CSIRO - June 1994 BIOLOGICAL EFFECTS AND SAFETY OF EMR |
10.0 RF SAFETY GUIDELINES AND REGULATIONSSUMMARYA number of international standards exist and have similarities. There is some concern about basing standards solely on results of a few studies on behavioural changes mediated through a significant increase in temperature of the whole body. The data base for more sensitive effects is equivocal and rather inadequate. The 7W exclusion clause for mobile telephones is considered to be inappropriate and measures are currently being adopted for its deletion from the ICNIRP standard. The German Radiation Protection regulations differ from others in that it requires data for the absolute worst-case exposure condition, regardless of whether or not it represents normal use of the device. They were first to drop the 7W exclusion clause for cellular phones. 10.1 EMR EXPOSURE GUIDELINESInitiatives of the Commission of the European CommunitiesThe Commission of the European Communities (EC) has proposed limits of exposure in the workplace for non-ionizing radiations through its Directorate General (DG) V (Health and Safety) (CEC, 1992). The proposed limits for electric and magnetic fields are intended as a European Council Directive on the minimum safety and health requirements regarding the exposure of workers to the risks arising from physical agents. DG XIII of the European Commission (Directorate General Telecommunications Information Industry Innovation) has mandated the European Committee for Electromechanical Standardisation (CENELEC) to prepare an exposure standard for the protection of people against electromagnetic fields. The work is being carried out by CENELEC technical committee TC111 “Human exposure to electromagnetic fields” and its subcommittees. DG XI has also initiated a COST (European Cooperation in the Field of Scientific and Technical Research) project on “Biological effects of electromagnetic fields”. This provides a forum for technical and scientific cooperation between nineteen European countries and various research fields. The bioeffects project (COST 244) was established to study exposure of people to electromagnetic fields associated with communication systems at frequencies from DC to 300 GHz to foster exchange of information on biological research, epidemiology, and dosimetry within Europe. This arrangement has been criticised because of the absence of any organised peer-review system to control the dissemination of information. A number of national and international bodies have published, or are currently developing standards (i.e. guidance and/or regulation) for safety of human exposure to electromagnetic fields. The standards/guidelines include: The international Commission for Non-Ionizing Radiation Protection (ICNIRP) of the International Radiation Protection Association (IRPA) for static magnetic fields and time-varying electric and magnetic fields at 50/60 Hz and between 100 kHz and 300 GHz (INIRC 1991). The American Institute of Electrical and Electronics Engineers (IEEE) and ANSI standard for safety levels with respect to human exposure to radiofrequency electromagnetic fields in the frequency range 30 kHz to 300 GHz, (IEEE 1991; ANSI 1992). The Physical Agents Committee of the American Conference of Governmental Industrial Hygienists (ACGIH) “Threshold limit Values” (TLVs) for occupational exposure to static and time-varying electromagnetic fields of frequencies less than 300 GHz (ACGIH 1992). The proposed European Council Directive on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents, for static electric and magnetic fields and time-varying fields of frequencies less than 300 GHz (CC 1992). The guidelines are based on data from biological and dosimetric studies and studies on exposed populations. They apply equally to workers and to members of the public but not to people who are exposed to electromagnetic fields and radiation for medical or therapeutic purposes. Electromagnetic interference with medical electronic devices, such as pacemakers, are effects which are not considered explicitly. Electrically or magnetically sensitive prosthetic medical devices may be adversely affected by levels of field strength below those advised by the guidelines for protection from exposure to humans. This rapidly developing topic is beyond the scope of the current report. The current standards apply restrictions on exposure to radiofrequency and microwave radiation to prevent adverse responses to increased heat load and elevated body temperature. There is some argument that this approach is incomplete as it does not consider the large amount of bioeffects data resulting from non-thermal interactions. As frequency increases, the depth of penetration of radiation in the human body decreases and energy deposition becomes more superficial. In the tens of GHz frequency range absorption of microwave energy occurs primarily in superficial layers of the skin and the cornea. It is then appropriate to quantify exposure by power flux density rather than SAR averaged over a broad expanse of a thin layer of skin. Guidelines do not effectively take account of differences in effectiveness of pulsed versus continuous wave radiofrequency and microwave radiations, or of nonlinear responses. 10.2 RF SAFETY GUIDELINES/REGULATIONSThe American National Standards Institute (ANSI) IEEE Standard for Safety levels with respect to human exposure to radiofrequency electromagnetic fields was recently revised (ANSI, 1992). In an uncontrolled environment in the frequency range 300 MHz to 6 GHz the permissible power density is 10 mW/cm2, although the duration of exposure limit is 6 min for frequencies below 3 GHz and reducing to 10 s at 300 GHz. There was a relaxation of power density limits (20 mW/cm2 at 300 GHz) for partial body exposures, except for the eyes and testes, for uncontrolled environments. The partial body exposure allows power density of 4 mW/cm2 for frequencies in the range of 300 MHz to 6 GHz. In determining these levels the ANSI committee set as their criteria for bioeffects data base as “only peer-reviewed reports of studies at SAR _ 10 W/kg, which had received favourable engineering and biological validation,...”