They're not a super strong fertilizer. According to a site I just checked, they're supposed to be a 3.6-0.7-0.45 fertilizer while in shell form, but take a while to break down. Peanut ash is more common and has lower fertilizer values, but is more readily available to the plants immediately.

I wouldn't eliminate the possibility of pesticides, but I wouldn't think there would be much chance of it being present since they grow underground. Most peanuts don't require pesticide, but fungicide treatments is common in commercial growing.