Electromagnetic Fields 2009 Update

7. Extremely low frequency fields like those from power lines and household appliances

• 7.1 What are the sources of extremely low frequency fields (ELF fields)?
• 7.2 What is the level of exposure to ELF fields?
• 7.3 Can ELF fields increase the risk of childhood leukaemia and other cancers?
• 7.4 Can exposure to ELF cause headaches or other health effects?
• 7.5 What can be concluded about ELF fields?

7.1 What are the sources of extremely low frequency fields (ELF fields)?

The SCENIHR opinion states:

3.5. Extremely low frequency fields (ELF fields)

3.5.1. Sources and distribution of exposure in the population

The exposure due to electric fields and magnetic flux densities in the ELF range arises from a wide variety of sources (IARC 2002). The most prominent frequencies are 50 and 60 Hz and their harmonics, often called power frequencies. For residential exposure, the major sources are household appliances, nearby power and high voltages transmission lines, and domestic installations. In some cases trains also need to be considered. Regarding occupational exposure, electric power installations, welding, induction heaters and electrified transport systems are important examples of ELF exposure sources. The highest electric field strengths typically occur close to high voltage transmission lines and can reach 5 kV/m, and in a few cases more than 5 kV/m. The highest magnetic flux densities can be found close to induction furnaces and welding machines. Levels of a few mT are possible.

It should be mentioned that the maximum possible exposure next to a specific source often differs by some orders of magnitude from the average individual exposure of a person (to specify time weighted average exposure, in many cases the arithmetic mean or the geometric mean or the median value are applied). To evaluate the distribution of the exposure in the population, meters are used. For assessment of compliance with exposure limits, the maximum possible exposure next to devices must be measured. An example might be a lineman: the average exposure due to magnetic flux density could be about 4 µT (IARC 2002), but the maximum exposure close to a transmission line can reach 40 µT or more. For the general population even larger variations between maximum and average exposure can be expected. Information on ELF exposure is mainly based on US and Western European data.

Source & ©: SCENIHR,  Health Effects of Exposure to EMF (2009),
3.5.1.Sources and distribution of exposure in the population, p. 37

7.2 What is the level of exposure to ELF fields?

The SCENIHR opinion states:

Exposure of the general population

Several fixed installed sources are operated in our environment. Prominent examples are high voltage transmission lines operated between 110 and 400 kV at 50 or 60 Hz. The exposure of bypassing people can typically reach values of 2 to 5 kV/m for the electric field strength. The exposure due to magnetic flux density depends on the actual current on the line; fields up to 40 µT are possible but are usually lower. It is important to note that such exposure levels occur only directly below the lines; exposure decreases with the square of distance to the lines. In addition, intermediate voltage transmission lines (10 kV to 30 kV) and distribution lines (400 V) have to be considered; exposure levels are in such cases much lower. Typically values from 100 to 400 V/m and 0.5 to 3 µT can be reached, and the exposure is usually instantaneous. Another approach to establish power supply is the use of underground buried cables. Electric field strength exposure can be neglected in this case; the distribution of the magnetic flux density differs compared to overhead power lines. Substations and power plants are usually not accessible to the general public. Railway power supply installations are often operated at 16 2/3 Hz. The exposure decreases linearly with the distance. The exposure levels for both electric and magnetic fields in areas accessible to the general public are below the limits set by ICNIRP. These reference levels are dependent on the frequency of the field. Regarding 50 Hz fields, the reference level for the E-field strength is 5 kV/m and the reference level for the magnetic flux density is 100 µT. The highest magnetic flux densities can be found close to several domestic appliances that incorporate motors, transformers, and heaters. Such exposure levels are very local and decrease rapidly with the distance, exposure is occasional. An example is a vacuum cleaner: at a distance of 5 cm magnetic flux densities of about 40 µT can occur, but at 1 m the exposure will be around 0.2 µT. Regarding individual exposure, a few percent of the European population are exposed to levels above a median magnetic flux density of 0.2 µT in their homes.

Exposure of workers

In a few locations in installations within the electric power industry the exposure limits given in the directive 2004/40/EC for occupational exposure can be reached or even exceeded. Safety measures for such areas have to be implemented. An example is a peak electric field strength of more than 20 kV/m that was measured in a power station. Other examples of industrial applications in the ELF range are induction and light arc ovens or welding devices. The frequencies of such applications fall both into the ELF and into the intermediate frequency range. Exposure of workers has to be controlled for such devices. Next to welding devices maximum flux densities of several hundred µT are possible, depending on the welding current and the type of application.

