|MadSci Network: Biochemistry|
Certainly on face value that does seem strange so I did some on-line research on your behalf.
According to Water Industry News' Miguel Llanos at http://www.waterindustry.org, arsenic is the 20th most common element in the Earth’s crust and the 12th most common element in the human body.
This is repeated (in remarkably identical language) in an article from a Mr Jerry Obrist in a Water Utility Council Report found at http://www.a wwaneb.org/articles/2000news/arsenic.html.
In fact I searched several sites and, apart from some spelling "twelfth" and some writing it as I have ("12th"), they all spout the exact same phrase. I can't find one that tells me otherwise. Most of the focus on arsenic relates to water quality and is generally put out by authorities or water quality companies.
My conclusion: Either it's true or the science community has given up on doing it's own research and just "cuts and pastes" info from other peoples articles. I going with it being true (gotta have some faith in the professionalism of my peers).
Still skeptical? Do some further research. A good start for you is http://www.askjeeves.com, as well as the EPA and any health organisations you can think of including the World Health Organisation.
[Moderator's Note: We have a few answers in our archives describing the major elemental components of the human body, and even decribing arsenic's relative standing in this list. In addition, more comprehensive lists can be found on the internet. - Steve Mack]
Try the links in the MadSci Library for more information on Biochemistry.