A week back, the Seattle Post-Intelligencer featured an article on the mass of debris that is slowly making its way over from Japan. It's possible that some of the debris would be radioactive, but the expert interviewed for this piece felt that the risk would be minimal after almost three years at sea.
The article included an interview with renowned west-coast oceanographer (and editor of the Beachcombers' Alert) Curt Ebbesmeyer, who has studied the effect of currents on everything from bath toys and running shoes lost at sea to dead bodies and severed feet. He and his colleague, Jim Ingraham, are also modeling the path of the debris, using a program that Ingraham originally developed determine the effects of ocean currents on salmon migration. Ebbesmeyer noted that while last month's tsunami was a particularly large one-time source of marine debris, it still pales in comparison to the total amount that is dumped into the ocean on a regular basis.