More packages of frozen shrimp potentially affected by radioactive contamination have been recalled, federal officials said Thursday.

The U.S. Food and Drug Administration (FDA) issued a warning that Great Value brand shrimp sold at Walmart in 12 U.S. states contained unsafe levels of the radioactive isotope cesium-137.

Specifically, the FDA warns that the main health concern from such long-term exposure to Cs-137 "is an elevated risk of cancer, resulting from damage to DNA within living cells of the body."