Occupational exposure to electromagnetic fields in relation to leukemia and brain tumors: a case-control study in Sweden

Epigenetic effects on broiler exposure to magnetic field on progeny meat production traits

This experiment was conducted to determine the effect of the exposure of Ross 308 broiler breeders to a magnetic field on the meat production traits of progeny. The experimental flock consisted of 60 hens and ten cocks of Ross 308 broiler breeders at 36 weeks of age, divided randomly into four groups; each group applied for treatment with three replicates. The treatments were control (T1), storage of semen in an 803 gauss magnetic field for 24 h (T2), storage of fertilized eggs in a magnetic field of 250 gausses for 72 h before entering the incubator (T3), and exposing individual cages to 250 gausses of magnetic field for 8 Weeks (T4). The progeny result from the broiler breeders groups was recorded for body weight and feed intake, compared with the control (T1). The results showed no significant differences among progeny groups in body weight, weekly weight gain and weekly feed intake during the rearing period. Keywords: Epigenetic, magnetic broiler breeders, broiler progeny performance

Malignant lymphoma and occupational exposure to extremely low frequency magnetic fields and electrical shocks: a nested case-control study in a cohort of four Nordic countries

BACKGROUND

Exposure to extremely low frequency magnetic fields (ELF-MFs) and electric shocks is a common occupational risk factor in many workplaces. Recent investigations have highlighted a possible association between such exposures and lymphoma risk. This study was carried out to further explore the association between occupational exposure to ELF-MFs and electric shocks and risk of lymphoma in a large Nordic census-based cohort.

METHODS

We included cases of non-Hodgkin's lymphoma (NHL, n=68 978), chronic lymphocytic leukaemia (CLL, n=20 615) and multiple myeloma (MM, n=35 467) diagnosed between 1961 and 2005 in Finland, Iceland, Norway and Sweden. Cases were matched to five controls by year of birth, sex and country. Lifetime occupational ELF-MF and electric shock exposures were assigned to jobs reported in population censuses using job-exposure matrices. The risk of cancer was assessed based on cumulative exposure to ELF-MF and electric shocks. ORs with 95% CIs were estimated using logistic models adjusted for occupational co-exposures relevant to lymphomas.

RESULTS

Less than 7% of the cases experienced high levels of ELF-MF. We observed no increased risks among workers exposed to high levels of ELF-MF for NHL (OR: 0.93; CI 0.90 to 0.97), CLL (OR: 0.98; CI 0.92 to 1.05) or MM (OR: 0.96; CI 0.90 to 1.01).

CONCLUSION

Our results do not provide support for an association between occupational exposure to ELF-MFs and electric shocks and lymphoma risk.

Occupational extremely low frequency magnetic fields (ELF-MF) exposure and hematolymphopoietic cancers - Swiss National Cohort analysis and updated meta-analysis

PURPOSE

Previous studies have examined risks of leukaemia and selected lymphoid malignancies in workers exposed to extremely low frequency magnetic fields (ELF-MF). Most studies evaluated hematolymphopoietic malignancies as a combined category, but some analyses suggested that effects may be contained to some specific leukaemia or lymphoma subtypes, with inconsistent results.

METHODS

We examined exposure to ELF-MF and mortality 1990-2008 from different types of hematolymphopoietic cancers in the Swiss National Cohort, using a job exposure matrix for occupations recorded at censuses 1990 and 2000. We analysed 3.1 million workers exposed at different levels to ELF-MF: ever-high, only-medium, only-low exposure using Cox proportional hazard models. We evaluated risk of death from acute myeloid leukaemia (AML), chronic myeloid leukaemia, lymphoid leukaemia, diffuse large B-cell lymphomas, follicular lymphoma, Waldenström's macroglobulinemia, multiple myeloma and Hodgkin lymphoma.

RESULTS

Mortality from hematolymphopoietic cancers was not associated with exposure to ELF-MF with the exception of an increase in ever-high exposed men of myeloid leukaemias (HR 1.31, 95% CI 1.02-1.67), and AML (HR 1.26, 95%CI 0.93-1.70). If workers had been high exposed during their vocational training and at both censuses, these HR increased to 2.24 (95%CI 0.91-5.53) and 2.75 (95%CI 1.11-6.83), respectively.

CONCLUSIONS

Our analysis provided no convincing evidence for an increased risk of death from a range of hematolymphopoietic cancers in workers exposed to high or medium levels of ELF magnetic fields. However, we observed an increased risk of acute myeloid leukaemia in workers exposed to high levels for a longer duration. Observed risks are in line with meta-analysed previous reports on ELF-MF exposure and AML risk, with a summary relative risk of 1.21 (95%CI 1.08-1.37).

Review of refractory ceramic fiber (RCF) toxicity, epidemiology and occupational exposure

This literature review on refractory ceramic fibers (RCF) summarizes relevant information on manufacturing, processing, applications, occupational exposure, toxicology and epidemiology studies. Rodent toxicology studies conducted in the 1980s showed that RCF caused fibrosis, lung cancer and mesothelioma. Interpretation of these studies was difficult for various reasons (e.g. overload in chronic inhalation bioassays), but spurred the development of a comprehensive product stewardship program under EPA and later OSHA oversight. Epidemiology studies (both morbidity and mortality) were undertaken to learn more about possible health effects resulting from occupational exposure. No chronic animal bioassay studies on RCF have been conducted since the 1980s. The results of the ongoing epidemiology studies confirm that occupational exposure to RCF is associated with the development of pleural plaques and minor decrements in lung function, but no interstitial fibrosis or incremental lung cancer. Evidence supporting a finding that urinary tumors are associated with RCF exposure remains, but is weaker. One reported, but unconfirmed, mesothelioma was found in an individual with prior occupational asbestos exposure. An elevated SMR for leukemia was found, but was absent in the highly exposed group and has not been observed in studies of other mineral fibers. The industry will continue the product stewardship program including the mortality study.

