Las Vegas-The deaths of 71 horses on the Nevada Wild Horse Range in 2007 within the Air Force Nellis Test and Training Range were not caused by nitrates from agriculture or industrial sources, according to a study released by the Bureau of Land Management (BLM). The study shows that the high nitrate toxicity present in water in a depression near Cactus Flat was from a combination of evaporative concentration, animal waste, and natural soil nitrogen from air deposition. The BLM study, conducted by the Desert Research Institute (DRI), determined the two sources of high nitrates that caused the deaths of the horses were from an increase in the concentration of naturally occurring nitrate due to high rates of evaporation of the water, and the chemical conversion of nitrogen to nitrate that occurs through a nitrification process of natural materials. Initial test results in July 2007 found high levels of nitrates in samples taken from water from the depression, as well as in the deceased horses’ blood serum and ocular fluid. These results indicated nitrate levels of more than 3,000 parts per million (ppm). The EPA standard for drinking water for human consumption is less than 10 ppm. Livestock can tolerate higher levels than humans, though problems are known to occur when levels exceed 400 ppm and acceptable levels should be below 100 ppm. DRI recommended filling in the depression or controlling access to it. For now, it remains fenced.
Transparency Across the Fertilizer Value-Chain