wrote:

no. chemicals are nasty. use cedar or pine. Ingrid

I'm not convinced that cedar is any safer than PT lumber - the dust is just
as unsafe to breath as the sawdust from PT lumber.

Completely untreated wood doesn't rot very quickly below the water line -
the problem tends to be right at the air-water interface. So, for anything
that will be submerged pine is plenty good enough. For edging, you're
probably best to use an untreated wood, and plan to replace it every 2 or 3
years.
--
derek