Dursban is a popular home and farm insecticide, used for 30 years. But popularity also is its problem. Targeted for eradication years ago, Dursban survived because it is safe when used properly. Existing regulations on Dursban rely on data from product testing on paid human volunteers given nontoxic doses. The tests show how much Dursban can be ingested without noticeable effect.
Animal tests used to determine safe human exposure levels involve guesswork.
Scientists record the highest tested dose with no effect. This reflects the guesswork of extrapolating animal data to humans. The safety factor is a judgment call, not a scientific need or number. The lower safety factor often leads to higher permitted exposure levels. But pesticide opponents want lower permitted exposure levels so low that pesticide use isn't practical.