It looks like most evacuated residents of Fort McMurray are able to go back over the next few days, but some people in the most severely burned areas can’t re-occupy their homes even if they look fine, because of contamination due to arsenic and various nasty compounds.
What I do not understand is where did the arsenic come from??? Poisonous compounds I can sort of understand, but arsenic is an element - if it is there now it was there before the fire.
So, any suggestions where the arsenic might have come from?
Chromated copper arsenate is a very common wood preservative. Burning will release the arsenic.
Arsenic is naturally occurring in soil, but not at the levels found in the ash. Most of it has to be from the burning of man-made materials. Fires of this magnitude burn all the hydrocarbon-based materials, leaving the metals.
The arsenic specifically is probably from treated wood.
(ETA like dtilque said)
Some may have come from burning wood treated with copper chromated arsenate wood preservative used in decks, porches, and other outside structures. It’s been discontinued in residential use in the US and Canada since 2003, but it’s still allowed for industrial use, and existing lumber is still in use.
Oh! That makes perfect sense. Thanks!