Is epidemiology implicating extremely low frequency electric and magnetic fields in childhood leukemia?

We have reviewed epidemiological studies examining the association between residential exposure to extremely low frequency electric and magnetic fields (ELF-EMF) and childhood leukemia. We have excluded studies focusing on electrical appliances, because it is difficult to consolidate transient exposure from multiple sources and equally difficult to control information bias. We have identified 24 studies of residential exposure to ELF-EMF and childhood leukemia. About half of these studies were reported as positive and the remaining as null. For each of the studies reported as positive, however, one or more sources of bias could not be confidently excluded. Moreover, studies which were methodologically more sound, or benefited from high quality registry data, were more frequently null than other investigations. We conclude that the empirical evidence in support of an association between ELF-EMF and childhood leukemia is weak.     

极低频电磁场与肿瘤关系研究进展

随着科技的进步和社会经济的迅速发展,各种电子、电力设备和设施的广泛应用使人们周围生活环境中的极低频电磁场强度日益增大,极低频电磁场与健康之间的关系引起了世界各国的关注,并开展了相应的研究.近些年来,对极低频电磁场与白血病、脑肿瘤、乳腺癌及其他肿瘤的发生的关系,国内外开展了大量的流行病学研究.该文综述了这些研究结果,并分析了极低频电磁场对肿瘤影响的可能作用机制.     

Assessment of biological changes of continuous whole body exposure to static magnetic field and extremely low frequency electromagnetic fields in mice

The question whether static magnetic fields (SMFs) and extremely low frequency electromagnetic fields (ELF-EMF) cause biological effects is of special interest. We investigated the effects of continuous whole body exposure to both fields for 30 days on some liver and blood parameters in mice. Two exposure systems were designed; the first produced a gradient SMF while the second generated uniform 50 Hz ELF-EMF. The results showed a gradual body weight loss when mice were exposed to either field. This is coupled with a significant decrease (P<0.05) in the levels of glucose, total protein and the activity of alkaline phosphatase in serum. A significant increase in lactate dehydrogenase activity was demonstrated in serum and liver paralleled with a significant elevation in hepatic γ-glutamyl transferase activity. The glutathione-S-transferase activity and lipid peroxidation level in the liver were significantly increased while a significant decrease in hepatic gluthathione content was recorded. A significant decrease in the counts of monocytes, platelets, peripheral lymphocytes as well as splenic total, T and B lymphocytes levels was observed for SMF and ELF-EMF exposed groups. The granulocytes percentage was significantly increased. The results indicate that there is a relation between the exposure to SMF or ELF-EMF and the oxidative stress through distressing redox balance leading to physiological disturbances.     

Quantification of lifetime accumulated ELF-EMF exposure from household appliances in the context of a retrospective epidemiological case-control study

In Europe household appliances are a major source of indoor 50 Hz magnetic field exposure. A number of epidemiological studies have reported associations between leukemia risk and personal use of household appliances. In the "Norddeutsche Leuk?mie und Lymphomstudie" (NLL), which was conducted in Northern Germany (Schleswig-Holstein and Lower Saxony) between 1997 and 2001, lifetime use of a preselected array of electric appliances (microwave ovens, hair-dryers, motorized electrical alarm clocks (i.e. that use a motor to move their hands or digits), electric blankets and pillows, heated waterbeds, computers with conventional screens, TVs, and electric sewing machines) was recorded in a standardized, personal, computerized interview. Exposure was assessed on three different levels of precision: ever use, cumulative appliance-years, and average time of daily use. Additional questions referred to exposure modifying factors, including distance from screen while watching TV, position of an alarm clock at the bed etc.). Exposure to ELF-EMF from household appliances was quantified as ever vs. never use, gross and net appliance-years of lifetime use and cumulative microT-hours. Flux densities were based on measurements of appliances from the published literature. These were used as weighting factors to account for the different device-specific contributions to overall ELF-EMF exposure. Resulting distributions (as quartiles) for exposure scores revealed systematic differences for different levels of precision. Our analysis indicates that valid assessment of ELF-EMF exposure from household appliances should be based on the highest possible degree of precision and hence provides a considerable challenge in analytic epidemiology.     

