Residential power-frequency magnetic fields (MFs) were labeled as a possible human carcinogen by the International Agency for Research on Cancer panel. In response to great public concern, the World Health Organization urged that further epidemiologic studies be conducted in high-exposure areas such as Japan. We conducted a population-based case-control study, which covered areas inhabited by 54% of Japanese children. We analyzed 312 case children (0-15 years old) newly diagnosed with acute lymphoblastic leukemia (ALL) or acute myelocytic leukemia (AML) in 1999-2001 (2.3 years) and 603 controls matched for gender, age and residential area. Weekly mean MF level was determined for the child's bedroom. MF measurements in each set of a case and controls were carried out as closely in time as possible to control for seasonal variation. We evaluated the association using conditional logistic regression models. The odds ratios for children whose bedrooms had MF levels of 0.4 lT or higher compared with the reference category (MF levels below 0.1 lT) was 2.6 (95% CI 5 0.76-8.6) for AML 1 ALL and 4.7 (1.15-19.0) for ALL only. Controlling for some possible confounding factors did not alter the results appreciably. Even an analysis in which selection bias was maximized did not fully explain the association. Most of the leukemia cases in the highest exposure category had MF levels far above 0.4 lT. Our results provided additional evidence that high MF exposure was associated with a higher risk of childhood leukemia, particularly of ALL. ' 2006 Wiley-Liss, Inc.Key words: residential magnetic fields; childhood leukemia; population-based; case-control study; Japan Exposure to residential power-frequency magnetic fields (MFs) has been suspected to increase the risk of childhood leukemia, although the risk suggested by the first report 1 has not consistently been supported by the following ones.2-10 Recently, however, pooled analyses conducted by Ahlbom et al.11 used geometric means of MF levels and showed that the estimated summary relative risk was 2.00 (95% CI 5 1.27-3.13) when 0.41 lT was compared with < 0.1 lT. Another pooled analysis by Greenland et al.12 used arithmetic means of MF levels and showed that the Mantel-Haenszel odds ratio comparing 0.31 lT with < 0.1 lT was 1.7 (95% CI 5 1.2-2.3).Still, the small number of cases in high-dose ranges remains one of the limitations of these pooled analyses, and the causal inference remains tenuous because of little evidence from animal experiments and lack of appropriate biologic models. Thus, the World Health Organization recommended conducting one or more epidemiologic studies to evaluate the risk with more subjects exposed to high MF levels in 1999, 13 although the International Agency for Research on Cancer (IARC) rated the power-frequency MF as a possible human carcinogen in 2002 14 mainly based on the above finding by the pooled analyses.Thus, the present nationwide case-control study of childhood leukemia was conducted in Japan, where high MF exposures were expected to be ...

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BackgroundThe strength of the association between brain tumors in children and residential power-frequency magnetic fields (MF) has varied in previous studies, which may be due in part to possible misclassification of MF exposure. This study aimed to examine this association in Japan by improving measurement techniques, and by extending measurement to a whole week.MethodsThis population-based case-control study encompassed 54% of Japanese children under 15 years of age. After excluding ineligible targeted children, 55 newly diagnosed brain tumor cases and 99 sex-, age-, and residential area-matched controls were included in the analyses. The MF exposures of each set of matching cases and controls were measured in close temporal proximity to control for seasonal variation; the average difference was 12.4 days. The mean interval between diagnosis and MF measurements was 1.1 years. The weekly mean MF level was defined as the exposure. The association was evaluated using conditional logistic regression analysis that controlled for possible confounding factors.ResultsThe odds ratios (95% CI) for exposure categories of 0.1 to 0.2, 0.2 to 0.4, and above 0.4 µT, against a reference category of <0.1 µT, were 0.74 (0.17–3.18), 1.58 (0.25–9.83), and 10.9 (1.05–113), respectively, after adjusting for maternal education. This dose-response pattern was stable when other variables were included in the model as possible confounding factors.ConclusionsA positive association was found between high-level exposure—above 0.4 µT—and the risk of brain tumors. This association could not be explained solely by confounding factors or selection bias.

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An ungrounded human, such as a substation worker, receives contact currents when touching a grounded object in electric fields. In this article, contact currents and internal electric fields induced in the human when exposed to non-uniform electric fields at 50 Hz are numerically calculated. This is done using a realistic human model standing at a distance of 0.1-0.5 m from the grounded conductive object. We found that the relationship between the external electric field strength and the contact current obtained by calculation is in good agreement with previous measurements. Calculated results show that the contact currents largely depend on the distance, and that the induced electric fields in the tissues are proportional to the contact current regardless of the non-uniformity of the external electric field. Therefore, it is concluded that the contact current, rather than the spatial average of the external electric field, is more suitable for evaluating electric field dosimetry of tissues. The maximum induced electric field appears in the spinal cord in the central nervous system tissues, with the induced electric field in the spinal cord approaching the basic restriction (100 mV/m) of the new 2010 International Commission on Non-Ionizing Radiation Protection guidelines for occupational exposure, if the contact current is 0.5 mA.