Dosimetric comparison between different quantities for limiting exposure in the RF band: rationale and implications for guidelines

While source type and its distance from the subject are influential parameters, the fundamental exposure metrics are the physically measurable quantities of currents, external electric field and magnetic field strengths, and incident power density (when appropriate), which induce electric and magnetic fields that bring about the interaction of radiofrequency (RF) electromagnetic energy with biological systems. Induced fields are the primary cause for biological effect of RF exposure, regardless of the mechanism. Thus, in order to achieve a quantitative understanding of biological response, the induced electric field and the derived dosimetric quantities of specific absorption rate (SAR) and current density must be quantified and correlated with the observed phenomenon. In the established exposure guidelines, reference levels expressed in terms of physical quantities are introduced for practical exposure assessment purposes since the basic restrictions are often specified as dosimetric quantities that may be impractical to measure. The dosimetric quantity SAR, current density, and their determinations are tissue-type dependent and require a region of specific tissue mass for averaging. Thus, a smaller averaging region is scientifically more relevant and precise. It is emphasized that the sensitivity and resolution of present-day computational resources and experimental measurement techniques can provide accurate SAR values with a spatial resolution on the order of a 1 mm, in dimensions. Furthermore, most exposure guidelines are promulgated on a 4 W kg SAR to prevent any whole-body exposure from raising the body temperature to 1 degrees C above the norm at 37 degrees C. Special guidance may be needed for higher ambient temperature and humidity variations.     

Health risks of exposure to non-ionizing radiation--myths or science-based evidence

INTRODUCTION: The non-ionizing radiation (NIR) contains large range of wavelengths and frequencies from vacuum ultraviolet (UV) radiation to static electric and magnetic fields. Biological effects of electromagnetic (EM) radiation depend greatly on wavelength and other physical parameters. OPTICAL RADIATION: The Sun is the most significant source of environmental UV exposure, so that outdoor workers are at risk of chronic over-exposure. Also exposure to short-wave visible light is associated with the aging and degeneration of the retina. Especially hazardous are laser beams focused to a small spot at the retina, resulting in permanent visual impairment. ELECTROMAGNETIC FIELDS: Exposure to EM fields induces body currents and energy absorption in tissues, depending on frequencies and coupling mechanisms. Thermal effects caused by temperature rise are basically understood, whereas the challenge is to understand the suspected non-thermal effects. Radiofrequency (RF) fields around frequencies of 900 MHz and 1800 MHz are of special interest because of the rapid advances in the telecommunication technology. The field levels of these sources are so low that temperature rise is unlikely to explain possible health effects. Other mechanisms of interaction have been proposed, but biological experiments have failed to confirm their existence.     

Evaluation of reproductive function of female rats exposed to radiofrequency fields (27.12 MHz) near a shortwave diathermy device

In recent years, there has been increased concern regarding effects of operator exposure to the electromagnetic (EM) field associated with shortwave diathermy devices. The present study was designed to investigate the effects, on rats, of repeated exposure to such an EM field. Following repeated exposure for 5 wk, a reduction in fertility occurred as indicated by a reduced number of matings in exposed rats compared to sham-irradiated rats and a reduction in the number of rats that conceived after mating. The data suggest that female operators could experience reduced fertility, if they remained close to the console for prolonged periods. This has particular significant for the physiotherapy profession.     

