Radiation emitted by the Fukushima plant include the following four types: iodine-131, cesium-137, strontium-90 and plutonium-239.

Iodine-131 causes thyroid cancer, even with the smallest of amount of exposure.

Strontium is similar to calcium, so the body absorbs it into the bones thinking it is calcium.  Strontium can remain in your bones for years, and can cause cancer like leukemia.

Cesium is like potassium, in that it circulates to every part of the body. It causes cancer in your body’s organs.

Plutonium-239 is what makes up most of a nuclear fuel rod. Causes lung cancer.

All these radiations are active for years. Plutonium is active tens of thousands of years. This is why the area directly surrounding Chernobyl is still off limits, since 1986. Also, there are islands that had been used in nuclear testing during the Cold War, that are still off limits.