According to the Center for Research on Globalization: Fukushima Radiation Levels Will Concentrate in Pockets at Specific US and Canada West Coast Locations
This is explained by Audrey Garric at le monde on 29 Oct 2013 (also Le blog de Wendy)
"These rates, which are about ten times higher than before the Fukushima disaster, are still very low.
le monde / Le blog de Wendy
1. That's one isotope of one element, cesium 137. And levels have been higher than ten times above normal, earlier in this crisis. (much higher)
2. Cesium 137, cesium 134, iodine 129, iodine 131, and tritium, are being produced still by the melted down cores of reactors 1 and 2. And they escape with water vapor or with flowing water.
3. These, and strontium 90, accumulate in living creatures.
The damage done from INTERNAL radiation is much greater than what you get from external sources.
4. The uranium and plutonium that has burned and become dust, is inhaled and is carcinogenic.
5. Chernobyl has killed a million people so far, and Fukushima was a hundred times worse, as of October 2011, said a Woods Hole Oceanographic Institution study.
6. Fukushima's reactors one and two, at least, are still fissioning in the ground, still adding to the contamination.
At present only the Japanese appear to be exposed to a substantial dose of radiation from Fukushima.
However, if one of the spent fuel pools overheats and the fuel is vaporized, the hazard will go global.