If a factory pours poison into a farmers water source they can already sue, I cannot imagine it would be significantly harder to enable similar regulation for fertilizers and pesticides.
The legal costs would bankrupt most non-corporate farms. (In fact that's what happened - as explained in the link in that comment, many farmers had to settle even if they believed themselves innocent.)
A lawsuit is rarely a good remedy to a problem, between legal costs, the time delay to any rewards, and the overloaded court system strongly encouraging people to settle out of court.
