The FDA’s investigation was prompted by alerts from U.S. Customers and Border Protection (CBP), which found the radioactive substance, Cesium-137 (Cs-137) in shipping containers at four major U.S. ports in Los Angeles, California; Houston, Texas; Savannah, Georgia and Miami, Florida.

Walmart is recalling three of its Great Value brand frozen shrimp products after U.S. agencies uncovered the presence of radioactive material in one sample of breaded shrimp.

The FDA asked Walmart to recall frozen shrimp over potential radioactive contamination. But what's the real risk level?