Editing Background radiation (section)

===Food and water===
Two of the essential elements that make up the human body, namely potassium and carbon, have radioactive isotopes that add significantly to our background radiation dose. An average human contains about 17 milligrams of [[potassium-40]] (<sup>40</sup>K) and about 24 nanograms (10<sup>−9</sup>&nbsp;g) of [[carbon-14]] (<sup>14</sup>C),<ref>{{Cite web |title=Radioactive Human Body |url=https://sciencedemonstrations.fas.harvard.edu/presentations/radioactive-human-body |access-date=2022-10-12 |website=sciencedemonstrations.fas.harvard.edu |language=en}}</ref> (half-life 5,730 years). Excluding internal contamination by external radioactive material, these two are the largest components of internal radiation exposure from biologically functional components of the human body. About 4,000 nuclei of <sup>40</sup>K <ref>{{cite web |url = http://sciencedemonstrations.fas.harvard.edu/icb/icb.do?keyword=k16940&pageid=icb.page102829&pageContentId=icb.pagecontent270775&state=maximize&view=view.do&viewParam_name=indepth.html#a_icb_pagecontent270775 |title = Radioactive human body&nbsp;– Harvard University Natural Science Lecture Demonstrations |archive-url=https://web.archive.org/web/20150612194741/http://sciencedemonstrations.fas.harvard.edu/icb/icb.do?keyword=k16940&pageid=icb.page102829&pageContentId=icb.pagecontent270775&state=maximize&view=view.do&viewParam_name=indepth.html#a_icb_pagecontent270775 |archive-date=12 June 2015 |url-status=dead}}</ref> decay per second, and a similar number of <sup>14</sup>C. The energy of [[beta particle]]s produced by <sup>40</sup>K is about 10 times that from the beta particles from <sup>14</sup>C decay.

<sup>14</sup>C is present in the human body at a level of about 3700 Bq (0.1&nbsp;μCi) with a [[biological half-life]] of 40 days.<ref>{{cite web|url = http://www.ead.anl.gov/pub/doc/carbon14.pdf|title = Carbon 14|work = Human Health Fact Sheet|date = August 2005|publisher = Argonne National Lab|archive-url = https://web.archive.org/web/20080227103725/http://www.ead.anl.gov/pub/doc/carbon14.pdf|archive-date = 27 February 2008|access-date = 4 April 2011|url-status = live}}</ref> This means there are about 3700 beta particles per second produced by the decay of <sup>14</sup>C. However, a <sup>14</sup>C atom is in the genetic information of about half the cells, while potassium is not a component of [[DNA]]. The decay of a <sup>14</sup>C atom inside DNA in one person happens about 50 times per second, changing a carbon atom to one of [[nitrogen]].<ref>{{cite book |last=Asimov |first=Isaac |author-link=Isaac Asimov |title=Only A Trillion |orig-year=1957 |edition=Revised and updated |year=1976 |publisher=ACE books |location=New York |pages=37–39 |chapter=The Explosions Within Us |isbn= 978-1-157-09468-5 }}</ref>

The global average internal dose from radionuclides other than radon and its decay products is 0.29&nbsp;mSv/a, of which 0.17&nbsp;mSv/a comes from <sup>40</sup>K, 0.12&nbsp;mSv/a comes from the uranium and thorium series, and 12&nbsp;μSv/a comes from <sup>14</sup>C.<ref name=UNSCEAR2008 />