Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
La Medicina Meci Lav 2006;del 97, Lavoro 2: Health risks of exposure to non-ionizing radiationMyths or science~based evidence MAILA HIETANEN Finnish Institute of Occupational Health, Helsinki, Finland KEYWORDS Non-ionizing radiation; UV radiation; EM fields SUMMARY Introduction: The non-ionizing radiation (NIR) contains large range of wavelengths and frequencies fOi um ultraviolet (UV) radiation to static electric and magnetic jields. Biological effects of electromagnetic (EA ation depend greatly on wavelength and other physical parameters. Optical radiation: The Sun is the most cant source of environmental UVexposure, so that outdoor workers are at risk· of chronic over-exposure. Al sure to short-wave visible light is associated with the aging and degeneration of the retina. Especially ha are laser beams focused to a small spot at the retina, resulting in permanent visual impairment. Electrom fields: Exposure to EM jields induces body currents and energy absorption in tissues, depending on frequen coupling mechanisms. Thermal effects caused by temperature rise are basically understood, whereas the challe understand the suspected non-thermal effects. Radiofrequency (RF) jields around frequencies of 900 M 1800 MHz are of special interest because of the rapid advances in the telecommunication technology. The fit of these sources are so low that temperature rise is unljkely to explain possible health effects. Other mechanisr. teraction ha ve been proposed, but biological experiments ha ve failed to conjirm their existence. RIASSUNTO «Rischi per la salute dovuti all'esposizione a radiazioni non ionizzanti: mito o evidenza scientijica?». L zioni non ionizzanti (NIR) contengono una vasta gamma di lunghezze d'onda e frequenze che vanno dall zioni ultraviolette (UV) nel vuoto a campi statiei, elettrici e magnetici. Cii effetti biologici delle radiazioni eli gnetiche (EM) dipendono molto dalla lunghezza d'onda e da altri parametri jisici. Radiazioni ottiche: II maggiore sorgente di esposizione ambientale ai raggi UV, cosicchi i lavoratori all'aperto sono a rischio di sov zione cronica. Anche l'esposizione alia luce visibile ad onda corta e associata all'invecchiamento e alia degen della retina. In particolare i pericoli sono i raggi laser concentrati in una piccola zona sulla retina, che esita; danno permanente della visione. Campi elettromagnetici: L'esposizione a campi elettromagnetici determina corporee ed assorbimento di energia nei tessuti la cui entita dipende dalie frequenze e dai meccanismi di accopp Cii effetti termici causati da aumenti di temperatura sono sostanzialmente noti, mentre la sfida e di capire i j effetti non termici. 1 campi delle radiifrequenze attorno a frequenze di· 900 MHz e di 1800 MHz sono di pc interesse per il rapido progresso della tecnologia nelle telecomunicazioni. Ilivelli dei campi di queste sorgenti bassi che il rialzo della temperatura e poco probabile che possa spiegare i possibili effetti sulla salute. Sono statl altri meccanismi di interazione, ma gli esperimenti biologici sono poco validi per confirmare la loro esistenza. Correspondence: Maila Hietanen, Finnish Institute of Occupational Health, Topeliuksenkatu 41 a A, FI-00250 Helsinki, E-mail: [email protected] HEALTH RlSKS OF NON-IONIZING RADIATION 185 INTRODUCTION The non-ionizing radiation (NIR) spectrum contains a large range of wavelengths and frequencies from vacuum ultraviolet (UV) radiation to static electric and magnetic fields. Biological effects of NIR depend greatly on wavelength, frequency and other physical parameters, with a variety of consequences for exposed human beings. Various categories ofNIR are separated, basically reflecting different biologic al interactions. Optical radiation consists of UV, visible and infrared (IR) radiation. The other parts of the NIR spectrum contain static electric and magnetic fields, extremely low frequency (ELF) and low frequency (LF) electromagnetic (EM) fields and radiofrequency (RF) radiation. Except for visible radiation, i.e. light, NIR is invisible to the human eye and not perceived by other senses at typical occupational exposure levels. HEALTH RISKS OF OPTICAL RADIATION Exposure to NIR has a variety of potential consequences for a human being. To begin with optical radiation, severely burned people, mostly young women, every summer need medical help after over-exposure to the Sun. Although the painful erythema ('sunburn') will fade gradually after a few days, recurrent over-exposures may still cause serious late effects. Chronic UV exposure has been indicated to be the primary factor in the induction of non-melanocytic skin cancers (NMSC). In addition, epidemiological studies on cutaneous melanoma suggest that UV erythema may be of particular importance in its initiation (9). Despite the high incidence, NMSC is usually diagnosed at an early stage and the mortality rate is relatively low compared with that of