Reuters on the Fukishima crisis:-
Radio active iodine in the sea samples was 126.7 times the allowed limit, while caesium was 24.8 times over. That still posed no immediate danger.
Watch UCL’s Arthur Miller explain the dangers of radiation in the BBC News Special Japan: The Catastrophe
There are two principle radioactive containments and one of them is Iodine 131 which goes for the thyroid that is relatively short lived and will be gone in just a few days. But the real danger is Caesium 137 which goes for muscle and bone. Depending on concentration, it could take a century before it is lowered to 1% of its initial concentration.