Pesticides are only found in rural watersheds associated with farming and agriculture.

No, that's false. Many farmers use their pesticides on their plants (obviously) as well as small gardeners doing it as a hobby.

Yes you are cute answer theories to explain the colonization of the new world the last great habitable landmass to be occupied by humans focus on the bering land bridge, or beringia, which emerge by siberia and alaska the last ice age.