On Mon, 28 Sep 2009 15:01:41 -0700, "Bob F"
wrote:

OhioGuy wrote:
They use copper napthenate to treat the lumber now, not the copper
arsenate they used until about 5 years ago. Copper arsenate was made
with - you guessed it - arsenic. Toxicology reports would suggest
that the old style was about 12 times as likely to cause problems as
the newer ones.
That said, you can always line the wood with something, like
plastic, or even sheet metal.

Upon inspection, the first bed I built with the old treated wood and lined with
rubber floor mat material is rotting where the rubber is pressed against the
wood by the soil. Pull the rubber back, and there a gaping holes visable in the
wood. The outside of the wood shows little damage. I am not sure whether wood
exposed directly to the soil would have rotted as much.

My understanding is the treating chemicals prevent insect damage but
do little if anything to prevent dry rot from constant exposure to
moisture.