Health effects relevant to the setting of EMF exposure limits

To date, electric and magnetic exposure limits for frequencies below 100 kHz have been based on vaguely defined neurobiological responses to electric fields induced in tissues in vivo by magnetic fields and on perceptual responses to external electric fields. Advances in tissue dosimetry, risk assessment methods, and biological research on stimulation thresholds and mechanisms are providing new bases for exposure limits. This paper reviews the historical basis for current electric and magnetic exposure limits in preparation for the development of the "next generation" of electric and magnetic occupational and public exposure guidelines. This is followed by an overview of reported neurobiological effects of electric and magnetic stimulation that should be considered in new exposure guidelines. For magnetic fields, there is stronger evidence for setting exposure limits to protect against adverse effects of nerve stimulation than for protecting against visual magnetophosphenes. Magnetophosphenes are not adverse, and the evidence that these perceptual responses of the eye are a precursor or surrogate for other adverse neurologic responses is weak. Rather than relying just on theoretical models to set exposure limits, data from human subjects exposed to pulsed magnetic fields should be used to estimate nerve stimulation thresholds. Such data can provide a solid basis for setting magnetic field exposure limits if uncertainties in the data and inter-individual variability are addressed. Research on sensory perception, spontaneous and evoked potentials, and epidemiologic studies of neuropsychiatric conditions in electric and magnetic exposed populations does not suggest a need for lower exposure limits. However, a report that a 60-mT magnetic field (below the threshold for peripheral nerve stimulation) produces prolonged alterations of brain excitability and "indisposure" of subjects should be investigated in future research.     

Cytogenetic observations in human peripheral blood leukocytes following in vitro exposure to THz radiation: a pilot study

Emerging technologies are considering the possible use of Terahertz radiation in different fields ranging from telecommunications to biology and biomedicine. The study of the potential effects of Terahertz radiation on biological systems is therefore an important issue in order to safely develop a variety of applications. This paper describes a pilot study devoted to determine if Terahertz radiation could induce genotoxic effects in human peripheral blood leukocytes. For this purpose, human whole blood samples from healthy donors were exposed for 20 min to Terahertz radiation. Since, to our knowledge, this is the first study devoted to the evaluation of possible genotoxic effects of such radiation, different electromagnetic conditions were considered. In particular, the frequencies of 120 and 130 GHz were chosen: the first one was tested at a specific absorption rate (SAR) of 0.4 mW g-1, while the second one was tested at SAR levels of 0.24, 1.4, and 2 mW g-1. Chromosomal damage was evaluated by means of the cytokinesis block micronucleus technique, which also gives information on cell cycle kinetics. Moreover, human whole blood samples exposed to 130 GHz at SAR levels of 1.4 and 2 mW g-1 were also tested for primary DNA damage by applying the alkaline comet assay immediately after exposure. The results obtained indicate that THz exposure, in the explored electromagnetic conditions, is not able to induce either genotoxicity or alteration of cell cycle kinetics in human blood cells from healthy subjects.     

实验动物从业人员的健康问题

目的了解实验动物从业人员的健康状况,探讨保障健康的防控重点。方法通过文献检索、实地考察,探讨实验动物从业人员所处的职业性暴露因素及其防控措施。结果实验动物从业人员职业性暴露因素主要有生物因素、化学因素、物理因素和心理因素4个方面。职业性暴露的潜在危害主要取决于以下3个方面：接触潜在危害的概率、接触潜在危害的数量、从业人员的心理状况。结论针对实验动物从业人员的职业性暴露因素,可通过采取严格执行相应的操作规程、加强监督管理和进行心理疏导等措施,确保实验动物从业人员的健康。     

Assessment of exposure to magnetic fields in occupational settings

OBJECTIVE: It is important to have data about occupational magnetic field intensity to consider the contribution of occupational magnetic field exposure on the human body. We conducted research on exposure to occupational magnetic fields and tried to qualify data on the distribution of magnetic field' intensity in certain general working environments with individual measurements. SUBJECTS AND METHODS: We performed sample research on the exposure to low-frequency magnetic fields of workers in certain occupations and in the working environment. We also assessed the relationship between working environmental magnetic field distribution and individual exposure. RESULTS: Some occupations were found to be exposed to high magnetic fields. We observed that some workspaces, such as the transformer substation, generally had a uniform and high magnetic field measurement but employees were exposed to a lower intensity. We also found that welders were exposed to high magnetic fields at about 600 microT in a very short time but with a geometrical value of 0.08 microT. CONCLUSION: The determination of administrative levels and control levels, not only of the time weighted average of threshold limits or short term exposure limits, but also ceiling limits should be considered. More systematic research is necessary to determine variables such as operating conditions, measuring position, and frequency bands. Also, further studies will be needed to make a job-exposure matrix for the magnetic fields for each occupation type and to combine it with exposure in non-occupational settings such as commuting and ordinary life situations to explore the causal relationship between exposure to magnetic fields and disease.     

