I think you have to be careful here. It's entirely unclear how small dose exposure over long times damage humans. There might be a threshold effect: Some people speculated that low doses actually help, as they trigger the DNA self-repair systems. Slightly more, and that self-repair can't help anymore. So 1 Chernobyl might be fine for people further way, let's say, in the US, 2 or 10 or ... and you suddenly get a lot of Cancer deaths.

If you look at what medicine deemed as safe, the limits were reduced every couple of years.