Nitrate poisoning that killed 71 wild horses last year on the Tonopah Test Range probably came from natural sources and not de-icing fluids used at a military airfield, concluded a controversial study released Monday by the Bureau of Land Management.
BLM officials cited findings from a long-awaited study by the Desert Research Institute that one former airfield worker described as a "farce" and a "waste of time."
Investigators waited more than seven months after the horses died in July 2007 to collect samples for the study, he said.
"It’s very inconclusive," said Kevin Dye, a former Air Force technical sergeant who worked from 1990-98 at the Tonopah range, 210 miles northwest of Las Vegas.
"They’re saying they’re using a magical mathematical formula, but they’re guessing," said Dye, who blames last year’s wild horse deaths on urea de-icing compounds used on the airfield’s runway and ethylene glycol used for de-icing aircraft.
The de-icing compounds had high nitrogen content and routinely produced runoff that streamed unchecked into the desert.
"We used the stuff by the tons. There were thousands of pounds used from 1982 until 1996 and this stuff was supposed to have magically gone away?" Dye said, questioning the study’s findings.
He estimated that 21,000 pounds per year of urea was used to de-ice the runway from 1982 to 1996.
The study, which cost $80,630, also refers to the death of 61 horses in the vicinity of the airfield in 1988. Documents obtained by Dye under the Freedom of Information Act show the BLM concluded from examining carcasses that the horses died from drinking water contaminated with up to 1,000 pounds of urea washed from a truck by a contractor.
Nitrate levels in the 3-inch-deep water that covered the Cactus Flats playa where the 71 wild horses drank last summer was 66 times higher than the safe drinking standards for humans and 30 times higher than the acceptable levels for livestock.
BLM officials who released the study Monday said it was unlikely the contamination stemmed from urea de-icers or other synthetic nitrogen compounds, according to isotope signatures analyzed by the institute’s scientists.
Instead, the study found that the high levels of nitrates in the water consumed by the dead horses were from natural nitrogen sources concentrated by evaporation.
Those sources included manure and natural soil nitrogen.
Patrick Putnam, assistant field manager for recreation and renewable resources at the BLM’s Las Vegas Field Office, said he feels "pretty confident" that the horses died of natural poisoning instead of contamination from industrial sources.
But the study written by five scientists — Sam Earman, Ronald L. Hershey, Greg Michalski, Christa Dahman and Todd Mihevc — didn’t completely eliminate glycol de-icers as the source of contamination.
"It appears unlikely that human influence, such as contamination from urea or glycol-based de-icing fluids, played a significant role in the high nitrogen concentrations," said the introduction to the 52-page report.
But the report also said that contamination by substances such as de-icers couldn’t be discounted because the organic materials in them can "quickly degrade with time."
When asked for his reaction to that part of the report, Putnam said, "I think that’s kind of interesting."
The seven water samples and 15 sediment samples that the study relied on were collected more than seven months after the horses died.
Because of the time lapse, the report "does not definitely affirm that glycol-based de-icers were not present in the Main Lake depression at the time of the wild horse deaths."
Putnam said the Air Force hasn’t used urea for de-icing since the mid-1990s when the Environmental Protection Agency recommended that more environmentally friendly de-icing agents be used.
Contact reporter Keith Rogers at firstname.lastname@example.org or 702-383-0308.ON THE WEB Evaluation of Chemical Data from Samples Collected February 2008 at the Cactus Flat Main Lake Depression and Surrounding Area, Nevada Test and Training Range Desert Research Institute’s Final Report, Poisoning of Wild Horses Desert Research Institute’s Data Report, Poisoning of Wild Horses