ST. PAUL, Min. (MNN) -  Trace amounts of radioactive material have been found in air samples in three Minnesota cities.  State health officials say the trace amounts are likely coming from the damaged nuclear power plant in Japan, but the amounts are well below levels that would be considered a health concern.  Air samples taken in St. Paul, Monticello and Red Wing in March detected very low concentrations of a nuclear fission byproduct called Iodine-131.