*Note: My MA is in applied linguistics. Sure, I had high school science and I like to read, but that hardly qualifies me to do more than ask questions and safely operate my microwave oven. If you’re a hard scientist, please feel free to correct any errors in my table.
This post will focus on iodine-131 because it’s become the Charlie Sheen of radionuclides. Iodine-131 is dangerous to living things because it is has highly energetic beta radiation. In other words, it likes to shake its tail feather. Beta radiation from iodine-131 can extend 0.6 – 2 mm. It’s a danger to humans because your thyroid slurps up iodine until its stuffed. Other parts of the body use/absorb iodine, but the thyroid gets its fill first. There’s a pecking order in your body and when it comes to iodine your thyroid is first in line. Unfortunately for us mortals, in its feeding frenzy, the human thyroid doesn’t distinguish between radioactive iodine and stable iodine.
Iodine-131 does have its uses, though. It can be used to treat certain types/stages of thyroid cancer. Getting a little iodine-131 dust on your skin is n reason to panic, as it isn’t rapidly absorbed that way. According to a study by Nyiri and Jannitti (1932), only 1-2% of iodine applied topically is absorbed into the blood stream readily. An additional 8-11% of the iodine applied to the skin will be absorbed into the skin, where it will slowly be released into the bloodstream. 12% of a miniscule amount is...to use a technical expression, “very, very little.”
Breathing in radioactive iodine attached to dust particles and pollen is something that’s been suggested in overseas media. Wearing a mask might protect you breathing in a lungful of pollen and a couple of hitchhiking atoms of iodine-131.
This reminds me of a joke that some BoE members made the other day in the hallway. Right now in Japan, cedar pollen is around its peak. Many people are terribly allergic to the pollen, so they wear masks to minimize their irritation and hay fever. The pollen is so plentiful that it was collecting on the roofs and awnings of buildings in the area. Since the pollen is a wild shade of neon yellow, several teachers made the joke that it was radioactive Godzilla dust, and not pollen at all.
You can see how seriously educators here take the threat of airborne radioactive dust. It’s a non-issue for them at this point.
As I mentioned at the beginning of this post, iodine-131 has a short half-life (roughly eight days). It was already in extremely low concentrations, and continues its rapid decay. Some foreigners in and around Tokyo and Chiba (and their relatives) are worried about recent reports of contaminated water. Admittedly, hearing that your tap water may be contaminated (with anything in however small an amount) is never a reason to celebrate. It’s natural to be concerned, I think. You can’t see it or smell it but you’re told it is there in X quantity.
Maybe the rest of this post will help assuage unreasonable fears by putting the matter into perspective.
The bad news is…if you were exposed to any iodine-131, and you swallowed (water, air, etc), the isotope made its way into your blood (so says Keith Baverstock).
The good news is…even if we assume dose effects to a linear no-threshold model (that is, a constant positive correlation between radiation and risk), your increased risk of cancer from exposure to contaminated tap water is roughly 0.003% for men and 0.02% for women (Hoffman)(It looks like we're all still insurable for cancer, huh?). The influence at this dose is so small, it’s said to be indistinguishable from the normal (random) rate of occurrence in a population. Not only that, but the estimated 0.003% increase in risk for men assumes that you’re drinking 2 L of 200 Bq tap water a day. If you’re over 40, relax-- you’re over 40; you have enough to worry about as it is (try not to light that cigarette, though). If you’re over 40, congratulations…your chances of increased cancer risk from Tokyo tap water seem non-existent (I’m guess that’s got to be the best news that you’ve heard since turning 40). So far, for those of us in and around Tokyo, worrying about low-dose radiation is probably the clearest danger to physical and mental well-being.
It get’s even better (maybe).
The absolute best-case scenario is… being exposed to a low dose of radiation may actually lessen your chances of developing cancer. There’s not a whole lot of evidence for this, and if something seems too good to be true, it probably is...
I’m a cautious guy, so I’m betting that the effect of iodine-131-infused tap water should be null (neither slightly good nor slightly bad). There are simply too many confounding variable to say much of anything about the effects of low dose radiation with confidence.
Am I groundlessly confident? Not really. Am I without concern? My concern is diminishing the more I learn about this (and so should yours!).
First, I should say that I’ve preemptively started on a strict red wine/sake regiment…indefinitely…
That’s got to be reducing my tap water intake, right?
More seriously, though…
I mentioned that Hoffman’s predicted 0.003% increase risk in developing cancer assumes consuming 2 L of 200 Bq of tap water, daily. In Chiba (where I live), the Bq level is significantly lower (0.79 Bq/kg). Even if I “recklessly” drank 6 L of this water, I shouldn’t see anything near as much as a 0.2% increase risk of thyroid cancer from contaminated tap water. Lucky for me, this “risk” is decreasing day-by-day, thanks to iodine-131’s relatively short half-life.
A word of caution, though…
Are you pregnant or preadolescent? Are you an infant or soon-to-be newborn? If so, you should try to avoid drinking contaminated tap water as much as possible. Adolescent development is very sensitive stuff, as you’ve probably heard. If you’re preadolescent and you have to drink the water, don’t panic—your increased risk of cancer (based on the available science) is still very low (but the increase is life-long). The closer to age zero (i.e. fetuses, infants) you are, the more dangerous radiation and carcinogens seem to be. That’s seems pretty intuitive, though.
One thing I was unable to find when preparing this post was this: how quickly is iodine processed by the thyroid? I’m not sure how relevant it is to the discussion of iodine-131, but I’m curious. Is iodine consumption by the thyroid a constant rate, or influenced by exercise, diet, age, gender, genetics, etc? Since metabolic rates differ so greatly among individuals, I’m guessing the rate this fuel is burned by the thyroid also differs…there should be a normal range, though.
If you're using what I've written to make a decision about your health, let me remind you that I'm not a doctor or a scientist, just a concerned reader.
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