Article

Contact Voltage Measured in Residences: Implications to the Association between Magnetic Fields and Childhood Leukemia

Authors:
  • Kavet Consulting LLC
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Abstract

We measured magnetic fields and two sources of contact current in 36 homes in Pittsfield, MA. The first source, V(P-W), is the voltage due to current in the grounding wire, which extends from the service panel neutral to the water service line. This voltage can cause contact current to flow upon simultaneous contact with a metallic part of the water system, such as the faucet, and the frame of an appliance, which is connected to the panel neutral through the equipment-grounding conductor. The second is V(W-E), the voltage between the water pipe and earth, attributable to ground currents in the water system and magnetic induction from nearby power lines. In homes with conductive water systems and drains, V(W-E) can produce a voltage between the faucet and drain, which may produce contact current into an individual contacting the faucet while immersed in a bathtub. V(P-W) was not strongly correlated to the magnetic field (both log transformed) (r = 0.28; P < 0.1). On the other hand, V(W-E) was correlated to the residential magnetic field (both log transformed) (r = 0.54; P < 0.001), with the highest voltages occurring in homes near high voltage transmission lines, most likely due to magnetic induction on the grounding system. This correlation, combined with both frequent exposure opportunity for bathing children and substantial dose to bone marrow resulting from contact, lead us to suggest that contact current due to V(W-E) could explain the association between high residential magnetic fields and childhood leukemia.

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... Results from the pilot study supported the critical assumption that children do have frequent contact with sources of electrical currents while bathing; physical contact in the bathtub (defined as touching the water spout and/or faucet) occurred while bathing 77% of the time for a child aged 1-6, with an average of one contact per bath. The feasibility of conducting residential contact voltage measurements (both point-in-time and long-term measurements) was demonstrated in prior studies (10,19,20). ...
... Although this is the first epidemiological study of contact currents and childhood leukemia, previous exposure studies have measured residential contact voltage. These studies include a pilot study of 36 residences in Pittsfield, MA (19), where the sample was weighted toward residences with proximity to highvoltage transmission lines or large three-phase primary ...
... Based on previous studies that reported a positive relationship between residential magnetic fields and measures of contact voltage (10,19,25), this study was designed to address whether exposure to contact voltage was an independent risk factor for childhood leukemia or served to confound the association of magnetic fields with childhood leukemia. We did not observe a positive association between contact voltage and childhood leukemia and, because there was no association of magnetic fields with childhood leukemia in this population, the opportunity for detecting confounding was minimal. ...
Article
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The objectives of this study were to examine the association between contact current exposure and the risk of childhood leukemia and to investigate the relationship between residential contact currents and magnetic fields. Indoor and outdoor contact voltage and magnetic-field measurements were collected for the diagnosis residence of 245 cases and 269 controls recruited in the Northern California Childhood Leukemia Study (2000-2007). Logistic regression techniques produced odds ratios (OR) adjusted for age, sex, Hispanic ethnicity, mother's race and household income. No statistically significant associations were seen between childhood leukemia and indoor contact voltage level [exposure ≥90th percentile (10.5 mV): OR  =  0.83, 95% confidence interval (CI): 0.45, 1.54], outdoor contact voltage level [exposure ≥90th percentile (291.2 mV): OR  =  0.89, 95% CI: 0.48, 1.63], or indoor magnetic-field levels (>0.20 µT: OR  =  0.76, 95% CI: 0.30, 1.93). Contact voltage was weakly correlated with magnetic field; correlation coefficients were r  =  0.10 (P  =  0.02) for indoor contact voltage and r  =  0.15 (P  =  0.001) for outdoor contact voltage. In conclusion, in this California population, there was no evidence of an association between childhood leukemia and exposure to contact currents or magnetic fields and a weak correlation between measures of contact current and magnetic fields.
... Limiter l'existence du champ E interne aux champs E et/ou B externes n'est pas exhaustif. Il existe une autre source qui a été mise en évidence par Kavet et al, 2000Kavet et al, , 2002Kavet et al, , 2004Kavet et al, , 2005Bowman et al, 2006 : le courant de contact. Lorsqu'une personne touche simultanément deux objets conducteurs qui sont à des potentiels différents, un dénommé courant de contact circule dans son corps. ...
... Cet article, basé sur une étude de la littérature et nos propres mesures, semble orienter la recherche dans une voie, suggérée auparavant par Kavet et al, 2000Kavet et al, , 2002Kavet et al, , 2004 : l'ensemble de la population devrait faire vérifier et modifier (si nécessaire) l'installation électrique de son habitation pour assurer la conformité de celleci avant de chercher une source externe au problème. ...
... Kavet und Kollegen haben in mehreren Publikationen die Kontaktstrom-Hypothese entwickelt, thematisiert und Daten und Argumente dazu vorgelegt: Kavet, Zaffanella et al. (2000), Kavet and Zaffanella (2002), Kavet, Zaffanella et al. (2004), Kavet (2005) ...
... und in 2.4.2.3 erwähnt einige 10 mV. Nur bei wenigen % der Haushalte übersteigen sie 100 mV -siehe:Kavet and Zaffanella (2002),Kavet, Zaffanella et al. (2004), Does, Scelo et al. (2011. Die daraus berechneten Körperströme -Kavet verwendete bei seinen Messungen einen Widerstand von 1000 Ω -liegen im Bereich von 0.01-0.05 ...
Technical Report
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The report collects and summarises the currently available scientific literature about stray voltages. It comments on technical issues, on exposure levels on farms and in houses, and on impacts of contact currents on cattle and humans, especially children. A glossary completes the report. Report is available in German only.
... T. W. Dawson responsible for health effects, most notably childhood leukemia [3]. Numerical modeling indicates that the electric fields in human tissue resulting from typical contact currents are much greater than those induced from typical exposures to electric and magnetic fields at power line frequencies [4]. ...
... The results for ESD are compared to the fields in tissue reported for contact currents [4]. The selection of tissues of interest is based on the possible interaction mechanisms, namely the hypothesized leukemia link to strong electric fields in bone marrow [3], and the established interaction with excitable tissue, namely heart, muscle and fat (where peripheral nerves are located). The brain is not explicitly considered, as the associated electric fields due to ESD involving limb-to-limb paths are very low. ...
Article
Full-text available
Electrostatic discharges (ESDs) occur when two objects at different electric potentials come close enough to arc (spark) across the gap between them. Such discharges may be either single-event or repetitive (e.g., 60 Hz). Some studies have indicated that ESDs may be a causative factor for health effects in electric utility workers. Moreover, a hypothesis has recently been forwarded imperceptible contact currents in the human body may be responsible for health effects, most notably childhood leukemia. Numerical modeling indicates that the electric fields in human tissue resulting from typical contact currents are much greater than those induced from typical exposures to electric and magnetic fields at power line frequencies. Numerical modeling is used here to compute representative spark-discharge dosimetry in a realistic human adult model. The frequency-domain scalar potential finite difference method is applied in conjunction with the Fourier transform to assess electric fields in selected regions and tissues of interest in the body. Electric fields in such tissues as subcutaneous fat (where peripheral nerves may be excited), muscle and bone marrow are of the order of kilovolts per meter in the lower arm. The pulses, however, are of short duration (approximately 100 ns).
