Exposure Risks

Studies show three different health effects of exposure to Radiofrequency RFR need to be investigated:

1) neurological effects of RFR describe mainly disturbances of noxious sensation (dysaesthesia)
2) thermal effects due to exposure
3) and electro-stimulatory effects



Safety Levels

Most safety standards for radiofrequency radiation (RFR) exposure (3 kHz–300 GHz) are based on either the avoidance of (i) heating effect sufficient to harm tissue due to frequencies >10 MHz or (ii) electrostimulatory effects of frequencies <10 MHz [1,2]. The ‘basic restrictions’ of the safety standard are based on RFR energy deposition into tissue, expressed as W/kg (watts per kilogram of tissue). On the basis of no consistent health effects having been observed at exposures <4 W/kg, and allowing a 10-fold safety factor, exposure standards are based on limiting exposures to <0.4 W/kg for occupational exposures. A further safety factor of 5 is used to protect the public to give a whole-body exposure limit of 0.08 W/kg. These data are then translated into ‘reference levels’, i.e. exposure levels expressed in mW/cm2 (or V/m or A/m) for compliance purposes, e.g. 1 mW/cm2 for occupational, or 0.2 mW/cm2 for public, exposures at 300 MHz. The underlying assumptions are that no health effects will occur other than ones with a thermal or electrostimulatory basis, and that RFR does not cause effects due to other means. Empirical confirmation of the hypothesis that no effects will occur in humans exposed below the safety levels and/or from other mechanisms than heating or electrostimulation has come mainly from epidemiological studies of cancer (which have not found clear evidence of a harmful effect). Another source of data is case reports, of which there have been several regarding peripheral neurological effects (dysaesthesia).

Occupational Medicine 2003;53:123–127; Neurological effects of radiofrequency radiation, Bruce Hocking1 and R.Westerman
Source: www.oxfordjournals.org



In general, both measured and predicted field strength values tended to show a decline in average field strength or power density with distance from the transmitter, although there are undulations in predicted field strength up to distances of about 6 km from the transmitter resulting from the vertical radiation pattern. The maximum total power density equivalent summed across frequencies at any one measurement point (at 2.5 m above ground) was 0.013 W/m2 for TV, and 0.057 W/m2 for FM. However, there was considerable variability between different measurement points at any one distance from the transmitter, as would be expected from the impact of reflections from the ground and buildings, and this variability was as great as that related to distance. Power density on average declines by a factor of at least 5 to 10 over 10 km. Field strength varies as the square root of power density, thus declining less steeply, and it is not clear which exposure measure would be biologically more relevant for athermal effects. These measurements cannot of course be converted to personal dose to residents, which depends on numerous factors, including building type, the amount of time spent inside the home as well as away from home, and the number of years spent at the residence.


Source: Cancer Incidence near Radio and Television Transmitters in Great Britain, OUP, 1997; www.oxfordjournals.org



Risk exposure due to Mobile Mast's radiation:



Facilitating Effects

Previous findings suggested the facilitating effect of the electromagnetic field emitted by mobile phones on human attention. This study aimed to examine the relationship between the facilitating effect and the duration of exposure to the electromagnetic field emitted by mobile phones on human attention. Seventy-eight university students were randomly assigned to either an experimental or a control group. Their performance in the administered attention tasks was compared. Participants in the experimental group performed better on one of the two measures of attention only after they had been exposed to the electromagnetic field emitted by the mobile phone for some time. The results seem to suggest that attention functions may be differentially enhanced after exposing to the electromagnetic field emitted by mobile phones. Furthermore, this transient facilitation effect might be dose dependent.

The effect of the duration of exposure to the electromagnetic field emitted by mobile phones on human attention; Neuroreport, 2003 Jul 18;14(10):1361-4, Pubmed



Some studies have reported that pineal gland exposure to EMFs from electric blanket use could be 10-40 times greater than exposure to EMFs associated with electrical wiring in or around the home (1-3). Several mechanisms have been suggested to explain the potential relation between EMF exposure and breast cancer risk.

Source: Exposure to Electromagnetic Fields from Use of Electric Blankets and Other In-Home Electrical Appliances and Breast Cancer Risk, Am. J. Epidemiol. 151:1103-1111, 2000, OUP.

