Americans are exposed to increased levels of radiation
BRATTLEBORO -- The average American receives 620 millirems of background radiation every year, as opposed to the 360 millirems as is often stated in the press.
The number has crept up in the last two decades, from 180 millirems to 300 millirems, then to 360 millirems and most recently, in 2006, to 620 millirems.
Two of the major reasons why the average dose has been adjusted is the recognition that radon poses a substantial threat to health, especially in areas where granite is in abundance, and an increase in the number of medical procedures involving radiation.
Many people never reach the average, which includes exposure rates to people who undergo medical treatments with high levels of radiation.
Ionizing radiation, the formation of ions by separating atoms or molecules or radicals or by adding or subtracting electrons from atoms by strong electric fields in a gas, can cause cancer.
Sources of ionizing radiation include nuclear weapons, nuclear reactors, X-rays, CT scans, carbon and potassium in our bodies, cosmic radiation from outer space, ultraviolet light, radon gas and radioactive material in the earth’s crust.
Emissions from coal-fired power plants and smoke from tobacco are also radioactive. Even granite countertops, kitty litter, bathing in a hot spring and bananas can emit ionizing radiation.
An airline passenger flying at an average altitude of 35,000 feet for a period of 160 hours -- about 75,000 miles -- during solar minimum, when radiation is the greatest, would receive an exposure at about the limit of the current acceptable level, according to the Health Physics Society.
But nuclear reactors produce a number of radioactive isotopes not found in the environment, said Ray Shadis, technical consultant for the New England Coalition on Nuclear Pollution, who insisted the Nuclear Regulatory Commission’s policy of including reactor-generated radionuclides as part of the average background radiation is misleading.
"Nature does not expose human beings to the several hundred radioactive isotopes that that are generated by and routinely released from the nuclear fuel cycle," he said. "Downplaying radiation impacts is an essential part of driving down costs in support of the nuclear renaissance. Everywhere else in science there is a growing recognition of incremental biological damage consistent with tiny increases in dose."
There are indications that low doses of ionizing radiation can cause cancer over long periods of time, according to the 2005 Biological Effects of Ionizing Radiation Report VII.
According to the BEIR, background radiation, excluding radon, is responsible for one incidence of cancer for every 100 people over a 70-year lifetime.
That equates to almost 61 million cases of cancer around the world.
Some medical procedures that utilize radiation, such as CT scans, could generate one incidence of cancer for every 300 to 400 procedures, according to the BEIR.
BEIR conducted a comprehensive review of documentation based on the linear-no-threshold risk model. The LNT is based on the premise that risk increases on a linear basis dependent on dosage.
But some experts have questioned the LNT, including Bernard Cohen, a professor emeritus of physics at the University of Pittsburgh, who wrote in "Validity of the Linear No-Threshold Theory of Radiation Carcinogenesis at Low Doses" that factors other than initiating events affect cancer risk.
"Our bodies have biological defense mechanisms which prevent the vast majority of initiating events from developing into a fatal cancer," he wrote.
Our bodies produce DNA repair enzymes, which repair the effects of initiating events with high efficiency, wrote Cohen.
But, he cautioned, "Radiation can alter cell-cycle timing, which can affect cancer development; damage repair is effective only until the next cell division process."
Reducing the amount of ionizing radiation a person is exposed to gives a body more time to repair its cells, wrote Cohen.
Natural background radiation varies depending on location.
Some areas in Iran, Brazil, India, Australia and China have elevated levels.
In Ramsar, Iran, the highest level of background radiation was recorded at 30,600 millirems.
According to the National Council on Radiation Protection, which determines the average background dose, 36 percent of the average background radiation dose is due to medical procedures and 12 percent is due to nuclear medicine.
Radon and its isotope thoron are responsible for 37 percent of the exposure and cosmic and internal sources are responsible for 5 percent.
Soil produces 2 percent of exposure and consumer products produce 2 percent.
Industrial and occupational exposure is responsible for .1 percent, according to the NCRP.
To calculate your average annual dose visit www.epa.gov/rpdweb00/understand/calculate.html
Bob Audette can be reached at email@example.com, or at 802-254-2311, ext. 273.
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