A naturopath I've consulted with occasionally explained to me once about some of the widespead health issues she treats and their relationship to the long term exposure of pesticides in human physiology. According to her, the mechanism by which at least some pesticides operate is a pathological effect on the innards or 'guts' of the insects. (My understanding from this was it is something like the effect of calcium oxalate crystals in rhubarb leaves on chewing insects, having lethal intestinal results.) Over time, humans repeatedly being exposed to a substance creating this effect in insects, creates a pathological effect on the GI tract of humans. Leaky gut syndrome is an example of the fallout she tells me, though there is a multitude of expressions, many of which can be devastating, especially to infants and children. Children in particular are suffering from conditions, often cognitively related though not excusively, at numbers previously unseen. Given the intestinal tract is the seat of human immunity, and the unique relationship between the gut and the brain (as guts precede brains from an evolutionary perspective) I think compromising that particular area of the body has a particularly damaging ripple effect. Quite a bit of research has been done about the enteric nervous system, and the remarkable relationship between our first brain and our second brain, the first being our gut. Then microbiota fits in there too, as well as epigenetic fallout from long term pesticide exposure.