NONIONIZING RADIATION

Nonionizing radiation, in contrast to ionizing radiation, is electromagnetic radiation that does not have sufficient energy to remove electrons from an atom or molecules to form an ion (or charged particle) during a collision. Instead, it imparts energy to other particles, which typically results in heating. Nonionizing radiation includes frequencies of the electromagnetic spectrum ranging from 1 hertz (Hz) up to 3×10¹⁰ Hz (300 gigahertz) and its wavelengths range from 10⁹ meters down to 10^-7meters. As the frequency of a wave decreases and the wavelength increases, the energy decreases. Included within this category of nonionizing radiation are—in order of decreasing energy: the lower frequency portion of ultraviolet (UV) radiation, visible light, infrared radiation (IR), microwave radiation, radio frequency radiation, and extremely low frequency (ELF) radiation.

Some types of nonionizing radiation have both beneficial and harmful effects on human health. For example, exposure to UV radiation facilitates the synthesis of vitamin D in the human body, and vitamin D plays an important role in intestinal calcium absorption. Lack of vitamin D can result in lead overdosing, kidney damage, and elevated serum cholesterol levels. UV is also used as an antimicrobial agent—it can penetrate food packaging and sterilize the contents—and it is used in tanning beds and salons. On the other hand, acute UV exposure can cause eye and skin damage in humans, and long-term exposure has been found to cause elastosis (loss of skin elasticity) and skin cancer in humans. The sun is the major source of UV radiation.

Lasers, one type of nonionizing radiation device that operates at below UV frequencies, are used for a variety of important scientific and industrial processes, but inappropriate exposures can cause severe injuries in humans. Infrared radiation, which can be used in home electrical appliances, welding, furnaces, and foundries, can cause skin and eye damage through excessive heating.

Lower-frequency nonionizing radiation, such as microwave, radio frequency, and ELF radiation, have many beneficial uses—such as tracking radar, weather radar, microwave ovens, radio navigation, satellite communication, broadcast radio and television, and a variety of other communications devices including two-way radios and cellular phones. Acute effects from direct exposure to high levels of this type of radiation can include severe burns, electric shocks, and even death. The human health effects of chronic exposure to these types of radiation are less clear. The higher frequencies in this range, such as microwaves, may cause adverse heating effects. The majority of studies, which have focused on exposure to ELF radiation, have examined cancer, adverse reproductive outcomes, neurodegenerative diseases, and cardiac abnormalities. However, difficulties in conducting these studies, including defining and measuring the biologically relevant exposure and variation in subjects' responses, have left substantial uncertainty.

The most effective means of preventing exposure to most types of nonionizing radiation is to maintain a safe distance from the source. Other means of preventing or limiting exposure, such as using shields, are far more difficult and costly, particularly as the size of the source increases. Unlike ionizing radiation, nonionizing radiation penetrates through most materials relatively unchanged. Special metallic grids can be designed to exclude radiation of particular frequencies, but this is not currently practical, physically, for handheld devices such as cellular phones and two-way radios, and is very onerous for large-scale implementation, such as around houses or buildings.

Daniel Wartenberg

(see also: Electromagnetic Fields; Radiation, Ionizing )

Bibliography

Ducatman, A. M., and Haes, D. L., Jr. (1994). "Nonionizing Radiation." In Textbook of Clinical Occupational and Environmental Medicine, eds. L. Rosenstock and M. R. Cullen. Philadelphia, PA: W. B. Saunders Company.

Michaelson, S. M. (1975). Fundamentals and Applied Aspects of Nonionizing Radiation. New York: Plenum.

Wilkening, G. M. (1991). "Nonionizing Radiation." In Patty's Industrial Hygiene and Toxicology, eds. G. D. Clayton and F. E. Clayton. New York: Wiley.