• 23 AUG 05
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    Rationale for China EMF Exposure Standards

    Note: I have created a new category for this list titled “Alternatives to ICNIRP Hegemony”. The following is the first listing in this category.

    Don

    Discussion on Rationale for China EMF Exposure Standards.
    Huai Chiang, Zhengping Xu.
    Bioelectromagnetics Lab, Zhejiang University School of Medicine
    Hangzhou 310031, China

    Paper presented at the Third International EMF Seminar, held in Guilin, China, in October of 2003

    1. Rationale for current China RF EMF Exposure Standards
    The current RF exposure standards were set up in 1988 and 1989, which based on a Chinese Tentative Standard (Chiang, 1981).

    (1) The basic consideration: Assessment of health hazard for setting standards should rely mainly on the health status of personnel exposed to RF EMFs. The results of experimental animals and theoretical calculation could be supplements to the human exposure data. We may evaluate whether the really exposure levels are hazardous according to the above data and set safe exposure limitation.

    (2) Some investigations on the health effects of occupational and environmental exposure to different frequency EMFs were performed in China. The results showed that chronic exposure to EMFs are associated with a variety of non – specific symptoms, including increased frequency of neuroses, liability of vegetation nervous system, and slight changes in peripheral blood, lens, and non – specific immune function. These effects seem to be similar to some animal experiments, and to other investigations conducted in some other countries. The threshold levels of health effects are 50-100 V/m at 0.1 – 30 MHz and 50-200 uW/cm2 for > 30 MHz.

    (3) Animal experiments: Changes in ECG and immune function may occur at 0.2 – 1.0 mW/ cm2

    (4) Possibility to meet the standards at no cost or low cost.

    2. Rationale for the current amending EMF exposure standards (draft) of China

    The current RF EMF exposure standards in China have been performed for over 10 years. They have promoted many valid measures to reduce significantly the exposure levels in work places and in environment in China. However, because of the new and rapid development of telecommunication facilities, the economic globalization, and the need for standard harmonization, a draft of the amended EMF exposure standards was proposed by an United Working Group in China. The EMF standard draft covers the entire frequency ranges of time-varying EMF as ICNIRP guidelines. Also there are two classes, i.e. basic (preliminary) restrictions and reference levels (exposure limits), and the basic restrictions are current density (for electric field only), SAR, and power density. Two tier standards, i.e. occupational and general public, are also adopted.

    The main differences ( with ICNIRP ) and its own rationale are as follows:

    (1) ICNIRP guidelines are based on short-term, immediate health effects such as stimulation of peripheral nerves and muscles, and elevated tissue temperature resulting from absorption of energy during exposure to EMF (thermal effects). However, there is a body of literature, which reports that health effects can be shown at such a level of radiation that does not produce heating or stimulation.

    For RF exposure, the SAR thresholds of behavior-disruption have been observed at the levels much lower than 4 W/kg. For example, D’Andrea et al (1986, a, b) reported that the threshold for behavior effects of chronic RF exposure in the rats occurs between 0.14 and 0.7W/kg. There are many other studies showing the lower threshold for behavior effects: DeWitt et al (1987): 0.14W/kg; Thomas et al (1975): 1.5-2.7 W/kg ; Schrot et al, (1980): 0.07 W/kg: Lai et al (1989): 0.6 W/kg. To elucidate the underlying neural mechanism in the last study, Lai et al revealed that both cholinergic and endogenous opioid neurotransmitter system in the brain are involved in the microwave-induced spatial memory deficit (Lai et al, 1989). Sanders et al (1985) reported a decrease in concentration of ATP and CP in the cerebral cortex following exposure of the rat to pulse microwave at SAR 0.1-0.5 W/kg, and concluded that the radiation decreased the activity of the mitochondrial electron transport system. A decrease in the mitochondrial marker enzymes, SDH and MAO, was also observed following exposure of mice to pulse microwave at SAR equal to or above 0.5 W/kg (Chiang et al, 1984).