Occupational solvent exposure and adult chronic lymphocytic leukemia: No risk in a population-based case-control study in four Nordic countries

The aim of this study was to assess the effect of occupational solvent exposure on the risk of adult chronic lymphocytic leukemia (CLL). The current case-control study was nested in the Nordic Occupational Cancer Study (NOCCA) cohort. 20,615 CLL cases diagnosed in 1961-2005 in Finland, Iceland, Norway, and Sweden, and 103,075 population-based controls matched by year of birth, sex, and country were included. Occupational histories for cases and controls were obtained from census records in 1960, 1970, 1980/1981, and 1990. Exposure to selected solvents was estimated by using the NOCCA job-exposure matrix (NOCCA-JEM). Odds ratios (OR) and 95% confidence intervals (95% CI) were estimated by using conditional logistic regression models. Overall, nonsignificant CLL risk elevations were observed for methylene chloride, perchloroethylene, and 1,1,1-trichloroethane. Compared to unexposed, significantly increased risks were observed for cumulative perchloroethylene exposure ≤13.3 ppm-years (OR = 1.85, 95% CI 1.16-2.96) and average life-time perchloroethylene exposure ≤2.5 ppm (1.61, 95% CI 1.01-2.56) among women, and cumulative methylene chloride exposure ≤12.5 ppm-years (OR = 1.19, 95% CI 1.01-1.41) and 12.5-74.8 ppm-years (OR = 1.23, 95% CI 1.01-1.51) among men in an analysis with 5 years lag-time, though without dose-response pattern. Decreased CLL risk was observed for aliphatic and alicyclic hydrocarbon solvents and toluene. This study did not support associations for solvent exposure and CLL. Observed weak associations for methylene chloride, perchloroethylene, 1,1,1-trichloroethane exposures, aliphatic and alicyclic hydrocarbons and toluene were not consistent across sexes, and showed no gradient with amount of exposure.

When theory and observation collide: Can non-ionizing radiation cause cancer?

This paper attempts to resolve the debate about whether non-ionizing radiation (NIR) can cause cancer-a debate that has been ongoing for decades. The rationale, put forward mostly by physicists and accepted by many health agencies, is that, "since NIR does not have enough energy to dislodge electrons, it is unable to cause cancer." This argument is based on a flawed assumption and uses the model of ionizing radiation (IR) to explain NIR, which is inappropriate. Evidence of free-radical damage has been repeatedly documented among humans, animals, plants and microorganisms for both extremely low frequency (ELF) electromagnetic fields (EMF) and for radio frequency (RF) radiation, neither of which is ionizing. While IR directly damages DNA, NIR interferes with the oxidative repair mechanisms resulting in oxidative stress, damage to cellular components including DNA, and damage to cellular processes leading to cancer. Furthermore, free-radical damage explains the increased cancer risks associated with mobile phone use, occupational exposure to NIR (ELF EMF and RFR), and residential exposure to power lines and RF transmitters including mobile phones, cell phone base stations, broadcast antennas, and radar installations.

Effects of pre- and postnatal exposure to extremely low-frequency electric fields on mismatch negativity component of the auditory event-related potentials: Relation to oxidative stress

In our previous study, the developmental effects of extremely low-frequency electric fields (ELF-EF) on visual and somatosensory evoked potentials in adult rats were studied. There is no study so far examining the effects of 50 Hz electric field (EF) on mismatch negativity (MMN) recordings after exposure of rats during development. Therefore, our present study aimed to investigate MMN and oxidative brain damage in rats exposed to EF (12 kV/m, 1 h/day). Rats were divided into four groups, namely control (C), prenatal (Pr), postnatal (Po), and prenatal+postnatal (PP). Pregnant rats of Pr and PP groups were exposed to EF during pregnancy. Following birth, rats of PP and Po groups were exposed to EF for three months. After exposure to EF, MMN was recorded by electrodes positioned stereotaxically to the surface of the dura, and then brain tissues were removed for histological and biochemical analyses. The MMN amplitude was higher to deviant tones than to standard tones. It was decreased in all experimental groups compared with the C group. 4-Hydroxy-2-nonenal (4-HNE) levels were significantly increased in the Po group with respect to the C group, whereas they were significantly decreased in the PP group compared with Pr and Po groups. Protein carbonyl levels were significantly decreased in the PP group compared with C, Pr, and Po groups. EF decreased MMN amplitudes were possibly induced by lipid peroxidation.

Occupational exposure to extremely low-frequency magnetic fields and electrical shocks and acute myeloid leukemia in four Nordic countries

OBJECTIVE

We studied the association between occupational exposure to extremely low-frequency magnetic fields (ELF-MF) and electrical shocks and acute myeloid leukemia (AML) in the Nordic Occupational Cancer cohort (NOCCA).

METHODS

We included 5,409 adult AML cases diagnosed between 1961 and 2005 in Finland, Iceland, Norway, and Sweden and 27,045 controls matched by age, sex, and country. Lifetime occupational ELF-MF exposure and risk of electrical shocks were assigned to jobs reported in the censuses using job-exposure matrices. We estimated hazard ratios (HRs) and 95 % confidence intervals (95 % CIs) using conditional logistic regression adjusted for concurrent occupational exposures relevant for AML risk (e.g., benzene, ionizing radiation). We conducted sensitivity analyses with different assumptions to assess the robustness of our results.

RESULTS

Approximately 40 % of the subjects were ever occupationally exposed to low levels and 7 % to high levels of ELF-MF, whereas 18 % were ever at low risk and 15 % at high risk of electrical shocks. We did not observe an association between occupational exposure to neither ELF-MF nor electrical shocks and AML. The HR was 0.88 (95 % CI 0.77-1.01) for subjects with high levels of ELF-MF exposure and 0.94 (95 % CI 0.85-1.05) for subjects with high risk of electrical shocks as compared to those with background-level exposure. Results remained materially unchanged in sensitivity analyses with different assumptions.

CONCLUSION

Our results do not support an association between occupational ELF-MF or electric shock exposure and AML.

Effects of extremely low-frequency electromagnetic fields (ELF-EMF) exposure on B6C3F1 mice

OBJECTIVE

Long-term exposure study was conducted to investigate the effects of extremely low-frequency electromagnetic field on the tumor promotion process and fertility.