The design, construction and calibration of a carefully controlled source for exposure of mammalian cells to extremely low-frequency electromagnetic fields.

Despite some epidemiological evidence for an association between increased risk of cancer and exposure to electromagnetic fields (EMFs), cancer causation by such exposure remains unproven. Furthermore, for reasons such as biological unresponsiveness of the chosen system, poor equipment design and experimental confounders, no reproducible effects on animals or mammalian cells in culture have been demonstrated following exposure to power frequency EMFs at levels normally encountered in residential settings (<10 to 1000 microT). The apparatus described here, designed specifically to perform large, well-controlled cell biology experiments, reduces extraneous variables to the absolute minimum, so that small effects cannot be ascribed to some cause unrelated to the experimental protocol. Our novel apparatus consists of two identical solenoids which, in use, only differ by whether the field-producing current is flowing or not; they do not influence one another in any way. They are supplied with conditioned air from a common tissue culture incubator, are completely screened from environmental a.c. fields with Mumetal shielding and can be operated under normal laboratory conditions. Furthermore, the arrangement is such that the investigator is unaware whether cells have, or have not, been exposed until after the results have been evaluated. We report the design, construction, calibration and potential uses of this source.     

SEX HORMONE STATUS IN MALE RATS AFTER EXPOSURE TO 50 HZ, 5 MTESLA MAGNETIC FIELD

The question of whether extremely low frequency magnetic fields can affect biological system has attracted attention. The theoretical possibility of such an interaction is often questioned and the site of interaction is unknown. The influence of extremely low frequency magnetic field of 50 Hz, 5 mTesla on sex hormone status was studied. 60 male albino rats were divided into 6 groups and were continuously exposed to 50 Hz, 5 mTesla magnetic field generated by magnetic field chamber for periods of 1, 2 and 4 weeks. For each experimental point, sham treated group was used as a control. Assay of serum testosterone LH, FSH, and prolactin were performed. Serum testosterone showed no significant changes. FSH showed significant increase than sham exposed group after 1 week magnetic field exposure. LH showed significant increase than sham exposed group only after 4 weeks magnetic field exposure, while serum prolactin hormone level showed a significant increase in all magnetic field exposed groups than sham exposed animals. Exposure to 50 Hz, 5 mTesla magnetic field for periods of 1, 2 and 4 weeks has no effect on testosterone level, some changes on FSH and LH serum levels and increase in serum prolactin level.     

Prospects for new information relevant to radiation protection from studies of experimental animals

The theory underlying radiation protection was developed from studies of people, laboratory animals, tissues, cells and macromolecules. Data on people were obtained from opportunistic studies of individuals previously exposed to radiation. Rarely has it been possible to conduct prospective studies of people exposed to known quantities of radiation, which sharply restricts the nature of questions that they can address. In contrast, studies using laboratory animals and simpler biological systems can be designed to address specific questions, using controlled exposure conditions. In-vitro research with macromolecules, cells and tissues leads to understanding normal and disease processes in isolated biological components. Studies of the intact animals provide opportunities to study in vivo interactive mechanisms observed in vitro and their role in development of radiation-induced diseases such as cancer. In the future, studies of intact animals should prove increasingly valuable in linking new knowledge at the subanimal level with the more fragmentary information obtained from direct observations on people. This will provide insight into important issues such as (a) effects of low-level radiation exposures, (b) mechanism of cancer induction at high versus low radiation doses, and (c) influence of factors such as nutrition and exposure to chemicals on radiation-induced cancer. This presentation describes strategies for conducting and integrating results of research using macromolecules, cells, tissues, laboratory animals and people to improve our understanding of radiation-induced cancer. It will also emphasize the problems encountered in studies at all levels of biological organization when the disease is observed in low "excess incidence" long after exposure to the toxicant.     

