Here's a good analysis: http://www.cdc.gov/nceh/radiation/fallout/feasibilitystudy/t...

Check out Table 3.3, which is deposition of radioactive fallout in the continental United States (not worldwide). You'll see that nearly 2,000 times as many Becquerels of radiation from nuclear fallout comes from isotopes other than Cs-137. That's because many of those isotopes are short-lived and so generate much higher doses of radiation.

You'll note that over 4,000 petabecquerels of radioactive nuclides were deposited on the continental US alone through nuclear testing. And that does not include the Pacific nuclear testing, such as Ivy and Castle, where most of the largest tests took place. Nor does it include the impact of Soviet, Chinese, or French tests (which included several multi-megaton tests including significant fission yields which would have produced enormous quantities of fallout).

Remember that folks who were 40 miles away from just one nuclear test, Castle Bravo, suffered from acute radiation poisoning. We haven't seen anything like that happen with Fukushima, because the radionuclide output is significantly different. The fact is that the majority of radionuclides from the Fukushima disaster come from old nuclear fuel, fuel that still contains Cs-137 but where the very much more hazardous short-lived isotopes have already decayed away.

This is in contrast to the situation with Chernobyl where the reactor itself experienced runaway nuclear fission activity before being disassembled by a steam explosion and catching fire, dispersing enormous quantities of extremely nasty isotopes into the air.

This isn't to downplay the seriousness of the Fukushima disaster but compared to what's been dumped into the Earth's biosphere already it's not terribly frightening. We're not all going to start glowing in the dark or growing extra arms and legs from Fukushima.