Effect of electromagnetic field exposure on chemically induced differentiation of friend erythroleukemia cells

Whether exposure of humans to extremely low frequency electromagnetic fields (ELF-EMF) can cause cancer is controversial and therefore needs further research. We used a Friend erythroleukemia cell line that can be chemically induced to differentiate to determine whether ELF-EMF could alter proliferation and differentiation in these cells in a manner similar to that of a chemical tumor promoter. Exposure of this cell line to 60 Hz ELF-EMF resulted in a dose dependent inhibition of differentiation, with maximal inhibition peaking at 40% and 40 mG (4 microT). ELF-EMF at 10 mG (1.0 microT) and 25 mG (2.5 microT) inhibited differentiation at 0 and 20%, respectively. ELF-EMF at 1.0 (100) and 10.0 G (1,000 microT) stimulated cell proliferation 50% above the sham-treated cells. The activity of telomerase, a marker of undifferentiated cells, decreased 100[times] when the cells were induced to differentiate under sham conditions, but when the cells were exposed to 0.5 G (50 microT) there was only a 10[times] decrease. In summary, ELF-EMF can partially block the differentiation of Friend erythroleukemia cells, and this results in a larger population of cells remaining in the undifferentiated, proliferative state, which is similar to the published results of Friend erythroleukemia cells treated with chemical-tumor promoters.     

Evaluation of genotoxic and/or co-genotoxic effects in cells exposed in vitro to extremely-low frequency electromagnetic fields

During the last two decades, concerns have arisen regarding a possible association between extremely-low frequency (ELF) electromagnetic fields (EMF) exposure and cancer incidence (e.g. childhood acute leukaemia, cancer of the nervous system, and lymphomas). In 1979, Wertheimer and Leeper firstly reported an excess of cancer mortality among children living in homes located near power lines and presumably exposed to elevated magnetic fields. Subsequently, a large number of epidemiological studies investigated the possible association between residential or occupational exposure to ELF-EMF and cancer. Several in vivo and in vitro models have been investigated with the effort to determine a link, if any, between such fields and mutagenesis and to determine the possible mechanism of cancer risk. However, a causal relationship between exposure to ELF-EMF and cancer has been suggested but has not been unequivocally demonstrated. In 1998, following an analysis of the results retrieved in the literature, the U.S. National Institute of Environmental Health Sciences proposed to apply a "possible human carcinogen" category (Group 2B) to ELF-EMF. More recently, in 2002, the same classification for ELF-MF was proposed by the International Agency for Research on Cancer. In this in vitro approach, to test the genotoxic and/or co-genotoxic potency of ELF-MF, we used the alkaline single-cell microgel-electrophoresis (comet) assay and the cytokinesis block micronucleus test. Co-exposure assays were performed in the presence of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), 4-nitroquinoline N-oxide (4NQO), benzene, 1,4-benzenediol (1,4-BD), or 1,2,4-benzenetriol (1,2,4-BT). An ELF-MF (50 Hz, 5 mT) was obtained by a system composed of capsulated induction coils. ELF-MF alone was unable to cause direct primary DNA damage. Whereas, an increased extent of DNA damage was observed in cells co-exposed to ELF-MF and MNNG, 1,4-BD, or 1,2,4-BT. An opposite trend was observed in cells treated with 4NQO and co-exposed to ELF-MF. Moreover, the frequency of micronucleated cells in ELF-MF-exposed cells was higher than in control cultures. Our findings suggest that the tested ELF-MF (50 Hz, 5 mT) possess genotoxic (micronucleus test) and co-genotoxic (comet assay) capabilities. The possibility that ELF-MF might interfere with the genotoxic activity of xenobiotics has important implications, since human populations are likely to be exposed to a variety of genotoxic agents concomitantly with exposure to this type of physical agent.     