SAR and temperature distribution in the rat head model exposed to electromagnetic field radiation by 900 MHz dipole antenna

Rats are often used in the electromagnetic field (EMF) exposure experiments. In the study for the effect of 900 MHz EMF exposure on learning and memory in SD rats, the specific absorption rate (SAR) and the temperature rise in the rat head are numerically evaluated. The digital anatomical model of a SD rat is reconstructed with the MRI images. Numerical method as finite difference time domain has been applied to assess the SAR and the temperature rise during the exposure. Measurements and simulations are conducted to characterize the net radiated power of the dipole to provide a precise dosimetric result. The whole-body average SAR and the localized SAR averaging over 1, 0.5 and 0.05 g mass for different organs/tissues are given. It reveals that during the given exposure experiment setup, no significant temperature rise occurs. The reconstructed anatomical rat model could be used in the EMF simulation and the dosimetric result provides useful information for the biological effect studies.     

The specific absorption rate of tissues in rats exposed to electromagnetic plane waves in the frequency range of 0.05–5 GHz and SARwb in free-moving rats

As electromagnetic exposure experiments can only be performed on small animals, usually rats, research on the characteristics of specific absorption rate (SAR) distribution in the rat has received increasing interest. A series of calculations, which simulated the SAR in a male rat anatomical model exposed to electromagnetic plane waves ranging from 0.05 to 5 GHz with different incidence and polarization, were conducted. The whole-body-averaged SAR (SARwb) and the tissue-averaged SAR (SARavg) in 20 major tissues were determined. Results revealed that incidence has great impact on SAR in the rat at higher frequencies owing to the skin effect and the effect on SARavg in tissues is much more apparent than that on SARwb; while polarization plays an important role under lower frequencies. Not only the incidence, but also the polarization in the rat keeps changing when the rat is in free movement. Thus, this article discussed a convenient way to obtain relatively accurate SARwb in a free-moving rat.     

Invited commentary: electromagnetic fields and cancer in railway workers

The ideal study of occupational exposure to electromagnetic fields and cancer risk would have a clear exposure source, historically stable exposures, and comparable groups of exposed and unexposed workers. Cohorts of railway workers have marked exposure contrasts and limited job changes and provide marginally adequate study sizes, but there have been important changes in their exposures over time, and the field frequency involved is unusual. The results of Minder and Pfluger's study (Am J Epidemiol 2001;153:825--35) add modest support for an association between electromagnetic field exposure and leukemia. However, given the large size and high quality of a number of previous studies of occupational electromagnetic field exposure and cancer, additional studies similar to past ones are unlikely to yield important new insights.     

Effects of 2.45 GHz electromagnetic fields with a wide range of SARs on bacterial and HPRT gene mutations

Present day use of mobile phones is ubiquitous. This causes some concern for human health due to exposure to high-frequency electromagnetic fields (HFEMF) from mobile phones. Consequently, we have examined the effects of 2.45 GHz electromagnetic fields on bacterial mutations and the hypoxanthine-guanine phosphoribosyl transferase (HPRT) gene mutations. Using the Ames test, bacteria were exposed to HFEMF for 30 min at specific absorption rates (SARs) from 5 to 200 W/kg. In all strains, there was no significant difference in the frequency of revertant colonies between sham exposure and HFEMF-exposed groups. In examination of mutations of the HPRT gene, Chinese hamster ovary (CHO)-K1 cells were exposed to HFEMF for 2 h at SARs from 5 to 200 W/kg. We detected a combination effect of simultaneous exposure to HFEMF and bleomycin at the respective SARs. A statistically significant difference was observed between the cells exposed to HFEMF at the SAR of 200 W/kg. Cells treated with the combination of HFEMF at SARs from 50 to 200 W/kg and bleomycin exhibited increased HPRT mutations. As the exposure to HFEMF induced an increase in temperature, these increases of mutation frequency may be a result of activation of bleomycin by heat. We consider that the increase of mutation frequency may be due to a thermal effect.     

