Acute nonlymphocytic leukemia and residential exposure to power frequency magnetic fields

Recent research has suggested that nonionizing radiation in the form of power-frequency magnetic fields may play some role in carcinogenesis in general and in acute nonlymphocytic leukemia in particular. Much of the epidemiologic evidence is preliminary in nature and the methods of previous studies have been criticized. In order to further evaluate this hypothesis, a population-based case-control study of adult acute nonlymphocytic leukemia and residential exposure to power-frequency magnetic fields was carried out in western Washington state. Analyses were based on 114 cases who were newly diagnosed from 1981 to 1984 and identified from a population-based cancer registry, and 133 controls who were chosen from the study area by random digit dialing. Magnetic field exposure was estimated from external electrical wiring configurations within 140 ft (42.7 m) of each subject's residence. In addition, magnetic fields were measured inside the subject's residence at the time of interview. Neither the directly measured magnetic fields nor the surrogate values based on the wiring configurations were associated with acute nonlymphocytic leukemia.     

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.     

Use of short-term measurements for assessing temporal variability of residential ELF magnetic field exposure

In this study, we introduced and tested a new approach to characterize residential magnetic field (MF) exposure. Short-term 20-min MF measurements were obtained by a person who carried out instantaneous spot measurements in residences. Compared to spot measurements, the 20-min measurement could potentially improve exposure assessment, because it contains information of temporal variations of MF, which have been suggested as biologically important characteristics of MF exposure. We have used this new exposure assessment method on a study of maternal MF exposure and reproductive outcomes. To validate the new method, the exposure of 30 subjects was measured with a more accurate "gold standard" method (24 h personal exposure measurements). The measures of validity used were the Spearman correlation coefficient (r), sensitivity, and specificity. We evaluated the validity of the 20-min measurements for estimating several different exposure metrics for the entire 24 h measurement period or for the hours spent at home: arithmetic mean, median, percentage of time above 0.15 microT, standard deviation, rate of change metric, standardized rate of change metric, constant field metric, and three metrics for the occurrence of high-peak exposures. The 20-min measurement was modestly associated with standard deviation and the rate of change metric, but gave very little information of other metrics of temporal variation. The 20-min measurement can also be used for assessing exposure metrics such as arithmetic mean and median, but it does not seem to offer any advantages compared to traditional 'spot' measurements. The 20-min measurement was not useful for assessing occurrence of high-peak exposures. We conclude that the 20-min measurement is useful for estimating some aspects of MF temporal variability.     

Epidemiological appraisal of studies of residential exposure to power frequency magnetic fields and adult cancers.

OBJECTIVES: To appraise epidemiological evidence of the purported association between residential exposure to power frequency magnetic fields and adult cancers. METHODS: Literature review and epidemiological evaluation. RESULTS: Seven epidemiological studies have been conducted on the risk of cancer among adults in relation to residential exposure to power frequency magnetic fields. Leukaemia was positively associated with magnetic fields in three case-control studies. The other two case-control studies and two cohort studies did not show such a link. Brain tumours and breast cancer have rarely been examined by these studies. Based on the epidemiological results, the analysis of the role of chance and bias, and the criteria for causal inferences, it seems that the evidence is not strong enough to support the putative causal relation between residential exposure to magnetic fields and adult leukaemia, brain tumours, or breast cancer. Inadequate statistical power is far more a concern than selection bias, information bias, and confounding in interpreting the results from these studies, and in explaining inconsistencies between studies. CONCLUSIONS: Our reviews suggested that the only way to answer whether residential exposure to magnetic fields is capable of increasing the risks of adult cancers is to conduct more studies carefully avoiding methodological flaws, in particular small sample size. We also suggested that the risk of female breast cancer should be the object of additional investigations, and that future studies should attempt to include information on exposure to magnetic fields from workplaces as well as residential exposure to estimate the effects of overall exposure to magnetic fields.     

50家企业工频电磁场职业暴露现况调查

目的 探讨职业人群工频电磁场职业暴露现况.方法 对各种存在工频电磁场的工作场所或工作岗位进行工频电场及磁场的测量及统计分析.结果 电厂主变及各种高压变电站近20%点电场强度大于5 kV/m,最高达17.46kV/m;部分变压器、变电站电抗器及变电柜工作场所12个点磁场强度大于100 μT,手动点焊工作岗位工频磁场集中趋势为492.49 μT,最大值为2 092.33 μT,94.7%的作业点磁场强度大于100 μT.结论 电厂主变及各种高压变电站存在高电场强度,手动点焊工人处于高强度工频磁场暴露之中.     