METHODS

Ten pregnant C57BL/6NCrj mice were exposed to 50 Hz field 500 mG for 1 week (12 h per day), and 24 male and 42 female B6C3F1mice born from them were further exposed up to 15.5 months. As a control group, 10 pregnant mice were bred without exposure, and 30 produced male and 32 female mice were observed without exposure for the same period.

RESULTS

Mean body weights of exposed groups of male and female mice were decreased significantly than those of the control groups. In exposed mice, there was no increased incidence of liver and lung tumor. In female mice, the incidence of chronic myeloid leukemia [3/42 (7%)] in the exposed group was significantly greater than in the control group. The size of seminiferous tubules in the EMF exposed groups were significantly less than the control group.

CONCLUSIONS

These data support the hypothesis that long-term exposure of 50 Hz magnetic fields is a significant risk factor for neoplastic development and fertility in mice.

Occupational exposure to extremely low-frequency magnetic fields and brain tumor risks in the INTEROCC study

BACKGROUND

Occupational exposure to extremely low-frequency magnetic fields (ELF) is a suspected risk factor for brain tumors, however the literature is inconsistent. Few studies have assessed whether ELF in different time windows of exposure may be associated with specific histologic types of brain tumors. This study examines the association between ELF and brain tumors in the large-scale INTEROCC study.

METHODS

Cases of adult primary glioma and meningioma were recruited in seven countries (Australia, Canada, France, Germany, Israel, New Zealand, and the United Kingdom) between 2000 and 2004. Estimates of mean workday ELF exposure based on a job exposure matrix were assigned. Estimates of cumulative exposure, average exposure, maximum exposure, and exposure duration were calculated for the lifetime, and 1 to 4, 5 to 9, and 10+ years before the diagnosis/reference date.

RESULTS

There were 3,761 included brain tumor cases (1,939 glioma and 1,822 meningioma) and 5,404 population controls. There was no association between lifetime cumulative ELF exposure and glioma or meningioma risk. However, there were positive associations between cumulative ELF 1 to 4 years before the diagnosis/reference date and glioma [odds ratio (OR) ≥ 90th percentile vs. < 25th percentile, 1.67; 95% confidence interval (CI), 1.36-2.07; PLinear trend < 0.0001], and, somewhat weaker associations with meningioma (OR ≥ 90th percentile vs. < 25th percentile, 1.23; 95% CI, 0.97-1.57; PLinear trend = 0.02).

CONCLUSIONS

Results showed positive associations between ELF in the recent past and glioma.

IMPACT

Occupational ELF exposure may play a role in the later stages (promotion and progression) of brain tumorigenesis.

The epidemiology of glioma in adults: a "state of the science" review

Gliomas are the most common primary intracranial tumor, representing 81% of malignant brain tumors. Although relatively rare, they cause significant mortality and morbidity. Glioblastoma, the most common glioma histology (∼45% of all gliomas), has a 5-year relative survival of ∼5%. A small portion of these tumors are caused by Mendelian disorders, including neurofibromatosis, tuberous sclerosis, and Li-Fraumeni syndrome. Genomic analyses of glioma have also produced new evidence about risk and prognosis. Recently discovered biomarkers that indicate improved survival include O⁶-methylguanine-DNA methyltransferase methylation, isocitrate dehydrogenase mutation, and a glioma cytosine-phosphate-guanine island methylator phenotype. Genome-wide association studies have identified heritable risk alleles within 7 genes that are associated with increased risk of glioma. Many risk factors have been examined as potential contributors to glioma risk. Most significantly, these include an increase in risk by exposure to ionizing radiation and a decrease in risk by history of allergies or atopic disease(s). The potential influence of occupational exposures and cellular phones has also been examined, with inconclusive results. We provide a “state of the science” review of current research into causes and risk factors for gliomas in adults.

Possible health benefits from reducing occupational magnetic fields

BACKGROUND

Magnetic fields (MF) from AC electricity are a Possible Human Carcinogen, based on limited epidemiologic evidence from exposures far below occupational health limits.

METHODS

To help formulate government guidance on occupational MF, the cancer cases prevented and the monetary benefits accruing to society by reducing workplace exposures were determined. Life-table methods produced Disability Adjusted Life Years, which were converted to monetary values.

RESULTS

Adjusted for probabilities of causality, the expected increase in a worker's disability-free life are 0.04 year (2 weeks) from a 1 microtesla (µT) MF reduction in average worklife exposure, which is equivalent to $5,100/worker/µT in year 2010 U.S. dollars (95% confidence interval $1,000-$9,000/worker/µT). Where nine electrosteel workers had 13.8 µT exposures, for example, moving them to ambient MFs would provide $600,000 in benefits to society (uncertainty interval $0-$1,000,000).

CONCLUSIONS

When combined with the costs of controls, this analysis provides guidance for precautionary recommendations for managing occupational MF exposures.

A meta-analysis of epidemiological studies on the relationship between occupational electromagnetic field exposure and the risk of adult leukemia

Since the first paper by Milham et al. suggested that occupational exposure to an electromagnetic field (EMF) could increase the risk of adult leukemia, many epidemiological studies on this problem have been published. In this report the method of meta-analysis was used to summarize the results from these papers quantitatively. The combined relative risk of all leukemia (RR=1.11), as well as acute lymphocytic leukemia (RR=1.38), acute myeloid leukemia (RR=1.07) and chronic lymphocytic leukemia (RR=1.14) increased but not significantly. So far, it is difficult to make a consistent conclusion about the relationship of the occupational exposure to EMF and adult leukemia. Further carefully designed case-control and cohort studies using the more valid means of exposure assessment are required.

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.

The Upper Midwest Health Study: industry and occupation of glioma cases and controls

BACKGROUND

Understanding glioma etiology requires determining which environmental factors are associated with glioma. Upper Midwest Health Study case-control participant work histories collected 1995-1998 were evaluated for occupational associations with glioma. "Exposures of interest" from our study protocol comprise our a priori hypotheses.