Medical applications

Bone growth stimulation is used as a therapeutic application in the ELF range. In this case coils are applied where the fracture is located to stimulate the healing process. Other applications include Transcranial Magnetic Stimulation, wound healing, or pain treatment. A diagnostic application is the bioimpedance measurement for cancer detection. Personnel exposure has to comply with the directive 2004/40/EC for occupational exposure.

Source & ©: SCENIHR,  Health Effects of Exposure to EMF (2009),
3.5.1 Sources and distribution of exposure in the population, p.37-38

7.3 Can ELF fields increase the risk of childhood leukaemia and other cancers?

The SCENIHR opinion states:

3.5.2. Cancer

3.5.2.1. Epidemiology

What was already known on this subject?

In the previous opinion of 2007, the evaluation of the “International Agency for Research on Cancer (IARC)” of carcinogenic risks of static and extremely low-frequency (ELF) electric and magnetic fields to humans (IARC 2002) was endorsed. In the IARC evaluation, ELF magnetic fields were classified into group “2B” (“possibly carcinogenic to humans”). Limited evidence of carcinogenicity in humans was chiefly based on epidemiological studies showing a consistent association between magnetic fields above 0.3/0.4 µT and the risk of childhood leukaemia. Experimental studies showing overwhelmingly negative results provided inadequate evidence of carcinogenicity in cell lines and experimental animals. For cancers other than childhood leukaemia there was either inadequate evidence or some evidence against an association.

What has been achieved since then?

An extension of a pooled analysis of studies on magnetic fields and childhood leukaemia (Ahlbom et al. 2000) showed that focussing on exposure during the night time period gives basically the same results as for exposures over 24 hours (Schüz et al. 2007). This does not support assumptions that exposure during the night is of higher biological relevance or that the restriction to the night time period reduces exposure misclassification. A replication study of a US study on magnetic fields and survival from childhood leukaemia (Foliart et al. 2006) utilising data from Germany, broadly confirms a somewhat poorer prognosis of exposed leukaemia patients, but numbers were very small (Svendsen et al. 2007). There is a need for further studies. No new influential study appeared on any other cancer site.

A recent molecular epidemiological study by Yang et al. (2008) investigated the possible interaction between six mutated genes for DNA repair enzymes and ELF EMF exposure in acute leukaemia in children. There were 123 patients included in this study, and their genotype and residential vicinity to power lines and electric transformers was documented. An interaction between a specific mutation (but not the other investigated alleles) and presence of transformer station and power lines within 50 and 100 m was noted (COR=4.39, 95% CI: 1.42-13.54 and COR=4.31, 95% CI: 1.54-12.08, respectively). Average spot-measured magnetic field intensity levels for houses of a smaller number of patients were done within 50 m (0.18 µT), 100 m (0.14 µT), and 500 m (0.13 µT) of the installations. The study is potentially interesting as it suggests an association between defects in DNA-repair systems and childhood leukaemia caused by residential EMF However, there are too many weaknesses in this study to allow any conclusions to be drawn.

3.5.2.2. In vivo

What was already known on this subject?

Animal studies discussed in the previous opinion of 2007 did not provide evidence that ELF magnetic field exposure alone causes tumours or enhances the growth of implanted tumours. Some inconsistent evidence suggested that ELF magnetic fields might be co- carcinogenic (enhance the effects of known carcinogens) and that they may cause cancer-relevant biological changes in short-term animal studies. However, it was concluded that the data were not sufficient to challenge IARC’s evaluation that the experimental evidence for carcinogenicity of ELF magnetic fields is inadequate.

What has been achieved since then?

Much of the evidence for co-carcinogenicity of ELF magnetic fields has originated from one research group, which has published several studies showing accelerated development of 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumours in female Sprague-Dawley rats (See SCENIHR 2007 for references and a discussion). These findings, however, were not supported by experiments of two other groups. The group that published the positive findings has recently published a study showing similar effects in Fisher 344 rats exposed to a 100 µT, 50 Hz magnetic field for 26 weeks (Fedrowitz and Löscher 2008). The choice of this strain of rat was based on prior experimental comparison of different rat strains (Fedrowitz and Löscher 2005), which showed that Fischer 344 was the only strain in which magnetic field exposure significantly increased cell proliferation in the mammary epithelium.