... A relatively weak contact current may generate a strong internal electric field, which can produce several carcinogenic effects, such as cell proliferation, disruption of signal transduction pathways and inhibition of differentiation. 54,55 A study by Kavet and Zaffanella found a correlation between the voltage between the water pipe and earth, attributable to ground currents in the water system, and the magnetic induction from nearby power lines and electromagnetic fields. The same study also revealed that the dose of contact current exposure is high enough to may cause biological effects to the bone marrow. ...
... The same study also revealed that the dose of contact current exposure is high enough to may cause biological effects to the bone marrow. 54 However, in a recent study by Does et al., 30 only a weak correlation was found between contact currents and EMF exposure and no relation between contact currents and CL was observed. ...
Article
The increasing exposure to electromagnetic fields (EMFs) has raised concern, as increased exposure may result in an increased risk of childhood leukemia (CL). Besides a short introduction of CL and EMF, our article gives an evaluation of the evidence of a causal relation between EMF and CL by critically appraising the epidemiological and biological evidence. The potential impact is also estimated by the population attributable risk. The etiology of CL is largely unknown, but is probably multifactorial. EMF may be one of the environmental exposures involved. Three pooled analyses of case-control studies showed a 1.4- to 1.7-fold increased CL risk for extremely low-frequency EMF (ELF-EMF) exposure levels above 0.3 μT. Several biases may have played a role in these studies, but are unlikely to fully explain the increased risk. For effects of radiofrequency ELF evidence is lacking. None of the proposed biological mechanisms by which ELF-EMF might cause CL have been confirmed. The estimated overall population attributable risk was 1.9%, with the highest estimates in Northern America and Brazil (4.2% and 4.1%, respectively). The potential impact of EMF exposure on public health is probably limited, although in some countries exposure might be relatively high and thus might have a more substantial impact. We recommend nationwide surveys to gain more insight into the contemporary exposure levels among children. Reducing exposure from power lines near densely populated areas and schools is advised. Future epidemiological studies should focus on limiting bias.
... To limit the existence of internal E-field to external E-field and/or B-field is not exhaustive. There is another source which has been first pointed out by Kavet et al, 2000Kavet et al, , 2002Kavet et al, , 2004Kavet et al, , 2005Bowman et al, 2006: the contact current. When a person simultaneously touches two conductive objects that are at different potentials, a so-called contact current flows through his/her body. ...
Article
Full-text available
Since the early seventies, potential health risks from ELF (Extremely Low frequency electromagnetic Fields) exposure (50 Hz) have been extensively treated in the literature (more than 1000 references registered by WHO (World Health Organisation), 2007). After 30 years of worldwide research, the major epidemiological output is the possible modest increased risk (by a factor 2) of childhood leukaemia in case of a long exposure to an ambient magnetic flux density (B-field) higher than 0.4 µT. However, this fact has not been confirmed by in vivo and in vitro studies. Moreover it has not been validated by any adverse health biological mechanisms neither for adults nor for children. International recommendations (ICNIRP, International Commission on Non-Ionising Radiation Protection) are currently, for general public, not to exceed a B-field of 100 µT (50 Hz) and an E-field of 5 kV/m (50 Hz). Herein, a rough overview of typical values of ELF fields will be presented followed by a brief literature survey on childhood leukaemia and ELF. The potential carcinogenic effect of ELF would be linked to electrical disturbances in cell behaviour. The major concern linking childhood leukaemia and ELF is thus to determine the response of bone marrow cells under ELF fields. With that purpose, transmembrane potential will be targeted and linked to the E-field at that level. This paper is three-folded: (1) the electric interactions between ambient ELF fields and the body are studied both qualitatively and quantitatively. Different sources of internal E-field are analysed and classified according to their potential risk; (2) the hypothesis of contact current is detailed; (3) key actions to undertake are highlighted. Based on the current state of the art and some authors' own developments, this paper proposes simple low cost enhancements of private electrical installations in order to anihilate the major source of potential effects of ELF.
... Contact currents can also result from induction caused by magnetic fields from nearby heavily loaded power lines. This form of exposure is more likely in residences with high magnetic fields, in which contact current from metallic fixtures during the bathing of children may lead to elevated bone-marrow doses of induced currents (Kavet and Zaffanella, 2002; Brain et al., 2003). Unfortunately, there are few data on the role of contact voltages, and further research is required in this area. ...
Article
Childhood exposure to physical contamination, including non-ionizing radiation, has been implicated in numerous diseases, raising concerns about the widespread and increasing sources of exposure to this type of radiation. The primary objective of this review was to analyze the current state of knowledge on the association between environmental exposure to non-ionizing radiation and the risk of childhood leukemia. Scientific publications between 1979 and 2008 that include examination of this association have been reviewed using the MEDLINE/PubMed database. Studies to date have not convincingly confirmed or ruled out an association between non-ionizing radiation and the risk of childhood leukemia. Discrepancies among the conclusions of the studies may also be influenced by confounding factors, selection bias, and misclassification. Childhood defects can result from genetic or epigenetic damage and from effects on the embryo or fetus, which may both be related to environmental exposure of the parent before conception or during the pregnancy. It is therefore critical for researchers to define a priori the type and "window" of exposure to be assessed. Methodological problems to be solved include the proper diagnostic classification of individuals and the estimated exposure to non-ionizing radiation, which may act through various mechanisms of action. There appears to be an urgent need to reconsider exposure limits for low frequency and static magnetic fields, based on combined experimental and epidemiological research into the relationship between exposure to non-ionizing radiation and adverse human health effects.
... To limit the existence of internal E-field to external E-field and/or B-field is not exhaustive. There is another source which has been first pointed out by Kavet et al, 2000Kavet et al, , 2002Kavet et al, , 2004Kavet et al, , 2005Bowman et al, 2006: the contact current. When a person simultaneously touches two conductive objects that are at different potentials, a so-called contact current flows through his/her body. ...
... However, because of the environmental conditions, in real life we are sometimes exposed to pure EF without magnetic field (7). For example, people are exposed to EFs generated by high voltage power lines with no current, mine processing plants using static electric as a power source, or idling high voltage power transformers (7,8). ...
Article
Full-text available
Aim: The effect of 50 Hz electric field (EF) on developing neural tissues is not known. We aimed to determine whetherthere would be any oxidative stress effect of 50 Hz EF on developing spinal cord tissues of pup rats by evaluatingmalondialdehyde (MDA), nitric oxide (NO) levels, and antioxidant enzyme activities such as superoxide dismutase(SOD) and catalase (CAT) measurement.Materials and methods: In the prenatal+postnatal group, the pregnant rat was exposed to continuous EF at 50 Hz 10 kV/suntil delivery. Then the female pups of this group (n = 7) were exposed to EF at the same doses and for the same durationuntil puberty. In the postnatal group, the pregnant rat was unexposed to EF during pregnancy, but the female pups fromthis group (n = 7) began to be exposed to EF at delivery, and continued to be exposed to EF at 50 Hz EF 10 kV/m for 24h until puberty.Results: In the prenatal+postnatal group, the MDA and NO levels in the spinal cord tissue of pup rats were significantlyhigher when compared to the control group. However, in the postnatal group, the MDA and NO levels in the spinal cordtissue of pup rats were not significantly different when compared to the control group.Conclusion: A 50 Hz electric field may cause oxidative stress in the spinal cord of rats in the prenatal+postnatal period.
