SAN FRANCISCO -- Authorities are planning to test all of the roughly 650 households on San Francisco's Treasure Island for elevated radiation levels due to increasing concern over the discovery of radioactive items buried underground.

The U.S. Navy said in a statement Monday that there are no known health hazards on the island but that it decided to conduct the testing underneath all occupied housing units in response to requests from residents and a recent radiological finding at an unoccupied unit.

Navy contractors retrieved a small radioactive fragment from the front yard of a family home in January. Several other fragments have been found over the last seven years.

The San Francisco Chronicle reports (http://bit.ly/1gvjy9L ) that Navy believes the radiation is left over from the decontamination of ships and other items left behind from a time when the military used radioactive paint.

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Information from: San Francisco Chronicle, http://www.sfgate.com