Assessing cumulative health risks from exposure to environmental mixtures - three fundamental questions

Differential exposure to mixtures of environmental agents, including biological, chemical, physical, and psychosocial stressors, can contribute to increased vulnerability of human populations and ecologic systems. Cumulative risk assessment is a tool for organizing and analyzing information to evaluate the probability and seriousness of harmful effects caused by either simultaneous and/or sequential exposure to multiple environmental stressors. In this article we focus on elucidating key challenges that must be addressed to determine whether and to what degree differential exposure to environmental mixtures contributes to increased vulnerability of exposed populations. In particular, the emphasis is on examining three fundamental and interrelated questions that must be addressed as part of the process to assess cumulative risk: a) Which mixtures are most important from a public health perspective? and b) What is the nature (i.e., duration, frequency, timing) and magnitude (i.e., exposure concentration and dose) of relevant cumulative exposures for the population of interest? c) What is the mechanism (e.g., toxicokinetic or toxicodynamic) and consequence (e.g., additive, less than additive, more than additive) of the mixture's interactive effects on exposed populations? The focus is primarily on human health effects from chemical mixtures, and the goal is to reinforce the need for improved assessment of cumulative exposure and better understanding of the biological mechanisms that determine toxicologic interactions among mixture constituents.     

Electromagnetic field strength levels surrounding electronic article surveillance (EAS) systems

Electronic article surveillance (EAS) is used in many applications throughout the world to prevent theft. EAS systems produce electromagnetic (EM) energy around exits to create an EM interrogation zone through which protected items must pass before leaving the establishment. Specially designed EAS tags are attached to these items and must either be deactivated or removed prior to passing through the EAS EM interrogation zone to prevent the alarm from sounding. Recent reports in the scientific literature have noted the possibility that EM energy transmitted by EAS systems may interfere with the proper operation of sensitive electronic medical devices. The Food and Drug Administration has the regulatory responsibility to ensure the safety and effectiveness of medical devices. Because of the possibility of electromagnetic interference (EMI) between EAS systems and electronic medical devices, in situ measurements of the electric and magnetic fields were made around various types of EAS systems. Field strength levels were measured around four types of EAS systems: audio frequency magnetic, pulsed magnetic resonant, radio frequency, and microwave. Field strengths from these EAS systems varied with magnetic fields as high as 1073.6 Am(-1) (in close proximity to the audio frequency magnetic EAS system towers), and electric fields up to 23.8 Vm(-1) (in close proximity to the microwave EAS system towers). Medical devices are only required to withstand 3 Vm(-1) by the International Electrotechnical Commission's current medical device standards. The modulation scheme of the signal transmitted by some types of EAS systems (especially the pulsed magnetic resonant) has been shown to be more likely to cause EMI with electronic medical devices. This study complements other work in the field by attaching specific characteristics to EAS transmitted EM energy. The quantitative data could be used to relate medical device EMI with specific field strength levels and signal waveforms. This is one of several efforts being made by the FDA, the electronic medical device industry and the EAS industry to mitigate the potential for EMI between EAS and medical devices.     

