Credit goes to The National Pesticide Information Center.
Bacillus thuringiensis (Bt) is a species of bacteria that lives in soil. It makes proteins that are toxic to some insects when eaten, but not others. The proteins are not toxic to humans because, like all mammals, we cannot activate them. Bt is not toxic to non-target wildlife. However, one type of Bt (aizawi) can be toxic to honeybees. Bt is used as an insecticide, typically, for insect larvae. Remember, it has to be eaten to work.
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So, it is already in most soils. Nothing to worry about as far as the bacteria itself getting into your plant and the consumption thereafter. What the mosquito dunks are being held together with would be my concern.
There is 89% of the dunk not being accounted for here. I couldn't find what is holding them together. Not listed on the EPA website. So there is this concern.
Binders aren't subject to strict rules like main ingredients are.
All I can seem to find on it is telling us not to worry but at the same time you certainly don't want to breathe it in or let it come into contact with mucosa.
So either there is an irritant in the binders used to form the dunks or there is some interaction with BT and humans which contradicts the above article.
If I was thinking about using them ,I would want to look deeper into the manufacturing process.
So...inconclusive ,for me at least.