melanoma. The risk of developing skin cancer varies greatly with skin type, and persons who readily sunburn are also more prone to develop skin cancer. Skin cancer of fair-skinned individuals is increasing at an alarming rate (4-6% per year) around the world (4). In USA, for example, skin cancers are the most common type of cancer, with about 1.3 million new cases each year (2). An unprotected eye exposed to direct UV radiation from the Sun or to reflected UV from snow may accumulate a sufficient dose to cause hazardous effects on the cornea, called photokeratitis. As with erythema of the skin, the symptoms are delayed for several hours. Within a few hours overexposure to UV radiation gradually gives rise to symptoms from a feeling of itchiness, 'sand in the eye' sensation, increased tearing, to severe pain and photophobia. The condition is referred to as 'snowblindness' or 'welders flash', depending on the source of exposure (12). In addition to corneal injury, epidemiological data shows an increased risk of cortical cataract with UV exposure (1). In the unusual situation where the UV absorbing lens or lens implant are not present, retinal injury is also possible for wavelengths over 300 nm (9). The global prevalence of blinding cataracts exceeds 50 million, and the prevention and slowing of the progress of lenticular opacities should be an important objective in occupational health activities. Though the intensity of the solar UV radiation depends on latitude, being the highest at the Equator, it is worthwhile to note some peculiarities concerning conditions in high geographicallatitudes. In summer, the daily duration of sunlight is very long and the height of the Sun predominantly low, so that it is difficult to avoid looking at it. In winter, the main contributing factor to the UV exposure is the reflection from snow and ice. Under these conditions, safe UV exposure limits can be easily exceeded without eye protection (11). Hence, outdoor workers, such as fishermen, merchants at marketplaces, and road constructors are at risk of chronic over-exposure to solar UV radiation. As for the adverse effects of visible radiation on the eye, there are numerous epidemiological studies indicating that chronic exposure to short-wave light, so called blue-light, is a contributing factor to aging and degeneration of the retina. Several studies have revealed that the shorter the wavelength, the more severe the ocular photochemical damage. Fortunately, the human eye is protected by the aversion reflex against hazardous light sources (11). Therefore, it is difficult to look at the sun when it is high and bright, hence being dangerous for the retina. The amount and the spectral distribution of the solar radiation changes with the height of the Sun, so that comfortable and safe viewing of it is possible only at angles of less than a few degrees a moment after the sunrise or before the sunset. Though the eyelids normally close at exposure to sudden bright light, this aversion response is too slow in some special situations. Especially hazardous are coherent laser beams that are focused to a small spot at the retina, resulting in permanent visual impairment (12). These examples clearly indicate that health hazards of high exposure to optical region of NIR are science-based and incontestable. Therefore, workplace campaigns emphasizing importance of individual responsibility and necessity of personal protection should be part of occupational health education. However, it should be also noted that other adverse effects, e.g. increasing prevalence of multiple sclerosis and type 1 diabetes in higher latitudes, have been associated with low sun exposure and vitamin D deficiency (l0). HEALTH RISKS OF ELECTROMAGNETIC FIELDS Correspondingly to optical radiation, people in technically developed countries are surrounded by ELF and RF electromagnetic fields. Natural background EM fields are several orders lower than those emitted by human-made sources, so that most occupational exposure is caused by sources that emit EM fields either intentionally or as byproducts (13). Whole-body or localized exposure to EM fields induces body currents and energy absorption in tissues, depending on specific frequencies and coupling mechanisms (8). Thermal effects caused by local or whole-body temperature rise are obvious and basically understood, whereas the principal scientific challenge is to reveal and understand the suspected or hypothesized non-thermal effects. For instance, as a matter of a scientific mystery, some occupationally or non-occupationally exposed persons in various countries claim to experience unpleasant feelings during or after exposure to EM fields. Typical hypersensitive reactions and symptoms are described as headache, dizziness, fatigue and nausea. These sensations are not regarded pathological, but they may seriously affect the physical or mental wellbeing of such persons. In 2002, International Agency for Risk of Cancer (IARC) classified ELF magnetic fields as a possible human carcinogen (Class 2B), based on the risk of leukaemia in children living near electric power transmission lines (5). Exposure to ELF magnetic fields has also been associated with several other end-points, such as increased risk of brain cancer, breast cancer, heart disease, and Alzheimer's disease, but these associations are speculative and not confirmed. At present, RF fields around frequencies of 900 MHz and 1800 MHz are of special interest because of the rapid advances in the telecommunication technology. As a result of the global expansion of the use of hand-held cellular phones, RF exposure is becoming ubiquitous, and the focus of public interest has moved from power lines to mobile telephones and base station antennas. The levels of these emissions are so low that the mechanism of temperature rise is unlikely to explain the alleged adverse health effects. Non-thermal mechanisms of interaction have been proposed, but biological and human experiments have failed to confirm their existence (7). WHO's INTERNATIONAL EMF PROJECT Several international bodies have realized the necessity of expanding interest in the RF radiation research in order to identify the gaps in scientific knowledge. For example, the World Health Organization (WHO) acknowledges that EM fields represent one of the fastest growing environmental factors, spreading anxiety and speculation also among working population. Ten years ago, the WHO launched an International EMF Project for providing independent scientific assessments of health effects from exposure to EM fields. The Project has encouraged setting of internationally accessible guidelines and standards for exposure limits and device emissions. It has also provided information on risk perception, risk communication and risk management of the EM fields (14). 186 HIETANEN retina. The amount and the spectral distribution of the solar radiation changes with the height of the Sun, so that comfortable and safe viewing of it is possible only at angles of less than a few degrees - a moment after the sunrise or before the sunset. Though the eyelids normally close at exposure to sudden bright light, this aversion response is too slow in some special situations. Especially hazardous are coherent laser beams that are focused to a small spot at the retina, resulting in permanent visual impairment (12). These examples clearly indicate that health hazards of high exposure to optical region of NIR are science-based and incontestable. Therefore, workplace campaigns emphasizing importance of individual responsibility and necessity of personal protection should be part of occupational health education. However, it should be also noted that other adverse effects, e.g. increasing prevalence of multiple sclerosis and type 1 diabetes in higher latitudes, have been associated with low sun exposure and vitamin D deficiency (l0). HEALTH RISKS OF ELECTROMAGNETIC FIELDS Correspondingly to optical radiation, people in technically developed countries are surrounded by ELF and RF electromagnetic fields. Natural background EM fields are several orders lower than those emitted by human-made sources, so that most occupational exposure is caused by sources that emit EM fields either intentionally or as byproducts (13). Whole-body or localized exposure to EM fields induces body currents and energy absorption in tissues, depending on specific frequencies and coupling mechanisms (8). Thermal effects caused by local or whole-body temperature rise are obvious and basically understood, whereas the principal scientific challenge is to reveal and understand the suspected or hypothesized non-thermal effects. For instance, as a matter of a scientific mystery, some occupationally or non-occupationally exposed persons in various countries claim to experience unpleasant feelings during or after exposure to EM fields. Typical hypersensitive reactions and symptoms are described as headache, dizziness, fatigue and nausea. These sensations are not regarded pathological, but they may seriously affect the physical or mental wellbeing of such persons. In 2002, International Agency for Risk of Cancer (IARC) classified ELF magnetic fields as a possible human carcinogen (Class 2E), based on the risk of leukaemia in children living near electric power transmission lines (5). Exposure to ELF magnetic fields has also been associated with several other end-points, such as increased risk of brain cancer, breast cancer, heart disease, and Alzheimer's disease, but these associations are speculative and not confirmed. At present, RF fields around frequencies of 900 MHz and 1800 MHz are of special interest because of the rapid advances in the telecommunication technology. As a result of the global expansion of the use of hand-held cellular phones, RF exposure is becoming ubiquitous, and the focus of public interest has moved from power lines to mobile telephones and base station antennas. The levels