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“There is no opinion, however absurd, which men will not readily embrace as soon as they can be brought to the conviction that it is generally adopted.” Chicago Tribune: No one knows how many people in the U.S. have been harmed by mercury in fish. But a recent government study estimated 410,000 babies are born each year at risk for mercury poisoning because of high levels in their mothers' bodies. (December 11, 2005) Response: Statistical Manipulations
The first sentence is true, and the “no one” includes Roe and Hawthorne. They did not produce a single, clinically verified case of harm. If anything approaching their claims were sound, they could have found an epidemic just in the Chicago area. The second sentence is a variation on the most emotive refrain driving the mercury alarmism campaign. It initially exclaimed that "630,000 American babies are born each year" with elevated concentrations of mercury in their blood, with the potential for "permanent brain damage and learning disabilities." CT has now reduced that number to 410,000 without any explanation as to why. Perpetual repetition of various perturbations of this baseless claim does not establish truth. It does, however, fuel the politically clamorous fires of maternal fear about fish consumption. Infants are said to be "poisoned" at birth because their mothers consumed fish containing micro traces of mercury. The statistic represents hypothetical pregnancies unjustifiably derived by mutating EPA’s RfD “safety threshold” into an actual risk calculation. Such a precise number derived from a sea of uncertainty and contrary data should have been the first clue that statistical mischief was afoot. The genesis of the calculation was the 2003 Centers for Disease Control release of its results from the 1999-2000 nutrition and health survey. It was reported that 8% of women of childbearing age (16-49 years old) had blood mercury concentrations above EPA’s RfD. Since there are over four million births in the U.S. annually, mercury opponents and several government scientists unofficially extrapolated that at least 320,000 babies born are "at risk" in the U.S. each year due to "unsafe" mercury levels in their mother's blood. There is no official “government study” making this claim anywhere, as far as we know.  Then, in January 2004, an EPA employee revised the number of babies born at risk upward to 630,000, based on "new information” that mercury in maternal cord blood (shared with the fetus) is more concentrated (by about a factor of 1.7 to 2.0) than in body blood. But the information was not "new," it was a double-counting, since EPA earlier accounted for the blood-concentration difference in 2001, helping justify its "safe" mercury dose (a factor of 10) as the most stringent in the world. Next, CDC released its 2001-2002 health survey results. The results should have suggested caution to the truly thoughtful. Instead of finding 8% of 1,709 women as surveyed in 1999-2000 above EPA’s “safe” mercury level, the CDC reported only about 5% of the 1,928 women surveyed in 2001-2002 exceeding EPA’s RfD. Extrapolating an average of 6% for the full 4 years of survey data yields an estimate of “410,000” (i.e., 0.06 times 1.7 times 4 millions). And now, the CDC has released its most recent blood mercury survey results. No more than 2% of the 1,824 women (16-49 year-olds) surveyed have MeHg levels exceeding EPA’s RfD. So the fraction above the RfD continues dropping dramatically - from around 8% for the first two years of data to about 5% in the next two and to about 2% currently. Thus, as world-wide, man-made Hg emissions rise (principally from China, India and South Africa), the reputed numbers of babies “born at risk” for mercury “poisoning” continues its dramatically precipitous decline. What is a possible explanation for this seeming inverse relationship for increased power plant emissions and declining human exposure levels?  Isolating the response data for actual pregnant women seems to indicate they are indeed being frightened away from fish meals. The change in survey data-sets from 1990-2000 to 2001-2002 reflected a sharp drop in pregnant women above EPA’s mercury RfD. The most recent 2003-2004 survey data show a continuing decline such that only a single pregnant woman of the 255 in the survey exceeded the RfD. Her level was measured at about 7.7 ppb. If only pregnant women (the focus of concern) are considered, then the number of babies claimed to be “born at risk” drops to statistical insignificance – 1/1824. Further, given that the EPA RfD of 5.8 ppb has an excessive safety factor of 10-fold, even she has an enormous safety cushion for actual risk. Even more significantly, the latest CDC data show that only one out of 911 children (ages 1 to 5 years) surveyed has a blood mercury concentration above EPA’s excessively stringent limit. This compares to only 11 of the 1,577 children previously surveyed in 1999-2002. The clearest fact is that, all things considered, there is not a single woman or child at actual risk in these data, let alone 410,000. This misleading statistical exercise perpetuated by the Tribune – and the alarming claims bred from it – first originated with the 2000 NRC Committee on the toxicological Effects of Methylmercury. On page 327 of their report they stated, “The committee estimates that over 60,000 children are born each year at risk for adverse neurodevelopmental effects due to in utero exposure to MeHg.” After the report was published, Dr. Robert Goyer, Chair of the committee, wrote that the number representing offspring of mothers considered “at risk” should “not be interpreted as an estimate of the annual number of cases of adverse neurodevelopmental effects. The committee does not believe it is possible to estimate a meaningful number of children that might be affected within the ‘at risk’ population.” But by then the damage was done. The “410,000” claim suffers from a number of additional, major problems. Revisit the RfD
