German authorities disclosed the weekend arrest of a 34-year-old man for smuggling weapons-grade plutonium into Bremen, the fourth seizure in a widening scandal traced to ex-military contacts in the former Soviet Union. Last weekend police arrested other couriers who arrived on a flight from Moscow. They were carrying more than 10.6 oz. of plutonium-239, a substance so toxic that a few millionths of a gram can kill. Another seizure netted 4 kg, the largest amount ever discovered in private hands. Though German analyses reportedly show that all the plutonium came from the former Soviet Union, red-faced officials in Moscow today denied it, claiming "no leak" had been detected. Unconvinced, Chancellor Helmut Kohl plans to send his national security adviser east for a chat with Russian President Boris Yeltsin.