Over at
XKCD he's got a very nice chart that shows exactly how 'dangerous' the levels of radiation involved are
click here
Hint: One Chest CT scan is about double the worst daily dosage found within 50km of the affected plants. Most probably levels have been
much higher at the plants - especially inside the containtment buildings but so far this is only a real problem in a
very local area. The traces being found further away from there are more of something to keep an eye on than something to worry about.