No effects of power line frequency extremely low frequency electromagnetic field exposure on selected neurobehavior tests of workers inspecting transformers and distribution line stations versus controls

We aimed to evaluate the interference of 50 Hz extremely low frequency electromagnetic field (ELF-EMF) occupational exposure on the neurobehavior tests of workers performing tour-inspection close to transformers and distribution power lines. Occupational short-term “spot” measurements were carried out. 310 inspection workers and 300 logistics staff were selected as exposure and control. The neurobehavior tests were performed through computer-based neurobehavior evaluation system, including mental arithmetic, curve coincide, simple visual reaction time, visual retention, auditory digit span and pursuit aiming. In 500 kV areas electric field intensity at 71.98 % of total measured 590 spots were above 5 kV/m (national occupational standard), while in 220 kV areas electric field intensity at 15.69 % of total 701 spots were above 5 kV/m. Magnetic field flux density at all the spots was below 1,000 μT (ICNIRP occupational standard). The neurobehavior score changes showed no statistical significance. Results of neurobehavior tests among different age, seniority groups showed no significant changes. Neurobehavior changes caused by daily repeated ELF-EMF exposure were not observed in the current study.     

Effects of short-term exposure to powerline-frequency electromagnetic field on the electrical activity of the heart

ABSTRACT The heart is a contractile organ that can generate its own rhythm. The contraction, or the rhythm, of the heart may be influenced by electromagnetic field (EMF) exposure, because of the heart's excitability characteristic. In previous studies, different methods have been used to study the possible effects of an extremely low frequency electromagnetic field (ELF-EMF) on the heart. But the studies' designs were not similar, and the results were also different. Recent studies have shown some evidence that short-term EMF exposure can influence the heart more than long-term exposure. This study investigated how the heart is affected in the first EMF exposure. In a simulation of the daily exposure of humans to a power frequency, Wistar albino rats were used. By utilizing the Helmholtz-coil set, we obtained a 50-Hz, 1-μT EMF and examined rat heart activity during short-term EMF exposure. No effect was observed under this exposure condition. The results obtained do not confirm a possible mechanism in the electrical activity of the rat heart model.     

Prenatal lead exposure in relation to gestational age and birth weight: A review of epidemiologic studies

Although the adverse effect on pregnancy outcomes at high levels of lead exposure in the workplace has been recognized for years, there is uncertainty regarding the impact of exposure at the lower community exposure levels commonly encountered today. This review summarizes the epidemiologic literature and discusses pertinent methodologic issues and possible sources of interstudy variation. The authors conclude that prenatal lead exposure is unlikely to increase the risk of premature membrane rupture but does appear to increase the risk of preterm delivery. Whether prenatal lead exposure decreases gestational age in terms of infants is unclear. Prenatal lead exposure also appears to be associated with reduced birth weight, but results vary in relation to study design and degree of control for confounding. Adjustment for gestational age, a possible confounder of the birth weight-lead exposure association, did not yield clearer results.     

A time-series analysis of any short-term effects of meteorological and air pollution factors on preterm births in London, UK

Although much is known about the incidence and burden of preterm birth, its biological mechanisms are not well understood. While several studies have suggested that high levels of air pollution or exposure to particular climatic factors may be associated with an increased risk of preterm birth, other studies do not support such an association. To determine whether exposure to various environmental factors place a large London-based population at higher risk for preterm birth, we analyzed 482,568 births that occurred between 1988 and 2000 from the St. Mary's Maternity Information System database. Using an ecological study design, any short-term associations between preterm birth and various environmental factors were investigated using time-series regression techniques. Environmental exposures included air pollution (ambient ozone and PM(10)) and climatic factors (temperature, rainfall, sunshine, relative humidity, barometric pressure, and largest drop in barometric pressure). In addition to exposure on the day of birth, cumulative exposure up to 1 week before birth was investigated. The risk of preterm birth did not increase with exposure to the levels of ambient air pollution or meteorological factors experienced by this population. Cumulative exposure from 0 to 6 days before birth also did not show any significant effect on the risk of preterm birth. This large study, covering 13 years, suggests that there is no association between preterm births and recent exposure to ambient air pollution or recent changes in the weather.     

