What's on your lettuce?

[Bring4th_Austin]

you also have to know his neighbours. and anyone that flies over his crops.

Any sort of runoff or chemical infringement from one property to another is the responsibility of the infringing property to handle, and a good farmer will make sure it is handled. Can't say the same about GMO seeds though, Monsanto seems to even have the judicial system in bed.

Either way, buying certified organic here in the US at farmers' markets (not grocery stores) can ensure that there are no chemical runoffs of any kind, as the inspection is thorough and any sort of infringement is double checked to be taken care of.