Personally i'd just go ahead and use it.You're talking about miniscule amounts of chemicals which're present in soil anyway and unless your plot's in an oxygen tent or something there's all kinds of probably worse stuff floating onto it from planes,cars etc.
Look in edible plants section for thread called pressure treated timber[search thing doesn't work so flick through yourself].
lol. wish I'd checked your response earlier. I went and bought 20 meters of planed untreated timber in the end. If it only lasts a few years then so be it, I'll have time to think about what to do next time round. Just seemed at odds to go with a chemically treated wood, when trying to grow organically. :)
I have been having a look around for "organic" or "eco friendly" wood preservatives to treat it with so might find a solution yet to make it last.
I'll also line the internal walls (run off from weed supressing membrane) so they will not be in as direct contact with the soil as they might have been.
Anyway, just want to get it done now as I'm way behind with things. These should have been sorted in Autumn really.
Thanks for the reply though.
Cheers,
Chappy.