... In a computer-modeled neighborhood, Kavet et al. (2000) observed that V P–W is highly correlated to the magnetic field attributable to the ground current within a particular residence. In a pilot study of 36 residences (Kavet and Zaffanella 2002), the degree of correlation between contact voltages and magnetic field measurements varied. V P–W was poorly correlated to spot-measured magnetic fields (B avg ) (both log-transformed). ...
Article
Full-text available
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, 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.
... Adjustments for age, sex, and socioeconomic indices have almost no direct impact on results; estimate changes arising from adjustment are attributable to changes in data sets arising from missing data, rather than from the actual adjustment (Greenland et al., 2000 ). To account for the fact that exposure is associated with housing factors that themselves may be associated with risk (e.g., via contact currents; see Brain et al., 2003; Kavet & Zaffanella, 2002), we based our prior distribution for uncontrolled confounding on the distribution of associations observed in Bracken et al. (1998). The log odds ratios from that survey were consistent with draws from a normal (0,5/6) distribution ; thus we modeled the odds ratios TU and UY for the relations of an unmeasured factor U to fields T and leukemia Y in a study s with D = d, W = w as ...
Article
Nearly every epidemiologic study of residential magnetic fields and childhood leukemia has exhibited a positive association. Nonetheless, because these studies suffer from various methodologic limitations and there is no known plausible mechanism of action, it remains uncertain as to how much, if any, of these associations are causal. Furthermore, because the observed associations are small and involve only the highest and most infrequent levels of exposure, it is believed that the public health impact of an effect would be small. We present some formal analyses of the impact of power-frequency residential magnetic-field exposure (as measured by attributable fractions), accounting for our uncertainties about study biases as well as uncertainties about exposure distribution. These analyses support the idea that the public health impact of residential fields is likely to be limited, but both no impact and a substantial impact remain possibilities in light of the available data.
... Adjustments for age, sex, and socioeconomic indices have almost no direct impact on results; estimate changes arising from adjustment are attributable to changes in data sets arising from missing data, rather than from the actual adjustment (Greenland et al., 2000). To account for the fact that exposure is associated with housing factors that themselves may be associated with risk (e.g., via contact currents; see Brain et al., 2003; Kavet & Zaffanella, 2002), we based our prior distribution for uncontrolled confounding on the distribution of associations observed in Bracken et al. (1998). The log odds ratios from that survey were consistent with draws from a normal (0,5/6) distribution ; thus we modeled the odds ratios TU and UY for the relations of an unmeasured factor U to fields T and leukemia Y in a study s with D ...
Article
Nearly every epidemiologic study of residential magnetic fields and childhood leukemia has exhibited a positive association. Nonetheless, because these studies suffer from various methodologic limitations and there is no known plausible mechanism of action, it remains uncertain as to how much, if any, of these associations are causal. Furthermore, because the observed associations are small and involve only the highest and most infrequent levels of exposure, it is believed that the public health impact of an effect would be small. We present some formal analyses of the impact of power-frequency residential magnetic-field exposure (as measured by attributable fractions), accounting for our uncertainties about study biases as well as uncertainties about exposure distribution. These analyses support the idea that the public health impact of residential fields is likely to be limited, but both no impact and a substantial impact remain possibilities in light of the available data.
... However, electricity-induced fields include harmonics of the base frequency, as well as high-voltage transient fields when currents are turned on and off (7). Ground currents are common, usually a result of wiring flaws and magnetic induction from nearby power lines (8). Contact currents, found in household plumbing as a result of multigrounded neutrals, may result in currents of tens of microamperes when a person touches the plumbing (9). ...
Chapter
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The present chapter deals with that portion of the electromagnetic spectrum that has lower energy and longer wavelengths than the infrared, including the extra low frequency (ELF) magnetic fields from electricity and radiofrequency (RF) fields used in communication. The energies at these frequencies are not sufficient to directly break chemical bonds, and the question to be examined is whether they have sufficient energy to cause human disease by other mechanisms, particularly at intensities that do not cause measurable heating. Present research indicates a consistent pattern of elevated risk of cancer, especially leukemia, and some neurodegenerative diseases at ELF magnetic field levels commonly found in residences and occupations. The relationship between childhood magnetic field exposure and brain cancer is also reviewed. Human studies and meta-analyses of research of mobile phone use show a consistent and elevated risk of brain cancer and acoustic neuroma upon intense and long-term use. International and national standards of human exposure to ELF and RF frequencies are presented and found to be inadequate for the protection of human health. The evidence of human harm from excessive exposure to both ELF and RF is stronger and more consistent for cancer and neurodegenerative diseases than is commonly recognized. While there is less strong reproducibility and consistency for some other proposed health outcomes, this indicates only the need for more research with better exposure assessment. Keywords: Leukemia; brain cancer; acoustic neuroma; Alzheimer's disease; amyotrophic lateral sclerosis; electromagnetic fields (EMFs); mutations; radiofrequency; Universal Mobile Telecommunications System
... Contact currents can also result from induction caused by magnetic fields from nearby heavily loaded power lines. This form of exposure is more likely in residences with high magnetic fields, in which contact current from metallic fixtures during the bathing of children may lead to elevated bone-marrow doses of induced currents (Kavet and Zaffanella, 2002;Brain et al., 2003). Unfortunately, there are few data on the role of contact voltages, and further research is required in this area. ...
... Kavet and colleagues (Kavet and Zaffanella, 2002;Bridges, 2002;Kavet et al., 2004;Kavet, 2005) proposed that effects on leukemia in children, which epidemiology has associated with domestic magnetic fields, are in fact due to small shocks that arise due to potential differences that build up between the water tap and the grounded drain of a tub. Shocks received in the bath were hypothesized to induce in a small child's body current densities of a magnitude known to induce a biological effect. ...
Article
Full-text available
Based on the epidemiological association between residential exposure to extremely low frequency-magnetic fields (ELF-MF) and childhood leukaemia, the International Agency for Research on Cancer classified ELF-MF as a possible human carcinogen. Since clear supportive laboratory evidence is lacking and biophysical plausibility of carcinogenicity of MFs is questioned, a causal relationship between childhood leukaemia and magnetic field exposure is not established. Among the alternative explanations, selection bias in epidemiological studies of MFs seems to be the most plausible hypothesis. In reviewing the epidemiological literature on ELF-MF exposure and childhood leukaemia, we found evidence both for and against the existence of selection bias. To evaluate the potential for selection bias, we examined the relationship of socioeconomic status to subject participation and exposure to MFs. We find that, often, reporting of selection processes in itself is biased and incomplete, making the interpretation and evaluation of a potential for bias difficult. However, if present, such a bias would have wide implications for case-control studies in general. We call for better reporting and for evaluation of the potential for selection bias in all case-control studies, as well as, for the development of novel methods in control selection and recruitment.
Article
Comparatively high exposures to power-frequency electric and magnetic fields produce established biological effects that are explained by accepted mechanisms and that form the basis of exposure guidelines. Lower exposures to magnetic fields (< 1 microT average in the home) are classified as "possibly carcinogenic" on the basis of epidemiological studies of childhood leukemia. This classification takes into consideration largely negative laboratory data. Lack of biophysical mechanisms operating at such low levels also argues against causality. We survey around 20 biophysical mechanisms that have been proposed to explain effects at such low levels, with particular emphasis on plausibility: the principle that to produce biological effects, a mechanism must produce a "signal" larger than the "noise" that exists naturally. Some of the mechanisms are impossible, and some require specific conditions for which there is limited or no evidence as to their existence in a way that would make them relevant to human exposure. Others are predicted to become plausible above some level of field. We conclude that effects below 5 microT are implausible. At about 50 microT, no specific mechanism has been identified, but the basic problem of implausibility is removed. Above about 500 microT, there are established or likely effects from accepted mechanisms. The absence of a plausible biophysical mechanism at lower fields cannot be taken as proof that health effects of environmental electric and magnetic fields are impossible. Nevertheless, it is a relevant consideration in assessing the overall evidence on these fields.
