[Arran]

It's borax based, maybe a boric acid solution, I don't know for sure. I use to have some that I salvaged from a bad cap and stored in a jar, the cap had a dead short so was useless even though it wasn't dried out. If I find it again maybe I will get the liquid analyzed. No it isn't particularly toxic, not to humans and higher animals anyway, but it does kill insects and it does kill mold. The reason it's effective in killing ants is that they can't taste it, so it will mix right into sugar, peanut butter, or other things they like, which, being the community spirited insects they are, will tell the other ants about it and then take some back to the nest.
Regards
Arran