|Betreff: Fwd: Leukemia....NEED TO MIMIC HUMAN EXPOSURES.....EPRI &Harvard..2003|
|Von: JCMPelican @aol.com|
|Datum: Wed, 14 Feb 2007 00:16:05 EST|
|Betreff: Leukemia....NEED TO MIMIC HUMAN EXPOSURES.....EPRI &Harvard..2003|
|Von: JCMPelican @aol.com|
|Datum: Tue, 13 Feb 2007 13:36:24 EST|
Numerous epidemiologic studies have reported associations between measures of power-line electric or magnetic fields (EMFs) and childhood leukemia. The basis for such associations remains unexplained. In children, acute lymphoblastic leukemia represents approximately three-quarters of all U.S. leukemia types. Some risk factors for childhood leukemia have been established, and others are suspected. Pathogenesis, as investigated in animal models [rats and mice??? jcm file note 2-13-07......] , is consistent with the multistep model of acute leukemia development. Studies of carcinogenicity in animals, however, are overwhelmingly negative and do not support the hypothesis that EMF exposure is a significant risk factor for hematopoietic neoplasia. We may fail to observe effects from EMFs because, from a mechanistic perspective, the effects of EMFs on biology are very weak. Cells and organs function despite many sources of chemical "noise" (e.g., stochastic, temperature, concentration, mechanical, and electrical noise), which exceed the induced EMF "signal" by a large factor. However, the inability to detect EMF effects in bioassay systems may be caused by the choice made for "EMF exposure." "Contact currents" or "contact voltages" have been proposed as a novel exposure metric, because their magnitude is related to measured power-line magnetic fields. A contact current occurs when a person touches two conductive surfaces at different voltages. Modeled analyses support contact currents as a plausible metric because of correlations with residential magnetic fields and opportunity for exposure. The possible role of contact currents as an explanatory variable in the reported associations between EMFs and childhood leukemia will need to be clarified by further measurements, biophysical analyses, bioassay studies, and epidemiology. Key words: childhood leukemia, contact currents, contact voltages, electric and magnetic fields, EMF, review.
Whether health risks result from exposure to power-line electric or magnetic fields (EMFs) remains unclear. Epidemiologic studies have repeatedly shown small associations between measures of residential power-line magnetic fields and childhood leukemia. The possibility that these associations are caused by bias or confounders, however, cannot be ruled out (Savitz 2003). In addition, extensive investigations in animals at much higher levels of EMFs have not demonstrated adverse effects (Boorman et al. 2000). Recently, the International Agency for Research on Cancer (IARC 2002) designated EMFs as a class 2B carcinogen ("possibly carcinogenic"), based on "consistent statistical associations of high-level residential magnetic fields with a doubling of the risk of childhood leukemia." The California Department of Health Services (CADHS 2002) recently issued a report concluding that "EMFs can cause some degree of increased risk of childhood leukemia, adult brain cancer, Lou Gehrig's disease, and miscarriage." Hence, the question of whether electric-power use has a possible role in childhood leukemia risk remains in the forefront of concern.
To assess past research and suggest future directions in the area of childhood leukemia and EMFs, the Electric Power Research Institute and the Harvard School of Public Health sponsored a workshop titled "Childhood Leukemia: Added Risk from the Use of Electricity?" on 8 November 2001, in Lexington, Massachusetts. This workshop brought together a number of experts.
The epidemiologic associations reported between EMFs and childhood leukemia remain unexplained. Integrating all the lines of evidence presents a challenge to accurately evaluating potential health effects from EMFs. Epidemiologic results, when available, often predominate over rodent bioassay and other laboratory data in hazard identification and risk assessment. However, the epidemiology studies of EMFs and childhood leukemia, all of case-control design, pose several issues, and the link between EMFs and leukemia has not been supported by laboratory data. In many of the epidemiology studies, the small proportion of the study population classified as receiving high exposure levels limits the precision of the effect estimate. In addition, confounding and differential selection and participation of controls by attributes associated with exposure can lead to biased effect estimates (Ahlbom et al. 2000; Hatch et al. 2000). Finally, the relevant exposure metric is not known; thus, it has not been possible for epidemiologists to quantify EMF exposure appropriately in the study populations. Experimental approaches also have limitations, such as a) requiring high-dose to low-dose extrapolation, b) requiring interspecies extrapolation, c) using "pure" EMF signals of specific frequency and field strength that may not mimic real human exposures, and d) being subject to practical and logistic bounds on study size (statistical power). Epidemiologists have been hampered because experimental studies of EMFs have not identified biologic mechanism(s) that could serve as the basis for designing new studies. The goal of the workshop described here was to review the science and consider new directions for EMF research in the areas of epidemiology, exposure metrics, animal studies, and biophysics.
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