U.S. Customs and Border Protection detected Cs-137 in shipping containers at four ports in the United States. The FDA tested a sample of frozen shrimp from Indonesia’s BMS Foods, which came back positive for Cs-137. No shrimp that has tested positive for Cs-137 has entered the U.S. food supply, per the FDA.

The Food and Drug Administration issued an alert earlier this week about shrimp sold at Walmart over concerns that it could be radioactive. And now more shrimp are being added to the list.

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