Article
Contact currents from touching objects with different voltages can produce electric fields within the body that produce neurological and other biological effects. To begin measuring these exposures among electric utility workers, a new contact current meter (CCM) was tested in a pilot study at Southern California Edison. The CCM was worn for 82 full-shift measurements by 76 volunteers from eight occupations who did not work directly with energized electrical equipment. The volunteers were exposed to an average of 285.8 contact current events above the meter's 1-microA threshold, but most of these were electrostatic spark discharges. Fourteen employees experienced an average of 135.1 contact currents events whose primary frequency was 60 Hz. Using a circuit model of the human body, the average contact currents going from arm to arm was 9.8 microA (maximum = 178.0 microA), and the average going down the torso was 25.5 microA (maximum = 662.0). The maximum exposures were experienced by a technical support employee working in a substation. All measurements in this pilot study were below the 3000 microA maximum permissible exposure for contact currents set by the Institute of Electrical and Electronic Engineers (IEEE). Combining these current measurements with the results of high-resolution dosimetry, the internal electric fields averaged an estimated 1.7 mV/m in the heart (maximum = 21.0 mV/m), and 1.9 mV/m in the hematopoietic bone marrow in the torso (maximum = 56.5 mV/m). These internal electric fields from contact currents are below the basic restriction of 943 mV/m in the IEEE exposure standards but are above 1 mV/m, a level where biological effects have been often reported in laboratory studies. Safety concerns limited the measurements to de-energized equipment, so we did not obtain data on work in energized high-voltage environments, the most likely sources of high contact currents. This pilot study identified other improvements to the contact current meter that would make it better able to measure exposures in future health studies.
Article
Limits on exposures to extremely low-frequency electric fields, magnetic fields and contact currents, designated as voluntary guidelines or standards by several organizations worldwide, are specified so as to minimize the possibility of neural stimulation. The limits, which we refer to as guidelines, derive from "basic restrictions" either on electric fields or current density within tissue, or on avoidance of annoying or startling interactions that may be experienced with spark discharge or contact current. Further, the guidelines specify more conservative permissible doses and exposure levels for the general public than for exposures in controlled environments, which most typically involve occupational settings. In 2001 we published an update on guideline science. This paper covers more recent developments that are relevant to the formulation and implementation of the next generation of guidelines. The paper deals with neurostimulation thresholds and the relevance of magnetophosphenes to setting guideline levels; dosimetry associated with contact current benchmarked against basic restrictions; tissue and cellular dosimetry from spark discharge; assessment of exposures to high electric fields in realistic situations (e.g., line worker in a transmission tower); a simplified approach to magnetic field assessment in non-uniform magnetic fields; and a quantitative approach to sampling workplace exposure for assessing compliance.
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Research conducted over the past 5 years has addressed the hypothesis that the reported association between residential magnetic fields and childhood leukemia may be explained by exposure to contact current. The use of multi-grounded neutrals in electrical distribution and residential electrical wiring systems in the United States results in a voltage on a residence's water line relative to earth that in turn creates a voltage between the water fixtures of a bathtub, sink, or shower and the drain, if the latter is made of conductive material. A bathing child may thus be exposed to contact current upon manual contact with the faucet, spout, or water stream. Dosimetry modeling indicates that modest and realistically anticipated currents (10s of microA) can produce electric fields in bone marrow (100s of mV/m) sufficient to overcome questions of biophysical plausibility. Both measurements in two regions of the United States and computer modeling of typical single-residence US neighborhoods indicate that residences with average magnetic fields in the high tail of the magnetic field distribution are more likely than residences with lower fields to also have higher contact voltage. The association of residential magnetic fields with contact voltage, the dosimetry results, and the indication from a behavioral survey that children tend to engage in behavior that results in exposure all support the hypothesis. Further research is needed to characterize electrical systems in other nations to determine whether contact current exposure occurs and whether it is associated with residential magnetic fields.
Article
Conventional analytic results do not reflect any source of uncertainty other than random error, and as a result readers must rely on informal judgments regarding the effect of possible biases. When standard errors are small these judgments often fail to capture sources of uncertainty and their interactions adequately. Multiple-bias models provide alternatives that allow one systematically to integrate major sources of uncertainty, and thus to provide better input to research planning and policy analysis. Typically, the bias parameters in the model are not identified by the analysis data and so the results depend completely on priors for those parameters. A Bayesian analysis is then natural, but several alternatives based on sensitivity analysis have appeared in the risk assessment and epidemiologic literature. Under some circumstances these methods approximate a Bayesian analysis and can be modified to do so even better. These points are illustrated with a pooled analysis of case-control studies of residential magnetic field exposure and childhood leukaemia, which highlights the diminishing value of conventional studies conducted after the early 1990s. It is argued that multiple-bias modelling should become part of the core training of anyone who will be entrusted with the analysis of observational data, and should become standard procedure when random error is not the only important source of uncertainty (as in meta-analysis and pooled analysis). Copyright 2005 Royal Statistical Society.
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This article examines the potential for misleading inferences from conventional analyses and sensitivity analyses of observational data, and describes some proposed solutions based on specifying prior distributions for uncontrolled sources of bias. The issues are illustrated in a sensitivity analysis of confounding in a study of residential wire code and childhood leukemia and in a pooled analysis of 12 studies of magnetic-field measurements and childhood leukemia. Both analyses have been interpreted as evidence in favor of a causal effect of magnetic fields on leukemia risk. This interpretation is contrasted with results from analyses based on prior distributions for the unidentified bias parameters used in the original sensitivity-analysis model. These analyses indicate that accounting for uncontrolled confounding and response bias under a reasonable prior can substantially alter inferences about the existence of a magnetic-field effect. More generally, analyses with informative priors for unidentified bias parameters can help avoid misinterpretation of conventional results and ordinary sensitivity analyses.
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All populations are exposed to varying degrees of electromagnetic fields (EMF); in this study we consider only extremely low frequency (ELF) and radio frequency (RF) fields. After the first study of ELF and childhood leukemia in 1979, intensive epidemiologic investigation has sought to shed light on the potential relation between EMF and childhood leukemia. Consistent associations from epidemiologic studies and two pooled analyses have been the basis for the classification of ELF as a possible carcinogen by the International Agency for Research on Cancer (IARC). The study of RF is still in its infancy and little is known about residential RF exposure or its potential effects on childhood leukemia. The purpose of this study, presented at the WHO Workshop on Sensitivity of Children to EMF in Istanbul, Turkey in June 2004, is to review and critically assess the epidemiologic evidence on EMF and childhood leukemia.
