I've read that some advocates of natural therapy caution against eating Brazil nuts because a) many commercial Brazil nut crops are heavily sprayed with pesticides, b) Brazil nuts (and peanuts) seem to be particularly susceptible to fungi, and it's not always evident from the shell or the nut if they have been contaminated. A shame, because otherwise they are a nutritious powerhouse.
The only place I've ever found organically grown Brazil nuts was in a health food store. For those who can find organically grown, that certainly might reduce half the risk.
Sincerely, Tre