MATERIALS AND METHODS

Year-long or longer jobs for 1,973 participants were assigned Standard Occupational Classifications (SOC) and Standard Industrial Classifications (SIC). The analysis file includes 8,078 SIC- and SOC-coded jobs. For each individual, SAS 9.2 programs collated employment with identical SIC-SOC coding. Distributions of longest "total employment duration" (total years worked in jobs with identical industry and occupation codes, including multiple jobs, and non-consecutive jobs) were compared between cases and controls, using an industrial hygiene algorithm to group occupations.

RESULTS

Longest employment duration was calculated for 780 cases and 1,156 controls. More case than control longest total employment duration was in the "engineer, architect" occupational group [16 cases, 10 controls, odds ratio (OR) 2.50, adjusted for age group, sex, age and education, 95% confidence interval (CI) 1.12-5.60]. Employment as a food processing worker [mostly butchers and meat cutters] was of borderline significance (27 cases, 21 controls, adjusted OR: 1.78, CI: 0.99-3.18).

CONCLUSIONS

Among our exposures of interest work as engineers or as butchers and meat cutters was associated with increased glioma risk. Significant associations could be due to chance, because of multiple comparisons, but similar findings have been reported for other glioma studies. Our results suggest some possible associations but by themselves could not provide conclusive evidence.

Intracellular Ca Mobilization and Beta-hexosaminidase Release Are Not Influenced by 60 Hz-electromagnetic Fields (EMF) in RBL 2H3 Cells

The effects of extremely low frequency electromagnetic fields (EMF) on intracellular Ca(2+) mobilization and cellular function in RBL 2H3 cells were investigated. Exposure to EMF (60 Hz, 0.1 or 1 mT) for 4 or 16 h did not produce any cytotoxic effects in RBL 2H3 cells. Melittin, ionomycin and thapsigargin each dose-dependently increased the intracellular Ca(2+) concentration. The increase of intracellular Ca(2+) induced by these three agents was not affected by exposure to EMF (60 Hz, 1 mT) for 4 or 16 h in RBL 2H3 cells. To investigate the effect of EMF on exocytosis, we measured beta-hexosaminidase release in RBL 2H3 cells. Basal release of beta-hexosaminidase was 12.3±2.3% in RBL 2H3 cells. Exposure to EMF (60 Hz, 0.1 or 1 mT) for 4 or 16 h did not affect the basal or 1 µM melittin-induced beta-hexosaminidase release in RBL 2H3 cells. This study suggests that exposure to EMF (60 Hz, 0.1 or 1 mT), which is the limit of occupational exposure, has no influence on intracellular Ca(2+) mobilization and cellular function in RBL 2H3 cells.

Exposure to extremely low frequency magnetic fields induces fos-related antigen-immunoreactivity via activation of dopaminergic d1 receptor

We previously demonstrated that repeated exposure to extremely low frequency magnetic fields (ELF-MF) increases locomotor activity via stimulation of dopaminergic D1 receptor (J. Pharmacol. Sci., 2007;105:367-371). Since it has been demonstrated that activator protein-1 (AP-1) transcription factors, especially 35-kDa fos-related antigen (FRA), play a key role in the neuronal and behavioral adaptation in response to various stimuli, we examined whether repeated ELF-MF exposure induces FRA-immunoreactivity (FRA-IR) in the striatum and nucleus accumbens (striatal complex) of the mice. Repeated exposure to ELF-MF (0.3 or 2.4 mT, 1 h/day, for consecutive fourteen days) significantly induced hyperlocomotor activity and FRA-IR in the striatal complex in a field intensity-dependent manner. ELF-MF-induced FRA-IR lasted for at least 1 year, while locomotor activity returned near control level 3 months after the final exposure to ELF-MF. Pretreatment with SCH23390, a dopaminergic D1 receptor antagonist, but not with sulpiride, a dopaminergic D2 receptor antagonist, significantly attenuated hyperlocomotor activity and FRA-IR induced by ELF-MF. Our results suggest that repeated exposure to ELF-MF leads to prolonged locomotor stimulation and long-term expression of FRA in the striatal complex of the mice via stimulation of dopaminergic D1 receptor.

Effect of Extremely Low Frequency Electromagnetic Fields (EMF) on Phospholipase Activity in the Cultured Cells

This study was conducted to investigate the effects of extremely low frequency electromagnetic fields (EMF) on signal pathway in plasma membrane of cultured cells (RAW 264.7 cells and RBL 2H3 cells), by measuring the activity of phospholipase A(2) (PLA(2)), phospholipase C (PLC) and phospholipase D (PLD). The cells were exposed to the EMF (60 Hz, 0.1 or 1 mT) for 4 or 16 h. The basal and 0.5 µM melittin-induced arachidonic acid release was not affected by EMF in both cells. In cell-free PLA(2) assay, we failed to observe the change of cPLA(2) and sPLA(2) activity. Also both PLC and PLD activities did not show any change in the two cell lines exposed to EMF. This study suggests that the exposure condition of EMF (60 Hz, 0.1 or 1 mT) which is 2.4 fold higher than the limit of occupational exposure does not induce phospholipases-associated signal pathway in RAW 264.7 cells and RBL 2H3 cells.

Exposure to magnetic fields of railway engine drivers: a case study in Italy

A case study of exposure assessment of railway workers to static and extremely low frequency (ELF) magnetic fields is presented. A measurement campaign was conducted in aboard Italian main line trains. All measurements were performed on board during regular service (two engine drivers were simultaneously present), in all places potentially accessible to personnel, considering routes ranging from a few tens of kilometres to hundreds of kilometres. The measurement protocol was mostly based on broadband metres and personal metres were employed to assess individual exposure. Surveys on static and ELF magnetic fields were performed for seven different models of engine or electrified train. Traction motors were fed by alternating current (AC) current, except for two engines, where AC current fed only auxiliary services. The final result is that the average exposure to static magnetic field was a little higher than the background geomagnetic field; occasionally in few areas it could reach levels of the order of millitesla. The average exposure to ELF magnetic fields was in the order of 1-2 μT, with higher levels (few microtesla) only for one engine; occasionally in hot spots, close to wiring or specific equipment, the field values could reach several tens of microtesla.

