I'm not a chemist nor physicist nor biologist, but..

What do you mean with "inert"? I'm pretty sure most radioactive elements are quite happy to react with other chemicals, like salt water.

Some of the new compounds will be water or fat solvable, and can find it's way in to our food chain. The gasses and particles from the nuclear tests around the world was also fairly localized, and if something was spread, it was diluted in a vast vast amount of air. Still, there was long lasting effects on humans and animals, some of which we are still discovering.