glyphosate, which is the main ingredient in RoundUp, Monsanto's GMO pesticide. The use of it per farmer has increased dramatically in the last few decades and it seems likely to be connected with health issues. There's a reason many countries are banning it. The plants are GMO'd to be immune to RoundUp, but human beings are not, which is a problem because it seeps in to the food.

The practice of wheat desiccation (using RoundUp to kill the wheat faster which aids in separating the wheat from the chaff) has increased dramatically in the last 10 years, and it seems likely to me that it's linked to the increase in wheat allergies/intolerance in the US.