The U.S. Food and Drug Administration (FDA) has issued a warning about Walmart’s popular Great Value Raw Frozen Shrimp, which may be contaminated with a radioactive isotope called Cesium-137 (Cs-137).

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.