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This study was designed to provide an experimental validation for a statistical model predicting past or future exposures to magnetic fields (MF) from power lines. The model estimates exposure, combining the distribution of ambient MF in the absence of power lines with the distribution of past or future MF produced by power lines. In the study, validation is carried out by comparing exposures predicted by the model with the actual measurements obtained from a large-scale epidemiological study. The comparison was made for a group of 220 women living near a 735 kV power line. Knowing that the individual arithmetic means of MF exposures follow a log-normal distribution, the Pearson correlation between the log-transformed measured means and the calculated ones was determined and found to be 0.77. Predicted values of MF exposures were slightly lower than measured values. The calculated geometric mean of the group was 0.33 microT, compared to 0.38 microT for the measured geometric mean. The present study shows good agreement between the measured MF exposure of an individual inside a house near a 735 kV line and the MF exposure calculated using a statistical model.
Article
Widespread concerns about whether electric and magnetic fields (EMF) could adversely affect human health have been raised in epidemiologic studies reported since the 1980s. Possible EMF health effects have been widely publicized in the popular press since that time. We consider here three possible mechanisms of action of EMF on childhood leukemia. We identify the first as "magnetic fields": this hypothesis relates the average level of magnetic field to the incidence of childhood leukemia. We identify a second, recently proposed, mechanism as "contact current": this hypothesis relates the low voltage and consequent current that occurs on the domestic water pipe, due to U.S. grounding practices, as a source for exposure of children. The third hypothesis is that the relationship observed is spurious. Using a modified example taken from the work of Von Winterfeldt and Keeney, we use Decision Analysis to estimate the value of information for distinguishing between the three hypotheses. We believe that this improves on the usual process for deciding on research budgets. Depending on which hypothesis we favor a priori, the value of being informed ranges from US 101 dollars to US 233 dollars per "problem household." Since there could be as many as 2 million such households, the value of information for resolving this issue could approach half a billion dollars! We find that there is no value of information for finding the odds ratio given the contact current hypothesis. In writing this article, we have consciously kept the computations as simple as possible so as to engage the reader's attention and interest. In a penultimate section, we suggest numerous possible extensions for a group interested in discussing and deciding on the value of research on the relationship between magnetic fields and cancer.
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Electric and magnetic fields are ubiquitous in the modern society, and concerns have been expressed regarding possible adverse effects of these exposures. This review covers epidemiologic research on health effects of exposures to static, extremely low-frequency (ELF), and radio frequency (RF) fields. Research on ELF fields has been performed for more than two decades, and the methodology and quality of studies have improved over time. Studies have consistently shown increased risk for childhood leukemia associated with ELF magnetic fields, whereas ELF fields most likely are not a risk factor for breast cancer and cardiovascular disease. There are still inadequate data for other outcomes. More recently, focus has shifted toward RF exposures from mobile telephony. There are no persuasive data suggesting a health risk, but this research field is still immature with regard to the quantity and quality of available data. This technology is constantly changing and there is a need for continued research on this issue. Almost no epidemiologic data are available for static fields.
Article
The US National Electrical Code's (NEC) requirement to ground a home's electrical service to the residential water line results in a voltage between the water line and earth, V W-E. The voltage may result from ground return current that flows into the earth via the water line or from inductive effects from other sources of magnetic fields, such as transmission lines. This voltage can, in turn, serve as a source for Vbath, the voltage between the water fixtures and conductive drain pipes sunk into the earth beneath a residence. Vbath can be a source of contact current exposure to a child touching a water fixture while bathing. Previous research has suggested that exposure to these currents could be the basis for the association between power-frequency magnetic fields and childhood leukemia. In this study, we assessed the association between measured Vbath and VW-E with the average spot-measured magnetic field, Bavg, in a sample of 191 single-family residences in the Denver metropolitan area. This area was the source of cases and controls for previous studies of electric and magnetic field (EMF) and childhood cancer. The association of both Vbath and VW-E with Bavg had upward trends across magnetic field strata (<0.1 microT (reference); 0.1-<0.3 microT; and > or = 0.3 microT). In addition, VW-E was associated with Vbath. Without further study, these results cannot be applied to multi-dwelling residences or to electrical systems prevalent in other nations. Nonetheless, when combined with the finding that contact current is a far more plausible candidate than the residential magnetic field for mediating biological effects on the basis of comparative dose to bone marrow, these associations indicate that contact current exposure deserves further study.
Article
There are numerous techniques for constructing confidence intervals, most of which are unavailable in standard software. Modern computing power allows one to replace these techniques with relatively simple, general simulation methods. These methods extend easily to incorporate sources of uncertainty beyond random error. The simulation concepts are explained in an example of estimating a population attributable fraction, a problem for which analytical formulas can be quite unwieldy. First, simulation of conventional intervals is illustrated and compared to bootstrapping. The simulation is then extended to include sampling of bias parameters from prior distributions. It is argued that the use of almost any neutral or survey-based prior that allows non-zero values for bias parameters will produce an interval estimate less misleading than a conventional confidence interval. Along with simplicity and generality, the ease with which simulation can incorporate these priors is a key advantage over conventional methods.
Article
A portable meter has been developed for measuring low frequency currents that flow in the human body. Although the present version of the meter was specifically designed to measure 50/60 Hz "contact currents," the principles involved can be used with other low frequency body currents. Contact currents flow when the human body provides a conductive path between objects in the environment with different electrical potentials. The range of currents the meter detects is approximately 0.4-800 microA. This provides measurements of currents from the threshold of human perception (approximately 500 microA(RMS)) down to single microampere levels. The meter has a unique design, which utilizes the human subject's body impedance as the sensing element. Some of the advantages of this approach are high sensitivity, the ability to measure current flow in the majority of the body, and relative insensitivity to the current path connection points. Current measurement accuracy varies with the accuracy of the body impedance (resistance) measurement and different techniques can be used to obtain a desired level of accuracy. Techniques are available to achieve an estimated +/-20% accuracy.
Article
Contact currents flow when a conducting object such as an animal touches conductive surfaces at different potentials. This completes a path for current flow through the body. These currents provide an additional coupling mechanism between the human body and low-frequency external fields to that due to direct induction effects. Recent research indicates that childhood exposure to residential contact currents may play a role in explaining any possible association between residential magnetic fields and childhood leukemia. To verify this hypothesis, laboratory experiments with rodents are planned. Thus, it is important to understand the relationship between fields induced in rodents and humans. Results from numerical computations are reported here. They are based on high-resolution anatomically based inhomogeneous models of adult and child male humans and male and female rats and mice, for a variety of 60-Hz contact current scenarios. It is hoped that this work will aid in the design of experiments involving rodents and in the interpretation of results as applied to humans. It is found that for geometrically similar models, the induced electric-field scales in an anticipated inverse-square manner with the geometric scaling factor. For dissimilar models, scaling can provide a crude estimate for translating induced field results between species. However, numerical modeling provides the most suitable analysis tool for more accurate estimates.
Article
The objectives of this study were to characterize temporal patterns of magnetic fields (Bavg) and two measures of neutral-to-earth voltage: the voltage between the water line and earth (VW-E), and the voltage between bathtub plumbing fixtures and the drain (Vbath). The latter is a source of exposure to contact current in bathing children that has been proposed to explain the reported association between power-frequency magnetic fields and childhood leukemia. These quantities were measured each minute in a sample of 15 single-detached residences in San Jose, CA. Generally, Bavg, VW-E, and Vbath were positively correlated with each other within residences, and displayed similar diurnal patterns. Weekday and weekend patterns displayed qualitative differences that reflect the more scheduled workday for weekdays, and a less structured pattern for weekends. When pooled with two prior measurement studies, positive associations across residences between Bavg and both VW-E and Vbath were observed. Home designs over the past 30-40 years have lead to a decreasing prevalence of Vbath as conductive drains have been swapped out for non-conductive materials. Nonetheless, the observed relationships within and across residences indicate that contact current has the characteristics of a factor that could explain the association of magnetic fields with childhood leukemia.
