Lab releases follow-up data on cyanide in runoff

Hydrologists with the Los Alamos National Laboratory have determined that the vast majority of cyanide found in storm water after the Cerro Grande Fire was not in a form that could injure humans, fish or other living organisms. In addition, the hydrologists have found that some of the cyanide may have been naturally created by combustion.

This clarifies an opinion expressed in a September 11 Laboratory news release, based on information then available, that the cyanide detected in the storm water is "most likely" from fire retardant slurry used to fight the Cerro Grande Fire. The water came from areas upstream of the Laboratory; in addition the Laboratory does not use cyanide in significant quantities.

"The really good part of this story is that we have new information that shows the potential hazards posed by short-term exposure to the cyanide are reduced," said Bruce Gallaher of the Laboratory's Water Quality and Hydrology Group. "Most test results show levels that are not known to pose a hazard to fish or wildlife. In fact, we have no reports of fish kills or impacts to the Rio Grande as a result of the Cerro Grande Fire."

In September, Laboratory hydrologists reported the presence of cyanide in storm water that was running onto Laboratory property. The hydrologists believed that a possible source for the chemical was sodium hexacyanoferrate (II) - also known as sodium ferrocyanide - used in slurry, an air-dropped fire retardant.

Sodium ferrocyanide is added to slurry as an anti-caking agent and corrosion inhibitor. U.S. Forest Service data show that approximately 167,000 gallons of slurry containing sodium ferrocyanide were dropped while fighting the Cerro Grande Fire. Scientific literature indicates that sodium ferrocyanide can degrade into free, or "amenable," cyanide in the presence of ultraviolet light, such as sunlight, and in water.

However, after reviewing research regarding forest-fire-created contaminants, the Laboratory hydrologists found scientific papers that indicate quantities of cyanide can be produced naturally by a smoldering fire as well. These cyanide-containing compounds may remain in ash.

Laboratory and New Mexico Environment Department results from the analysis of ash samples from areas burned by the Cerro Grande Fire, but apparently untouched by slurry fire retardant, show cyanide in concentrations of several parts per million. Accordingly, cyanide can come from naturally occurring sources as well as possibly from the slurry. Laboratory researchers will continue to work with U.S. Forest Service staff to investigate contaminants resulting from the fire in storm water.

In addition, the majority of the cyanide found in runoff samples to date is in a form that is not harmful to fish, animals or people. When analyzing samples for cyanide, technicians look for "amenable cyanide" - the form that can kill fish or poison living things - and "bound cyanide," a form of the chemical that is less harmful and more stable, provided that bound cyanide does not undergo changes induced by ultraviolet light and water, or other factors.

The original storm water samples were analyzed by an independent laboratory and the results were returned to Los Alamos hydrologists. Due to a reporting error by the independent laboratory, the results caused Los Alamos hydrologists to believe that a significant quantity of the cyanide was in the amenable form.

A subsequent analysis showed that the first results were erroneous and that cyanide found in the storm water samples was predominantly "bound cyanide" and did not pose a risk to living things. To be sure, scientists with the U.S. Environmental Protection Agency subjected a species of minnow and a species of insect to acute (short-term) and chronic (long-term) exposures of the storm water. The water had no deleterious effect on the test subjects in acute-exposure tests. However, in some of the chronic-exposure tests, the insect species died; scientists are unsure whether the cyanide or other factors were responsible.

Taken together, the new test results indicate that the cyanide found in storm water poses little risk to fish, animals or people in short-term exposures. The tests also indicate a potential concern that some organisms might be harmed if exposed to cyanide-containing runoff for a period of several days or longer.

Because the Los Alamos area is naturally dry and thunderstorms typically lasts for just a few hours or less, the risk for chronic exposure is not high. Tests of longer-lived water bodies such as Los Alamos Canyon creek and the Los Alamos Reservoir show no indication that hazardous levels of cyanide are present.

Larger mammals such as elk and deer are relatively unaffected by low concentrations of cyanide, and these mammals tend to excrete the chemical and tend not to accumulate it in their muscles or bones. Plant species that are known to accumulate and store cyanide in their tissues over time are not abundant on the Pajarito Plateau.

The fate of cyanide in a relatively dry environment like Los Alamos is not well studied. Scientists will need to perform more field studies that focus on the long-term risk posed by cyanide compounds. The key question to researchers is what happens to cyanide after it is exposed to alternating cycles of sunlight and rainfall.

Los Alamos researchers are collaborating with researchers from EPA, NMED and the U.S. Forest Service to compare samples collected here with samples collected at other nearby fire-damaged areas. Scientists also will use areas within the Cerro Grande Fire burn zone as a natural study site to look at cyanide and other fire-chemistry issues. Los Alamos hydrologists will continue to test for and report on cyanide and other substances of concern in runoff.

--James Rickman - Nov. 1, 2000