Certain raw frozen shrimp products sold in Walmart under the Great Value brand have been recalled after Cesium-137, or Cs-137, was detected in shipping containers at four U.S. ports, according to the Food and Drug Administration.

Some packages of Great Value frozen shrimp sold at Walmart are at risk for potential for Cesium-137 contamination, the FDA says.

The FDA detected Cesium-137, a radioactive isotope, in one shipment of Great Value frozen raw shrimp to Walmart. It said the affected shipment wasn’t sold.