The recalled frozen shrimp were sent to 13 different states and were shipped into the country through four different ports.

Although there’s been no confirmation of radiation risk in food purchased at Walmart stores, the FDA said that it has detected unsafe levels of cesium-137 contamination at four U.S. ports. This contamination likely suggests that the shrimp was packaged in unsanitary conditions.

The FDA is currently investigating reports of Cesium-137 radioactive contamination in shipping containers and frozen shrimp products.