    Immune system is very important for health. A series of experiments on immune function of chronic exposure were reported in Russia. Using methods of complement binding reaction, degranulation of basophils, and plaque-forming cell assay, chronic exposure of animals (rats, guinea pigs, and rabbits) to 2450 MHz microwave at 50 mW/cm2 or 500 uW/cm2 resulted in damage to brain protein structures and production of cytotoxic antibodies with subsequent development of the autoimmune process (Vinogradov and Dumanskij, 1975; Shandala et al, 1985). Vinogradov et al (1991) further demonstrated that the prolonged microwave exposure at 500 mW/cm2 induced autoimmue reactions by tranfering the immunocompetent cells from the exposed animals to recipient rats. The development of autoimmune status in pregnant rats induced by 500 mW/cm2 microwave exposure was demonstrated, and a marked suppression of mitogen induced lymphocyte blast transformation was also observed (Shandala et al, 1982). Suppression of neutrophil phagocytosis occurred after chronic exposure of guinea pigs to microwave at 50 mW/cm2 (Vinogradov and Dumanskij, 1975). Though there were no SAR values provided in the above-mentioned experiments, the estimated SAR for about 2450 MHz microwave exposure must be far below 0.5 W/kg at any polarization in these animals under reported irradiation conditions. That chronic exposure of mice to microwave at even lower power densities resulted in bi-phasic changes in immune system was reported. Exposure of mice to sinusoidal microwave at 1 mW/cm2 for 24 h increased the TNF production in peritoneal macrophages, and chronic exposure for 7 days induced the decreasing of TNF production (Fesenko et al,1999). The effects of exposure of mice to pulsed microwave at 30 mW/cm2 rms (0.01W/kg), both with and without concurrent amplitude modulation (AM), were studied. In the absence of AM, no changes in immune functions (with plaque-forming cell assay) was observed. In contrast, under the combined–modulation condition the radiation resulted in significant augmentation or weakening of immune responses (Veyret et al, 1991). The bi-phasic changes in immune function of neutrophil phagocytosis were also observed in human exposed to environmental low-level RF radiation (Chiang et al, 1989).

    In vitro studies, the evidence of RF non-thermal bioeffects is increasing (de Pomerai et al, 2000; Kwee et al, 2001), and the knowledge regarding the molecular mechanisms of low-level EMF potentially adverse health effects is growing (Goodman and Blank, 2002; Lin et al, 2001; Leszczynski et al, 2002). Increase in brain barrier permeability and induction of DNA strand breaks by low level microwave exposure were reported once again (Leszczynski et al, 2002; Phillips et al, 1998).
    In summary, there are many reports of non-thermal potential health effects from microwave radiation using both in vivo and in vitro, and some of them are cited above. The SAR threshold for the adverse effects in the frequency range from 100 kHz to 10 GHz may be at 0.5 to 1.0 W/kg, rather than 4.0 W/kg. Thus, a whole body average SAR of 0.1 W/kg is chosen as the restriction for occupational exposure, and 0.02 W/kg for general public exposures in the draft of amending China exposure standard .

    For power frequency (ELF) magnetic field (MF), the exposure limits in ICNIRP were derived from the assumption that magnetic fields act through its induced electric fields, and the current density of 10 mA/m2 is adopted as the basic restriction to prevent stimulation of peripheral nerves and muscles for occupational exposure. However, there is growing evidence that the magnetic fields penetrate cells, tissues and cause bio-effects by themselves. For example, the suppression of gap junction intercellular communication (GJIC) is induced by MF itself rather than the induced electric field (Chiang et al, 2002). GJIC plays an important role in the maintenance of cell proliferation and differentiation, and is regarded as an index of inspection of possible cancer promoter.. The threshold of GJIC suppression caused by 50 Hz MF exposure is about 0.4 mT, and 0.2 mT MFs enhanced TPA induced GJIC suppression (Hu et al, 2002; Li et al, 1999). The mechanisms of the GJIC inhibition induced by 50 Hz MF exposure, hyperphosphorylation of connexin43 and internalization of connexin43 from plasma membrane to cytoplasm, have been also discovered in our laboratory (Hu et al, 2001; Zeng et al, 2003). Goodman and Blank and their colleagues have reported rapid induction of heat shock proteins by 60 Hz MF exposure at only microtesla level with the related molecular mechanism. They found that the induction of HSP70 gene expression is at transcription level and mediated through C-myc protein binding at 3 sequence sites that are not required for commom heat shock responsiveness. And the ELF MF may interact directly with moving electrons in DNA (Goodman and Blank, 2002; Lin et al, 2001; Blank and Soo, 2001). Chronic exposure decreases HSP70 level and lowers cytoprotection (Di Carlo et al, 2002).
    There are many reports showing that 0.1 mT ELF MF exposure may affect cell functions. For example, 50 Hz MF at 0.1 mT specifically interacts with 5-HT1B receptors, inducing structural changes of the protein that result in a functional desensitization of the receptors. Thus it may be involved in mood disorders complained by exposed workers (Massot et al, 2000). Induction of DNA strand breaks by intermittent exposure to 50 Hz was observed with a dose-response relationship at the threshold level of 0.07 – 0.1 mT (Ivancsits et al, 2002).
    Coincidently, adverse health effects induced by 0.1 mT ELF MF exposure were also reported in in vivo studies. For example, 0.1 mT 50 Hz MF exposure significantly facilitates the development and growth of mammary tumors, particularly in cranial cervical part of the mammary gland, in the DMBA rat model of breast cancer (Thun-Battersby S et al, 1999; Loscher, 2001). Enhancing activity of OCD, a key enzyme in cell proliferation, after exposure of rats to 0.1 mT 50 Hz MF for two weeks was also observed. And it was found that the cranial cervical complexes being particular sensitive to ODC alterations in response to the MF (Mevissen et al, 1999). The cytotoxicity of NK cell in male mice was significnstly affected following exposure to 0.1 mT 60 Hz for 49 and for 105 days (Marino et al, 2000).

