LAS VEGAS, July 25 (UPI) -- U.S. officials said the deaths of 71 wild horses last summer in Nevada came from naturally occurring nitrates.
The U.S. Bureau of Land Management said a study conducted by the Desert Research Institute found nitrate concentrations soared because of evaporation and animal waste and natural nitrogen in the soil, The Las Vegas Sun reported.
The dead horses were found around a shallow pond on the U.S. Air Force's Nellis Test and Training Range in June.
The U.S. Environmental Protection Agency standard for nitrates in human drinking water is less than 10 parts per million. The newspaper said livestock can generally tolerate higher levels, but the levels in the horses exceeded 3,000 parts per million.
The site of the pond where the nitrate-laced water was found was fenced last year so horses cannot drink out of it, the Bureau of Land Management said.
