Submitted by Furrypocketpussy t3_y2nydl in askscience
I just learned about the synthesis of triiodothyronine and thyroxine and it got me wondering what benefits does iodine have against radiation exposure? Like when people in Chernobyl were given them
It's a bit like giving ethanol for methanol poisoning then?
I think the principle is similar with a caveat. The Thyroid doesn't differentiate between radioactive Iodine and the non-radioactive one when it absorbs it (I could be wrong. I assumed that radioisotopes are biologically processed the same).
On the other hand, there is a higher preference for Ethanol to be metabolised rather than Methanol.
From my knowledge of biochemistry (and chemistry in general), this is correct, there isn’t any difference in how biological systems handle different isotopes of a given element, with the notable exception of hydrogen isotopes, which are apparently different enough from each other atomically that they have notably different effects on biochemistry (in particular, an organism that is given only heavy water in lieu of regular water will eventually become “deuterated”—meaning that the majority of its hydrogen-1 is replaced by hydrogen-2 or deuterium—and suffer a variety of symptoms strikingly reminiscent of radiation poisoning, even though deuterium is not itself radioactive, before eventually dying, apparently because the added mass of deuterium just throws off a bunch of key cellular processes enough on a molecular level that basic enzymes don’t work correctly; note that this doesn’t happen just from consuming small amounts of heavy water, which is actually considered non-toxic on its own, just so long as most of the water you’re consuming has H-1), but this is the one unique exception to my knowledge (at least this is what my chemistry professor claimed).
EDIT: I looked more into this, and it does indeed appear to be the case, as there have actually been studies with oxygen-18 (which like hydrogen-2 is to hydrogen-1, is a rarer, heavier, but non-radioactive isotope of oxygen that makes up something like 0.2% of Earth’s atmosphere) which have shown that aerobic organisms can safely breathe it exclusively with no ill-effects, unlike replacing an organism’s water intake with heavy water. So essentially, biology really doesn’t distinguish between isotopes, and it usually doesn’t matter unless it’s a heavier isotope of hydrogen, or a given isotope is giving off ionizing radiation.
Thank you for confirming. Interesting to know about Hydrogen isotopes though. Knew that H2O and D2O differ quite a bit in chemical properties but never knew how much magnified it is at the biochemical scale.
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>So essentially, biology really doesn’t distinguish between isotopes, and it usually doesn’t matter unless it’s a heavier isotope of hydrogen, or a given isotope is giving off ionizing radiation.
It's true that biology doesn't distinguish between isotopes on a biochemically-relevant level (except, as you mentioned, in extreme examples like if an organism was exposed solely to heavy water), but isotopic discrimination is strong enough that it can be used to track large-scale, long-term changes in biogeochemical cycling. One prominent example is the use of isotopic signatures to differentiate between CO2 of organic vs nonorganic origin, which is a crucial piece of evidence in showing that modern CO2 concentrations are rising due to the burning of fossil fuels and not volcanic activity. Plants which use C3 photosynthesis also have a different 13C:12C ratios than those which use C4 photosynthesis, since the former's carboxylation reaction takes gaseous carbon dioxide as an input and the latter's aqueous carbonate.
Is that really biological systems distinguishing, though, or is that just human researchers looking at isotope ratios and using them to determine where a given element in a biochemical context came from? Like do plants that use C3 photosynthesis have a different ratio than C4 plants because something about the process causes them to preferentially take in one carbon isotope over another, or is it just because (as you said) they’re getting their carbon from different sources?
>Is that really biological systems distinguishing, though, or is that just human researchers looking at isotope ratios and using them to determine where a given element in a biochemical context came from?
Those are the same thing. The biochemical discrimination is the mechanism that causes the difference in isotope ratios.
However, if you're asking whether the discrimination is teleological in nature - i.e. that it has a biological "purpose" that has been acted upon by selection pressure - then the answer is no, it is not "intentional", but rather a correlate of the differences in photosynthetic strategies that were directly selected for.
Edit: To specifically address the last bit: they're both getting the same atmospheric carbon, just different isotope fractionations of it.
To clarify, I guess what I meant by “distinguish” is whether or not different isotopes behave fundamentally differently as far as biochemistry is concerned (apart from the obvious difference that some are radioactive and give off ionizing radiation that destroys biological macromolecules, etc.), like in the way that different elements do, and the only specific example of that it seems is with different hydrogen isotopes. It seems that basically apart from deuterium, as long as an isotope isn’t radioactive, it can be used biologically just the same as the more common isotope of that element (assuming a biochemically-relevant element here, obviously) without causing any problems.
Although tbf, I guess the comment that started this thread was asking if the human body (in particular the thyroid gland) “knew the difference” between different isotopes of iodine, and I guess sort of what I’m asking here is, do C3 plants take in more or less of a given isotope than C4 plants because something is making a distinction between the isotopes (regardless whether or not there’s a specific “purpose” to taking in more of one than the other), or is it just a side effect of getting carbon from CO2 in the air versus carbonic acid/carbonate in the water?
