Tuesday, May 3, 2011

Notes About Radiation Exposure

Originally published as a note on my Facebook page Mar 29, 2010

Is any level of radiation exposure "safe"? Is all radiation exposure "harmful". Below I apply a bit of logic and sanity to examining the effects of radiation exposure:

There is no difference between "naturally occurring" and "man-made" radiation exposure at the same level. However, there is a difference between external (radiation source outside your body) and internal (radiation source inside your body) radiation. Internal or external radiation can come from natural or man-made sources. Again, there is no difference between the two, when the dosage and internal/external are the same. In general, inhaled radioactive particles are most dangerous, since they're more likely to get into the blood stream where they can affect any part of the body. Ingested radioactivity is usually not absorbed as effectively and it's less likely to reach as much of the body. Both should be taken seriously. See the "Treatment" section below if you suspect you have received significant exposure,

Radiation comes in basically four varieties:

Alpha - can be very damaging if it reaches living tissue, however, it's easily stopped. A piece of paper or your skin will block almost all alpha particles. It's only a significant health risk if inhaled or ingested in notable quantities.

Beta - can be moderately damaging, but is also relatively easy to stop. It will penetrate slightly below the skin, so external beta sources are similar to a sunburn (for high levels) and the most likely health effects are similar to sun exposure, including possible skin cancer if the exposure is high enough for a long term.

Gamma - X-rays and "cosmic rays" are types of gamma radiation (technically, x-rays and gamma rays are different, but the difference is not important here). Because it's very common and more difficult to block, this is the type of radiation that we hear most about. There is little difference between internal and external exposure to gamma radiation because your skin and clothing provide almost no protection from it. It's a mixed blessing, as most will pass through the body without any effect, but some percentage will interact with atoms in your body. The percentage that interacts with your body can do significant damage in high enough doses.

Neutron - rarely encountered in notable levels outside of a nuclear reactor (or nuclear weapon), but it does exist in low levels in nature. This can cause atoms to split, or absorb a neutron, which may then give off a minute amount of one of the above 3 types of radiation. Most will pass through your body without interaction. Most of the atoms in your body are not prone to splitting, so low doses will have minimal impact on living tissues.

With any of those 4 types, low dose has no measurable effect on your body because most damage will either cause cell to die and be replaced, or your body is able to repair the damage quickly. However, a sufficiently high dose of any type, or an "unlucky hit" from a lower level, can cause more damage than the body can repair, or a type of damage that the body can't repair, thus causing short term or long term damage.

Given the above, it is incorrect to say that all radiation is harmful, as the vast majority of it will either have no effect at all or will do less damage than the body can repair. It's equally incorrect to say that any level is harmless, as an "unlucky hit" from a very small dose can cause a long term problem, it's just statistically extremely improbable.

Below the maximum "safe" levels, you have much better odds of winning a huge lottery jackpot than of having measurable long term effects. Between the maximum "safe" levels, and approximately 500 mSv in less than 48 hours, your chances of both short term and long term effects increase significantly with increasing dosage. Above 500mSv in 48 hrs, your chances of short term and/or long term effects become probable (e.g. at those doses, you're likely to have effects).

Because your body is constantly repairing and replacing cells, the same total dosage received as a lower dosage over a longer time (e.g. 5 mSv/day for 100 days rather than 500 mSv in one day) is dramatically less likely to cause any measurable short term or long term effects.

Clearly, minimizing your exposure minimizes your risk. But also realize there are levels below which the risk is not even measurable. Worrying about exposure below (or even slightly above) the maximum "safe" levels is about as useful as worrying about getting hit by an asteroid or whether the sun will rise in the morning. Likewise, for worrying about brief exposure to higher levels such as receiving a CT scan or PET scan.

A simple analogy:
To put radiation exposure in terms just about everyone can understand, it's a lot like alcohol.

Too much in a short time will make you ill, or possibly kill you. That same amount spread out over days, weeks, or months won't even make you ill. However, too high a level long term can cause problems (e.g. cirrhosis, pancreatitis, cancer, infertility, etc.). Low doses for a long time are not known to cause problems (and at least with alcohol, appear to be beneficial).

In either case, if the dose is below what your body can process and repair any minor damage caused, there are few or no long term effects. If you exceed that level by too much, or for too long, the risks increase with both dosage and duration.

The first thing to know about getting treatment for any suspected radiation exposure is to seek medical treatment and decontamination immediately. If you have reason to believe you've been exposed to more than the maximum "safe" level, do not hesitate, seek immediate testing, decontamination, and treatment. This is particularly important if you may have inhaled or ingested a radioactive substance. Most common radioisotope inhalation or ingestion can be treated, but urgent treatment is critical to effective treatment.

For the two most common isotopes that released in nuclear power plant accidents, treatments are commonly available. For iodine-131 (aka 131I or I-131), treatment is usually done by taking potassium iodide (KI) tablets. This saturates the thyroid with non-radioactive iodine, minimizing the amount of I-131 that will be absorbed. For cesium-137 (aka 137Cs or Cs-137), treatment is usually done with medical grade "prussian blue". Prussian blue binds to many heavy metals, including Cs-137, and carries it out of the body. In both cases, the key is to get treatment BEFORE any significant amount has been absorbed by the body.

Most other radioisotopes can be treated, if treatment begins quickly enough.

Activated charcoal filters are effective at reducing the amount of iodine in air/water, so if your water supply has elevated levels of I-131, a good charcoal filter will help. Air purifiers that use activated charcoal will help remove I-131 from the air.

Charcoal filters will also remove some heavy metals, so they may reduce the level of Cs-137, but unless they've been specifically designed to remove Cs, they are not as effective at removing Cs as they are at removing iodine.

Useful links:
Fukushima FAQ from Woods Hole Oceanographic Institution

This one is easy to comprehend, but some the the technical details are wrong so don't rely on the details. The overview and debunking of false claims are solid. True facts about Ocean Radiation and the Fukushima Disaster

Natural sources of radiation (background radiation and foods):

Another viewpoint (his facts are valid, his proposals may be a little excessive)

MIT Nuclear Science Engineering, useful info on terminology and technical info.

Information on acute radiation syndrome (radiation poisoning):

NYTimes article on effects of low level radiation exposure.

IAEA international reference standards for radioisotope intake limits.

FDA's 6 age ranges and DC (Dose Coefficient) if various isotopes.

LLNL Evaluation of Radiation Doses Due to Consumption of Contaminated Food Items and Calculation of Food Class-Specific Derived Intervention Levels

ICRP Publications (most are not free)

Updated: 2011-03-29 @ 20:30 MDT - added notes about inhalation, ingestion, treatment, and prevention.
Updated: 2011-04-01 @ 09:30 MDT - added link on radiation poisoning.
Updated: 2011-04-01 @ 11:00 MDT - added simple analogy.

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