I still encounter, on occasion, animals poisoned by gaining access to old farm outbuildings containing bags/boxes of Paris Green from bygone days when it was used extensively in this part of the country.

As I recall, Paris Green (Copper Arsenate, I believe) was not only used as an insecticide, but also as a paint pigment. Pretty strong poison for those wetting the brush on their lips.

Paris Green was a contemporary of lead arsenate. My father-in-law said he remembered using lead arsenate on squash bugs on the farm when he was a kid.

That was the best insecticide at the time, even though it was terribly dangerous and extremely destructive to the environment. It's no wonder when DDT was introduced, it was viewed as a panacea. Comparatively speaking, it was.