Actually, I remember that on iceland they were injecting CO2 into rock, and it was shipped to them from ... Swicerland, I think, in shipping tanks. It was captured from concrete manufacturing plants, which apparently produce a ton if it. So there you go - cheap CO2 is not a problem

I doubt the amount used in what I presume is a closed system like this will be significant on a atmosphere level, but it could certainly be the source. If nothing else would make a great headline.