Histopathological and ultrastructural studies on the effects of electromagnetic fields on the liver of preincubated white Leghorn chicken embryo

There are several reports indicating a linkage between exposures to 50-60 Hz electromagnetic fields and abnormalities in the early stages of embryonic development of chicken embryos. The present study was designed to demonstrate whether electromagnetic fields could be an environmental factor invoking histopathological and ultra-structural changes in livers of preincubated chicken embryos exposed to EMFs. Following other researchers and our previous results from different groups of Developmental Biology at the Animal Sciences, Faculty of Biological Sciences, Shahid-Beheshti University, effects of most effective intensities (1.33, 2.66, 5.52, and 7.32 mT) of electromagnetic fields (EMFs, 50 Hz ) on livers of pre-incubated white leghorn chicken embryos were investigated . 150 healthy, fresh, and fertilized eggs (55-65 gr) were divided into 6 groups of experimental(1-4, n = 30), control (n = 60), and sham (n = 50). Experimental eggs (inside coil) were exposed to 4 different intensities (1.33, 2.66, 5.52, and 7.32 mT). Sham groups were located inside same coil, with no exposure, for 24 h before incubation. Control, sham, and experimental groups (1-4) were then incubated in an incubator (38 +/- 0.5 degrees C, 60% humidity) for 17 days. At the end of this period, livers of experimental, sham, and control groups were processed for light and transmission electrom microscopes (TEM and SEM) studies. So, livers of 17-day old chicken embryos were removed by C-sections, fixed in formalin 10%, stained with H&E and reticulin, and studied under light microscope. Others were prepared for electron microscopes (TEM and SEM) investigations. Morphological observations indicated exencephalic embryos, embryos with asymmetrical faces, crossed beak, shorter upper beak, deformed hind limbs, gastroschesis, anophthalmia, and microphthalmia. H&E and reticulin stainings, TEMS, and SEMs studies indicated EMFs would create hepato-cytes with fibrotic bands, severe steatohepatitis, vacuolizations, swollen and extremely electron-dense mitochondria, reduced invisible cristae, crystalized mitochondria with degenerated cristae, myelin-like figures, macrophages engulfing adjacent cells, dentated nuclei, nuclei with irregular envelopes, degenerated hepatocytes, abnormal lipid accumulations, lipid droplets pushing hepatocytes' nuclei to the corner of the cells, abundant cellular infiltrations cellular infiltrations inside sinusoid and around central veins, disrupted reticulin plexus, and release of chromatin into cytosol,, with partially regular water layers. An elevated oxyradical generation and, subsequently, cell membrane disruptions were the reasons for electromagnetic fields inducing cell damages.

Natural Killer Cell Activity Decreases in Workers Occupationally Exposed to Extremely Low Frequency Magnetic Fields Exceeding 1 μt

In a preliminary study a reduction in Natural Killer (NK) cell activity in peripheral blood lymphocytes (PBL) was observed in a group of workers exposed to levels of Extremely Low Frequency-Magnetic Fields (ELF-MF) exceeding 1 μT. This study was performed to confirm the results. In 121 workers engaged in various occupational activities, individual ELF-MF exposure was monitored for 2 work shifts. Exposure levels were calculated as Time-Weighted Average (TWA). Subjects were classified as Low exposure (TWA ≤ 0.2 μT), Medium exposure (TWA 0.21–0.99 μT), or Higher exposure (TWA ≥1 μT). In higher exposure workers NK activity proved significantly reduced compared to low exposure, (p<0.01). In medium exposure a reduction was also observed, but the difference was not significant. Multivariate analysis also confirmed the relation between exposure and NK activity. It has been suggested that ELF might affect tumour progression by inducing changes in the immune system: due to the role played by NK activity in host defence against cancer, the interference with the NK cell activity observed in this study is in agreement with this hypothesis. Furthermore, an increased risk for some neurodegenerative disorders has been reported in some epidemiological studies in ELF-MF-exposed workers: changes in NK function were also described in these diseases. Our results, showing the effect on NK activity of exposure exceeding 1 μT, suggest a possible mechanism for ELF-MF effects. This could open new horizons regarding the adverse long-term effects of these fields.

Occupational exposure to magnetic fields and the risk of brain tumors

We investigated the association between occupational exposure to extremely low-frequency magnetic fields (MFs) and the risk of glioma and meningioma. Occupational exposure to MF was assessed for 489 glioma cases, 197 meningioma cases, and 799 controls enrolled in a hospital-based case-control study. Lifetime occupational history questionnaires were administered to all subjects; for 24% of jobs, these were supplemented with job-specific questionnaires, or "job modules," to obtain information on the use of electrically powered tools or equipment at work. Job-specific quantitative estimates for exposure to MF in milligauss were assigned using a previously published job exposure matrix (JEM) with modification based on the job modules. Jobs were categorized as < or =1.5 mG, >1.5 to <3.0 mG, and > or =3.0 mG. Four exposure metrics were evaluated: (1) maximum exposed job; (2) total years of exposure >1.5 mG; (3) cumulative lifetime exposure; and (4) average lifetime exposure. Odds ratios (ORs) were calculated using unconditional logistic regression with adjustment for the age, gender, and hospital site. The job modules increased the number of jobs with exposure > or =3.0 mG from 4% to 7% relative to the JEM. No statistically significant elevation in ORs or trends in ORs across exposure categories was observed using four different exposure metrics for the three tumor types analyzed. Occupational exposure to MFs assessed using job modules was not associated with an increase in the risk for glioma, glioblastoma, or meningioma among the subjects evaluated in this study.

Effects of extremely low frequency electromagnetic fields on distortion product otoacoustic emissions in rabbits

OBJECTIVE

Humans are continuously exposed to extremely low frequency (ELF), electromagnetic fields (EMF), transmitted from the common sources like power stations, electric transmission lines, communication and radio-television signal transmission units. The present study aimed to assess the effects of 50 Hz ELF-EMF of 5.068 and 10.182 kV/m electric fields, which refer to the lower and upper intensity limits beyond which hazardous effects can be observed, on the auditory functions of rabbits via Distortion Product Otoacoustic Emission (DPOAE) recordings.

