That's almost worse in this context: a place that kills within hours will be shunned quickly after being (re)discovered, after killing only a small handful of p

That's almost worse in this context: a place that kills within hours will be shunned quickly after being (re)discovered, after killing only a small handful of people. Somewhere that subtly poisons over twenty years could blight multiple generations with radiation related illness that a less scientifically sophisticated culture is unable to tie to the materials we hide.