Can concrete blocks be used safely as a border for a vegetable garden?

to be exact in answering what concrete blocks?

I have never heard that. I think they would be fine to use and I'm almost positive we have put tomatoes in flower beds with concrete block borders.

Its only concrete and maybe a bit of lime and mineral salts might leach out. Never heard of them being treated.... now pallet wood or railroad ties, or tires is another story.

https://www.youtube.com/watch?v=_V87w5KgPrM

I can't see why not and you can plant in them herbs that you want to keep from going all over the place,just don't let them reseed. You can use them in natural state don't paint them because then that's a different story. I think that if you planted the flowers that deter animals from eating your garden up that it would be great.

I don't see why it would be different than pavers or other tiles used as edging. Concrete is just sand and dust you add water to form concrete.

Regular block's are fine but I wouldn't used colored block's. No telling what's in the dye.

The only issue might be changing the ph of the soil... check it since ph controls availability of nutrients to plants