References:
1. Florig HK, Hoburg JF. Power-frequency magnetic fields from electric blankets. Health Phys 1990;58:493-500.
2. Florig HK, Hoburg JF. Magnetic field exposure associated with electric blankets. In: Proceedings of the 1988 contractors review. Biological effects from electric and magnetic fields, air ions, and ion currents associated with high voltage transmission lines, Phoenix, AZ, October 30-November 3, 1988.
3. Preston-Martin S, Peters JM, Yu MC, et al. Myelogenous leukemia and electric blanket use. Bioelectromagnetics 1988; 9:207-13


Occupational Exposure to Radio Frequency/Microwave Radiation and the Risk of Brain Tumors
No significant association between occupational exposure to RF/MW-EMF and brain tumors was found. For glioma, the adjusted odds ratio for highly exposed persons compared with persons not highly exposed was 1.21 (95% confidence interval: 0.69, 2.13); for meningioma, it was 1.34 (95% confidence interval: 0.64, 2.81). However, the slight increase in risk observed with increasing duration of exposure merits further research with larger sample sizes.

www.oxfordjournals.org; American Journal of Epidemiology, July 27, 2006




Lack of effect of 94 GHz radio frequency radiation exposure in an animal model of skin carcinogenesis

Recent developments in electromagnetic technology have resulted in the manufacture of RFR sources capable of generating frequencies in the millimeter wavelength (MMW) range (30–300 GHz). Because absorption of MMW energy occurs in the skin, it is to be expected that long-term detrimental health effects, if any, would most likely be manifest in the skin. In this study we investigated whether a single (1.0 W/cm2 for 10 s) or repeated (2 exposures/week for 12 weeks, 333 mW/cm2 for 10 s) exposure to 94 GHz RFR serves as a promoter or co-promoter in the 7,12-dimethylbenz[a]anthracene (DMBA)-induced SENCAR mouse model of skin carcinogenesis. Neither paradigm of MMW exposure significantly affected papilloma development, as evidenced by a lack of effect on tumor incidence and multiplicity. There was also no evidence that MMW exposure served as a co-promoter in DMBA-induced animals repeatedly treated with 12-O-tetradecanoylphorbol 13-acetate. Therefore, we conclude that exposure to 94 GHz RFR under these conditions does not promote or co-promote papilloma development in this animal model of skin carcinogenesis.

As stated above only three studies have investigated carcinogenic effects of RFR in models of skin cancer. In two of these studies (performed in the same laboratory), exposure to 2450 MHZ RFR, either prior to or during initiation and promotion with 3,4-benzopyrene, accelerated the development of skin cancer and consequently decreased animal survival time(1,2).............It is therefore most likely that if any long term carcinogenic effects exist, they would be observed in the skin. If such effects exist, it is also probable that MMW exposure would promote rather than initiate carcinogenesis. Hence, the goal of this study was to determine whether a single or repeated exposure to 94 GHZ RFR serves as either a promoter or a co-promoter in the development of skin cancer.

Source: Carcinogenesis, Vol. 22, No. 10, 1701-1708, October 2001







RADIO FREQUENCY RADIATION: Case Report


Effects of exposure to very high frequency radiofrequency radiation on six antenna engineers in two separate incidents

Six men are likely to have been accidentally exposed to high levels of very high frequency (VHF) radiofrequency radiation (100 MHz) while working on transmission masts; four men in one incident and two in another. They experienced symptoms and signs which included headache, parasthesiae, diarrhoea, malaise and lassitude. The condition of four men, two men from each incident likely to have had the highest exposure, has shown no significant improvement. The first incident occurred in 19 and the second in 1996.


.........The term radiofrequency, when applied to the electromagnetic spectrum, covers the frequency range 3 kHz-300 GHz. The range 30-300 MHz is denoted very high frequency (VHF). The effect of exposure to VHF radiofrequency is primarily that of heating, in which the rate of energy absorption per unit mass of body tissue is described as
the specific absorption rate (SAR) expressed as watts per kilogram (W/kg) and depends on the frequency (Hz) and the power density expressed in watts per square metre (W/m2) or milliwatts per square centimetre (mW/cm2). (1 mW/cm2 equals 10 watts per square metre (10 W/m2). Power density can be described as the power crossing a unit area normal to the direction of wave propagation. The deposition of RF energy in body tissue varies with their absorption characteristics, which depend to a considerable extent on their water content.

