Thanks, Callum.

It is a common misconception that B12 is obtained from soil bacteria. The fact is that it can only be made in the guts of certain animals (not us, sadly) by certain bacteria. It then migrates from gut to muscle. Therefore ruminants are a particularly good source. But interestingly, so too are shellfish. Eating dirty plant foods, with or without chemical contamination, will give you no B12 whatsover.