Three US government studies find that the children of mothers exposed during pregnancy to organophosphate-based pesticides, often used on food crops, have lower IQs that decrease in proportion to the mother’s exposure to the chemicals.

http://edition.cnn.com/2011/HEALTH/04/21/womb.pesticide/index.html?hpt=T2
http://www.reuters.com/article/2011/04/21/us-pesticides-babies-idUSTRE73K0VE20110421
http://ehp03.niehs.nih.gov/article/fetchArticle.action?articleURI=info%3Adoi%2F10.1289%2Fehp.1003183