METHODS

The study was performed on 20 healthy adult female New Zealand White rabbits randomly divided into two groups and applied 50 Hz ELF-EMF with either 5.068 kV/m (Group 1) or 10.182 kV/m (Group 2) of electric field for 3h/day during 14 days. DPOAE responses recorded on the 0th day before exposure (B-EMF) and on the 6th (A-EMF-6th) and 14th (A-EMF-14th) days after exposure (AE). Mean stimulus intensity and emission amplitudes at 1.0-8.0 kHz were analyzed.

RESULTS

In Group 2 rabbits, on 6th and 14th days, the DPOAE amplitudes were observed as increased at 1.5-4.0 kHz (at 2.0 and 4.0 kHz significantly) than B-EMF values. At 6.0 kHz, A-EMF-14th amplitudes were significantly lower than A-EMF values.

CONCLUSION

These results suggest that ELF EMFs might affect hearing functions by frequency dependent manner. Higher ELF EMFs exposure caused increase of cochlear activity. Ototoxic effect of 10.182 kV/m ELF EMFs may begin at the basal turn of the cochlea by reducing DPOAEs at high frequencies.

A population-based job exposure matrix for power-frequency magnetic fields

A population-based job exposure matrix (JEM) was developed to assess personal exposures to power-frequency magnetic fields (MF) for epidemiologic studies. The JEM compiled 2,317 MF measurements taken on or near workers by 10 studies in the United States, Sweden, New Zealand, Finland, and Italy. A database was assembled from the original data for six studies plus summary statistics grouped by occupation from four other published studies. The job descriptions were coded into the 1980 Standard Occupational Classification system (SOC) and then translated to the 1980 job categories of the U.S. Bureau of the Census (BOC). For each job category, the JEM database calculated the arithmetic mean, standard deviation, geometric mean, and geometric standard deviation of the workday-average MF magnitude from the combined data. Analysis of variance demonstrated that the combining of MF data from the different sources was justified, and that the homogeneity of MF exposures in the SOC occupations was comparable to JEMs for solvents and particulates. BOC occupation accounted for 30% of the MF variance (p << 10(-6)), and the contrast (ratio of the between-job variance to the total of within- and between-job variances) was 88%. Jobs lacking data had their exposures inferred from measurements on similar occupations. The JEM provided MF exposures for 97% of the person-months in a population-based case-control study and 95% of the jobs on death certificates in a registry study covering 22 states. Therefore, we expect this JEM to be useful in other population-based epidemiologic studies.

Occupational exposure to low frequency magnetic fields and the risk of low grade and high grade glioma

OBJECTIVE

The purpose of this population-based case control study was to investigate a possible association between occupational exposure to low frequency magnetic fields and the risk of low grade glioma (LGG) and high grade glioma (HGG).

METHODS

The study population consisted of 414 histologically confirmed cases of glioma (LGG=110, HGG=304), first diagnosed between July 1987 and December 1991, and 421 controls from Melbourne, Australia, matched by age, sex and postcode of residence. A detailed occupational history was obtained for each subject. Exposure to low frequency magnetic fields was estimated using three different methods: self-report, expert hygienist review and a job exposure matrix (JEM).

RESULTS

Elevated but statistically non-significant risk estimates were found for all glioma and HGG when exposure was assessed by the expert hygienist. The odds ratios (OR) for the highest exposed group of workers when assessed by the expert hygienist were 1.4 (95% confidence interval, CI: 0.85-2.27) and 1.51 (95% CI: 0.90-2.53) for all glioma and HGG, respectively. There were inverse associations for the self-reported and JEM exposures for both LGG and HGG but these may reflect limitations in these exposure assessment methods.

CONCLUSIONS

Our results do not support a role for occupational exposure to low frequency magnetic fields in the development of either LGG or HGG.

Are gliomas preventable?

Gliomas are a family of primary central nervous system tumors of variable malignancy that are derived from supporting glia (astrocytes, oligodendrocytes, ependymal cells) or their progenitors/stem cells. There are two potential strategies to prevention: preventing gliomas from forming and preventing lower-grade gliomas from developing into higher-grade gliomas. Each would lower time-dependent mortality. Each also depends on an understanding of what causes gliomas so that these factors can be modulated. In this presentation, I will discuss primary prevention, chemoprevention, and screening. I will first focus on the known chromosomal, genetic, and protein changes associated with the different histologic varieties of glioma and the environmental, hereditary, and infectious/viral factors that may promote glioma development and malignant progression. I will discuss a number of clinical scenarios that eventuate from the known genetic patterns of these tumors and the changes in genetic patterns that reflect malignant progression. The basic thinking is that if one could prevent specific gene mutations and/or deletions or gains of specific chromosomes that lead to the development of low-grade (WHO 2) gliomas, then theoretically this would reduce the occurrence of high-grade (WHO 3 and 4) gliomas and hence the almost certain death that now is the fate of most patients with these tumors. In the case of de novo WHO 3 and 4 tumors, being able to prevent or counter specific gene mutations and/or the deletion of specific chromosomes would in itself reduce the occurrence of these gliomas and increase survival. Alternatively, a curative treatment for low-grade glioma that prevents these chromosomal/gene changes would prevent some glioblastomas (WHO 4) from forming and would have the same desired effect on survival. Obviously, for the latter to be achieved, we must also be able to diagnose and treat low-grade gliomas earlier.

