Cesium-137 From Fukushima Meltdown
Good question, but I'm not sure if anyone really knows the answers. The governments of Japan and the U.S. have both been very secretive at best, while an army of propagandists have made it very difficult to distinguish between truth and fiction.

Any health effects are likely to be too small and gradual to make headlines. For example, suppose there was a 1% increase in thyroid cancer in California due to Fukushima radiation. How could investigators prove there's a link with Fukushima radiation?

Adding to the confusion is the fact that the Pacific Ocean and neighboring land masses are being battered by more than nuclear radiation. Ongoing reports of mass dieoffs of various creatures are variously linked to radiation, global warming, pollution or unknown causes. One famous example is the "melting starfish" disease.

A lot has been written about increases in radiation in tuna. For example, see Is Tuna Safe to Eat Post Fukushima?. Some sources say we shouldn't eat any seafood from the Pacific Ocean, period. Others say "Don't worry." The propagandists particularly like to focus attention on radiation that originated from atomic bomb tests.

When investigating the amount of radiation in North America, keep in mind that the levels are presumably increasing, as contaminated water is still being dumped into the sea (hundreds of tons a day, according to some sources).

You can glean more specific information from the Internet, but it's just very hard to know how truthful or accurate it is. I wanted to write an article about this very topic but gave up in frustration. I decided it might be better to wait until there was more irrefutable evidence - like several new extinct species. ;)

You might get a better feel for the potential damage by doing some research on a similar event that has received even less publicity - the dumping of nuclear wastes off the coast of East Africa. For example, read the article You are being lied to about pirates.

Regarding the effects of cesium on human health, you can start with Public Health Statement for Cesium. But you should solicit similar information from several other sources before reaching any tentative conclusions.