There's a good post about EDC's (Endocrine-Disrupting Chemicals) that highlight environmental threats. We don't know really if these chemicals are harmful, but the evidence is mounting.
Deformities, threats to immune system as well as hormone disturbances would be the ones worth keeping an eye on and so far investigations on frog deformities may shed more light on agricultural chemicals interacting with water supplies.
Keeping the endocrine system functioning at optimal level is more important than one might care. Trust us, living with Zaki and CAH made us realize that.
On another note, read about the relationship between the stress hormone, cortisol, hunches and how they may prove better than the brain in identifying threats.