of these emissions are so low that the mechanism of temperature rise is unlikely to explain the alleged adverse health effects. Non-thermal mechanisms of interaction have been proposed, but biological and human experiments have failed to confirm their existence (7). WHO's INTERNATIONAL EMF PROJECT Several international bodies have realized the necessity of expanding interest in the RF radiation research in order to identify the gaps in scientific knowledge. For example, the World Health Organization (WHO) acknowledges that EM fields represent one of the fastest growing environmental factors, spreading anxiety and speculation also among working population. Ten years ago, the WHO launched an International EMF Project for providing independent scientific assessments of health effects from exposure to EM fields. The Project has encouraged setting of internationally accessible guidelines and standards for exposure limits and device emissions. It has also provided information on risk perception, risk communication and risk management of the EM fields (14). HEALTH RlSKS OF NON-IONIZING RADIATION 187 THE ROLE OF ICNIRP IN HEALTH RISK ASSESSMENT The principal scientific organization supporting the work by WHO is the International Commission on Non - Ionizing Radia tion Protection (ICNIRP). The main activity of ICNIRP is to provide guidance on safe exposure and protection of workers and members of the public by issuing statements and recommendations. ICNIRP monitors continuously and periodically carries out critical reviews of the scientific literature concerned with the sources and possible biological and adverse health effects of NIR. ICNIRP performs critical scientific analysis by evaluating the relevance, scientific quality and credibility of each report (6). The exposure limits developed by ICNIRP are intended to protect against diseases and other adverse health effects. Because risk assessment is focused to humari health, ICNIRP prefers the data derived from human studies. The relationship between exposure and certain short-term biological effects can be evaluated from human laboratory studies, whereas data on long-term human effects can only be derived from epidemiological studies. However, the epidemiological studies are not considered sufficient to provide evidence of caus al relationships without biological data from experimental studies. In its exposure guidelines, ICNIRP defines occupational and public exposures in general terms. When applying the guidelines to specific situations, it is ICNIRP's opinion that authorities in each country should decide on whether occupational or general public guideline levels are to be applied, according to existing national rules or policies. EUROPEAN DIRECTIVE ON WORKERS' EM FIELD EXPOSURE In Europe, it has been considered necessary to introduce specific measures protecting workers from the risks associated with EM fields. Therefore, a new Directive given by the European Commission and Council was published in 2004 (3). Similar to ICNIRP's philosophy, this Directive refers to the health risks of workers due to known short-term adverse effects caused by the circulation of induced currents and by energy absorption as well as by contact currents. Hence, it does not address suggested long-term effects, including possibIe carcinogenic effects, stating that there is no conclusive scientific evidence establishing a causal relationship. REFERENCES 1. BALASUBRAMANIAN D: Ultraviolet radiation and cataract. J Ocular Pharmacol Therap 2000; 88: 329-344 2. BENvENUTo-ANDRADE C, ZEN B, FONSECA G, et al: Sun exposure and sun protection habits among highschool adolescents in Porto Alegre, Brazil. Photochem Photobiol2005; 81: 630-635 3.Directive of the European Parliament and of the CounciI on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (electromagnetic fields) (2004/40/EC). Official Journal of the European Union 2004; L 184: 1-9 4. GODAR DE: UV doses worldwide. Photochem Photobio12005; 81: 736-749 5. INTERNATIONAL AGENCY FOR RESEARCH ON CANCER: Static and extremely low-Jrequency (ELF) electric and magnetic jields. Lyon: IARC, 2002 (IARC Monographs on non-ionizing radiation no 80) 6. INTERNATIONAL COMMISSION ON NON-IONIZING RADIATION PROTECTION (ICNIRP): General approach to protection against non-ionizing radiation. Health Physics 2002; 82: 540-548 7. INTERNATIONAL EXPERT GROUP ON MOBILE PHONES: Mobile phones and health. IEGMP, 2000. (Report of an Independent Expert Group on Mobile Phones). ISBN 0-85951-450-1 8. NATIONAL RAmOLOGICAL PROTECTION BOARD: Advice on limiting exposure to electromagnetic jields (0-300 GHz). Chilton, UK: Documents of the NRPB 2004: 15 (2) 9. NATIONAL RADIOLOGICAL PROTECTION BOARD: Health effects Irom ultra violet radiation. Chilton, UK: Documents of the NRPB 2002: 13 (1) 10.PONSONBY AL, LUCAs RM, VAN DER MEI AF: UVR, Vitamin D and three autoimmune diseases - Multiple sclerosis, type 1 diabetes, rheumatoid arthritis. Photochem Photobiol2005; 81: 1267-1275