While human exposure to electromagnetic fields has occurred throughout history, over the past century, exposure levels have steadily increased as electricity use, technologies and changes in social behavior have created an abundance of man-made sources. Dr Lisa Bushby examines whether there is cause for concern over the health effects of this exposure.
The difficulty in evaluating the effects of long-term low-level exposure to potential environmental hazards is that the effects may be cumulative, ie they build up in the body over time. Consequently, the research into the hazards they pose is long-term and painstaking. In addition, owing to vociferous public concern, much of the research into the genotoxicity of electromagnetic fields (EMFs) is not wholly occupational (as we all suffer exposure to some degree from proximity to electricity power lines and from mobile telephones), although it will be interesting to learn the results of this research to apply in an occupational setting.
A genotoxin is an agent that can damage DNA and possibly lead to cancer. So far, no convincing links between exposure to low-level EMFs and damage to health have been found.
Virtually, every workplace will have a plethora of EMF sources, with the strength of the EMF depending on equipment design and current flow. Examples include large electric motors, generators, power tools, laptops and mobile phones. However, while most equipment that produces EMF will not produce it at levels that are considered harmful, Directive 2013/35/EU on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (electromagnetic fields) comes into force in July 2016 to protect workers from all known biophysical effects and other indirect effects caused by EMF.
Biophysical effects means effects in the human body directly caused by EMF, including thermal effects, such as tissue heating through energy absorption from EMF, and non-thermal effects, such as the stimulation of muscles, nerves or sensory organs. These might have a detrimental effect on the mental and physical health of exposed workers with the stimulation of sensory organs potentially leading to transient symptoms, such as vertigo or seeing lights that are not there.
Indirect effects are caused by the presence of an object in an EMF that may become the cause of a safety or health hazard, such as: interference with medical electronic equipment and devices (eg pacemakers), projectiles from ferromagnetic objects in static magnetic fields, initiation of electro-explosive devices (detonators), fires and explosions from the ignition of flammable materials caused by induced magnetic fields, contact currents or sparks, contact currents.
The Directive lays down two types of value for exposure of workers, as follows.
Exposure limit values (ELVs) that cover only scientifically well -established links between short-term direct biophysical effects and exposure to electromagnetic fields. There are two main types of ELV:
health effect ELVs which are values of EMF above which workers might be subject to adverse health effects, such as thermal heating
sensory effect ELV which are values of EMF above which workers might be subject to disturbed sensory perceptions and/or minor changes in brain functions.
Action levels (ALs) are dependent on the type of field.
For electric fields low and high ALs means levels which relate to the specific protection or prevention measures specified
For magnetic fields, low ALs are levels that relate to sensory effects and high ALs to health effects.
Recently, the SCIENHR published an opinion on the potential health effects of exposure to EMF discussing biophysical interaction mechanisms and the potential role of co-exposures to environmental stressors.
Several interaction mechanisms are well established. These enable extrapolation of scientific results to the entire frequency range and wide-band health risk assessment. They have been used to formulate guidelines limiting exposures to EMF in the entire frequency range from static fields to 300GHz. According to the opinion, there is no evidence to suggest that any interaction mechanism operates in humans at levels of exposure found in the everyday environment.
Effects of exposure to RF
A number of studies have suggested that exposure to radiofrequency (RF) waves (3kHz–300GHz), eg from mobile phones or microwave ovens, may affect brain activities. However, given the variety of applied fields, duration of exposure, number of considered leads and statistical methods it is difficult to derive firm conclusions.
A reasonable body of experimental evidence suggests that exposure to RF does not trigger symptoms, at least in the short-term. While additional observational studies are required to assess whether longer-term exposure could be associated with symptoms, the evidence to date weighs against a causal effect, for example, human studies on neurological diseases and symptoms show no clear effect, and effects of exposure on foetuses from mobile phone use during pregnancy are not plausible owing to extremely low foetal exposure.
Overall, the epidemiological studies on RF EMF exposure do not show an increased risk of brain tumours or for other cancers of the head and neck region. Epidemiological studies do not indicate increased risk for other malignant diseases including childhood cancer. A considerable number of well-performed in vivo studies using a wide variety of animal models have been mostly negative in outcome. These studies are considered to provide evidence for the absence of a carcinogenic effect.
Effects of exposure to IF
The intermediate frequency (IF) part of the frequency spectrum (300Hz–10MHz) remains poorly investigated with respect to potential health effects resulting from exposure to EMF. Common sources of IF fields in industry include dielectric heater sealers, induction and plasma heaters, broadcast and communications transmitters, anti-theft devices at the entrance of shops, medical equipment such as MRI systems, and high frequency (HF) transmitters.
Existence of effects of exposure to IF waves depends on two superimposed phenomena: absorption of the external field in the organism at the macroscopic level and the stimulation of biological effects by the penetrating fields. Those two phenomena depend on the kind of field, electric or magnetic, and on the frequency. Well-known biological effects are nerve stimulation at low frequencies and heating at high frequencies.
Effects of exposure to ELF
Exposure to extremely low frequencies (ELF) waves (generally between 50 and 60Hz) in occupational settings can occur from equipment such as welding equipment, induction heaters and electrified transporting systems.
It is difficult to draw any conclusions from the studies to date investigating possible effects of ELF MF exposure. Only a few new epidemiological studies on neurodegenerative diseases have been published and they do not provide support for the previous conclusion that ELF magnetic field exposure could increase the risk for Alzheimer's disease or any other neurodegenerative diseases or dementia. Animal studies that have suggested beneficial effects of strong magnetic fields require confirmation. The evidence with respect to self-reported symptoms is discordant. The new epidemiological studies are consistent with earlier findings of an increased risk of childhood leukaemia, however, with estimated daily average exposures above 0.3–0.4µT.
Effects of exposure to THz
The number of studies investigating potential biological, non-thermal effects of THz fields (0.3–3THz) is small, but has been increasing over recent years, due to the availability of adequate sources and detectors. The THz sensors are used in cell and tissue imaging and THz technologies are being increasingly integrated into a host of practical medical, military and security applications.
In vivo studies indicate mainly beneficial effects on disorders of intravascular components of microcirculation in rats under immobilisation stress, but do not address acute and chronic toxicity or carcinogenesis. In vitro studies on mammalian cells differ greatly with respect to irradiation conditions and endpoints under investigation. Studies suggesting effects of exposure have not been replicated in independent laboratories. Some theoretical mechanisms have been proposed, but no conclusive experimental support is available.