Pressure treated wood should not be a problem unless you build your hives
out of it or water collects on it (e.g., use of pressure treated wood to
build a barrel to provide water or hive stands that catch water).
Arsenic in pressure treated wood should not be a problem unless the bees are chewing on the wood  or
unless somehow the arsenic is being leached out of the wood into bee food
or water.
 
 
Industrial sources of arsenic emit some very toxic forms as a fine
particulate, so fine it acts almost like a gas.  Arsenic poisoning seems
to occur after long-term gradual accumulation (which may explain the
winter kills) or during very dry periods of the summer.  During wet
summers, less arsenic blows around and less gets taken up by the bees.
Dry years and the bees get it from the air on from plant surfaces where
it is deposited.
 
Arsenic in water is a more obvious route of poisoning, but one that we
only occassionally encounter.
 
Cheers
 
Jerry Bromenshenk
The University of Montana-Missoula
jjbmail@selway,umt.edu