Occupational exposure to power frequency magnetic fields and risk of non-Hodgkin lymphoma

Objectives

To investigate the risk of non‐Hodgkin lymphoma (NHL) using a job‐exposure matrix (JEM) to assess exposure to occupational magnetic fields at the power frequencies of 50/60 Hz.

Methods

The study population consisted of 694 cases of NHL, first diagnosed between 1 January 2000 and 31 August 2001, and 694 controls from two regions in Australia, matched by age, sex and region of residence. A detailed occupational history was given by each subject. Exposure to power frequency magnetic fields was estimated using a population‐based JEM which was specifically developed in the United States to assess occupational magnetic field exposure. The cumulative exposure distribution was divided into quartiles and adjusted odds ratios were calculated using the lowest quartile as the referent group.

Results

For the total work history, the odds ratio (OR) for workers in the upper quartile of exposure was 1.48 (95% CI 1.02 to 2.16) compared to the referent (p value for trend was 0.006). When the exposure was lagged by 5 years the OR was 1.59 (95% CI 1.07 to 2.36) (p value for trend was 0.003). Adjusting for other occupational exposures did not significantly alter the results.

Conclusions

These findings provide weak support for the hypothesis that occupational exposure to 50/60 Hz magnetic fields increases the risk of NHL.     

电脑显示器极低频磁场的强度分析

目的　研究电脑阴极射线管显示器正前方不同距离和不同方位的极低频磁场(ELFMF)强度 ,就如何减少ELFMF的影响提出初步建议。方法　测定 2 0 0台阴极射线管显示器及10台液晶显示器的ELFMF强度。在显示器正前方距离 0～ 5 0cm ,每隔 5cm设一测定点 ,各点测定3次 ,并测定显示器不同方位 0cm处的磁场强度。结果　 38cm和 4 3cm两种阴极射线管显示器在操作电脑的习惯性位置 (30～ 4 0cm)的ELFMF强度比屏前 0cm处有明显衰减。 38cm显示器在屏前 15cm以内的ELFMF强度超过 0 4 μT ,4 3cm显示器在 10cm以内其强度超过 0 4 μT。两种显示器不同方位的测定结果显示 ,以显示器正上方的强度最大 ,38cm显示器为 (9 5 4± 0 16 ) μT ,4 3cm显示器为 (6 38± 0 16 ) μT。 结论　建议使用电脑时与显示屏保持一定的距离 ,尽量减少视频前的持续操作时间。加大各台电脑之间的距离 ,避免其相互间的干扰对人体产生更大的危害。     

Human body exposure to power lines: relation of induced quantities to external magnetic fields

Induced electric field and corresponding current density values in various organs of the human body can be computed numerically using a heterogeneous, anatomically representative voxel model. Such computations are available for uniform magnetic fields of various directions with respect to the body. The highest exposure levels occur for non-uniform fields, most often in occupational settings. Various organ induced dosimetric measures of the induced quantities can also be computed, although the associated computational complexity and effort are greater than for uniform fields. A simplified method of estimation of the induced measures is described and validated. The method is based on evaluation of the external (exposure) magnetic flux density in locations corresponding to those occupied by various organs and dosimetry for the uniform fields. Computations of the external fields are relatively simple even for very complex geometries of current-carrying conductors. Computational methods are available for external fields. The external magnetic fields can also be measured. Detailed organ dosimetry is already published. In this contribution, the proposed simplified dosimetry is verified using accurate, numerically computed dosimetry for four non-uniform field exposure scenarios. For most dosimetric measures and organs, the proposed method gives conservative estimates. Only in rare cases when a large organ is in a weak exposure field compared to the whole-body average exposure, the induced dosimetric measures may be underestimated by up to 10%. Another exception is the maximum induced electric field in spatially distributed tissues such as bone marrow, muscle, or skin when a part of the limb is in a very strong magnetic field close to the conductor. However, both of these situations are easily recognizable from the mutual configuration of the human body and the current-carrying conductors. Thus, additional corrections can be applied to the estimates.     

Adult glioma in relation to residential power frequency electromagnetic field exposures in the San Francisco Bay area.

