Tobacco and radioactivity

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p1t1o
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Tobacco and radioactivity

Postby p1t1o » Tue Apr 23, 2013 7:11 pm UTC

Hi all,

I have a question that i have found it quite hard to google the answer for - there is plenty of data but I dont think i can get to the bottom of it without some pretty serious digging through piles of some fairly dry journals.

I have heard that tobacco contains radioactive isotopes of I think potassium, taken up from the soil it grows in. I have also heard that this is a significant factor in the carcinogenicity of tobacco smoke, but thats by-the-by.

What i want to know is - does the tobacco plant contain these radioisotopes simply because they exist in the soil it grows in;

Or: does the plant selectively uptake the radioactive form more than the common-or-garden variety, thus concentrating it within the plant to levels greater than that in the surrounding environment?

Thinking of a way for a biological system to do this has proved difficult - does it exist anywhere in nature? The ability to selectively uptake different isotopes?

Thanks :)

Alexius
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Re: Tobacco and radioactivity

Postby Alexius » Tue Apr 23, 2013 7:39 pm UTC

p1t1o wrote:Hi all,

I have a question that i have found it quite hard to google the answer for - there is plenty of data but I dont think i can get to the bottom of it without some pretty serious digging through piles of some fairly dry journals.

I have heard that tobacco contains radioactive isotopes of I think potassium, taken up from the soil it grows in. I have also heard that this is a significant factor in the carcinogenicity of tobacco smoke, but thats by-the-by.

What i want to know is - does the tobacco plant contain these radioisotopes simply because they exist in the soil it grows in;

Or: does the plant selectively uptake the radioactive form more than the common-or-garden variety, thus concentrating it within the plant to levels greater than that in the surrounding environment?

Thinking of a way for a biological system to do this has proved difficult - does it exist anywhere in nature? The ability to selectively uptake different isotopes?

Thanks :)

I sincerely doubt that radioactive potassium is responsible for the carcinogenicity of tobacco smoke. For one thing, it's also pretty abundant in various foods (like bananas) and in the human body. For another, it's not actually that radioactive, with a half-life of over a billion years.

Apparently the dangerous radioisotopes in tobacco are lead-210 and polonium-210, both of which come from small impurities in mineral fertilisers spread on the tobacco crop. On the other hand, the main reason why smoking causes cancer is organic compounds in smoke that bind to DNA and cause mutations.

I don't think there's a way for a biological system to uptake isotopes of elements that heavy with much selectivity. Different isotopes of hydrogen do have different chemical properties, so you could have a biological system that selectively took up deuterium (though I'm not sure if one exists)- but once you get to the size of lead, the effect is negligible.

p1t1o
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Re: Tobacco and radioactivity

Postby p1t1o » Tue Apr 23, 2013 7:55 pm UTC

I'm not too fussed about discussing carcinogenicity, I'm already familiar, and I'm not too sure which element is at the forefront - though you have to admit, inside your lungs is a really bad place to store even really, really low level radioactive dust.

More interested in the biological possibility of selective uptake.

PS: amusingly, a quick google just now turned up the equivalent radiation does from eating a banana - 0.1uSv

PPS: if you're interested, data on the equivalent dose from smoking

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Jorpho
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Re: Tobacco and radioactivity

Postby Jorpho » Wed Apr 24, 2013 3:14 am UTC

p1t1o wrote:More interested in the biological possibility of selective uptake.
That seems mighty unlikely. The separation of isotopes is exceptionally challenging even by artificial means; if there was an efficient way to do it biologically, some folks would be all over that.

I can imagine there might be some very, very slow means of accumulation, but I would think any biome would have to remain undisturbed for a very long time before it became significant.

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sardia
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Re: Tobacco and radioactivity

Postby sardia » Wed Apr 24, 2013 4:27 pm UTC

Jorpho wrote:
p1t1o wrote:More interested in the biological possibility of selective uptake.
That seems mighty unlikely. The separation of isotopes is exceptionally challenging even by artificial means; if there was an efficient way to do it biologically, some folks would be all over that.

I can imagine there might be some very, very slow means of accumulation, but I would think any biome would have to remain undisturbed for a very long time before it became significant.

Wasn't there a plan for plants(the green kind) being used to mine gold? It wasn't very fast, but the cost efficiency was comparable to mining, especially with low yield gold mines.

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gmalivuk
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Re: Tobacco and radioactivity

Postby gmalivuk » Wed Apr 24, 2013 6:56 pm UTC

sardia wrote:Wasn't there a plan for plants(the green kind) being used to mine gold?
As already mentioned, selectively uptaking a particular element (with all of its unique chemical properties) is very different from selectively uptaking a particular isotope, which tends not to involve different chemical properties for any particularly heavy elements, of which gold is one.
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PM 2Ring
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Re: Tobacco and radioactivity

Postby PM 2Ring » Thu Apr 25, 2013 7:30 am UTC

Alexius wrote:I don't think there's a way for a biological system to uptake isotopes of elements that heavy with much selectivity. Different isotopes of hydrogen do have different chemical properties, so you could have a biological system that selectively took up deuterium (though I'm not sure if one exists)- but once you get to the size of lead, the effect is negligible.


The effect's already pretty small by the time you get to carbon, so bio-concentrating particular isotopes of heavy elements is extremely unlikely. I guess there could be an organism that has evolved the ability to selectively take up deuterium (or conversely has the ability to reject it *), but given the low level of deuterium in the environment (and its low toxicity) such mechanisms have a low probability of evolving naturally, IMHO.

Heavier isotopes have a lower average speed at the same temperature (because temperature is a measure of the mean kinetic energy). This has some direct effect on the reaction rate, but more significantly it also affects the vibrational frequency and hence the length & strength of chemical bonds. This effect is significant for isotopes of hydrogen, but quite small for heavier elements.

According to https://en.wikipedia.org/wiki/Kinetic_isotope_effect
Isotopic rate changes are most pronounced when the relative mass change is greatest, since the effect is related to vibrational frequencies of the affected bonds. For instance, changing a hydrogen atom to deuterium represents a 100% increase in mass, whereas in replacing carbon-12 with carbon-13, the mass increases by only 8%. The rate of a reaction involving a C-H bond is typically 6 to 10 times faster than the corresponding C-D bond, whereas a 12C reaction is only ~1.04 times faster than the corresponding 13C reaction (even though, in both cases, the isotope is one atomic mass unit heavier).



* EDIT: I guess all organisms naturally have the ability to absorb small protium (regular hydrogen) compounds (like water) faster than the equivalent deuterium compounds, due to the slower reaction rate of deuterium, and the higher viscosity of such compounds. But I'd be quite surprised if any organisms utilise such effects to either exclude deuterium from their structure or to accumulate it.


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