CHARLESTON, W.Va. -- Faced with limited information and no regulatory guidelines on a chemical that's put drinking water off limits for 300,000 West Virginians, government scientists have come up with a level of Crude MCHM they believe is safe.Federal and state officials have put out a number -- 1 part per million -- and are noting hopefully that chemical concentrations in the region's Elk River water supply are dropping ever closer to that figure.At the same time, officials in the Tomblin administration and with West Virginia American Water are refusing to make public the results of their testing. And they're saying precious little about how the number was derived, or what exactly it really means.Bernadette Burden, a senior press officer for the U.S. Agency for Toxic Substances and Disease Registry, said federal officials believe "this number is extremely conservative and protective of public health."And local officials are publicly assuring residents that ATSDR and the U.S. Centers for Disease Control and Prevention devised the figure, and that experts with those agencies should be trusted on the matter."Not only are experts from West Virginia reviewing the samples, but experts from the U.S. EPA, the Agency for Toxic Substances and Disease Registry, and the Centers for Disease Control and Prevention are reviewing the samples to be sure that the system is safe before it is reopened," said Dr. Letitia Tierney, commissioner for the state Department of Health and Human Resources' Bureau for Public Health. "All of this is being done to ensure the public health and safety of our citizens.After National Guard Gen. James Hoyer first mentioned the figure Friday afternoon, Amy Goodwin, spokeswoman for Gov. Earl Ray Tomblin, referred questions about it to Tierney. Late Friday night, Tierney initially declined to answer questions about how the figure was derived, saying she hadn't done the work and did not want to "walk down this path" of explaining it.
Later, Tierney provided some details in an email message forwarded by an agency media spokesman.In the email message, Tierney explained that the CDC looked for relevant studies of the chemical's health effects but found only one -- a 1990 study by Eastman, maker of the product, that was not published in peer-reviewed literature and is considered proprietary.That study, she said, was the basis for the median lethal dose, or LD50, listed on an Eastman "material safety data sheet," or MSDS that's been circulated by local emergency responders, health officials and the media.On that MSDS, the LD50 for Crude MCHM is listed as 825 milligrams per kilogram. This means that, when tested on rats, an 825 milligram dose per kilogram of body weight was enough to kill half the rats.
Here's how Tierney said CDC experts took that LD50 and came up with the 1-part-per-million figure that West Virginia officials are now citing as a safe level in local water:"The experts then took this number and calculated the uncertainty factors," she wrote. "In this situation there were two. The first uncertainty factor was translating these results from rats to humans. The second uncertainty factor took into account sensitive populations. This includes the elderly, the sick, the immuno-compromised and children, amongst others."Uncertainty factors range from 5 to 10 percent," she wrote. "Given the dearth of data and an abundance of caution, both uncertainty factors were rated at 10 percent."This, Tierney explained, changed the level that would cause death to 8.25 milligrams per kilogram of body weight.
LD50 figures, though, consider only death. They would tell officials nothing about what levels at which chemical exposure would cause other health effects, even serious ones.To address this, they changed the figure to 1 milligram per kilogram of body weight, which is equal to 1 part per million.It's not clear though -- and Tierney did not explain -- the scientific basis for the change from 8.25 milligrams per kilogram to 1 milligram per kilogram.But Dr. Elizabeth Scharman, director of the West Virginia Poison Center, reviewed the issue and said she's comfortable with Tierney's explanation of it."There are processes and decision algorithms that are used based on all of the data that is known," Scharman said."In this case, it is the entire toxicity profile of a chemical that is unknown. However, predictions are based on what we do know looking at the chemistry and the available data," she said. "In this case, we are dealing with a short-term exposure as opposed to situations in which people have been exposed for weeks to months to years."
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