Mercury levels in mothers.I read with great interest the excellent article by Mahaffey et al. (2004), which further describes the characteristics of the 1,709 women from the National Health and Nutrition Examination Survey (NHANES NHANES National Health and Nutrition Examination Survey (US CDC) ) 1999-2000 who were sampled for total and organic mercury levels in blood. It adds valuable detail to the initial report published last year (Schober et al. 2003). I would appreciate clarification on one important point: in the "Discussion," the authors cited a new analysis which indicates that the cord blood cord blood
Blood present in the umbilical vessels at the time of delivery. :maternal blood ratio is not 1:1 as assumed by the National Research Council (NRC NRC
1. National Research Council
2. Nuclear Regulatory Commission
Noun 1. NRC - an independent federal agency created in 1974 to license and regulate nuclear power plants ) in 2000 (Committee on the Toxicological Effects of Methylmercury 2000), but rather 1.7:1. Using the same benchmark dose lower limit and uncertainty factor used by the NRC, Mahaffey et al. (2004) calculated that blood total mercury levels > 3.5 [micro]g/L in mothers could be associated with increased risk to the developing fetal nervous system. I am very interested in the details of this analysis and particularly in understanding why the uncertainty factor applied by the NRC to account in part for toxicokinetic variability does not compensate for uncertainty related to the cord blood:maternal blood mercury ratio. This is a critical concept because it has a dramatic impact on how many women may carry mercury levels in excess of what is believed to be safe for a fetus fetus, term used to describe the unborn offspring in the uterus of vertebrate animals after the embryonic stage (see embryo). In humans, the fetal stage begins seven to eight weeks after fertilization of the egg, when the embryo assumes the basic shape of the newborn .
The author declares she has no competing financial interests.
Committee on the Toxicological Effects of Methylmercury, Board on Environmental Studies and Toxicology toxicology, study of poisons, or toxins, from the standpoint of detection, isolation, identification, and determination of their effects on the human body. Toxicology may be considered the branch of pharmacology devoted to the study of the poisonous effects of drugs. , Commission on Life Sciences, National Research Council. 2000. Toxicological Effects of Methylmercury. Washington, DC:National Academy Press. Available: http://www.nap.edu/books/0309071402/html/ [accessed 28 October 2004].
Mahaffey KR, Clickner RP, Bodurow CC. 2004. Blood organic mercury and dietary mercury intake: National Health and Nutrition Examination Survey, 1999 and 2000. Environ Health Perspect 112:562-570.
Schober SE, Sinks TH, Jones RL, Bolger PM, McDowell M, Osterloh J, et al. 2003. Blood mercury levels in U.S. children and women of childbearing child·bear·ing
Pregnancy and parturition.
childbearing adj. age, 1999-2000. JAMA JAMA
Journal of the American Medical Association 289:1667-1674.
Katherine M. Shea
One Buttons Lane
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Editors note: In accordance with journal policy, Mahaffey et al. were asked whether they wanted to respond to this letter, but they chose not to do so.