How are permissible exposure limits determined if you of course can’t test dangerous substances on people?

Question

I am doing some research on the toxicity of a particular ‘mildly neurotoxic’ gas and I can’t quite find how the permissible exposure limit is determined. I can find research on acute exposure LC50’s in mice and rats, but an acute LC50 is of course very different from the concentration at which irreversible health effects start to occur after years of exposure.

Obviously you can’t place a number of humans in a room with a substance for several years and see what happens, which led me to wonder how these limits are set.

In: Biology

Answer 1

There were a lot of human LD50 tests performed in the late 1930’s through the early 1940’s in a certain European country…