The Center for Investigative Reporting has obtained a state health department memo from June that says workers found radioactive shards buried in lawns near apartments on the western side of the island.
State officials said there was no guarantee the area was safe. The memo warned there could still be radioactive waste in the ground where children could uncover it.
Earlier this year, the city of San Francisco sent letters to residents on the island saying low-level radioactivity in the soil did not pose a threat.
Treasure Island resident Andre Patterson says his brother lives right next to where they recently found a highly radioactive hunk of metal. He lives in subsidized housing and says he was never told about these radioactive risks.
"If we put you out here on radiation, and we failed to disclose that there was radiation out here... because I would have never moved on this island here had they told me there was radiation," said Patterson.
The U.S. Navy left Treasure Island in 1997 and it has been cleaning up parcels of contaminated land before turning them over to the city of San Francisco. Environmental advocates say that process is taking a long time because more and more contaminated items are being found.
Saul Bloom from ARC Ecology says the Navy sometimes buried radioactive materials to help train technicians how to find them.
Mayor Ed Lee says these new reports are a concern, but there have been no incidents where residents have discovered these radioactive items, yet. He told ABC7 News, "There are speculative ideas that if you dig up certain areas, you may find something and that's why we insist that the Navy continue making sure all their cleanup efforts are thorough."
More than 500 radioactive fragments have been found by crews since 2011.
ABC7 News reporter Sergio Quintana contributed to this report.