Electromagnetic Radiation

Electromagnetic radiation comes from both naturally-occurring and manmade sources and is generally classified as either ionizing or nonionizing, depending upon the amount of energy carried by the radiation’s wave particles, or photons. The energy level is directly proportional to and often expressed using the oscillation frequency of the photons. Ionizing radiation is that occurring in the high energy ranges – e.g., gamma rays, ultraviolet light, x-rays - which is capable of stripping electrons from atoms struck by the photons. The energy transferred in this reaction can cause cellular damage or other harmful changes in chemical or biological structures.

Nonionizing radiation, on the other hand, is that which occurs in lower energy ranges – generally from the lower end of the ultraviolet spectrum on down. Although generally thought of as safer, there are in some ways more questions surrounding the biological effects of nonionizing forms of radiation. Although we may know a great deal about the benefits and potential dangers of infrared radiation (i.e., heat), we are still learning about the effects of electric and magnetic fields.

Our understanding of ionizing radiation, which led to our understanding of atomic structure, dates back to the late 19^th century. Early experiments led to an understanding of natural sources of radiation, such as uranium and radium, as well as our ability to produce radiation via a high charge electrical field, such as is done today with diagnostic x-ray equipment.

And although there are benefits to be gained from the utilization of ionizing radiation – nuclear fission to produce electricity, x-rays for medical diagnosis, radioisotope therapy for some forms of cancers, etc. – there are also potentially harmful biological effects. When electrons are stripped from atoms within a living cell, the remaining anion is highly reactive and can trigger a series of chemical reactions which damage cellular structures and function. While some of this damage can be repaired, damage to DNA can result in cellular death or can result in changes that lead, sometimes several years later, to the development of cancer.

For this reason, exposures to manmade sources of radiation are typically tightly regulated. Within my own work setting, our x-ray and CT rooms are required to be lead-lined to prevent transmission of x-rays through walls. Personnel are required to wear lead-lined personal protective gear to limit exposure when we must be present in the room for imaging (which is most of the time when taking x-rays), and all staff who use the equipment must wear radiation dosimetry badges, so that our monthly and cumulative doses can be monitored.

Natural sources of ionizing radiation are somewhat more difficult to control and monitor. We are all bombarded with cosmic rays constantly, as these high energy rays can pass readily through buildings. People who fly frequently in commercial jets are exposed to even higher levels, since there is less attenuation by the atmosphere at higher altitudes. Here in New England, the large concentration of granitic deposits are also a terrestrial source for ionizing radiation, as they contain numerous radioactive isotopes, including uranium.

One of the by-products of radioactive decay in granitic substrates is radon gas, which can accumulate in basements with dirt floors (such as my own). Because radon is heavier than air and because it decays rapidly to a solid radionuclide, it can accumulate in the lungs and act as a source of long-term exposure, which can increase the risk of lung cancer. Because Maine has a fairly shallow soil layer overlying largely granitic rock, much of the state is classified as Zone 1 for radon exposure potential by the EPA, which means exposures here are among the highest (http://www.epa.gov/radon/zonemap.html).

Of course, we are almost all constantly exposed now to mandmade nonionizing radiation. Most houses are replete with electronic devices, such as computers, stereos, microwave ovens, televisions, etc. – all of which produce magnetic fields. Most Americans now own cell phones, many use Bluetooth devices to communicate through their phones, and cell towers are continuing to pop up all over the country to expand network coverage. All of these things increase ambient nonionizing radiation levels.

Cell phones, in particular, have been a source of considerable controversy in the last several years, at least since Hardell, et al. (1999) first posited a possible link between cell phone usage and brain tumors. The most recent report on the Interphone Study conducted by the International Commission for Non-Ionizing Radiation Protection Standing Committee on Epidemiology, however, found no association between cell phone usage and an increase in glioma or meningioma occurrence at this time. Although the authors did report some limitations with the study, they noted that the heaviest users were actually more likely to overestimate past usage, which would tend to bias findings toward a positive association (Swerdlow, et al., 2011). Additionally, these findings do not preclude the possibility that an association might become apparent in another 5 to 10 years or longer.

Perhaps the take-home message should be: Don’t be afraid to use your cell phone, but try to turn it off and walk away from time to time.

REFERENCES

Moeller, D.W. Environmental Health, Fourth Edition. Harvard University Press. 2011.

Hardell, L., et al. “Use of cellular telephones and the risk for brain tumours: A case-control study”. International Journal of Oncology. 15(1): 113-116. 1999.

Swerdlow, A.J., et al. “Mobile phones, brain tumors, and the Interphone Study: Where are we now?”. Environmental Health Perspectives. 119(11): 1534-1538. 2011.