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.

In my case, I simply built my raised bed using concrete blocks, done two
blocks high. I lined it with very thick poly film. In retrospect, I think
if I had it to do over again, I would probably just buy a bunch of ge
silicone II, and apply it with a paintbrush to the inside of the blocks.
The blocks are working out pretty well, though.