Cytogenetic effects were studied in bone marrow cells from Wistar rats exposed to a 50Hz, 1.0 mT magnetic field for 45 days, 4h/day (Erdal et al. 2007) using the chromosomal aberration (CA) and micronucleus (MN) assays. A statistically significant (p<0.01) increase of MN was detected. However, this was a small study (four animals per group).

3.5.2.3. In vitro

What was already known on this subject?

In the opinion of 2007 (SCENIHR 2007) it was concluded that in vitro studies conducted so far had shown inconsistent results regarding cellular effects. Since a possible interaction mechanism was not known, it was concluded that published in vitro studies cannot explain the epidemiologic findings of increased childhood leukaemia incidence in relation to ELF magnetic fields, but that they do not contradict these results either.

What has been achieved since then?

Co-exposure to ELF magnetic fields and bleomycin showed a cooperative or synergistic effect on chromosomal instability in normal human fibroblast (Cho et al. 2007). As a marker for genotoxicity, apurinic/apyrimidinic (AP) sites were investigated using 5.0 mT exposure of human glioma A172 cells, showing that co-exposure to ELF magnetic fields and genotoxic agents (methyl methane sulfonate (MMS) or hydrogen peroxide) induce increased number of AP sites (Koyama et al. 2008). Treatment with menadione (inducing radical production and DNA damage) of L929 cells pre-exposed to 50 Hz, 0.10 mT for 24 h showed an altered cell cycle (Markkanen et al. 2008). The authors concluded that pre- exposure to ELF-EMF alter cellular responses to other agents.

Changes in the redox and differentiation status were reported in neuroblastoma cells (Falone et al. 2007). The results suggest that a 50 Hz, 1 mT magnetic field modulates the redox status of the cells. Although no major oxidative damage was detected, positive modulation of antioxidant enzyme expression, as well as a significant increase in reduced glutathione level was observed, indicating a shift of cellular environment towards a more reduced state. A 96-h MF treatment also enhanced H₂O₂-induced reactive oxygen species production and DNA strand breaks.

3.5.2.4. Discussion on cancer

The previous assessments are unchanged. The fact that the epidemiology findings of childhood leukaemia have little support from known mechanisms or experimental studies is intriguing and it is of high priority to reconcile these data. A recent study on rats has provided additional evidence of co-carcinogenic effects from exposure to ELF magnetic fields at 100 µT. However, the findings still need independent confirmation.

Although many earlier in vitro studies did not show any effects, some studies indicated that ELF magnetic fields alone and in combination with carcinogens induce both genotoxic and other biological effects in vitro at flux densities of 100 µT and higher. Recent studies support this effect. Direct field-inducing damage to DNA is unlikely; therefore alternative mechanisms must be hypothesised. As already pointed out in the last opinion there is still a need for independent replication of certain studies suggesting genotoxic effects and for better understanding of combined effects of ELF magnetic fields with other agents and their effects on free radical homeostasis.

Source & ©: SCENIHR,  Health Effects of Exposure to EMF (2009),
3.5.2. Cancer, p.38-40

7.4 Can exposure to ELF cause headaches or other health effects?

The SCENIHR opinion states:

3.5.3. Symptoms

What was already known on this subject?

A variety of symptoms (dermatological symptoms such as redness, tingling and burning sensations as well as for example fatigue, headache, concentration difficulties, nausea, heart palpitation) have been suggested to be caused by ELF field exposure. The term “electromagnetic hypersensitivity” (EHS) has come into common use based on the reported experience by the afflicted individuals that electric and/or magnetic fields, or vicinity to activated electrical equipment trigger the symptoms. The 2007 opinion concluded that no consistent relationship between ELF fields and self-reported symptoms (sometimes referred to as EHS) had been demonstrated in scientific studies.

What has been achieved since then?