Additional considerations As already pointed out in Sec. 1, a number of issues suggest EPA’s underlying RfD is almost certainly too conservative, inappropriately derived, non-transparent and should be revised upward. There has been a persistent pattern of suspicious behavior noted for many years. In a 1994 National Academy of Science report, the panel found, “In the absence of convincing scientific knowledge or data, EPA relies on assumptions [default options], often conservative in nature, about such questions as how exposure to low doses of a contaminant affects human health.” A 2006 Govt. Accounting Office investigation reported that “EPA should more transparently communicate which default assumptions were used in risk assessments, why the defaults were chosen, and what judgments EPA was making when it employed certain methods.” In this context of suspicion, first consider that a recent peer-reviewed survey reported that over 5,900 Japanese, 87% of the sample, including 74% of child-bearing aged women, had mercury concentrations above EPA’s “safe” level. Yasutake et al. (2003) cautioned that these levels do not present a hazard to the fetus: “The present hair mercury data would reflect a portion of the food habits of the current Japanese population. Although it was suggested that a large proportion of the Japanese population is exposed to [MeHg] at doses over the EPA/NRC [U.S. National Research Council] recommended level through the daily intake of fish/shellfish, this does not necessarily imply that they are exposed to doses with a substantial hazard to a fetus. However, a very little portion (0.4%) of females at reproductive ages, that show hair mercury levels above 10 [ppm or ten times above the EPA's RfD], may have to change the amount or species of fish consumed in their daily life concerning pregnancy to avoid possible adverse effects on a developing fetus. The results of the present study should be helpful to establish a healthy diet with an appropriate consumption of fish and shellfish, which are nutritionally outstanding foods containing valuable nutrients such as n-3 polyunsaturated fatty acids.” Similarly, a recent hair-mercury survey of 1,066 Taiwanese in 23 counties and cities yielded a mean hair mercury level of about 2.4 ppm. These results are similar to the Japanese ones, but significantly higher compared to the average level of 0.2 ppm for U.S. women of childbearing age. These results confirmed that 80% of Taipei residents surveyed had hair mercury levels exceeding the U.S. EPA's RfD, without reports of derived health complaints. Still, another recent survey by the Faroes investigators found 56% of Inuit cord blood samples exceeded the EPA’s RfD, without reported harm. Logically, one must either conclude generations of Japanese, Taiwanese and the Canadian Intuits are “brain-damaged,” suffering “severe and permanent” learning deficits, or that EPA’s “safe” mercury dose is too stringent, extreme and untrustworthy for safe and effective policy outcomes. In other words, CT needs to account for the absence of generational epidemics that would have long characterized these societies if its series of reports were remotely scientifically evident. (see Sec. 20) Secondly, the “safe” level of mercury exposure established by EPA is widely recognized as the most stringent in the world by at least 10 times any actual levels of concern or harm established elsewhere. To repeat, by a reasonable safety margin, no women in the CDC 1999-2002 survey (the blue data curve in Fig 2-B) had blood mercury above levels of actual harm or concern (vertical purple lines). The mean level was 0.92 ppb, with a data outlier (red circle) around 40.0 ppb reporting no fish consumption at all. By comparison, no cases of Minamata disease were recorded for any child whose mother had mercury levels below 212 ppb (upper blue arrow). Third, the CDC’s own ethical guide lines do not require notifying survey participants of potential harm until a blood concentration of 200 ppb is exceeded. What does the CDC know that EPA apparently doesn’t? Fourth -- and almost never reported -- the CDC also surveyed actual blood mercury levels for children ages 1-5 years. The 1999-2000 survey documented only 7 out of 705 (or 1%) above the EPA’s RfD, while the 2001-2002 survey found only 4 out of 872 (or 0.5%) exceeding it. As noted above, the latest 2003-2004 survey by CDC reported only one out of 911 (0.1%) children aged 1-5 has blood mercury above EPA’s limit. Even the highest measurement for the entire 6-year survey still enjoyed a safety cushion of more than 500%. None of the representative U.S. children were exposed to mercury levels even approaching the threat of mental retardation, even within the limits of EPA’s RfD. No Bright Line of Harm
In other words, EPA’s mercury safety factor is unjustifiably stringent, and carries no credible justification for morphing it into a bright line of harm. This was confirmed in EPA's own technical document, "Methodology used to generate deposition, fish tissue methylmercury concentrations, and exposure for determining effectiveness of utility emission controls" dated March 18, 2005: “The RfD does not represent a "bright line" above which individuals are at risk of significant adverse effects. Rather, it reflects a level where EPA can state with reasonable certainty that risks are not appreciable. The Agency further notes that a number of other national and international scientific bodies have assessed the health effects of methylmercury and have adopted other health-based benchmarks greater than EPA's RfD. Health Canada established its Tolerable Daily Intake (TDI) level at twice the EPA's RfD. Their benchmark is 0.2 micro-g/kg bw/day. The agency for Toxic Substances and Disease Registry (ATSDR) has set a Minimal Risk Level (MRI) of 0.3 micro-g/kg bw/day – three times EPA's RfD level. The World Health Organization's (WHO) benchmark is set at 0.23 micro-g/kg bw/day. Of these major agencies, EPA's RfD has established the lowest risk benchmark to define levels of exposure that are without appreciable risks. As exposure levels increase beyond RfD, the possibility of deleterious effects increases, but the point at which they become "unacceptable" must be determined on a case-by-case basis. In making this determination, the Agency considers a number of factors including: A general summary of mercury RfD talking points: • It is inappropriate to speak of a linear relationship between MeHg and IQ (or other neurological effects). Conclusion
In sum, the Chicago Tribune’s reporting apparently fails at any depth of critical analysis. Tragically, the Mercury Menace series itself may represent the real menace to public health. Its wide, continuing distribution will misinform and frighten off a population already remarkably deficient in fish nutrition – especially pregnant women and a vulnerable, aging population. |
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