Apparently they have to much treatment on/in them and it will leach out into the soil and could possibly make your veg poisonous! I would think long and hard before using them. If you have to buy them then you could buy untreeted ones for not much more.
Good luck with them.

Ian is right.The old ones were treated with creosote,I think,so not good for veg,or anything else really...

I wouldn't use them as they tend to seep their protective treatment into the surrounding area and poison the ground. But you are able to buy 'new' ones in some areas.