Hmmm, interesting. I can see plants accidentally utilizing arsenic in some molecules. It will react similar to phosphorous, but it's a larger molecule, so it could be able to incorporate itself into organic phosphates disrupting ATP production, citrus cycle, glycolysis, and might even work as an inhibitor to some phosphate activated enzymes.
Ah, here ya go. Much better article.
http://medicalxpress.com/news/2011-1...-exposure.html
Basically we know it's there, but we haven't really determined the potential impact (if any) of the As levels. For pregnant women and infants, it's a fairly safe bet even low levels are concerning enough to not eat too much, but for a healthy adult? Don't know. It's As's affinity to oxidate and then react with other molecules that makes it so dangerous, this and it's not part of the human pathways but readily replaces phosphorous which is everywhere. I suspect you would have to have a fairly high level and long term exposure to As to see serious damage. P is even more oxidatively reactive and we have harnessed this to our advantage millions of years ago in our bodies. P also produces more peroxides within our cells than As would also, but we have peroxidase enzymes to counteract these effects.
I would like to see more information from current research on acceptable levels of As ingestion before calling this one alarming. For all we know, rice plants have always had an affinity to absorb As and we have always ingested these levels without any serious health problems. It does beg to have a few questions answered though.