Ethylene oxide: an assessment of the epidemiological evidence on carcinogenicity.

Mortality from cancer among workers exposed to ethylene oxide (EtO) has been studied in 10 distinct cohorts that include about 29,800 workers and 2540 deaths. This paper presents a review and meta-analysis of these studies, primarily for leukaemia, non-Hodgkin's lymphoma, stomach cancer, pancreatic cancer, and cancer of the brain and nervous system. The magnitude and consistency of the standardised mortality ratios (SMRs) were evaluated for the individual and combined studies, as well as trends by intensity or frequency of exposure, by duration of exposure, and by latency (time since first exposure). Exposures to other workplace chemicals were examined as possible confounder variables. Three small studies by Hogstedt initially suggested an association between EtO and leukaemia, but in seven subsequent studies the SMRs for leukaemia have been much lower. For the combined studies the SMR = 1.06 (95% confidence interval (95% CI) 0.73-1.48). There was a slight suggestion of a trend by duration of exposure (p = 0.19) and a suggested increase with longer latency (p = 0.07), but there was no overall trend in risk of leukaemia by intensity or frequency of exposure; nor did a cumulative exposure analysis in the largest study indicate a quantitative association. There was also an indication that in two studies with increased risks the workers had been exposed to other potential carcinogens. For non-Hodgkin's lymphoma there was a suggestive risk overall (SMR = 1.35, 95% CI 0.93-1.90). Breakdowns by exposure intensity or frequency, exposure duration, or latency did not indicate an association, but a positive trend by cumulative exposure (p = 0.05) was seen in the largest study. There was a suggested increase in the overall SMR for stomach cancer (SMR = 1.28, 95% CI 0.98-1.65 (CI 0.73-2.26 when heterogeneity among the risk estimates was taken into account)), but analyses by intensity or duration of exposure or cumulative exposure did not support a causal association for stomach cancer. The overall SMRs and exposure-response analyses did not indicate a risk from EtO for pancreatic cancer (SMR = 0.98), brain and nervous system cancer (SMR = 0.89), or total cancer (SMR = 0.94). Although the current data do not provide consistent and convincing evidence that EtO causes leukaemia or non-Hodgkin's lymphoma, the issues are not resolved and await further studies of exposed populations.     

Gases in agricultural slurry stores

The evolution of gases during the handling of animal slurry was investigated at five sites. Particular attention was paid to the mixing and emptying operations since it is when performing these that personnel are most likely to be at risk of exposure. The main hazard was found to be high transient concentrations of hydrogen sulphide presenting in some cases a serious acute toxicity problem. Time-weighted average exposures did not generally indicate any long-term exposure risk. Other features noted were the evolution of ammonia and methane, although not at high levels, and some increase in the carbon dioxide concentration. Some reduction in oxygen concentration was measured, but generally the risk of poisoning by hydrogen sulphide was more serious than the risk of asphyxiation.     

Are children living near high-voltage power lines at increased risk of acute lymphoblastic leukemia?

In the National Cancer Institute/Children's Cancer Group case-control study of childhood acute lymphoblastic leukemia (1989-1993), living in a home with a high-voltage wire code was not associated with disease risk. To further investigate risk near power lines, the authors analyzed distance to transmission and three-phase primary distribution lines within 40 m of homes and created an exposure index of distance and strength of multiple power lines (408 case-control pairs). Neither distance nor exposure index was related to risk of childhood acute lymphoblastic leukemia, although both were associated with in-home magnetic field measurements. Residence near high-voltage lines did not increase risk.     