>To clarify, I guess what I meant by “distinguish” is whether or not different isotopes behave fundamentally differently as far as biochemistry is concerned
I would maintain that if the isotopes are incorporated at different rates (as they indeed are), then they behave differently by definition. I'm not sure what "fundamentally" means here - if you mean "substantially" in the sense of having biological relevance, then I would say no, they do not. But "biological relevance" itself has no objective definition. I could say that they form the same sort of chemical bonds, but that's not actually entirely true, just mostly true, of isotopes.
>or is it just a side effect of getting carbon from CO2 in the air versus carbonic acid/carbonate in the water?
I should specify that CO2 ultimately comes from the atmosphere in both cases. The difference is the carboxylation reaction in C3 plants uses carbon dioxide directly, whereas in C4 plants, CO2 first reacts with water to form bicarbonate before being conjugated to an organic molecule. The relevant factors for fractionation are therefore the diffusion rate of 13CO2 and 12CO2 in the gaseous state, and the preferences for the relevant enzymes for each carbon isotope.
The underlying physical principles are the same here as in the case of neutron-free hydrogen vs. deuterium. The difference is just one of degree. Carbon-13 is 8.3% heavier than Carbon-12, while deuterium is twice as heavy as hydrogen. Moreover, hydrogen atoms (of all isotopes) are commonly transferred between compounds individually, whereas single carbon atoms do not appear in biological reactions. (In the specific case of carbon fixation, the carbon makes up a minority of the mass of the molecule that actually participates in the reaction.) The discrimination between hydrogen and deuterium in chemical and physical processes is therefore as high as it could possibly be for stable isotopes, and the differences in rates between them is therefore maximal compared to other elements. These discrepancies in rates, which differ in relative magnitude direction for different processes, are enough to upset the balance of biological systems if they are supplied with too much deuterated water. However, I also can't say for certain that a biological system supplied with only 13C wouldn't suffer a similar fate. After all, we're comparing the partitioning of naturally-occurring isotopic ratios of stable carbon isotopes to the extreme hypothetical of exposing an organism to pure heavy water.
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Your thyroid gland takes up iodine naturally, and radioactive iodine-131 is a common waste product from nuclear plants. Taking iodine pills in a nuclear emergency basically saturates your thyroid with safe iodine so that it doesn’t absorb iodine-131.
From what I gather, it's technically Potassium Iodide, (KI) rather than elemental Iodine that is prescribed for radiation exposure.
The CDC's page on this goes into more detail.
Basically, it can only protect the Thyroid from injury due to radioactive Iodine. It's ineffective when there is no radioactive Iodine and doesn't protect other organs.
The way it works is by supplying enough non-radioactive Iodine to your Thyroid that it can't absorb any of the radioactive Iodine that you are exposed to.
What the others have said.
BTW, if you have no thyroid, like the distaffbopper, then you don't need to take Iodine because Iodine, radioactive or not, is only taken up by the thyroid.
In fact, after they removed her thyroid, they put her on a low Iodine diet to "starve" any remaining thyroid cells (cancerous or not) and then gave her a dose of Iodine-131. The littlebopper and I had to stay away for a couple of days, and then limit close contact with her for a week or two. We stayed with relatives over the weekend, then I slept on the couch until it was safe to sleep in the same bed.
Always wild to trip over somebody from that other den of iniquity floating around here. Normally I'd just chalk it up to coincidence in usernames, but I'll be genuinely shocked if anybody else on earth uses the term "distaffbopper."
Well, there is another "Dittybopper" here on Reddit, and by coincidence he also shoots muzzleloaders and was also a Morse interceptor, so I had to tack the _05H on my name to distinguish.
Yeah, I'm here now, because apparently I've been shadow-banned on the F-word. I think it was specifically one mod, and he didn't even have the guts to tell me I was banned. Just gave me a 30 day time out, and then it looked like I could post, but I couldn't. Only I could see the posts, and they "fell off" after a day or so.
And yeah, distaffbopper is kind of unique.
Here's why I use it:
https://en.wiktionary.org/wiki/distaff
(also collective) A woman, or women considered as a group.
Iodine is a chemical element that is found in many foods, and it's also added to salt to help prevent goiters. The thyroid gland needs iodine to function properly, and too much or too little iodine can cause health problems. When there is a nuclear accident, radioactive iodine can be released into the air. If people breathe in this radioactive iodine, it can be absorbed by the thyroid gland and cause cancer. Taking an iodine pill helps to prevent this from happening by filling up the thyroid gland so that it can't absorb any more iodine, including the radioactive kind.
Oh interesting. I thought there might be some more systemic effects involved
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Sentient111 t1_is4wsr9 wrote
During a nuclear explosion, one byproduct is radioactive iodine (I-131). This can bioaccumulate in the thyroid and damage it or lead to thyroid cancer. One way to prevent that is to swamp the body with non-radioactive iodine (mostly I-127) so that you don’t absorb the radioactive version.