Walmart has recalled frozen, raw shrimp sold in 13 U.S. states after federal health officials warned the seafood could have radioactive contamination, reports the Guardian.

The U.S. Food and Drug Administration (FDA) warned the public not to eat frozen shrimp sold under Walmart's Great Value label could have been exposed to a dangerous isotope in shipping shipping containers, says BBC News. The FDA asked Walmart to pull three lots of Great Value brand frozen shrimp from stores after federal officials detected Cesium-137, a radioactive isotope, in shipping containers and a sample of breaded shrimp imported from Indonesia.

The FDA is investigating reports of Cesium-137 contamination in shipping containers and products processed by PT Bahari Makmur Sejati, doing business as BMS Foods of Indonesia. U.S. Customs and Border Protection officials alerted FDA that they found Cesium-137 in shipping containers sent to U.S. ports in Los Angeles, Houston, Miami and Savannah, Georgia.

FDA officials collected several product samples and detected contamination in one sample of frozen breaded shrimp. The shipping containers and products were denied entry into the U.S.

However, the FDA then learned that Walmart had received potentially affected products imported after the first detection, from shipments that did not trigger contamination alerts.

Walmart immediately recalled the products, a company spokesperson said. 

Cesium-137 is a byproduct of nuclear reactions, including nuclear bombs, testing, reactor operations and accidents. It’s widespread around the world, with trace amounts found in the environment, including soil, food and air.

The level detected in the frozen breaded shrimp was far lower than FDA intervention levels. However, the agency said that avoiding potentially contaminated products could reduce exposure to low-level radiation that could lead to health problems over time.