasis Dairy to dump their milk and stop sales pending the outcome of the FDA tests.

All dairies around Fallon sell their milk to the Dairy Farmers of America cooperative, which in turn markets the milk to Model Dairy in Reno and to plants in Northern California.

"I am glad that today's test results literally put them back into business as well as reassuring Nevadans that our milk has been safe all along," said Mendy Elliott, who as state Business and Industry Division chief oversees the state Dairy Commission.

The U.S. Geological Survey's study found polonium-210 in 24 private wells and one public well. The naturally occurring radioactive isotope is known to cause cancer and can damage tissues and organs at high doses.

Concentrations of polonium-210 found in the wells ranged from less than 0.1 to 67.7 picocuries per liter. Thirteen of the wells had amounts greater than 15, which is the maximum allowed by the Environmental Protection Agency for public wells. The EPA does not regulate private wells.

Officials said they think the elevated levels stem from natural causes, and there's no known health risk at this time. Research to determine whether there's a risk is being conducted by state and federal agencies.

Alexander Litvinenko, a former Russian security agent, was killed in London last year with a dose of polonium-210. But officials said the amount that killed him was hundreds of millions times greater than the level the public would be exposed to by drinking well water in Fallon.