{"id":2945,"date":"2014-01-16T19:34:47","date_gmt":"2014-01-17T00:34:47","guid":{"rendered":"http:\/\/blogs.edf.org\/health\/?p=2945"},"modified":"2024-02-12T11:01:32","modified_gmt":"2024-02-12T16:01:32","slug":"cdc-finally-describes-its-derivation-of-safe-level-in-wv-spill-but-erroneously-claims-it-to-be-highly-conservative","status":"publish","type":"post","link":"https:\/\/blogs.edf.org\/health\/2014\/01\/16\/cdc-finally-describes-its-derivation-of-safe-level-in-wv-spill-but-erroneously-claims-it-to-be-highly-conservative\/","title":{"rendered":"CDC finally describes its derivation of \u201csafe\u201d level in WV spill \u2013 but erroneously claims it to be \u201chighly conservative\u201d"},"content":{"rendered":"

Richard Denison, Ph.D.<\/em>,<\/em> is a Senior Scientist.\u00a0 Jennifer McPartland, Ph.D.<\/em><\/a>,<\/em> is a Health Scientist.<\/p>\n

Slowly but surely, like the movement downstream of the spill\u2019s plume, we are learning more about how government officials derived the 1 ppm \u201csafe\u201d level in the drinking water for the chemical MCHM that was spilled into West Virginia\u2019s Elk River late last week.<\/span><\/span><\/span><\/p>\n

A few more slivers of light were cast today onto what has been a remarkably opaque procedure used by CDC and other officials to set the 1 ppm level, which got even more confused with last night\u2019s <\/span>issuance of a \u201cWater Advisory for Pregnant Women\u201d<\/span><\/a> by the West Virginia State Department of Health.\u00a0 <\/span><\/span><\/span><\/p>\n

The slivers come from a <\/span>story today<\/span><\/a> in the Charleston Gazette<\/i> by Ken Ward, Jr. and David Gutman reporting on their conversation with an official from the Centers for Disease Control (CDC), and a media call today with the same official.\u00a0 <\/span><\/span><\/span><\/p>\n

CDC finally gave a fuller description of their methodology, and while it appears to have more closely followed standard practice than the methodology they initially described, many questions remain about the study used as the starting point.\u00a0 Release of these studies, therefore, is essential.\u00a0 [UPDATE:\u00a0 EVENING OF 1\/16\/14:\u00a0 Late today, Eastman finally made its studies public:\u00a0 they are available here<\/a>.]<\/em>\u00a0<\/span><\/span><\/span><\/p>\n

We discuss the details further below.\u00a0 But first:<\/span><\/span><\/span><\/p>\n

CDC\u2019s erroneous claim that its “safe” level is \u201chighly conservative\u201d<\/span><\/span><\/span><\/b><\/p>\n

CDC\u2019s claim that the 1 ppm level is \u201chighly conservative\u201d is not warranted on scientific grounds.\u00a0 This claim is based on its use of three 10-fold adjustments, referred to by CDC as \u201cuncertainty factors,\u201d to extrapolate from a dose identified in an animal study to a level in drinking water consumed by people.<\/span><\/span><\/span><\/p>\n

    \n
  1. An \u201cinterspecies extrapolation\u201d uncertainty factor to account for the fact that humans may be much more sensitive to the effects of a chemical exposure than rats.<\/span><\/span><\/span><\/li>\n
  2. An \u201cintraspecies extrapolation\u201d uncertainty factor to account for the fact that humans differ in their sensitivity to a chemical exposure (e.g., infants or the elderly vs. healthy adults).<\/span><\/span><\/span><\/li>\n
  3. A third uncertainty factor to account for how few data are available on the chemical and hence the likelihood that its health effects that have not been identified may occur at doses much lower than the doses for the health effect that has been studied.<\/span><\/span><\/span><\/li>\n<\/ol>\n

    The CDC official referred to these adjustments as \u201csafety factors\u201d \u2013 implying they provide for a large margin of safety.\u00a0 This is FALSE.\u00a0 These are REALITY FACTORS.<\/span><\/span><\/span><\/p>\n

    Each of these accounts for known circumstances with regard to the effects of chemical exposures on people in the real world<\/span>.\u00a0 There are plenty of examples of chemicals where:<\/span><\/span><\/span><\/p>\n

      \n
    1. humans are 10x (or more) more sensitive than rats to a chemical effect, and<\/span><\/span><\/span><\/li>\n
    2. the most vulnerable\/sensitive human is 10x (or more) more sensitive than the least vulnerable\/sensitive, and<\/span><\/span><\/span><\/li>\n
    3. an effect not considered in a given study occurs at a dose that is 10x (or more) lower than the effect looked at in the study.<\/span><\/span><\/span><\/li>\n<\/ol>\n

      Don\u2019t take our word for it, but rather the National Academy of Sciences, in a seminal 2009 report titled <\/span>Science and Decisions:\u00a0 Advancing Risk Assessment<\/span><\/a><\/i> (p. 132, emphases in original):<\/span><\/span><\/span><\/p>\n

      Another problem \u2026 is that the term uncertainty factors <\/i>is applied to the adjustments made to calculate the RfD [reference dose, derived from, e.g., a no-effect level] to address species differences, human variability, data gaps, study duration, and other issues. The term engenders misunderstanding: groups unfamiliar with the underlying logic and science of RfD derivation can take it to mean that the factors are simply added on for safety or because of a lack of knowledge or confidence in the process. That may lead some to think that the true behavior of the phenomenon being described may be best reflected in the unadjusted value and that these factors create an RfD that is highly conservative. But the factors are used to adjust for differences in individual human sensitivities, for humans\u2019 generally greater sensitivity than test animals\u2019 on a milligrams-per-kilogram basis, for the fact that chemicals typically induce harm at lower doses with longer exposures, and so on. At times, the factors have been termed safety factors<\/i>, which is especially problematic given that they cover variability and uncertainty and are not meant as a guarantee of safety.<\/span><\/span><\/span><\/p>\n

      CDC\u2019s Methodology Revealed<\/span><\/span><\/span><\/b><\/p>\n

      Until yesterday, all indications were that the 1 ppm level was derived from a single oral lethality study in rats that is not publicly available but reported a median lethal dose value (LD50).\u00a0 Yesterday, CDC referred to \u201c<\/span>additional animal studies<\/span><\/a>\u201d that were under review.\u00a0 In today\u2019s Charleston <\/i>Gazette<\/i> story and this afternoon\u2019s call, the CDC official indicated for the first time that CDC used a second study \u2013 also not publicly available \u2013 as the starting point for the calculations.\u00a0 This second study was stated as identifying a \u201cNo Observable Adverse Effects Level (NOAEL)\u201d for MCHM of 100 milligrams per kilogram of body weight per day (mg\/kg\/day).\u00a0<\/span><\/span><\/span><\/p>\n

      [UPDATE 1\/17\/14:\u00a0 This study,<\/a> finally made available late yesterday,\u00a0was performed using “pure MCHM” (97.3%) rather than the “crude MCHM” mixture that was the material actually spilled.\u00a0 This adds some additional uncertainty; if other components besides MCHM present in the crude mixture are more or less toxic than MCHM, the mixture’s toxicity would differ from that found for the pure material.]<\/span><\/i><\/i><\/span><\/p>\n

      Numerous questions about this study remain unanswered that bear on its relevance for the purpose to which it has been put. \u00a0Just a couple key ones:<\/span><\/span><\/span><\/p>\n