In a population-based study, we examined residential power frequency electromagnetic field exposures for 492 adults newly diagnosed with histologically confirmed glioma between August 1, 1991 and April 30, 1994, in the San Francisco Bay area and 462 controls, obtained through random-digit dialing frequency, matched to cases for age, gender, and race. Residential exposure assessment consisted of spot measures with EMDEX (Enertech Consultants, Campbell, CA) meters and wire codes based on characterization and location of nearby power lines. We considered the index residence at the time of the case's diagnosis or the control's interview and all other California residences of each subject for 7 years before study entry. We obtained wire codes for eligible residences of 76% and for index residences of 99% of subjects. Using the Kaune-Savitz wire code classification, the relative risk for longest held residences coded as "high" compared with "low" was 0.9 [95% confidence interval (CI) = 0.7-1.3], while relative risk and 95% CIs for front door spot measures of 1.01-2 milligauss, 2.01-3 milligauss, and higher than 3 milligauss compared with < or =1 milligauss were 1.0 (0.7-1.4), 0.6 (0.3-1.1), and 1.7 (0.8-3.6). Adjustment for age, gender, race, and whether the subject owned the residence did not meaningfully alter these findings, nor did comparisons using index or highest coded residence. Because of potential exposure misclassification and the unknown pertinent exposure period, these data cannot provide strong support against, but clearly do not support an association between, adult glioma and residential power frequency electromagnetic field exposures.     

强磁场下家兔行为及脑电图的变化

目的　研究强磁场对健康家兔行为及脑电图的影响。方法　家兔 2 6只 ,随机分成两组 ,磁场组和对照组各13只 ,观察工频强磁场长期连续暴露 ,家兔行为及脑电图的变化。结果　磁场组 13只家兔暴露 1周后活动增多 ,烦躁不安 ,半月后脱毛 ,每月较对照组体重少增加 2 0 0～ 2 5 0g ,其中 11只 (11/ 13 )家兔脑电图Q波及δ波增多 ,波幅增加。结论　工频强磁场长期连续暴露可引起家兔行为改变以及脑电图慢波增多。     

Assessment of selection bias in the Canadian case-control study of residential magnetic field exposure and childhood leukemia

The authors evaluated the role of selection bias in the 1999 Canadian case-control study of residential magnetic field exposure and childhood leukemia. They included cases, participating controls, and first-choice nonparticipating controls in their analyses. Exposure was assessed by wire coding, a classification system based on the distribution line characteristics near homes. Although an imperfect measure of magnetic field exposure, wire coding is the only method applicable to nonparticipating subjects. First-choice nonparticipant controls tended to be of lower socioeconomic status than their replacements (non-first-choice participant controls), and lower socioeconomic status was related to higher wire code categories. The odds ratios for developing childhood leukemia in the highest exposure category were 1.6 (95% confidence interval: 1.0, 2.6) when the actual participating controls were used and 1.3 (95% confidence interval: 0.8, 2.1) when the first-choice ideal controls were used, regardless of their participation. Overall, the authors conclude that, although there is some evidence for control selection or participation bias in the Canadian study, it is unlikely to explain entirely the observed association between magnetic field exposure and childhood leukemia. Inherent problems in exposure assessment for nonparticipating subjects, however, limit the interpretations of these results, and the role of selection bias cannot entirely be dismissed on the basis of these results alone.     

高压输电线周边居民神经系统症状及血液系统的横断面研究

目的 研究高压输电线电磁场暴露对神经系统症状的影响.方法 以高压输电线周边居住的居民为调查对象,并根据距离高压输电线20、100、500 m分为3组;采用面对面问卷调查方式对居民生活情况、健康状况进行调查研究,同时测定研究对象的白细胞数(WBC)、红细胞数(RBC)、血红蛋白量(HGB)、血小板数(PLT)、IgG和IgM等水平.结果 在居民日常生活习惯,如吸烟、饮酒上,不同距离组间的差异无统计学意义(P＞0.05).比较不同距离组间健康调查的结果显示,离高压输变电线不同距离,居民头痛或头晕、失眠和乏力易疲劳等神经系统症状发生率差异有统计学意义(P＜0.05).血液学检查显示,居民PLT水平随着离高压输电线水平距离的减少而下降,且差异有统计学意义(P＜0.001),而各组间居民的WBC、RBC、HGB、IgG和IgM的差异均无统计学意义(P＞0.05).结论 近距离暴露电磁场可能与头痛等神经系统症状发生率和PLT水平降低有关.     