Article
It has been suggested that residential exposure to contact currents may be more directly associated with the potential for an increased risk of leukemia in childhood than magnetic fields. Contact current exposure occurs when a child contacts a bathtub's water fixtures, which are usually contiguous with a residence's electrical ground, and when the drainpipe is conductive. The Northern California Childhood Leukemia Study (NCCLS) is the only epidemiological study known to address whether contact current may confound the reported association between residential magnetic fields and childhood leukemia. The study contributed contact voltage and magnetic-field data for over 500 residences of leukemia cases and control children. We combined these data with the results of previous measurement studies of contact voltage in other communities to conduct an analysis of the relationship of magnetic fields with contact voltage for a total sample of 702 residences. The Spearman correlation of magnetic field with contact voltage was 0.29 (Spearman, P < 0.0001). Magnetic-field and contact voltage data were both divided into tertiles, with an upper magnetic-field cutpoint of 0.3 μT suggested by values used in epidemiological results and an upper contact voltage cutpoint of 60 mV based on dosimetric considerations. Expressed as an exposure odds ratios (EOR), we report an association of contact voltage with magnetic fields of 15.1 (95% CI 3.6-61) as well as a statistically significant positive trend across magnetic-field strata (EOR of 4.2 per stratum with 95% CI 2.4-7.4). The associations appear to be large enough to support the possibility that contact current could be responsible for the association of childhood leukemia with magnetic fields.
Article
This article examines the potential for misleading inferences from conventional analyses and sensitivity analyses of observational data, and describes some proposed solutions based on specifying prior distributions for uncontrolled sources of bias. The issues are illustrated in a sensitivity analysis of confounding in a study of residential wire code and childhood leukemia and in a pooled analysis of 12 studies of magnetic-field measurements and childhood leukemia. Both analyses have been interpreted as evidence in favor of a causal effect of magnetic fields on leukemia risk. This interpretation is contrasted with results from analyses based on prior distributions for the unidentified bias parameters used in the original sensitivity analysis model. These analyses indicate that accounting for uncontrolled confounding and response bias under a reasonable prior can substantially alter inferences about the existence of a magnetic field effect. More generally, analyses with informative priors for unidentified bias parameters can help avoid misinterpretation of conventional results and ordinary sensitivity analyses.
Article
Full-text available
To investigate the reproducibility of wire codes to characterise residential power line configurations and to determine the extent to which wire codes provide a proxy measure of residential magnetic field strength in a case-control study of childhood leukaemia conducted in nine states within the United States. Misclassification of wire codes was assessed with independent measurements by two technicians for 187 residences. The association between categories of wire code and measured level of magnetic field was evaluated in 858 residences with both a wire code measurement and a 24 hour measurement of the magnetic field in the bedroom. The strength of the association between category of wire code and risk of leukaemia was examined in two regions with different average levels of magnetic field in homes with high categories of wire code. The reproducibility of any of three different classifications of wire codes was excellent (kappa > or = 0.89). Mean and median magnetic fields, and the percentage of homes with high magnetic fields increased with increasing category for each of the wire code classification schemes. The size of the odds ratios for risk of leukaemia and high categories of wire code did not reflect the mean levels of the magnetic field in those categories in two study regions. Misclassification of categories of wire code is not a major source of bias in the study. Wire codes provide a proxy measure of exposure to residential magnetic fields. If magnetic fields were a risk factor for leukaemia, however, there would be some attenuation of risk estimates based on wire codes because of misclassification of exposure to magnetic fields at both extremes of the wire code range. The lack of an association between high categories of wire code and risk of leukaemia cannot be explained by a failure of the wire code classification schemes to estimate exposure to magnetic fields in the study area.
Article
A case-control study was conducted to test the hypothesis that exposure to magnetic fields of the type generated by high-voltage power lines increases cancer incidence in children. The study base consisted of everyone under age 16 years who had lived on a property located within 300 meters of any of the 220 and 400 kV power lines in Sweden during the period 1960–1985. Subjects were followed from their entry into the study base through 1985. A total of 142 cancer cases were identified through a record linkage to the Swedish Cancer Registry. There were 39 leukemia and 33 central nervous system tumor cases. A total of 558 controls were selected at random from the study base. Exposure was assessed by spot measurements and by calculations of the magnetic fields generated by the power lines, taking distance, line configuration, and load into account. Information about historical loads on the power lines was used to calculate the magnetic fields for the year closest in time to diagnosis. When historical calculations were used as exposure assessment for childhood leukemia with cutoff points at 0.1 and 0.2 microtesla (μT), the estimated relative risk increased over the two exposure levels and was estimated at 2.7 (95% confidence interval (Cl) 1.0–6.3) for 0.2 μT and over; p for trend = 0.02. When the upper cutoff point was shifted to 0.3 μT, the relative risk was 3.8 (95% Cl 1.4–9.3); p for trend = 0.005. These results persisted when adjustment for potential confounding factors was made. For central nervous system tumor, lymphoma, and all childhood cancers combined, there was no support for an association.
Chapter
Epidemiology studies seeking to determine whether magnetic field (MF) exposure is linked to health outcomes, particularly cancers of specific types, have relied on a range of exposure assessment techniques. For residential studies, a wire coding technique for categorically classifying presumed exposure on the basis of the type and proximity of power line adjacent to study subjects ' homes has been used in several key studies in the United States. Since its introduction, wire coding has been joined by other techniques in epidemiology studies, involving direct measurements of fields in homes and personal exposure monitoring. Engineering research has identified outdoor power lines and residential grounding systems as important sources of residential MFs. Occupational studies initially relied on an intuitive relationship between job title and MF exposure. Here too, measurements of MFs on job sites and personal monitoring studies have enhanced our understanding of occupational exposure, particularly within the electric utility industry. Outstanding issues concern (1) the use of contemporaneous measurements for retrospective estimation of MF exposure, particularly when a substantial time has elapsed since the exposure of interest, and (2) the absence of a biologically based metric for characterizing the aspect(s) of MF exposure potentially relevant to health outcomes.
Article
A nationwide survey of 1000 residences is underway to determine the sources and characteristics of magnetic fields in the home. This report describes the goals, statistical sampling methods, measurement protocols, and experiences in measuring the first 707 residences of the survey. Some preliminary analysis of the data is also included. Investigators designed a sampling method to randomly select the participating utilities as well as the residential customers for the study. As a first step in the project, 18 utility employee residences were chosen to validate a relatively simple measurement protocol against the results of a more complete and intrusive method. Using the less intrusive measurement protocol, researchers worked closely with representatives from EPRI member utilities to enter customer residences and measure the magnetic fields found there. Magnetic field data were collected in different locations inside and around the residences. Twenty-four-hour recorders were left in the homes overnight. Tests showed that the simplified measurement protocol is adequate for achieving the goals of the study. Methods were developed for analyzing the field caused by a residence's ground current, the lateral field profiles of field lines, and the field measured around the periphery of the residences. Methods of residential source detection were developed that allow identification of sources such as ground connections at an electrical subpanel, two-wire multiple-way switches, and underground or overhead net currents exiting the periphery of a residence.
