Radiation
by JP Saleeby, MD
As a prologue to my larger article on EMF I will discuss some risks inherent to ionizing radiation exposures during daily life activities and during radiological examinations in medicine. There are many sources of radiation and unavoidably we are exposed daily. Some sources are natural such as cosmic radiation from the sun and other distant stars, there is radiation that is under our feet as the earth contains radioactive material in our soil from sources such as uranium and thorium. There is probably not a thing we do today that will not expose us to radiation from the food we eat, cigarettes we smoke and television we watch. The man-made radiation is one we may exert some control over. We will cover the sources and come up with an estimated annual radiation dose that would be considered safe, tolerated and not to be exceed.
Cosmic radiation comes from our Sun and other stars in our galaxy. Fortunately for us, our Earth's atmosphere blocks much of these damaging rays. The closer we are to sea level the better protected we are. At sea level we received annually about 25 mrem. To clarify; a mrem is a measurement of radiation. Roentgen Equivalent in Man (REM) is a rather high dose of radiation exposure, so millirem (mrem) which is a thousandth the dose is used. Those living a mile above sea level will receive twice the dose. When we fly in an airplane the lack of atmosphere between the solar rays and our bodies will increase our exposure drastically, but typically flights are short and a the usual dose rate is 0.5 mrem per hour in flight.
On average we will be exposed to about 30 mrem a year from the soil around us that contains radioactive material. Some places are safer (such as coastal areas) while the state of Colorado can expose an individual to an annual dose that is twice the average (60 mrem). Radon gas (a radioactive gas) that is inhaled gives us an average of about 200 mrem per year per person. Again some areas of the world have higher Radon exposures. There are towns in India and Brazil with rates as high as 1,000 mrem per year. If you are in a high risk area it may be worth you while to have your home checked for this gas.
Even the food we eat has some naturally occurring radiation. Almost all the food we eat contains carbon. Carbon-14 is radioactive as is some small amounts of Potassium which are present in our diet. There are also some plant and animals that accumulate radioactive materials making our intake even higher. On average our dose is around 20 mrem per year. If we are introspective and look at ourselves, believe it or not, we are also radioactive beings. Because we contain within our bodies potassium and carbon-14 and other radionuclides we in turn produce 40 mrem a year, so if you are around other people you expose them as they expose you.
The simple act of watching TV gives you a 1 mrem per year dose. Porcelain teeth and crowns give a dose of about 0.1 mrem/yr. Counter intuitive would be the idea that one is exposed to more radiation living close to a nuclear power plant, but the fact is that this would only raise your risk by 0.01 mrem while those living near a coal fired power plant will receive 0.03 mrem per year on average. This fact is due to the release of uranium and other radionuclides when the coal is burned. For those who have a plutonium powered pacemaker you receive an annual dose of 100 mrem and if your spouse has one you will get a dose of 7.5 mrme from them per year from just being around him/her (don't be alarmed there are less than 100 people in the USA with this type of device).
Iatrogenic radiation (that generated by the medical field on their patients) is probably a major radiation exposure to those that require frequent radiological studies. For example, according to the American Nuclear Society some typical doses from studies are as follows: An x-ray of the arm or leg will yield 1 mrem. Dental x-rays will give you a 1 mrem dose. A Chest X-ray will expose you to 6 mrem. A skull x-ray results in 20 mrem. A CAT scan will dose you up with 110 mrem and a barium enema will give you a whopping 405 mrem.
On average you will probably receive around 300 mrem per year and perhaps more if you are a frequent flyer or unfortunate enough to require a lot of hospital visits and x-rays. Typically naturally occurring radiation gives us a larger dose than our man-made radiation sources in most cases. To put things in perspective, our chances of dying from cancer increases 10% if you accumulate 250,000 mrem over your lifetime. It is estimated that over 3,000 mrem per year over an 80 year period would be required to achieve the accumulated amount to cause this risk. That is a lot of radiation considering in the USA we on average get a dose of 360 mrem a year. So the typical annual dose is still pretty low for most Americans.
References:
http://www.chestx-ray.com/GenPublic/GenPubl.html
http://www.blackcatsystems.com/GM/safe_radiation.html
http://www.nci.nih.gov/cancertopics/causes/radiation-risks-pediatric-CT
http://www.orau.org/PTP/collection/Miscellaneous/pacemaker.htm
(c) 2009
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