Tissue such as blood, skin, muscle, brain and peripheral nerves will absorb much more energy than fat and bone, with the result that much of the incident radiofrequency energy tends to pass through the surface of fatty tissue to be deposited in deeper tissue such as muscle and brain. The degree to which radiofrequency penetrates the body depends also on the frequency.

Radiofrequency results in an electric and a magnetic field. Meters used to measure RF fields generally measure the electric field (£) expressed as volts per metre (V/m) although some express the E field in terms of equivalent plane wave power density in mW/cm2 or W/m2. Instruments which measure magnetic field (H) measure amps per metre (A/m) although these meters often express this in terms of equivalent plane wave power density.

Radiofrequency fields can be divided into near and far fields, the border between them being approximately A/ 2k, where A is the longest dimension of the antenna and X
is the wavelength. Far fields can be predicted quite accurately from the power of the antenna and the electric and magnetic fields are in phase and measuring one allows the other to be determined. In the near field this relationship breaks down and it is necessary to measure both components to establish RF power. This is difficult to achieve in the field. Additionally, on transmitter masts the lattice structure, antennas and feeders can cause complex reflections and fields, which can give rise to local 'hot spots' typically the size of a football, giving meter indications two or three times ambient.

- Radiofrequency radiation is difficult to measure in the near field, even in ideal conditions.
- Radiofrequency exposures at 100 MHz VHF are not detectable by the body unless they are significantly higher than the NRPB investigation levels and as a result can go undetected for relatively long periods, which makes the task of minimizing the risk of high levels of exposure all the more problematic.
- The effects of exposure to radiofrequency radiation, particularly those on the nervous system, appear to be greater than would be expected from tissue heating.
The question arises as to whether or not the NRPB investigation levels, based on calculations of power absorption in the human body expressed as specific absorption rate, give sufficient protection against the type of effects that have been experienced by the men in these case reports.

- The symptoms and signs are consistent with effects on the nervous system with central effects resulting in headache, fatigue and malaise; peripheral effects resulting in parasthesiae, dysathesia, impaired perception of light touch and pain; effects on the ganglia of autonomic system either in the neck or splanchnic region causing diarrhoea. It is possible that diarrhoea is caused by a direct effect on the cells of the lining of the gastrointestinal tract.

- Further research needs to be undertaken into systems of monitoring radiofrequency fields and into the acute and long-term effects of exposure to radiofrequency.

Occupational Medicine; Occup. Med. Vol. 50, 49-56, 2000
www.oxfordjournals.org


What are the limitations of Meta-analysis study? In general, the administered meta-analysis is a very useful technique to objectively aggregate single results of a number of separate studies. It not only gives a conclusive overview about a certain field of research, but also overcomes the problem of reduced power due to small sample sizes by an enhanced pooled sample size, and therefore leads to more accurate estimations of the effect size. However, to conduct a conclusive meta-analysis the requirements already mentioned in the statistical section must be fulfilled. Moreover, the main problem was the fact that many instruments were applied in only one study and therefore could not be included in the meta-analysis—for example, spatial item recognition task (FACE) used by Eliyahu et al,7 word-recall task used by Smythe and Costall3 or tests from the Cognitive Drug Research (CDR) used by Preece et al.2 From a scientific point of view, it is not efficacious to apply new and non-standardised test procedures. Moreover, some studies omitted certain statistics—for example, Hladky et al14 and Smythe and Costall3 did not include means and standard deviations in their results. As meta-analyses will be used more frequently in the future, a statistical standard should be set, such as documenting effect sizes or correlations in the case of repeated measurements.

A meta-analysis for neurobehavioural effects due to electromagnetic field exposure emitted by GSM mobile phones.Barth A, Winker R, Ponocny-Seliger E, Mayrhofer W, Ponocny I, Sauter C, Vana N.

Institute of Management Science, Division Ergonomics and Organization, Vienna University of Technology, Theresianumgasse 27, A-1040 Vienna, Austria. barth@imw.tuwien.ac.at; Published Online First: 10 October 2007. doi:10.1136/oem.2006.031450
Occupational and Environmental Medicine 2008;65:342-346
Copyright © 2008 by the BMJ Publishing Group Ltd.