Personal digital assistant (PDA) cell phone units produce elevated extremely-low frequency electromagnetic field emissions

Initial tests indicate that personal and occupational use of personal digital assistants (PDAs or palm-held wireless units) produce high intensity bursts of extremely-low frequency electromagnetic fields (ELF-EMF). These emissions could result in comparatively high ELF-EMF exposure in persons that carry a PDA close to the body (i.e., in a pocket or on a belt); or held to the head for cell phone conversations. ELF-EMF emissions of 10 microT were recorded on PDAs during normal office use over a 24 h test period. Results of ELF-EMF measurements show that email transmit and receive functions produce rapid, short-duration ELF-EMF spikes in the 2-10 microT range, each lasting several seconds to over a minute apparently depending on file download size. Some units produced spikes as high as 30-60 microT during email activities. Cell phone activity on PDAs produced continuously elevated ELF-EMF readings in the 0.5-1 microT range, as opposed to the rapid spiking pattern for email receipt and transmission. Switching the PDA unit from "OFF" to "ON" position resulted in single ELF-EMF pulses of over 90 microT on two units. Email downloads into the PDA can occur randomly throughout the day and night when the unit is "ON"; thus the user who wears the PDA may be receiving high-intensity ELF-EMF pulses throughout the day and night. The frequency of email traffic on the PDA, and the power switching unit (battery unit) may affect the frequency and intensity of ELF-EMF emissions.

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.

Occupational magnetic field exposure and the risk of acoustic neuroma

BACKGROUND

Acoustic neuroma is the intracranial tumor subtype showing the highest relative risk in relation to ionizing radiation but other environmental risk factors are largely unknown. This study was performed to investigate the effect of power frequency magnetic fields.

METHOD

A total of 793 cases between 1987 and 1999 were identified through the Swedish cancer registry and 101,762 controls were randomly selected from the total population. Information about occupation was obtained from censuses and linked to gender specific job-exposure matrices based on actual measurements of 50 Hz magnetic field exposure.

RESULT

We investigated time-weighted average, peak values, and rate of change of magnetic field exposure considering several different time windows in relation to cancer diagnosis. We found no increases in risks regardless of exposure metric or time window of exposure.

CONCLUSION

This study is the largest ever on acoustic neuroma and the first study to evaluate this tumor subtype specifically in relation to extremely low frequency magnetic fields. The results do not support the hypothesis that 50 Hz magnetic fields increase the risk of acoustic neuroma.

Perspectives on familial chronic lymphocytic leukemia: genes and the environment

Chronic lymphocytic leukemia (CLL) comprises a substantial proportion of leukemias in adults in the western hemisphere. Male gender, increasing age, ethnicity (high in Caucasians, lowest in Asians), and family history are risk factors. Although no specific extrinsic etiologic factors have been established, farming and pesticide exposure are associated with increased risk. Migration studies confirm that ethnic groups retain the risk associated with their origin rather than their new location, favoring a role for heredity. Kindreds with multiple cases of CLL have been well described in the literature and studies in large populations confirm that lymphoproliferative malignancies and especially CLL occur together at a rate that cannot be attributed to chance. Since environmental factors cannot readily explain the familial aggregations, a hereditary factor that affects susceptibility to CLL is likely. The identification of clones that are immunophenotypically identical to CLL in healthy individuals from CLL kindreds (14% to 18%) as well as in the general population (3.5% in age bracket >65 years) suggests a possible precursor condition, but longitudinal studies will be necessary to establish significance in the general population. Family (linkage) and population (candidate gene) studies to date have been too small to identify the specific genes that account for increased susceptibility; larger studies including planned consortia to identify additional high-risk kindreds for genetic studies, as well as the application of advanced technologies such as genomics, cytogenetic, expression, and proteomics, are widely expected to advance understanding over the next few years.

Residential and occupational exposure to 50-Hz magnetic fields and brain tumours in Norway: A population-based study

Our case-control study was conducted to investigate whether residential and occupational exposure to magnetic fields increased the risk for brain tumours in adults. Data from an occupational exposure matrix was also evaluated. The study population in this nested case-control study was made up of subjects aged 16 years and older who had resided in a broad corridor around a high-voltage power line in 1980 or during one of the years from 1986-1996. The cases were incident cases diagnosed during 1980-96. Two controls were matched to each case by year of birth, sex, municipality and first year entering the cohort. The time-weighted average exposure to residential magnetic fields generated by the power lines was calculated for the exposure follow-up from 1 January 1967 to diagnosis. In addition, job titles and branches of industry were classified as categories of hours per week in a magnetic field above background level (0.1 microT). Exposures were cumulated over occupationally active years for the exposure follow-up from 1 January 1955 to diagnosis. When residential magnetic fields are evaluated, the 2 upper residential, time-weighted, average magnetic field categories showed elevated odds ratios (ORs) for all brain tumours (OR = 1.6; 95% confidence interval [95%CI] 0.9-2.7 and OR = 1.3; 95% CI 0.7-2.3). Occupational exposure showed no association to exposure for any site. We found an elevated risk for residential exposure to magnetic fields and brain tumours, although the risk was not significant, and no clear exposure-response pattern was found. The findings for the occupational exposure groups showed an inverse association.

Occupational Magnetic Field Exposure and Myocardial Infarction Incidence

BACKGROUND

Studies on healthy volunteers have seen reduced heart rate variability after exposure to extremely low-frequency electric and magnetic fields (EMF). Because reduced heart rate variability has been linked to cardiovascular disease risk, it has been hypothesized that exposure to EMF might increase the risk of cardiovascular disease. One epidemiologic study has shown increased mortality from cardiovascular conditions in utility workers with elevated exposure to magnetic fields, but several other epidemiologic studies have failed to confirm this result. We tested the hypothesis that occupational EMF exposure increases the risk of myocardial infarction in a large population-based case-control study of myocardial infarction, with detailed information on potential confounders.

METHODS

We used data from the SHEEP study, which is a population-based case-control study of acute myocardial infarction in Stockholm. Occupational EMF exposure was based on job titles 1, 5, and 10 years before diagnosis. We used 2 approaches to classify exposure: first, specific individual job titles with presumed elevated EMF exposure, and second, classification of subjects according to a job-exposure matrix.

RESULTS

We found no increased risk of myocardial infarction in subjects classified as having elevated EMF exposure. For the highest exposure category of > or = 0.3 microT according to the job-exposure matrix, the adjusted relative risk was = 0.57 (95% confidence interval = 0.36-0.89).

CONCLUSIONS

The results of this study do not support the hypothesis that occupational EMF exposure increases the risk of myocardial infarction.

