This news article (which refers to this study (PDF)) about radioactivity from Fukushima found in bluefin tuna says there’s nothing to worry about. Whether or not that’s true, what I’d like to know is whether all kinds of radiation that might turn up in our bodies are the same, with the same health implications.
The news article says:
For instance, a typical 200g restaurant serving of Fukushima-contaminated Pacific bluefin tuna would deliver only about five percent of the amount of radioactivity one would get from eating an uncontaminated banana, which contains natural amounts of radioactive potassium.
And the study’s abstract says:
The additional dose from Fukushima radionuclides to humans consuming tainted PBFT in the United States was calculated to be 0.9 and 4.7 μSv for average consumers and subsistence fishermen, respectively. Such doses are comparable to, or less than, the dose all humans routinely obtain from naturally occurring radionuclides in many food items, medical treatments, air travel, or other background sources.
My question is this: Is the dose of radiation the only issue to consider, or is the source of radiation – say, potassium vs. cesium, or air travel vs. contaminated food – also an issue? I want to know if we’re really comparing apples to apples when we compare fish to bananas.
There are several different types of radiation - alpha, gamma, etc - that vary in their danger, but when comparing a single type, the dose is all that matters. Source is irrelevant.
For internal (ingested, etc.) sources, the element in question can matter. Iodine holes up in the thyroid. Calcium in bones. A fixed dose of these will have different implications than, say, potassium-40 which goes all over the body. In the study you linked to, the isotopes in question are cesium-134 and cesium-137, both beta emitters. These can be reasonably compared to potassium-40 in terms of biological effect for a given dose. The article also makes comparisons to polonium-210, an alpha emitter. Alpha particles are more biologically damaging than beta particles (electrons). The article, though, makes appropriate adjustments for this by reporting doses in terms of sieverts (Sv), a unit of dose that has a weighting factor folded in that accounts for the different biological impact of different radiation types.
To expand a bit on what Pasta said, the element itself matters when talking about ingested radioactive particles.
Different isotopes emit different sorts of radioactive particles, with alpha particles being more damaging when inside cells than beta or gamma.
The radioactive isotopes of some elements are taken up by the body and concentrated in bones and other organs- Radium and Radon are notorious for this. They basically sit there and emit radioactive particles as part of your body, and constantly irradiate the surrounding tissues.
Yeah, sieverts aren’t actually a measure of radiation per se, they’re a measure of how dangerous radiation is to the human body. Now, there are always complicating factors, of course (it’s biology, after all, and biology is always complicated), but if you’re looking for one number that compares how bad two sources of radiation are, sieverts are about the best you can do.
Thanks for the answers so far. Another thing I don’t understand about comparing potassium and cesium is that it seems the level of potassium in the body stays fairly constant (Wikipedia citation). I’m guessing this is not true for cesium? So that extra radiation would hang around longer?
I don’t think the trees intentionally concentrate radioactive isotopes. It’s just that they have very large and deep root systems, and they inadvertently absorb a lot of radium, some of which ends up in the nuts. Note that it’s probably not a significant hazard, unless you eat pounds of the nuts every day.
I may be a bit fuzzy on some of this, but here goes anyway:
Some of this involves how the body deals with chemicals. One of the dangers of radioactive iodine is that the body uses it just like non-radioactive iodine, which becomes concentrated in the thyroid, which is why radioactive iodine increases your risk of thyroid cancer more than the risk of other sorts of cancers. Your body tends to treat cesium much as it treats potassium due to chemical similarity (if I’m understanding this correctly). Radioactive cesium tends to displace potassium, and can hang around due to the body trying to use it. Cadmium is toxic whether radioactive or not due to tending to displace calcium in the bones.
So, if a radioactive element is either one the body uses, or chemically similar to it, then it’s more likely to be absorbed into the body and hang around than a chemical that is more inert/useless to your body that is more likely to simply pass through your system and exit.