# If I ingested 100 molecules of C-14 - what will be the residence time ? **URL:** \ **Category:** Factual Questions\ **Created:** [May 3, 2016, 11:56pm UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828 "2016-05-03T23:56:31Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [May 3, 2016, 11:56pm UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/1 "2016-05-03T23:56:31Z")
So if I were to ingest 100 molecules of say alpha-glucose with one of the carbon atoms in each glucose molecule replaced by C-14, how long will it take for the C-14 atoms to leave the body. I am looking for a cumulative chart like : Day 1 : 100 atoms injested Day 2 : 80 atoms remain in the body, 5 exited through defecation and 15 through exhalation. Day 3 : 70 atoms remain in the body, 7 exited through defecation and 23 through exhalation … … I understand it is dependent on the person - so assume a 30 year old, woman with normal metabolism. ---
**Author:** ![boffking](https://avatars.discourse-cdn.com/v4/letter/b/858c86/32.png) [@boffking](https://boards.straightdope.com/u/boffking)\ **Post date:** [May 3, 2016, 11:58pm UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/2 "2016-05-03T23:58:58Z")
C-14 is unstable. Don’t forget to account for radioactive decay. ---
**Author:** ![lisiate](https://avatars.discourse-cdn.com/v4/letter/l/f05b48/32.png) [@lisiate](https://boards.straightdope.com/u/lisiate)\ **Post date:** [May 4, 2016, 12:33am UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/3 "2016-05-04T00:33:07Z")
With a [half life of 5730 years](https://www.math.upenn.edu/~deturck/m170/c14/carbdate.html)I think we can leave that out of the calculations. It’ll take 83 years for decay to drop the amount of C-14 by 1%… ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 4, 2016, 12:36am UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/4 "2016-05-04T00:36:19Z")
The biological half-life is going to be so much shorter than the radioactive half-life that that’s going to be completely irrelevant, though. And I say that even without knowing just how long the biological half-life is: It’s certainly shorter than 70 years, which is already well short enough. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 4, 2016, 12:38am UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/5 "2016-05-04T00:38:23Z")
And now that I’ve said that, it turns out that “biological half-life of carbon 14” is [easily-googleable.](https://www.google.com/?gws_rd=ssl#q=biological%20half%20life%20of%20carbon%2014) It’s about 10 days. ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [May 4, 2016, 1:34am UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/6 "2016-05-04T01:34:46Z")
> [@Chronos](#): > > And now that I’ve said that, it turns out that “biological half-life of carbon 14” is [easily-googleable.](https://www.google.com/?gws_rd=ssl#q=biological%20half%20life%20of%20carbon%2014) It’s about 10 days. Subject to the circumstances being the same. For example, ingesting elemental C14 blows it out to a 40 day half life. Some extremes… I figure if a person ingested the C14 in sugar and straight away ran a marathon, the half life would be an hour ± an hour… If it was a person who consumed an enormous amount of food each day, and was rapidly gaining weight, then it might be blown out to 10 or 50 years… ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [May 4, 2016, 2:18am UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/7 "2016-05-04T02:18:21Z")
> [@Isilder](#): > > Subject to the circumstances being the same. > > For example, ingesting elemental C14 blows it out to a 40 day half life. Elemental carbon like diamond? I’d suspect that would pass right through the system completely. ---
**Author:** ![Anaglyph](https://avatars.discourse-cdn.com/v4/letter/a/ed8c4c/32.png) [@Anaglyph](https://boards.straightdope.com/u/Anaglyph)\ **Post date:** [May 4, 2016, 7:25am UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/8 "2016-05-04T07:25:36Z")
Given that the natural abundance of 14C is about one in 10 to the twelveth, to ingest only 100 C14-atoms would be extremly difficult - a single teaspoon of sugar contains on the order of 10 million atoms of C14. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [May 4, 2016, 10:36pm UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/9 "2016-05-04T22:36:52Z")
I’m late to this party, so excuse my impertinence: not that GQ OPs ever really have to have a discernible reason, but is there a discernible reason to this OP, leaving aside the quantification of ingestion and actual answers? In other words, is conjecture about ingesting c-14 a thing? For runners? Mad scientists? ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [May 4, 2016, 11:57pm UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/10 "2016-05-04T23:57:27Z")
Leo - I have done several radioactive tracer tests on chemical reactors which give valuable information as to how the reactor is behaving in terms of internal mixing zones and dead zones. Also detect some otherwise undetectable leaks. This is what inspired the question. Incidentally, the half life of 10 days does not answer if the exiting C-14 comes out in farces or exhaled. Thanks ---
**Author:** ![snfaulkner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snfaulkner/32/433_2.png) [@snfaulkner](https://boards.straightdope.com/u/snfaulkner)\ **Post date:** [May 5, 2016, 12:14am UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/11 "2016-05-05T00:14:24Z")
> [@am77494](#): > > Incidentally, the half life of 10 days does not answer if the exiting C-14 comes out in farces or exhaled. > > Thanks I’ve heard bad jokes before, but never RADIOACTIVE jokes! (sorry, i couldn’t resist) ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [May 5, 2016, 1:23am UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/12 "2016-05-05T01:23:06Z")
Sorry - I meant feces. Good catch. ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [May 5, 2016, 2:05am UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/13 "2016-05-05T02:05:39Z")
> [@am77494](#): > > Sorry - I meant feces. Good catch. Catching feces. Not a good idea. ---
**Author:** ![snfaulkner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snfaulkner/32/433_2.png) [@snfaulkner](https://boards.straightdope.com/u/snfaulkner)\ **Post date:** [May 5, 2016, 2:06am UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/14 "2016-05-05T02:06:41Z")
> [@Yllaria](#): > > Catching feces. Not a good idea. Especially radioactive feces. ---
**Author:** ![Carl\_Pham](https://avatars.discourse-cdn.com/v4/letter/c/e9a140/32.png) [@Carl\_Pham](https://boards.straightdope.com/u/Carl_Pham)\ **Post date:** [May 6, 2016, 11:00pm UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/15 "2016-05-06T23:00:25Z")
Glucose is about as digestible as a substance can get. A reasonable assumption is that it will all be immediately absorbed and come to equilibrium with all the various ways in which glucose is shuffled around the body. Assuming you’re normally active, I would expect most of it to be burned in oxidative respiration within hours and exhaled as CO2. A small proportion may be converted to glycogen, which you would burn over a period of days. A very small amount may be converted to fat, which would stick around longer. I wouldn’t expect any of it to end up in poo or urine. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [May 7, 2016, 12:52am UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/16 "2016-05-07T00:52:39Z")
So there’s no carbon-dating–or another similar technique–in physical anthropology at all? But there must be something they do with bone physics, no? Of all the hominid fossils, let alone Egyptian mummies, bog-men, and similar folk. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 7, 2016, 2:12am UTC](https://boards.straightdope.com/t/if-i-ingested-100-molecules-of-c-14-what-will-be-the-residence-time/753828/17 "2016-05-07T02:12:38Z")
Of course there’s carbon dating. Yes, carbon 14 very quickly leaves the body. But it’s also continually replenished. Some fraction of carbon we consume is carbon 14, and that’s going to also be roughly the fraction in our bodies. But after we die, it’s no longer being replenished, and so the clock starts.