Children's IQs: Trasande et al. respond.Schwartz makes a number of claims regarding our methodology (Trasande et al. 2005) that are inaccurate and based on a selective reading of the literature.
In our article (Trasande et al. 2005), we estimated the health and economic consequences of prenatal methylmercury (MeHg) exposure in the 2000 U.S. birth cohort. Our major findings were that at least 316,588 children in that birth cohort suffered IQ (intelligence quotient intelligence quotient
n. Abbr. IQ
An index of measured intelligence expressed as the ratio of tested mental age to chronological age, multiplied by 100. ) loss of 0.2-24.4 points as a result of MeHg toxicity sustained in utero in utero (in u´ter-o) [L.] within the uterus.
In the uterus.
in utero adv. . This loss of intelligence causes diminished economic productivity that will persist, and this lost productivity is the major monetary consequence of methylmercury toxicity. We used the most up-to-date publicly available data on mercury exposures and health outcomes, applied a risk assessment approach developed 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 1994), and made conservative assumptions throughout.
To compute decrements in IQ that resulted from prenatal mercury exposures, we used data from Mahaffey et al. (2004) on percentages of women of childbearing age in 1999-2000 with mercury concentrations [greater than or equal to] 3.5, 4.84, 5.8, 7.13, and 15.0 [micro]g/L. These data most closely reflect exposure to women in the years 1999-2000, when toxicity to the developing brains of children in the 2000 birth cohort would have occurred. We then applied logarithmic logarithmic
pertaining to logarithm.
when the logs of two variables plotted against each other create a straight line. and linear models to these data, and we calculated a range of IQ decrements for each subpopulation sub·pop·u·la·tion
A part or subdivision of a population, especially one originating from some other population: microbial subpopulations.
Noun 1. born with a cord blood cord blood
Blood present in the umbilical vessels at the time of delivery. mercury concentration > 5.8 [micro]g/L. To assess a range of possible outcomes, we conducted a sensitivity analysis in which we applied a range of IQ decrements for each increase in mercury concentration. We described our methods in great detail (Trasande et al. 2005). Through this series of calculations, we generated upper and lower ranges of possible IQ decrements for each subpopulation among the most highly exposed children in the 2000 U.S. birth cohort.
In his letter, Schwartz asserts that it is impossible to impute impute v. 1) to attach to a person responsibility (and therefore financial liability) for acts or injuries to another, because of a particular relationship, such as mother to child, guardian to ward, employer to employee, or business associates. effects on children's intelligence of prenatal exposures to mercury near the U.S. Environmental Protection Agency's (EPA EPA eicosapentaenoic acid.
n.pr See acid, eicosapentaenoic.
n. ) reference dose (RfD). In proffering this assertion, he appears to ignore a recent meta-analysis of the three studies that confirmed a dose-response relationship between low-level prenatal MeHg exposure and IQ (Cohen cohen
(Hebrew: “priest”) Jewish priest descended from Zadok (a descendant of Aaron), priest at the First Temple of Jerusalem. The biblical priesthood was hereditary and male. et al. 2005). A recent U.S. cohort study has also detected decrements in visual recognition memory among children exposed prenatally to MeHg (Oken et al. 2005).
Schwartz suggests that we should have used the U.S. EPA benchmark dose level (BMDL BMDL Benchmark Dose (Lower Confidence Limit)
BMDL Barony-Marche of the Debatable Lands
BMDL Below Minimum Detectable Limits ) of 58 [micro]g/L as a cutoff. He apparently assumes that no injury occurs to fetal brains from exposure to MeHg below that level. That approach does not reflect biologic or epidemiologic reality. We based our selection of 5.8 [micro]g/L as a no adverse effect level on the epidemiologic evidence, not on the U.S. EPA's regulatory documents (Budtz-Jorgensen et al. 2004; Grandjean et al. 1999; Kjellstrom et al. 1986, 1989). We relied especially upon the NRC's report on prenatal exposure to MeHg (NRC 2000), which concluded that the likelihood of subnormal subnormal /sub·nor·mal/ (-nor´m'l) below normal.
below or less than normal. scores on neurodevelopmental tests increased as cord blood mercury concentrations increased from levels as low as 5 [micro]g/L. Methylmercury exposure has also been associated with persistent delays in peak I-III brainstem-evoked potentials at cord blood levels < 5 [micro]g/L (Murata et al. 2004).
Schwartz misrepresents Crump et al.'s findings (1998), stating that they "superseded previous reports and found no IQ reduction." In fact, the NRC (2000) stated that Crump et al.
reported nonsignificant results from a regression analysis on all the children in the New Zealand cohort, but [that these results became significant] after omission of a single child whose mother's hair Hg concentration was 86 ppm (4 times higher than that of the next highest exposure level in the study).
Schwartz misrepresents our characterization of the Seychelles Islands study (Landrigan and Goldman 2003; Myers et al. 2003), accusing us of stating that it had half the statistical power of the Faroe Islands study (Grandjean et al. 1999). In actuality, we stated that the Seychelles study "had only 50% statistical power to detect the effects observed in the Faroes" (Trasande et al. 2005). Schwartz asserts that the NRC's choice not to apply the Seychelles data in setting an RfD represents equivocation about the health effects of MeHg. In actuality, the NRC came to the same conclusion as we did: "[t]he weight of the evidence of developmental neurotoxic neurotoxic
pertaining to or emanating from a neurotoxin.
a case of poisoning by a neurotoxin.
neurotoxic adjective effects from exposure to MeHg is strong" (NRC 2000).
Recent work (Trasande et al. 2006) suggests that our calculation of the economic costs (Trasande et al. 2005) may, in fact, be an underestimate. The new study indicates that downward shifts in IQ are also associated with thousands of excess cases of mental retardation mental retardation, below average level of intellectual functioning, usually defined by an IQ of below 70 to 75, combined with limitations in the skills necessary for daily living. (defined as IQ < 70) in the United States each year. Care of these children is associated with needs for health care, special education, and other services that impose a great burden on society.
All of these adverse consequences can be prevented by prevention of prenatal exposure to MeHg.
The authors declare they have no competing financial interests.
Phillip J. Landrigan
Center for Children's Health Children's Health Definition
Children's health encompasses the physical, mental, emotional, and social well-being of children from infancy through adolescence. and the Environment
Department of Community Medicine
Mount Sinai School of Medicine
Mount Sinai School of Medicine is a medical school found in the borough of Manhattan in New York City.
New York New York, state, United States
New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of , New York
Clyde B. Schechter
Department of Family Medicine
Albert Einstein College of Medicine
The Albert Einstein College of Medicine (AECOM) is a graduate school of Yeshiva University. It is a private medical school located in the Jack and Pearl Resnick Campus of Yeshiva University in the Morris Park
Bronx, New York
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Cohen JT, Bellinger DC, Shaywitz BA. 2005. A quantitative analysis Quantitative Analysis
A security analysis that uses financial information derived from company annual reports and income statements to evaluate an investment decision.
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