高等真核细胞受极低频磁场辐照后基因差异表达的分析

目的　从基因水平研究电磁场的非热效应及其可能的机制。方法　以高等真核细胞（ 人恶性淋巴瘤细胞） 为模型,运用ｍ ＲＮＡ 差异显示法（ｍ ＲＮＡ ｄｉｆｆｅｒｅｎｔｉａｌ ｄｉｓｐｌａｙ ,ＤＤ） 技术分析受５０ Ｈｚ 极低频磁场（ＥＦＬＭＦ） 辐照及假辐照２４ 小时后的细胞基因转录的差异。结果　用７５ 个引物组合获得１１个对ＥＬＦＭＦ 显示差异反应的ｃＤＮＡ 片段,表现为：（１） 片段只出现在受辐照的细胞,而未出现在非辐照的细胞中;（２） 片段只出现在非辐照的细胞中,而未出现在受辐照的细胞中;（３） 片段在辐照和非辐照细胞中均有表达,但表达强度有明显差异。回收这些片段,经ＰＣＲ 重扩增及反向Ｎｏｒｔｈｅｒｎ 初步筛选,结合Ｎｏｒｔｈｅｒｎ ｂｌｏｔ 鉴定,部分ｃＤＮＡ 得到证实为磁场特异反应基因。结论　低强度ＥＬＦＭＦ 可影响基因表达。     

Whole-body and local dosimetry in rats exposed to 2.45-GHz microwave radiation

Rat cadavers oriented parallel to the electric field were exposed to 2.45-GHz microwave radiation. The weights of the cadavers ranged from approx. 5 to 320 g and their lengths ranged from approx. 5 to 21.5 cm. Whole-body specific absorption rates (SAR) were measured using calorimetric techniques, and local specific absorption rates were obtained from time-temperature profiles measured with a non-interacting thermistor probe (Vitek). The whole-body SARs decreased by a factor of 12 in rat pups weighing 5 g as compared to adult rats weighing 320 g. The local SARs in the colon were slightly higher than the whole-body SARs for animals in the weight range from 40 to 320 g and approx. 2.5 times higher in animals ranging from 10 to 30 g. The local SARs in the brain were two to three times higher than the whole-body SARs for animals ranging in weights from 20 to 320 g. The data show that it is important to measure both whole-body SARs and local SARs when conducting experiments to determine biological effects in order to adequately explain any biological changes and to extrapolate data from different sizes and species of animals.     

Application of in vitro biotransformation data and pharmacokinetic modeling to risk assessment

The adverse biological effects of toxic substances are dependent upon the exposure concentration and the duration of exposure. Pharmacokinetic models can quantitatively relate the external concentration of a toxicant in the environment to the internal dose of the toxicant in the target tissues of an exposed organism. The exposure concentration of a toxic substance is usually not the same as the concentration of the active form of the toxicant that reaches the target tissues following absorption, distribution, and biotransformation of the parent toxicant. Biotransformation modulates the biological activity of chemicals through bioactivation and detoxication pathways. Many toxicants require biotransformation to exert their adverse biological effects. Considerable species differences in biotransformation and other pharmacokinetic processes can make extrapolation of toxicity data from laboratory animals to humans problematic. Additionally, interindividual differences in biotransformation among human populations with diverse genetics and lifestyles can lead to considerable variability in the bioactivation of toxic chemicals. Compartmental pharmacokinetic models of animals and humans are needed to understand the quantitative relationships between chemical exposure and target tissue dose as well as animal to human differences and interindividual differences in human populations. The data-based compartmental pharmacokinetic models widely used in clinical pharmacology have little utility for human health risk assessment because they cannot extrapolate across dose route or species. Physiologically based pharmacokinetic (PBPK) models allow such extrapolations because they are based on anatomy, physiology, and biochemistry. In PBPK models, the compartments represent organs or groups of organs and the flows between compartments are actual blood flows. The concentration of a toxicant in a target tissue is a function of the solubility of the toxicant in blood and tissues (partition coefficients), blood flow into the tissue, metabolism of the toxicant in the tissue, and blood flow out of the tissue. The appropriate degree of biochemical detail can be added to the PBPK models as needed. Comparison of model simulations with experimental data provides a means of hypothesis testing and model refinement. In vitro biotransformation data from studies with isolated liver cells or subcellular fractions from animals or humans can be extrapolated to the intact organism based upon protein content or cell number. In vitro biotransformation studies with human liver preparations can provide quantitative data on human interindividual differences in chemical bioactivation. These in vitro data must be integrated into physiological models to understand the true impact of interindividual differences in chemical biotransformation on the target organ bioactivation of chemical contaminants in air and drinking water.