Possibly as an effect of the failure of scientific studies to provide support for a relationship between ELF fields and symptoms (WHO 2005, Rubin et al. 2005), studies on EHS have come to focus on characterisation and alternative possible factors influencing the well-being of the group that reports EHS. The prevalence of individuals who report EHS was estimated to be 4% in the study by Eltiti and al. (2007b) as compared to 1.5% in Sweden (Hillert et al. 2002), 3% in California (Levallois et al. 2002) and 5% in Switzerland (Schreier et al. 2006). The British study (Eltiti et al. 2007b), designed to evaluate a symptom questionnaire also confirmed the results in an earlier Swedish study (Hillert et al. 2002), i.e. no specific symptom profile was identified. The EHS group scored higher on all eight subscales (neurovegetative, skin, auditory, headache, cardiorespiratory, cold related, locomotor and allergy related symptoms). Another Swedish study investigating personality, mental distress and health complaints among persons with so called idiopathic environmental intolerance attributed to different factors also presented similar results (Österberg et al. 2007). The percentage of subjects who reported experiencing health complaints at least once a week was significantly higher in all eight subscales for the EHS group as compared to the reference group.

A study on personalities of individuals who report EHS observed that this group scored higher on somatic and psychic trait anxiety, stress susceptibility, embitterment and mistrust in Swedish university Scales of Personality (SSP) and on somatization, depression and anxiety as well as on global severity index (GSI) in SCL-35 (Symptom Checklist 35) as compared to referent groups (Österberg et al. 2007). Earlier published results from the same group showed that EHS subjects scored significantly higher on GHQ-12 (General Health Questionnaire-12) than the reference group (Carlsson et al. 2005). Higher scores indicate lower mental well-being. Rubin et al. (2008) did not find a higher prevalence of individuals classified as psychiatric cases using the GHQ-12, but EHS subjects showed a significantly higher level of depression symptoms than control subjects.

Schröttner et al. (2007) studied electric current perception thresholds in three different groups reporting electromagnetic hypersensitivity: a group recruited from a self aid group, a group who had responded to a newspaper call and a group who had actively contacted researchers in order to find help to investigate their health problems (primarily sleep problems attributed to RF fields). When the three groups were pooled together, the EHS subjects differed significantly from a general population sample (lower perception thresholds in the EHS subjects, p<0.001). There was however a considerable overlap in perception thresholds between the groups and the EHS groups also contained subjects with higher perception thresholds. As noted by the authors, this study was not designed to test whether electromagnetic fields trigger health complaints and it is thus not possible to draw any conclusion on a possible causal relationship between electromagnetic fields and health complaints. It is possible that the deviating results in the EHS groups may be a consequence of the health problems per se or of the dysbalance of the autonomic nervous system regulation indicated in these groups in other studies (e.g. Lyskov et al. 2001, Sandström et al. 2003).

Discussion

In conclusion, no new information has been published in support of a relationship between ELF field exposure and self reported symptoms.

3.5.4. Other health effects

3.5.4.1. Epidemiology

The previous opinion concluded that while quite a number of health effects had been associated with ELF fields many of these had been dismissed based on information from later research. This holds, for example, for cardiovascular disease. However, for some diseases it was concluded that it still remains open as to whether there is a link to ELF exposure. This was true in particular for neurodegenerative diseases, such as ALS and Alzheimer's disease (Garcia et al. 2008, Hug et al. 2006). Some new Swiss data that were published after the previous opinion seem to support the previous notion that Alzheimer's disease indeed might be linked to exposure to ELF. These studies include one study on railway workers (Röösli et al. 2007) and another on people residing in the proximity of power lines (Huss et al. 2009).

3.5.4.2. In vivo

What was already known on this subject?

The previous opinion of 2007 discussed studies that have addressed ELF magnetic field effects on the nervous system and behaviour, reproduction and development, and endocrine, cardiovascular and immune systems. Although some studies have described ELF magnetic field effects on the nervous system, animal development, and melatonin production, the evidence for such effects was found to be weak and ambiguous, and inadequate for drawing conclusions concerning possible human health risks.

What has been achieved since then?

Three recent studies have provided suggestive evidence that long-term exposure of laboratory rodents to 50 Hz magnetic fields of 1.10 – 2.00 mT may impair (Fu et al. 2008) or improve (Liu et al. 2008b) memory and increase anxiety-related behaviour (Liu et al. 2008a) in behavioural tests. Effects on the alpha activity of human EEG have been reported in subjects exposed to special pulsed ELF magnetic field sequences with peak magnetic flux densities of 200 µT (Cook et al. 2009).