Article
We obtained original individual data from 15 studies of magnetic fields or wire codes and childhood leukemia, and we estimated magnetic field exposure for subjects with sufficient data to do so. Summary estimates from 12 studies that supplied magnetic field measures exhibited little or no association of magnetic fields with leukemia when comparing 0.1-0.2 and 0.2-0.3 microtesla (μT) categories with the 0-0.1 μT category, but the Mantel-Haenszel summary odds ratio comparing >0.3 μT to 0-0.1 μT was 1.7 (95% confidence limits = 1.2, 2.3). Similar results were obtained using covariate adjustment and spline regression. The study-specific relations appeared consistent despite the numerous methodologic differences among the studies. The association of wire codes with leukemia varied considerably across studies, with odds ratio estimates for very high current vs low current configurations ranging from 0.7 to 3.0 (homogeneity P = 0.005). Based on a survey of household magnetic fields, an estimate of the U.S. population attributable fraction of childhood leukemia associated with residential exposure is 3% (95% confidence limits = -2%, 8%). Our results contradict the idea that the magnetic field association with leukemia is less consistent than the wire code association with leukemia, although analysis of the four studies with both measures indicates that the wire code association is not explained by measured fields. The results also suggest that appreciable magnetic field effects, if any, may be concentrated among relatively high and uncommon exposures, and that studies of highly exposed populations would be needed to clarify the relation of magnetic fields to childhood leukemia.
Article
A case-control study was conducted to test the hypothesis that exposure to magnetic fields of the type generated by high-voltage power lines increases cancer incidence in children. The study base consisted of everyone under age 16 years who had lived on a property located within 300 meters of any of the 220 and 400 kV power lines in Sweden during the period 1960-1985. Subjects were followed from their entry into the study base through 1985. A total of 142 cancer cases were identified through a record linkage to the Swedish Cancer Registry. There were 39 leukemia and 33 central nervous system tumor cases. A total of 558 controls were selected at random from the study base. Exposure was assessed by spot measurements and by calculations of the magnetic fields generated by the power lines, taking distance, line configuration, and load into account. Information about historical loads on the power lines was used to calculate the magnetic fields for the year closest in time to diagnosis. When historical calculations were used as exposure assessment for childhood leukemia with cutoff points at 0.1 and 0.2 microtesla (microT), the estimated relative risk increased over the two exposure levels and was estimated at 2.7 (95% confidence interval (CI) 1.0-6.3) for 0.2 microT and over; p for trend = 0.02. When the upper cutoff point was shifted to 0.3 microT, the relative risk was 3.8 (95% CI 1.4-9.3); p for trend = 0.005. These results persisted when adjustment for potential confounding factors was made. For central nervous system tumor, lymphoma, and all childhood cancers combined, there was no support for an association.
Article
Childhood cancer has been modestly associated with wire codes, an exposure surrogate for power frequency magnetic fields, but less consistently with measured fields. We analyzed data on the population distribution of wire codes and their relationship with several measured magnetic field metrics. In a given geographic area, there is a marked trend for decreased prevalence from low to high wire code categories, but there are differences between areas. For average measured fields, there is a positive relationship between the mean of the distributions and wire codes but a large overlap among the categories. Better discrimination is obtained for the extremes of the measurement values when comparing the highest and the lowest wire code categories. Instability of measurements, intermittent fields, or other exposure conditions do not appear to provide a viable explanation for the difference between wire codes and magnetic with respect to the strength and consistency of their respective association with childhood cancer.
Article
The Wertheimer-Leeper wire code, originally developed as a surrogate for magnetic-field exposure, has been associated with childhood leukemia in several epidemiologic investigations. However, these and other studies indicate that most between-residence variability in measured magnetic fields remains unexplained by wire codes. To better understand this remaining variability, engineering and demographic data were examined for 333 underground (UG) and very-low current configuration (VLCC) single-family or duplex residences, selected from a database of nearly 1000 residences specifically because their magnetic fields are most likely affected negligibly by overhead power lines. Using linear regression techniques, four factors predictive of the log-transformed residential field were identified: the square-root of the 24-h average net service drop current (this current is equivalent to the current in the grounding system), the log of the number of service drops on the same secondary serving the residence, residence age (four categories), and area type (rural, suburban, or urban). Complete data on ground current and service drops, the two factors with the strongest individual relationships to measured fields, were available for only half of the residences in the sample. However, these data were determined to be "missing at random" according to established statistical criteria. The full-sample or "composite" models thus relied on a method similar to regression imputation, accounting for missing data with binary dummy variables. When applied to the samples from which they were derived, these models accounted for 25% of the variance of the log-spot-measured magnetic field values in the full sample, while models that considered only those residences with complete data (n = 167) explained about 35%. The model validated well against a sample of 201 ordinary low current configuration (OLCC) homes selected from the same database.
Article
We update our 1997 publication by reviewing 29 new reports of tests of magnetic fields (MFs) in six different in vivo animal models of carcinogenesis: 2-year, lifetime, or multigeneration exposure studies in rats or mice; and promotion/progression models (rat mammary carcinoma, rat liver focus, mouse skin, several models of human leukemia/lymphoma in rats and mice, and brain cancer in rats). Individual experiments are evaluated using a set of data quality criteria, and summary judgments are made across multiple experiments by applying a criterion of rough reproducibility. The potential for carcinogenicity of MFs is discussed in light of the significant body of carcinogenesis data from animal bioassays that now exists. Excluding abstracts, approximately 80% of the 41 completed studies identified in this and our previous review roughly satisfy data quality criteria. Among these studies, the criterion for independent reproducibility is not satisfied for any positive results but is satisfied for negative results in chronic bioassays in rats and mice and for negative results in both promotion and co-promotion assays using the SENCAR mouse skin model. Results of independent replication studies using the rat mammary carcinoma model were conflicting. We conclude that long-term exposure to continuous 50- or 60-Hz MFs in the range of 0.002-5 mT is unlikely to result in carcinogenesis in rats or mice. Though results of most promotion/progression assays are negative, a weak promoting effect of MFs under certain exposure conditions cannot be ruled out based on available data.
Article
A weak association between residential or occupational exposure to electric and magnetic fields (50/60 Hz fields) and an increased incidence of leukemia has been reported. Numerous animal studies have evaluated the potential association between magnetic-field exposure and leukemia. These include long-term (up to 2(1/2) years) bioassays, initiation/promotion studies, investigations in transgenic models, and tumor growth studies. Exposure to 60 Hz circularly polarized magnetic fields at 1,400 microT for 28 months did not affect lymphoma incidence in mice. The study included over 2000 C57BL/6J mice. In another study, 1000 B6C3F(1) mice exposed to 60 Hz magnetic fields up to 1000 microT for 2 years showed no increase in lymphomas. Approximately 400 transgenic Emu-Pim1 mice exposed to 50 Hz fields up to 1000 microT for up to 18 months had no increased incidence of leukemia. Similarly, Trp53(+/-) mice and Pim1transgenic mice exposed to 60 Hz magnetic fields for 23 weeks showed no increased incidence of lymphoma. Three studies in F344 rats exposed to 50 or 60 Hz magnetic fields up to 5 mT showed no increased incidence of leukemia. The combined animal bioassay results are nearly uniformly negative for magnetic-field exposures enhancing leukemia and weaken the possible epidemiological association between magnetic-field exposures and leukemia in humans as suggested by epidemiological data.
