The cash triggered an alarm when passing through the radioactivity monitoring system inspection process at Pudong International Airport on October 10. The notes contained a high level of radioactivity. They were being carried in the bag of a male passenger. They were found to contain Americium-241 - a highly toxic radioactive substance, according to the Shanghai Airport Entry-Exit Inspection and Quarantine Bureau. Americium-241 has a half-life of 433 years. Furthermore, it promotes the formation of cancer cells because of its radioactivity. If cash is contaminated by radioactivity, it poses a serious threat because banknotes are circulated quickly, bureau officials said. It is also difficult to track the source of contamination during circulation and users are usually unaware of the risks, the officials added. This was the first time that banknotes severely contaminated by radioactivity were found at a Shanghai port, the bureau said. Health products and health cushions, however, have been seized in Fujian and Shandong provinces for having excessive levels of radioactivity. Meanwhile, the male passenger has had his money confiscated, but he has not been arrested and is considered an innocent party in the matter, officials said. Investigation is still under way, but no further details were revealed.