Using plywood for raised bed borders

Having built one raised hugelbed with 2x4 lumber, I've been considering switching to plywood as I expand to include more beds. The construction should be much quicker and far cheaper than the 2x4 method was. I've made peace with the idea that I'll have to replace the borders every few years; my main concern is that the glues in plywood, which are formaldehyde-based, could release toxins into the soil. The research I've seen so far indicates that formaldehyde is a toxin and carcinogen when off-gassing into areas without ventilation, so is a respiratory concern that doens't really apply here. Of course, most articles are concerned with human risk, not the risk to the innocent tomatoes I will be putting in harm's way. SO...it doesn't seem that I have to worry about it as a soil contaminant, but I'm interested to see what people think on the matter, especially anyone with experience doing something similar or extertise in toxic substances.

Many thanks!

Have you considered hardboard?

http://m.lowes.com/product?langId=-1&storeId=10702&catalogId=10051&productId=3014304&store=1160&view=detail

I use pallets marked HT for heat treated, wired to together and/or slid over the top of long stakes.
Add layers of card board if too much soil is escaping between the slats.
I am pretty relaxed about contaminants compared to most people here but I still cant see paying for and purposefully installing plywood into my yarden.

I hadnt considered many other materials yet. The hardboard looks like it will work almost as well structurally and obviates the toxicity concern rather nicely. Pallets also seem like a decent option, the newspaper in town gives away theirs so I will have to see if those are just heat-treated or not. (At least from this source I can know what was transported on the pallet and probably leaked all over it)