The Food and Drug Administration urged consumers to discard certain packages of frozen shrimp sold in 18 states. A food safety expert said the risk to the public was low.

A radioactive isotope known as Cesium-137, or Cs-137, has been detected in some packages of shrimp sold under Walmart's Great Value brand.

The U.S. Food and Drug Administration issued a public warning to not eat certain Great Value shrimp sold at Walmart because of it being possibly linked to contamination with the…