Falone et al. (2008) reported changes in the antioxidant defence system in the brain cortices of female rats (10 animals per group) exposed to 100 µT, 50 Hz magnetic fields for 10 days. The changes were of opposite direction in young (enhanced defence) and old (weakened defence) animals. This finding, if confirmed in further studies, might be relevant to neurodegenerative diseases (Alzheimer's disease, ALS) associated with ELF magnetic fields in some epidemiological studies. No effects were found in a mouse model of ALS, when seven animals per group were exposed for 7 weeks to 50 Hz magnetic fields at 0.10 or 1.00 mT (Poulletier de Gannes et al. 2008).

3.5.4.3. In vitro

What was already known on this subject?

The previous opinion stated that few in vitro studies investigating associations between ELF and diseases other than cancer were published. ELF in vitro studies are important for mechanistic understanding.

What has been achieved since then?

Very few relevant in vitro studies have been published since the last opinion. Among the exceptions is a study by Del Giudice et al. (2007) which showed the stimulation of beta- amyloid peptide secretion in cultured human neuroglioma cells using 3.1 mT 50 Hz ELF magnetic fields. This peptide plays an important role during Alzheimer's disease development.

Another finding was presented by Sakurai et al. (2008b) using 5.0 mT flux density. In a hamster-derived insulin-secreting cell line (HIT-T15) an increased insulin secretion was reported after 2 or 5 days exposure, showing an activation effect of cells.

It has been suggested that a common and possibly general response to EMF exposure is the activation of the genes encoding the so-called heat shock proteins, a family of chaperone proteins that are up-regulated in response to many forms of stress. In two separate papers (Gottwald et al. 2007, Bernardinie et al. 2007) it was reported that a 50 Hz ELF magnetic field at various flux densities (2 µT-4 mT) in certain cases could increase the levels of the mRNAs for several HSP protein species. However, in none of the cases with increased mRNA levels was there any concomitant increase in HSP protein level. The mRNA up regulation was thus not shown to have any biological significance.

3.5.4.4. Discussion on Other Health Effects

Since the previous opinion, new epidemilogical data on both occupational and residential exposure support the notion that Alzheimer's disease might be linked to ELF exposure.

Recent animal studies have provided some additional evidence for effects on the nervous system from ELF magnetic fields above about 0.1-1.0 mT. However, there are still inconsistencies in the data, and no definite conclusions can be drawn concerning human health effects.

Very few recent in vitro studies have investigated effects from ELF fields on diseases other than cancer and those available have very little relevance for understanding any disease connection. There is a need for hypothesis-based in vitro studies to examine specific diseases.

Source & ©: SCENIHR,  Health Effects of Exposure to EMF (2009),
3.5.3, Symptoms and 3.5.4, Other health effects, 41-43

7.5 What can be concluded about ELF fields?

The SCENIHR opinion states:

3.5.5. Conclusions about ELF fields

The previous opinion stated that ELF magnetic fields are a possible carcinogen. This conclusion was chiefly based on childhood leukaemia results.

It was also concluded that a consistent relationship between ELF fields and self-reported symptoms has not been demonstrated.

Regarding breast cancer and cardiovascular disease, an association was considered unlikely. For neurodegenerative diseases and brain tumours, the link to ELF fields remained uncertain.

The new information available is not sufficient to change the conclusions of the 2007 opinion.

The few new epidemiological and animal studies that have addressed ELF exposure and cancer do not change the previous assessment that ELF magnetic fields are a possible carcinogen and might contribute to an increase in childhood leukaemia. At present, in vitro studies did not provide a mechanistic explanation of this epidemiological finding.

No new studies support a causal relationship between ELF fields and self-reported symptoms.

New epidemiological studies indicate a possible increase in Alzheimer's disease arising from exposure to ELF. Further epidemiological and laboratory investigations of this observation are needed.

Recent animal studies provided an indication for effects on the nervous system at flux densities from 0.10-1.0 mT. However, there are still inconsistencies in the data, and no definite conclusions can be drawn concerning human health effects.

Very few recent in vitro studies have investigated effects from ELF fields on diseases other than cancer and those available have very little relevance. There is a need for hypothesis-based in vitro studies to examine specific diseases.

It is notable that in vivo and in vitro studies show effects at exposure levels (from 0.10 mT and above) to ELF fields that are considerably higher than the levels encountered in the epidemiological studies (µT-levels) which showed an association between exposure and diseases such as childhood leukaemia and Alzheimer's disease. This warrants further investigation.

Source & ©: SCENIHR,  Health Effects of Exposure to EMF (2009),
3.5.5 Conclusions about ELF fields, p.43-44