Occupational risk factors for cancer of the central nervous system (CNS) among US women.

BACKGROUND: In a recent report, we found an elevated risk of cancer of the central nervous system (CNS) in several occupations and industries, and a modest association with exposure to solvents and to contact with the public. METHODS: To further explore the occupational risk of CNS cancer among women, we extended the analysis of the previous death certificate-based case-control study, including 12,980 female cases (ICD-9 codes 191 and 192) in 24 US states in 1984-1992 and 51,920 female controls who died from diseases other than malignancies and neurological disorders. We applied newly designed job-exposure matrices for 11 occupational hazards, previously reported as brain cancer risk factors, to the occupation and industry codes in the death certificates. We also conducted a separate analysis of 161 meningioma cases (ICD-9 codes 192.1 and 192.3), a tumor more frequent among women, particularly in the postmenopausal age group. RESULTS: Overall, CNS cancer risk showed a 20-30% increase among women exposed to electromagnetic fields (EMF), methylene chloride, insecticides and fungicides, and contact with the public. Risk for meningioma was elevated among women exposed to lead (OR = 1.9; 95% CI 1.0, 3.9). CNS cancer did not show a clear pattern of risk increase by probability and intensity of exposure to any of the explored risk factors. Cross-classification by probability and intensity of exposure did not reveal any significant trend. Cases were too few to explore trends of meningioma by probability and intensity of exposure to lead. CONCLUSIONS: We did not find evidence of a strong contribution of 11 occupational hazards to the etiology of CNS cancer. However, limitations of the occupational information might have reduced our ability to detect clear patterns of risk.     

Simulation study of the effect of the early mortality exclusion on confounding of the exposure-mortality relation by preexisting disease.

The authors conducted a simulation study to evaluate whether exclusion of the early mortality (deaths occurring during a prespecified period immediately after baseline) reduces confounding of the exposure-mortality relation by preexisting disease. The simulation specified an exposure that decreased mortality risk in the absence of confounding and then introduced confounding by preexisting disease that biased the "true" protective effect of exposure towards greater risk. In 2,000 cohorts, exclusion of the early mortality (deaths occurring during the first 25 months of a 60-month follow-up period) did not alter the mean hazard ratio for exposure under conditions of confounding by preexisting disease that produced a constant, threefold increase in mortality risk during follow-up (the mean hazard ratio was 1.72 for all subjects and 1.72 after exclusion of the early mortality). However, when the authors specified confounding by preexisting disease which produced a threefold increase in mortality risk that attenuated over time, exclusion of the early mortality consistently identified the "true" protective effect of exposure (the mean hazard ratio was 1.07 for all subjects and 0.31 after exclusion of the early mortality). Thus, under conditions of confounding by preexisting disease which produces an increase in mortality risk that attenuates over time--an effect that does have empirical support-the early mortality exclusion can be very effective in revealing the "true" exposure-mortality relation.     

Intermittent extremely low frequency electromagnetic fields cause DNA damage in a dose-dependent way

Objectives Epidemiological studies have reported an association between exposure to extremely low frequency electromagnetic fields (ELF-EMFs) and increased risk of cancerous diseases, albeit without dose–effect relationships. The validity of such findings can be corroborated only by demonstration of dose-dependent DNA-damaging effects of ELF-EMFs in cells of human origin in vitro.Methods Cultured human diploid fibroblasts were exposed to intermittent ELF electromagnetic fields. DNA damage was determined by alkaline and neutral comet assay.Results ELF-EMF exposure (50 Hz, sinusoidal, 1–24 h, 20–1,000 T, 5 min on/10 min off) induced dose-dependent and time-dependent DNA single-strand and double-strand breaks. Effects occurred at a magnetic flux density as low as 35 T, being well below proposed International Commission of Non-Ionising Radiation Protection (ICNIRP) guidelines. After termination of exposure the induced comet tail factors returned to normal within 9 h.Conclusion The induced DNA damage is not based on thermal effects and arouses concern about environmental threshold limit values for ELF exposure.     

