unless of course you use shelf lives when you add in (not small) amounts of preservatives.
Shelf life boilies, when made correctly, need only tiny amounts of preservatives. The danger only occurs when untrained people decide to make their own and add ridiculous amounts. I also wince at the levels of chemical flavours that are being used by some people - way into the toxic levels I would think.
The most toxic baits being introduced to waters at the moment are coloured maggots. Highly toxic dyes are still being used in spite of decades of evidence warning people against them.