Assessment of biological changes of continuous whole body exposure to static magnetic field and extremely low frequency electromagnetic fields in mice☆
Introduction
Until recently, the natural electromagnetic background was relatively constant, but the situation changed markedly and precipitously with the development of modern communications and electrical power systems. The environment is now heavily laden with man-made electromagnetic fields (EMFs) from radio; TV, microwave relay, and many similar sources.
Static magnetic fields (SMFs) are time-independent fields of constant strength. On the contrary to electrostatic fields, SMFs are difficult to shield and can penetrate biological tissues freely. They can interact directly with moving charges (ions, proteins, etc.) and magnetic materials found in tissues through several physical mechanisms, (WHO, 1989). For SMFs, acute effects are only likely to occur when there is a field gradient or/and a movement in the field, for example motion of a person or internal body movement, such as blood flow or heart beat (WHO, 2006).
Residential and environmental exposure to SMFs is dominated by the Earth's natural field, which ranges from 0.03 to 0.07 mT, depending on location. SMFs under direct current (DC) transmission lines are about 0.02 mT. Small artificial sources of static fields are common, ranging from the specialized (audio speakers components, battery-operated motors, microwave ovens) to trivial (refrigerator magnets). These small magnets can produce fields of 1–10 mT within a centimeter or so of their magnetic poles and decrease with square distance and could reach to the level of few μT. The highest SMF exposures to the general public are from magnetic resonance imaging, where the fields range from 150 to 4000 mT, (Kowalczuk et al., 1991; Stuchly, 1986).
A large numbers of SMF studies have been performed on cells and cellular components, genetic material, embryogenesis, the central nervous system. When taken as a whole, they do not suggest any detrimental effects on major development, behavioral or physiological parameters for short-term exposures. However, long-term toxicology experiments on animals still need to be conducted to assess effects of chronic exposure (Feychting, 2005; WHO, 2006).
Extremely low frequency electromagnetic fields (ELF-EMF) are electromagnetic oscillating fields defined as having frequencies below 300 Hz. ELF-EMFs are very important from a public health standpoint because of the widespread use of electrical power at 50 or 60 Hz in most countries. Electric and magnetic fields exist around electrical equipment and wiring throughout industry. Workers who maintain transmission and distribution lines may be exposed to very large electric and magnetic fields. Within generating stations and substations electric fields in excess of 25 kV/m and magnetic fields in excess of 2 mT may be found (WHO, 1998). Welders can be subjected to magnetic field exposures as high as 130 mT. Near induction furnaces and industrial electrolytic cells magnetic fields can be as high as 50 mT. Office workers are exposed to very much smaller fields when using equipment such as photocopying machines and video display terminals (WHO, 1998). There is still much concern in the general public about the consequences of exposure to these fields near power lines and in industries.
Despite the large number of studies already reported, further research is still necessary in order to make a complete assessment of health effects of exposure to SMF and ELF fields. Many investigations have shown that exposure to ELF-MFs does not cause harmful effects to bacterial and mammalian cells (McCann et al., 1993, McCann et al., 1998). However, other reports have suggested possible toxicity of magnetic fields (Li and Chow, 2001; Sabine et al., 2003). In addition, epidemiological studies have indicated a correlation between ELF-EMF and an increased incidence of some types of cancer (Feychting et al., 2003; IARC, 2002).
Free radicals including superoxide anion radicals, hydroxyl radicals, and hydrogen peroxides are formed as by-products in various metabolic processes. Reactive oxygen species (ROS) are involved in intracellular signal transduction pathways and regulation of gene expression determining the anti-inflammatory response, cell growth, differentiation, proliferation and stress response (Halliwell, 2001; Halliwell and Gutteridge, 1999). In cells, free radical concentration is determined by the balance between their rate of production and their rate of clearance, controlled by different enzymes and antioxidant compounds. These regulatory processes are important to reset the original state of redox homeostasis after temporary production of free radicals (Halliwell, 1999; Halliwell and Whiteman, 2004). Excessive production of free radicals leading to high levels of oxidative response is generated by activated immune defense biotransformation systems and cell respiration. In mammals, several antioxidant defense mechanisms scavenge free radical production and tissue damage, including glutathione (GSH) and glutathione-S-transferase (GST) (Jagetia et al., 2003).
The present study aimed to perform a more thorough study examining the effects of continuous whole body exposure to EMF emitted from two different sources (static and time varying EMF) for 30 days, focusing on changes in physiological parameters mainly in the liver and the blood of male mice.
Section snippets
Exposure system
Two systems were designed in order to obtain two kinds of exposure:
- 1.
Static magnetic field system (SMF): The designed system does not depend on the DC but it depends on the permanent magnets. Magnets in the form of discs (of different diameter and strength) were arranged on five faces of the Perspex cage box (four walls and the floor), see Fig. 1(a). Each two opposite faces of the box, except the upper and floor ones are identical in magnet construction. These had been done by placing identical
Results
Mice exposed to either SMF or ELF-EMF displayed initial insignificant change in body weight till the first week post exposure, and then showed gradual body weight losses which become significantly decreased at days 12, 20 and 30 of the exposure compared to the control group (Fig. 2). The decrease in the body weight in ELF-MEF exposed animals at days 12, 20 and 30 is significant compared to SMF exposed group.
This is coupled with a significant (P<0.05) decrease in glucose in serum for ELF-MEF
Discussion
The changes demonstrated in the present study indicate that a pathological response was associated with oxidative stress under the present exposure condition. The body weight showed considerable decrease in mice exposed to SMF or ELF-EMF for 30 days. Sandrey, 1999, Sandrey, 2002 reported that a correlation between initial body weight and maximum weight drop for EMF exposed rats indicates that the initial mass is not the main factor in explaining the EMF effects on body weight. Thus, it is
Conclusion
The present study demonstrates striking effect of ELF field on physiological parameters in the exposed animals. In addition, other disturbances evoked by the applied fields must be also taken in consideration, because whole body was exposed. Interestingly, in most cases, both ELF-SMF and ELF-EMF showed similar trend of action. Future studies should therefore be aimed at identifying the specific intracellular pathways that transduce EMF-induced changes in the redox state into a signal capable of
Acknowledgment
This study was kindly supported by grants from Faculty of Sciences, Mansoura University Research Unit.
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Animal welfare ethics: All experiments were performed in accordance with protocols approved by the national experimental ethics committee and guidelines for protection of animal welfare.