    Since IARC has concluded that the power-frequency MF are possible human carcinogens, and the increasing in the biological plausibility in mechanism and supportive data from animal experimental studies, the exposure limit for ELF MF exposure are suggested to be lower than ICNIRP’s, i.e. for occupational exposure: < 0.08 mT , and for general public: < 0.03 mT in the draft. It is noteworthy that in the research field of bioelectromagnetics, the published reports lacked consistency, and there are many negative results reported. Why the pattern of positive and negative reports occurs so commonly? Using different animal substrain or cell line, with different genotype composition, might be one of the main reasons. For example: The Hannover group (Fedrowitz et al, 2003) compared MF effects in the DMBA model with different substrains of SD rats. The results showed that the MF exposure increased mamary tumor development and growth in SD1 but not SD2 rats. The inhibition of melatonin antiproliferative effect of ELF MF on MCF-7 cells (from UCLA, Berkey) were reported independently by some laboratories, but they have not been reproduced with the MCF-7 cells supplied by the American Type Culture Collection (Ishido et al, 2001). Using genomics and proteomics, the observed varying responses of cells with different genotype composition suggest that the response and possibly its severity might be influenced by the genotype (Leszcynski F et al, 2003). Secondly, Marino et al (2001) indicated that relationship between an applied EMF and its associated bioeffects was general nonlinear in nature. But it was assumed that any response of a subject to a field would be governed by a linear law, and that inter-subject measurement differences were due solely to stochastic processes. With nonlinear laws, they found statistically significant changes in lymphoid phenotype (ten immune parameters) after mice were exposed continuously to 0.1 mT 60 Hz MF for 175 days. However, no significant differences were observed in the above experiments with linear statistical analysis. Besides, the statistical chance to reproduce weak effects of EMF exposure is also a factor causing inconsistency of the study results. For instance, the chance of repeating the potential co-carcinogenic effect of ELF MF exposure, reported by Hannover group, with 100 rats per exposure group is only 75% (Anderson, 2000). Thus, some important effects, such as those just mentioned above, will be considered as not established effects and rejected as providing a basis for standard setting. Because of the inconsistency, the public health significance of EMF has been underestimated. (2) Limitation and application of SAR The SAR is a valid measure of energy absorption rate during RF exposure, but not a quantity indicator of biological effects. For example, the significantly different bioeffects between continuous and intermittent RF exposure, between modulated and unmodulated microwave exposure, under the same SAR questioned the issue of using SAR as a basic restriction. Since the mechanism of low level RF exposure is not well known, the SAR is now useful at extrapolations from animal experiments to human at specific frequencies, but has its limitations. In the draft of amending exposure standards of China, actually the named basic restriction is preliminary restriction. The exposure limits (reference levels) are not only derived from the SAR values, which are also based on exposure duration and considering the data of human epidemiological studies (including non-cancer). The ICNIRP guidelines indicated that if measured values are higher than reference levels, it does not necessarily mean that the basic restrictions have been exceeded. However, in the draft, the exposure limits rather than the preliminary restriction SAR is used to determine if it is compliance with the standards. (3) As to the localized SAR restrictions, ICNIRP sets up the partial body limits to prevent any possible temperature rise which may occur in the eye to 1°Êor less. With the same reason as the whole-body exposure and the practical possibility, half of the ICNIRP’s SAR limits were suggested in the draft. For example, the localized SAR (head and trunk) for public exposure is 1.0 W/kg in any 10 g of tissue, which is close to 1.6 W/kg in any 1 g tissue adopted by IEEE at present. However, since the exposure duration for mobile phone users are very short, usually less than one hour per day, and actually mobile phones are consumer products related to individual behavior like smoking, it may be further loosen if it is needed. 3. The present knowledge in assessment of possible health effects related to exposure to EMF has not provide sufficient rationale for establishing satisfactory and general acceptable exposure limits yet, though there are growing evidences of highly potential health effects from EMF exposure. The draft of the amending exposure standard in China is still questionable and far from perfect, but it is reasonable and has scientific basis. As the scientific advances, including the rapid development of molecular biology with powerful techniques and adoption of novel concepts, researchers may settle many arguments about the health effects of EMFs. 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