Contending with Contradictory Data in a Risk Assessment Context: The Case of Methylmercury
Section snippets
INTRODUCTION
In 1998, the US Congress passed legislation requiring the US Environmental Protection Agency (EPA) to fund a National Academy of Sciences (NAS) expert panel to evaluate the toxicological effects of methylmercury. This legislation was passed in response to the EPA’s announcement of plans to conduct a new risk assessment for methylmercury based on findings from two recently published, large-scale, prospective longitudinal studies — one in the Seychelles Islands in the Indian Ocean (Davidson et
THE SEYCHELLES AND FAROE ISLANDS STUDIES
The Seychelles and Faroe Islands studies were conducted during the 1990s to investigate the neurodevelopmental risks associated with chronic, low-level exposure to methylmercury from fish. Both examined heavy fish consuming populations and performed extensive neuropsychological assessments during childhood. The Faroes are also exposed to methylmercury from a second source; namely, pilot whale meat, which bioaccumulates very significant levels of methylmercury. Methylmercury concentrations in
THE RALEIGH WORKSHOP
The contrasting findings from these two well-designed, state-of-the-art epidemiological studies presented a quandary to scientists and government regulators. How is it possible for one study to provide consistent evidence of adverse effect across a range of developmental outcomes while a second, well-designed large sample study does not find even a suggestion of adverse effect? To address this question, a peer review workshop was convened in Raleigh, NC, in November 1998, sponsored by the
THE NATIONAL ACADEMY OF SCIENCES (NAS) PANEL
In the fall of 1998, the EPA proposed new regulations to limit mercury emissions from coal-powered utility power plants in the midwest. Based on the contradictory findings from the Faroes and Seychelles studies, several midwestern Congressional representatives argued that the scientific basis for methylmercury toxicity at contemporary levels of environmental exposure is uncertain. Congressional representatives from the northeast, however, strongly supported reductions in the levels of
CONCLUSIONS
Prospective epidemiological studies in humans are often hampered by limited control over confounding and other factors, including unmeasured between cohort differences in genetic vulnerability, nutritional adequacy, and pattern of exposure. In the final analysis, inferences about toxicity, therefore, often depend heavily on qualitative assessments regarding the weight of the evidence across multiple studies, some of which are clearly sounder and more convincing than others. The New Zealand
Acknowledgements
I would like to thank the other members of the NAS panel (National Research Council, 2000) — Robert L. Goyer (chair), H. Vasen Aposhian, Lenore Arab, David C. Bellinger, Thomas M. Burbacher, Thomas A. Burke, Lynda M. Knobeloch, Louise M. Ryan, and Alan H. Stern — all of whom made significant contributions to the thinking and analyses reviewed in this paper.
References (27)
- et al.
Cognitive deficit in 7-year-old children with prenatal exposure to methylmercury
Neurotoxicol. Teratol.
(1997) - et al.
Effects of environmental exposure to polychlorinated biphenyls and dioxins on cognitive abilities in Dutch children at 42 months of age
J. Pediatr.
(1999) - et al.
Maternal seafood diet, methylmercury exposure, and neonatal neurological function
J. Pediatr.
(2000) - et al.
Intra-uterine methylmercury poisoning in Iraq
Pediatrics
(1974) - et al.
Alcohol-induced neuronal loss in developing rats: increased brain damage with binge exposure
Alcohol Clin. Exp. Res.
(1990) - Cohen J, 1988. Statistical power analysis for the behavioral sciences. Hillsdale (NJ): Lawrence Erblaum...
- Cordier S, Garel M, 1999. Neurotoxic risks in children related to exposure to methylmercury in French Guiana. INSERM...
Calculation of benchmark doses from continuous data
Risk Anal.
(1995)- et al.
Influence of prenatal mercury exposure upon scholastic and psychological test performance: benchmark analysis of a New Zealand cohort
Risk Anal.
(1998) - et al.
Effects of prenatal and postnatal methylmercury exposure from fish consumption on neurodevelopment: outcomes at sixty-six months of age in the Seychelles child development study
JAMA
(1998)
Early postnatal alcohol exposure that produces high blood alcohol levels impairs development of spatial navigation learning
Psychobiology
Impact of maternal seafood diet on fetal exposure to mercury selenium, and lead
Arch. Environ. Hlth.
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