. The findings of the Risk Assessment Working Group were that the existing ANSI 1982 base criterion for 4 W/kg remained. 10.2.1 ANSI Standard: Is it Appropriate?Although the current standard was issued in 1992, the accompanying bibliography forming the data base for the development of the standard mostly dated from the early 1970's to early 1980's. Out of a total 60 references only 19 are on biological effects. There are only six references that post-date the 1982 ANSI publication. Four of the bioeffects papers deal with the single subject of microwave induced hearing sensation and were written by the same individual. The list of so-called peer-reviewed publications includes a number of proceedings of workshops and conferences. Nevertheless, an important study on potential cancer production by chronic exposure to microwaves (Guy et al 1992) was not included, although the research had concluded many years earlier. Another long-term study has only been reported in a limited fashion (Toler) and has yet to be published. Although there have been a few publications on long term studies of behavioural effects (D’Andrea & de Lorge 1990) these were not considered for the ANSI standard. Some of these studies were carried out at 918 MHz frequency and found a threshold SAR value around 2 W/kg for disruption of behavioural activities in male rats (Moe et al 1976; D’Andrea et al 1980; Lovely et al 1977, 1983). Effects observed included reduced food intake, decreased blood sugar level and some increased activity. The exposures were repeated daily for many weeks. Altered behaviour was reported in studies carried out at 2450 MHz frequency (cw) at SAR values from 0.14 W/kg (D’Andrea et al 1986; De Witt et al 1987) to 3.2 W/kg (Lovely et al 1983). In a review of the topic D’Andrea and de Lorge (1990) specify that the SAR threshold for significant behavioural effects from long-term exposure at 2450 MHz is between 0.4 - 0.7 W/kg, and at 915 MHz is between 0.9 - 2.0 W/kg. By comparison, short-term acute exposure behavioural changes were associated with a minimum whole-body temperature increase of at least 1°C from SARs approximately 4 W/kg. It is interesting that although the bibliography extends back as far as 1950 so few publications were judged to meet the ANSI criteria. The rationale for the ANSI guideline is based on the absence of verified reports of injury or adverse effects on the health of humans who have been exposed to RF electromagnetic fields. The ANSI guideline is based on behavioural effects on laboratory animals which the committee assumes as being the most sensitive indicator of biological effects. (This view is not necessarily shared by all scientists, some of whom consider this to be a rather crude endpoint). Since the reported threshold for disruption of ongoing behaviour in non-human primates always exceeded a whole-body SAR of 4 W/kg, this value was adopted as the working threshold for unfavourable biological effects in human beings in the frequency range from 100 kHz to 300 GHz. Some biologists are concerned about the apparent reliance on thermal mechanism of biological response when responses at the cellular level would be more sensitive. A safety factor of 10 was applied to obtain a maximum permitted whole-body SAR of 0.4 W/kg. Perhaps this may account in some way for the uncertainties involved. This is also a response to an acute exposure. It would seem to be more appropriate to base the standard on the effects of low level chronic exposures. The US Environmental Protection Agency (EPA) has voiced its objection to the proposed incorporation by the US Federal Communications Commission (FCC) of the ANSI Standard because of its use of gross effects as a criteria for safety. Justification of the ANSI criteria is given as: “The disruption of a highly demanding operant task is a statistically reliable endpoint that is associated with whole-body SARs in a narrow range between 3.2 and 8.4 W/kg, despite considerable differences in carrier frequency (400 MHz to 5.8 GHz), species (rodents to rhesus monkeys), and exposure parameters (near and far-field, multi-path and planewave, cw- and pulsed-modulated)”. The robust nature of this effect and the use of body temperature as an indicator illustrates that a substantial biological response is evoked. To put into perspective an increase in SAR value by a factor of three for a much smaller animal, the rat, results in circulatory collapse and is followed by death within 15 mins. The effect has been reported at frequencies of 1 and 10 GHz at SAR of 12 W/kg (Frei et al 1994) which was associated with a significant increase in body temperature, and at 35 GHz where colonic temperature was unchanged. An important issue of the effect on SAR due to absorption as a function of increasing frequency was demonstrated by Gandhi (1990). Based on the premise that, due to the high loss tangent of water in the millimeter wave band (30 - 300 GHz) penetration into the body is restricted to 1 to 2 mm, Gandhi estimated resulting SAR for a given incident power density of 5 mW/cm2. Increasing the frequency from 30 to 60 GHz resulted in an increased SAR from 65 to 138 W/kg. In a study on absorption in pregnant women, Fleming and Joyner (1992) modelled the anatomical geometry of a pregnant woman and found that their estimates of SAR exceeded the current exposure limits prescribed by IRPA, ANSI and SAA in certain circumstances. The results indicated that the specific absorption rate in the embryo or fetus exceeded the safety standard limits for the general population (uncontrolled) in the frequency ranges 80-100 MHz in early pregnancy and for 300-1500 MHz in late pregnancy when the pregnant mother is exposed to the occupational limit of 0.4 W/kg. The standard for the general population, non-occupational (uncontrolled) exposure is an SAR of 0.08 W/kg averaged over the body of the embryo or fetus. At frequencies of 900 and 1200 MHz the estimated SAR in the fetus exceeded by a factor of three the limit set by the ANSI standard. Continued....
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