Article
Previous studies have suggested an association between exposure to 50-60 Hz magnetic fields (EMF) and childhood leukaemia. We conducted a pooled analysis based on individual records from nine studies, including the most recent ones. Studies with 24/48-hour magnetic field measurements or calculated magnetic fields were included. We specified which data analyses we planned to do and how to do them before we commenced the work. The use of individual records allowed us to use the same exposure definitions, and the large numbers of subjects enabled more precise estimation of risks at high exposure levels. For the 3203 children with leukaemia and 10 338 control children with estimated residential magnetic field exposures levels < 0.4 microT, we observed risk estimates near the no effect level, while for the 44 children with leukaemia and 62 control children with estimated residential magnetic field exposures >/= 0.4 microT the estimated summary relative risk was 2.00 (1.27-3.13), P value = 0.002). Adjustment for potential confounding variables did not appreciably change the results. For North American subjects whose residences were in the highest wire code category, the estimated summary relative risk was 1.24 (0.82-1.87). Thus, we found no evidence in the combined data for the existence of the so-called wire-code paradox. In summary, the 99.2% of children residing in homes with exposure levels < 0.4 microT had estimates compatible with no increased risk, while the 0.8% of children with exposures >/= 0.4 microT had a relative risk estimate of approximately 2, which is unlikely to be due to random variability. The explanation for the elevated risk is unknown, but selection bias may have accounted for some of the increase.
Article
Residential electrical wiring safety practices in the US result in the possibility of a small voltage (up to a few tenths of a volt) on appliance surfaces with respect to water pipes or other grounded surfaces. This "open circuit voltage" (V(OC)) will cause "contact current" to flow in a person who touches the appliance and completes an electrical circuit to ground. This paper presents data suggesting that contact current due to V(OC) is an exposure that may explain the reported associations of residential magnetic fields with childhood leukemia. Our analysis is based on a computer model of a 40 house (single-unit, detached dwelling) neighborhood with electrical service that is representative of US grounding practices. The analysis was motivated by recent research suggesting that the physical location of power lines in the backyard, in contrast to the street, may be relevant to a relationship of power lines with childhood leukemia. In the model, the highest magnetic field levels and V(OC)s were both associated with backyard lines, and the highest V(OC)s were also associated with long ground paths in the residence. Across the entire neighborhood, magnetic field exposure was highly correlated with V(OC) (r = 0.93). Dosimetric modeling indicates that, compared to a very high residential level of a uniform horizontal magnetic field (10 mu T) or a vertical electric field (100 V/m), a modest level of contact current (approximately 18 mu A) leads to considerably greater induced electric fields (> 1 mV/m) averaged across tissue, such as bone marrow and heart. The correlation of V(OC) with magnetic fields in the model, combined with the dose estimates, lead us to conclude that V(OC) is a potentially important exposure with respect to childhood leukemia risks associated with residential magnetic fields. These findings, nonetheless, may not apply to residential service used in several European countries or to the Scandinavian studies concerned with populations exposed to magnetic fields from overhead transmission lines.
Article
We obtained original individual data from 15 studies of magnetic fields or wire codes and childhood leukemia, and we estimated magnetic field exposure for subjects with sufficient data to do so. Summary estimates from 12 studies that supplied magnetic field measures exhibited little or no association of magnetic fields with leukemia when comparing 0.1-0.2 and 0.2-0.3 microtesla (microT) categories with the 0-0.1 microT category, but the Mantel-Haenszel summary odds ratio comparing >0.3 microT to 0-0.1 microT was 1.7 (95% confidence limits = 1.2, 2.3). Similar results were obtained using covariate adjustment and spline regression. The study-specific relations appeared consistent despite the numerous methodologic differences among the studies. The association of wire codes with leukemia varied considerably across studies, with odds ratio estimates for very high current vs low current configurations ranging from 0.7 to 3.0 (homogeneity P = 0.005). Based on a survey of household magnetic fields, an estimate of the U.S. population attributable fraction of childhood leukemia associated with residential exposure is 3% (95% confidence limits = -2%, 8%). Our results contradict the idea that the magnetic field association with leukemia is less consistent than the wire code association with leukemia, although analysis of the four studies with both measures indicates that the wire code association is not explained by measured fields. The results also suggest that appreciable magnetic field effects, if any, may be concentrated among relatively high and uncommon exposures, and that studies of highly exposed populations would be needed to clarify the relation of magnetic fields to childhood leukemia.
Article
Contact currents occur when a person touches conductive surfaces at different potentials and completes a path for current flow through the body. Such currents provide an additional coupling mechanism to that, due to the direct field effect between the human body and low-frequency external fields. The scalar potential finite difference method, with minor modifications, is applied to assess current density and electric field within excitable tissue and bone marrow due to contact current. An anatomically correct adult model is used, as well as a proportionally downsized child model. Three pathways of contact current are modeled: hand to opposite hand and both feet, hand to hand only, and hand to both feet. Because of its larger size relative to the child, the adult model has lower electric field and current-density values in tissues/unit of contact current. For a contact current of 1 mA [the occupational reference level set by the International Commission on Non-ionizing Protection (ICNIRP)], the current density in brain does not exceed the basic restriction of 10 mA/m2. The restriction is exceeded slightly in the spine, and by a factor of more than 2 in the heart. For a contact current of 0.5 mA (ICNIRP general public reference level), the basic restriction of 2 mA/m2 is exceeded several-fold in the spine and heart. Several microamperes of contact current produces tens of mV/m within the child's lower arm bone marrow.
Article
Several organizations worldwide have issued guidelines to limit occupational and public exposure to electric and magnetic fields and contact currents in the extremely low frequency range (<3 kilohertz). In this paper, we evaluate relevant developments in biological and health research, computational methods for estimating dosimetric quantities, and exposure assessment, all with an emphasis on the power frequency (60 hertz in North America, 50 hertz in Europe). The aim of each guideline is to prevent acute neural effects of induced electric fields. An evaluation of epidemiological and laboratory studies of neurobiological effects identified peripheral nerve stimulation as the response most suitable for establishing a magnetic-field guideline. Key endpoints that merit further study include reversal of evoked potentials; cardiovascular function, as measured by heart rate and heart rate variability; and sleep patterns. High-resolution computations of induced electric fields and current densities in anatomically correct human models are now achieved with finite-difference methods. The validity and limitations of these models have been demonstrated by computations in regular geometric shapes, using both analytic and numeric computations. Calculated values for average dosimetric quantities are typically within a few percent for the two approaches. However, maximum induced quantities are considerably overestimated by numerical methods, particularly at air interfaces. Overestimates are less pronounced for the upper 99th percentile level of a dosimetric quantity, making this measure a more useful indicator of maximum dose. Neural stimulation thresholds are dependent on the electric field around the excitable cell rather than on the current density, making the former preferable for expression of basic restrictions based on nervous system function. Furthermore, modeling data indicate that the induced electric field is much less strongly influenced by tissue conductivity than is the induced current density. In the electric utility industry, most magnetic-field exposures at or near guideline levels occur in highly nonuniform fields. Two methods are described for simplified estimation of induced quantities in such fields, with each method using as input modeling results for uniform field exposure. These methods have practical value for assessing occupational exposures relative to guideline levels.
Study of ground cur-rents in proximity of substations
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King KG, Sullivan TP, Zaffanella LE. 1997. Study of ground cur-rents in proximity of substations. Palo Alto, CA: Electric Power Research Institute, TR-109272.