Evaluation of Residential Exposure to Intermediate Frequency Magnetic Fields

The authors measured the exposure to intermediate-frequency (IF: 10 kHz to 30 MHz) electromagnetic fields (EMF) in residential environments. They developed a system to acquire and record waveforms of IF magnetic fields (MFs) and set 5 nanotesla (nT) for the trigger level of acquisition. They operated the system near power lines, railroads, and electrical appliances as possible sources of IF-MFs. Most of the maximum values of magnetic flux density and the time derivative for each wave were below the upper limit of the measurable range of our system (i.e., 53 nT and 10 T/s); these values were much lower than the minimum amplitudes that can theoretically induce heating or membrane excitation within biological systems. Moreover, the amplitudes of the IF-MFs were not related to those of extremely low frequency (ELF) MF measured simultaneously, indicating that IF-MFs do not underlie the associations, observed in several epidemiological studies, between residential exposure to ELF-EMF and childhood cancer.     

Evaluation of residential exposure to intermediate frequency magnetic fields

The authors measured the exposure to intermediate-frequency (IF: 10 kHz to 30 MHz) electromagnetic fields (EMF) in residential environments. They developed a system to acquire and record waveforms of IF magnetic fields (MFs) and set 5 nanotesla (nT) for the trigger level of acquisition. They operated the system near power lines, railroads, and electrical appliances as possible sources of IF-MFs. Most of the maximum values of magnetic flux density and the time derivative for each wave were below the upper limit of the measurable range of our system (i.e., 53 nT and 10 T/s); these values were much lower than the minimum amplitudes that can theoretically induce heating or membrane excitation within biological systems. Moreover, the amplitudes of the IF-MFs were not related to those of extremely low frequency (ELF) MF measured simultaneously, indicating that IF-MFs do not underlie the associations, observed in several epidemiological studies, between residential exposure to ELF-EMF and childhood cancer.     

The effect of pressure drop on respirator faceseal leakage

Users of particulate air-purifying respirators are typically told to change their filters when breathing resistance becomes uncomfortable. It has been proposed that a noticeable increase in breathing resistance (pressure drop) may increase airflow through respirator faceseal leaks. This logic has been extended to suggest that respirator user exposure to contaminants may increase because of this theoretical increase in air leakage. Procedures similar to those of previous investigators were used to study this issue. Repeated faceseal leak rate measurements were made at -5.6 through -20.1 mm water pressure drops across the faceseal. Subjects were divided into two groups, representing acceptable fit or unacceptable fit, based on leak rate criteria prescribed by the Occupational Safety and Health Administration (OSHA). Subjects with acceptable fit did not experience an increase in faceseal leak rate with increased pressure drop. Leak rates for subjects with unacceptable fit were highly variable and did not show an association with pressure drop. Results of this study do not support the concept of increased faceseal leakage with increased pressure drop. The evidence does not suggest increased risk of contaminant exposure through the face seal as pressure drop increases.     

Exposure to asbestos: psychological responses of mesothelioma patients

Thirty-eight patients with a diagnosis of malignant mesothelioma participated in a semi-structured interview to evaluate asbestos exposure, acquisition of increased risk information, and retrospective reporting of cognitive and behavioral reactions (particularly smoking behavior) to risk information. Twenty-eight patients (74%) had direct occupational contact with asbestos, and six patients (16%) reported indirect nonoccupational exposure to asbestos. Only two (10%) of the directly exposed patients acquired risk information from professional sources prior to diagnosis of mesothelioma. The most frequently reported reaction to learning of increased risk of cancer was a denial of the risk by minimizing personal exposure. Few patients reported being concerned about the information of increased risk. Smoking behavior did not change as a result of risk information, nor was there any increase in visits to physicians. Guidelines for psychosocial management of at-risk groups are recommended.