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How do they know water's safe at 1 ppm?

CHARLESTON, W.Va. -- Tomblin administration officials continued on Monday to decline to provide detailed answers why they think 1 part per million of Crude MCHM is safe for West Virginians to drink.Federal agencies also refused to explain how they calculated that figure in the absence of any real regulatory guidelines or published health standards for the material, also known as 4-methylcyclohexanemethanol.A Ph.D. chemist who works with the Environmental Defense Fund wrote on his organization's blog that West Virginia officials are trusting "shaky science" in their "rush to restore water service" to 300,000 residents in a nine-county region.Richard Denison wrote that officials "made significant leaps in their calculation of a 'safe' exposure level -- including assumptions that deviate from generally accepted practices.""As a result, these estimates fail to adequately account for either acute or chronic effects from ongoing exposure to water contaminated at the 1 ppm level," Denison wrote. "At a bare minimum, the public deserves to know a lot more about the calculations behind officials' insistence that a 1 ppm level in drinking water is safe."Tomblin administration officials have emphasized that water samples in the last two days have begun to more consistently show far less than 1 part per million of MCHM in drinking water from West Virginia American Water's Elk River treatment plan. Some samples, they note, are coming back with none of the chemical at all being detected."The numbers we have today look good," Tomblin said at a noon briefing Monday.Top Tomblin aides continue to point to the U.S. Centers for Disease Control and Prevention, which, along with the federal Agency for Toxic Substances and Disease Control, came up with the figure 1 part per million.When asked for more information about where the number came from, Department of Health and Human Resources Secretary Karen Bowling pointed to the "material safety data sheet," or MSDS, from Eastman, the maker of the chemical that leaked.Bowling, though, downplayed the fact that there is precious little toxicological data and few -- if any -- public and peer-reviewed studies of what the chemical would do to humans if ingested. "It's like any chemical that's out there," Bowling said. "There are many chemicals of which we don't have all the information. There's been no indication that what we're doing is improper."State officials have told the Gazette to ask the CDC for more information. But on Monday, the CDC referred questions to West Virginia American Water.Late last week, Dr. Letitia Tierney, commissioner for DHHR's Bureau for Public Health, said that the state's announced limit was based on a paper from 1990 by Eastman that was never published in publicly available journals.That study, she said, was the basis for the median lethal dose, or LD50, listed on an Eastman 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.In his blog post, Denison took issue with two things that government officials did in putting together their number.
First, he wrote, the tenfold uncertainty factors should not have been applied to the LD50 value. In standard risk assessment, Denison wrote, those factors would instead be applied to something called the "no observable adverse effect level," or NOAEL, or, if that's not available, the Lowest Observable Adverse Effect, or LOAE."That is the dose at which no effect of a chemical exposure is observed," Denison wrote. "It doesn't take a risk assessor to recognize that the dose at which no effect is seen is going to typically be far, far lower than the dose that outright kills half of the exposed subjects."Denison said that by using the LD50, they started out with the wrong value."No doubt they did so because the values they should have used -- the NOAEL or the LOAEL -- are not available for this chemical," Denison wrote. "But that's no excuse for not compensating for this major problem, at the very least through application of an additional large uncertainty factor."Second, Denison wrote, officials assumed without any basis that any nonlethal effects of the chemical would occur at low doses that were at most 8.25-fold lower than the lethal dose that would kill half of the exposed subjects."This assumption can only have been pulled out of thin air," Denison wrote. "Put aside the convenience of selecting a factor that allowed a nice round number of 1 ppm to be set as the safe level."On what possible basis could it be assumed that the dose of the chemical that would, for example, be moderately toxic even in the short term to the liver or kidney, be only about one-eighth the dose that would kill someone outright in just 24 hours? Many health effects of chemicals occur at doses that are orders of magnitude lower than the lethal dose."Denison concluded, "Now, let me be clear. I am not saying that the level of 1 ppm is unsafe."I am saying that we have no way of knowing whether or not it is safe. The data needed to make that assessment simply do not exist for this chemical."Staff writers David Gutman and Rachel Molenda contributed to this report.Reach Ken Ward Jr. at or 304-348-1702.
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