People are afraid that the radiation from the Nuclear Reactors is going to flush to the United states west coast and kill off vegitation and the animals that inhabit it. Even though its a low amoutnt of radiation it can still cause a dramatic effect.
http://www.cbsnews.com/stories/2011/03/17/national/main20044164.shtml
Why Radiation will not be a problem as this website stated. The website said that the radiation would have to go into the atmospere then fall. By the time that it did this the radiaton would be really weak and not effect anything.