Assessment of exposure to magnetic fields in occupational settings

OBJECTIVE

It is important to have data about occupational magnetic field intensity to consider the contribution of occupational magnetic field exposure on the human body. We conducted research on exposure to occupational magnetic fields and tried to qualify data on the distribution of magnetic field' intensity in certain general working environments with individual measurements.

SUBJECTS AND METHODS

We performed sample research on the exposure to low-frequency magnetic fields of workers in certain occupations and in the working environment. We also assessed the relationship between working environmental magnetic field distribution and individual exposure.

RESULTS

Some occupations were found to be exposed to high magnetic fields. We observed that some workspaces, such as the transformer substation, generally had a uniform and high magnetic field measurement but employees were exposed to a lower intensity. We also found that welders were exposed to high magnetic fields at about 600 microT in a very short time but with a geometrical value of 0.08 microT.

CONCLUSION

The determination of administrative levels and control levels, not only of the time weighted average of threshold limits or short term exposure limits, but also ceiling limits should be considered. More systematic research is necessary to determine variables such as operating conditions, measuring position, and frequency bands. Also, further studies will be needed to make a job-exposure matrix for the magnetic fields for each occupation type and to combine it with exposure in non-occupational settings such as commuting and ordinary life situations to explore the causal relationship between exposure to magnetic fields and disease.

Occupational exposure to electromagnetic fields and acute leukaemia: analysis of a case-control study

AIMS

To investigate whether the risk of acute leukaemia among adults is associated with occupational exposure to electromagnetic fields.

METHODS

Probable occupational exposure to electromagnetic fields at higher than typical residential levels was investigated among 764 patients diagnosed with acute leukaemia during 1991-96 and 1510 sex and age matched controls. A job exposure matrix was applied to the self reported employment histories to determine whether or not a subject was exposed to electromagnetic fields. Risks were assessed using conditional logistic regression for a matched analysis.

RESULTS

Study subjects considered probably ever exposed to electromagnetic fields at work were not at increased risk of acute leukaemia compared to those considered never exposed. Generally, no associations were observed on stratification by sex, leukaemia subtype, number of years since exposure stopped, or occupation; there was no evidence of a dose-response effect using increasing number of years exposed. However, relative to women considered never exposed, a significant excess of acute lymphoblastic leukaemia was observed among women probably exposed to electromagnetic fields at work that remained increased irrespective of time prior to diagnosis or job ever held.

CONCLUSION

This large population based case-control study found little evidence to support an association between occupational exposure to electromagnetic fields and acute leukaemia. While an excess of acute lymphoblastic leukaemia among women was observed, it is unlikely that occupational exposure to electromagnetic fields was responsible, given that increased risks remained during periods when exposure above background levels was improbable.

Neurodegenerative diseases in welders and other workers exposed to high levels of magnetic fields

BACKGROUND

Previous work has suggested an increase in risk of amyotrophic lateral sclerosis (ALS) and Alzheimer's disease among workers exposed to extremely low-frequency magnetic fields (ELF-MF). We evaluated the relation between ELF-MF from occupational exposures and mortality from neurodegenerative diseases.

METHODS

The study was based on a cohort of Swedish engineering industry workers, comprising 537,692 men and 180,529 women. The cohort was matched against the 3 most recent censuses and The Causes of Death Registry. Levels of ELF-MF exposure were obtained by linking occupation according to the censuses to a job exposure matrix. We used 4 levels of exposure and considered both the primary and contributing causes of death, 1985-96.

RESULTS

The risk of Alzheimer's disease as primary or contributing cause of death increased with increasing exposure to ELF-MF among both men and women, with a relative risk (RR) of 4.0 and a 95% confidence interval (95% CI) of 1.4-11.7 in the highest exposure group for both sexes combined. There was a RR of 2.2 (95% CI: 1.0-4.7) for ALS in the highest exposure group with the suggestion of an exposure-response relationship. No evidence of increased risk was seen for Parkinson's disease or multiple sclerosis.

CONCLUSIONS

The findings support previous observations of an increased risk of Alzheimer's disease and ALS among employees occupationally exposed to ELF-MF. Further studies based on morbidity data are warranted.

Occupational exposure assessment in case-control studies: opportunities for improvement

Community based case-control studies are an efficient means to study disease aetiologies, and may be the only practical means to investigate rare diseases. However, exposure assessment remains problematic. We review the literature on the validity and reliability of common case-control exposure assessment methods: occupational histories, job-exposure matrices (JEMs), self reported exposures, and expert assessments. Given the variable quality of current exposure assessment techniques, we suggest methods to improve assessments, including the incorporation of hygiene measurements: using data from administrative exposure databases; using results of studies identifying determinants of exposure to develop questionnaires; and where reasonable given latency and biological half life considerations, directly measuring exposures of study subjects.

Exposure guidelines for low-frequency electric and magnetic fields: report from the Brussels workshop

The EMF Exposure Guidelines Science Workshop was held to evaluate the information base for guidelines for electric and magnetic field exposures at extremely low frequencies, to identify research needs, and to discuss how best to apply scientific knowledge in developing exposure recommendations. Although the existing guideline values are based on electrostimulation of nerve and muscle tissues, guidelines must also consider controversial studies of potential health effects from chronic exposures at environmental levels that are far too weak to cause electrostimulation. The size of the safety factor applied in specifying exposure limits reflects a variety of factors that introduce uncertainties. These include confidence in existing dose-effect relationships, population diversity, the reliability and precision of techniques to control over-exposure, and completeness of the information base, particularly regarding long-term effects. Specific research questions that can change the level of uncertainty meaningfully were identified in these areas: biophysical mechanisms of electrostimulation; the range of thresholds throughout exposed populations; cancer causation in children and adults, including a possible role for contact currents; cognitive, behavioral, and physiological effects on the central nervous system; improved dosimetry; and better understanding of electromagnetic interference with implanted biomedical devices such as pacemakers, defibrillators, and physiological monitors. This report introduces ten papers from the workshop that address these and related topics in detail.