500kV输变电线周边工频电磁场强度调查

目的了解丘陵地区500kV输变电线路工频电磁场强度分布状况。方法对边导线一侧20m范围内工频电场强度、工频磁场强度进行测量。结果距边导线垂直投影线0、5、10、15、20m处工频电场总场强度4kV/m分别占点次数的21.1%、18.4%、21.1%、12.4%、7.1%;工频磁场总场强度均0.1mT。结论不同线高的工频电磁场垂直分量的分布不全相同。应将线高列为工频电磁场检测参数之一。     

供电企业工频电磁场职业暴露现况

目的 检测和评估某供电企业工频电磁场职业暴露现况.方法 采用德国PMM8053电磁场测量系统(EHP-50工频电磁场测量探头)对作业环境进行测量,使用美国EMDEX LITE个体磁场剂量仪对作业岗位进行抽样测量,运用GBZ 2.2 2007《工作声所物理因素测量第3部分:工频电场》以及ICNIRP的限值标准对结果进行评估.结果 超高压变电站500 kV电压区90％以上测点工频电场强度超过5 kV/m,电抗器和电容器附近磁场强度常超过100μT,可达几百微特斯拉.供电作业工人日暴露平均水平在0.04～5.0 μT之间,70％作业工人高于0.4 μT.结论 500 kV及以上超高压变电站高压区、各级变电站电抗器和电容器为供电企业工频电磁场关键控制点,存在急性健康影响风险.供电企业作业工人累计磁场暴露水平较高.     

The epidemiology of electric and magnetic field exposures in the power frequency range and reproductive outcomes

Some laboratory studies have reported effects of extremely low frequency electric and magnetic fields on calcium homeostasis and pineal gland function which potentially could have consequences for reproductive health. The purpose of this review is to report results of research to date in humans on maternal, paternal and fetal exposure to the 50-60 Hz fields associated with electricity, and to propose populations, endpoints and strategies for future research.     

The contribution of local distribution substations and associated area distribution system to personal exposure to power frequency magnetic fields

A number of epidemiological studies has shown a significant correlation between wire coding, magnetic fields and childhood cancer, although a more recent study has not [McBride et al. (1999) Am. J. Epidemiol. 149 (9), 831-842]. In the UK there is currently no equivalent to wire-codes and there is some uncertainty about the extent to which the UK medium-voltage electricity distribution systems contribute to personal exposure and how this compares with US overhead supply systems. Studies on four different area types were carried out to measure magnetic field intensities from typical electricity supply utility substations and cabling in the vicinity of domestic housing. Typically at distances of two metres from the substations mean magnetic field intensities were 20 nano teslas (nT) or less, increasing to 0.98 microT or less at the closest public access point. The mean magnetic field exposure level sampled around the four main test areas varied between 0.012 and 0.27 microT increasing to 0.30-0.80 microT at road junctions.     

职业暴露和生活接触的低频电磁场与成年人急性髓系白血病——基于病例对照研究的Meta分析

目的 研究职业或居住环境中暴露于电磁场与成年人罹患急性髓系白血病(AML)危险因素的关系.方法 收集发表于1980-2010年共9篇相关病例对照研究,用RevMan5.0软件进行Meta分析.结果 电磁场暴露与AML的OR值为1.24(95%CI:1.11～1.37).以暴露强度＜0.1μT为参照,当暴露值分别为0.1～0.2 μT和≥0.2 μT时,分别为OR=1.17(95%CI:0.98～1.39)和OR=1.5l(95%CI:1.15～1.98).结论 Meta分析显示极低频电磁场可能是成年人AML的危险因素之一.进一步对暴露距离、职业暴露或居住环境暴露进行亚组分析,也均揭示电磁场可增加成年人AML的患病风险.

Abstract：

Objective Studies had suggested that risk of leukemia might be associated with occupational or residential exposures to electromagnetic fields and varied at distance to and level of the exposure or type of occupations. Through pooled analyses, etiologic insight on the associations between exposure and disease might be explained. Methods We carried out a Meta-analysis based on primary data (1980-2010) from 9 studies related to the electric and magnetic fields exposure and acute myeloid leukemia in adults to assess whether the combined results, adjusted for potential confounding, would indicate an association between them. Results In this study the overall estimated OR value was 1.24(95%CI: 1.11-1.37). The odds ratios for exposure categories of 0.1-0.2 μT, ≥0.2 μT, compared with ＜0.1 μT, were 1.17(95%CI: 0.98-1.39) and 1.51 (95%CI: 1.15-1.98),respectively. Conclusion Through employing the alternate cut points, stratification by level of exposure or distance and the relation on different ways of exposure, there appeared consistent evidence of increased risk between acute myeloid leukemia in adults and the extremely low frequency-electromagnetic to field exposure.