Global Research has an essay (linked above) posted on how Fukushima radiation is spreading worldwide. It is a nice overview.
Levels of radiation outside of Japan are still "low" but cumulative exposure from air, food, water, etc will increase risks for cancer, birth defects, immunological problems, etc.
The cummulative and damaging effects of ionizing radiation have been well documented. Here are some relevant cites:
Site dedicated to the subject
here is a link to a research study on the dangers of mixed-oxide fuel