Always give your crustaceans a once-over with your handy Geiger counter.

• The U.S. Food and Drug Administration (FDA) issued a warning that Great Value brand shrimp sold at Walmart in 12 U.S. states contained unsafe levels of the radioactive isotope cesium-137.
• Although not enough to cause acute radiation poisoning—which could cause serious health issues or even death—repeated exposure over a long period could increase risk for cardiovascular disease and cancer.
• The agency hasn’t recorded unsafe radiation levels in products sold at Walmart, but did detect the isotope’s presence at four U.S. ports.

Finding radiation in human food can be a pretty natural phenomenon. Bananas, for example, is technically radioactive, as it contains the naturally occurring isotope potassium-40. Luckily, this radiation is not cumulative, and the isotope is typically excreted to maintain the body’s homeostasis. In fact, this is such a well-known source of agriculture radiation that scientists have informally labeled safe radiation levels as “banana equivalent dose” (or BED) for decades.

Other times, however, radiation can enter the food supply in ways that are less than natural.

Earlier this week, the U.S. Food and Drug Administration issued an alert that frozen shrimp originating from Indonesia—specifically from a company operating under PT. Bahari Makmur Sejati, or BMS Foods—tested positive for unsafe levels of the radioactive isotope cesium-137. This is the most common isotope of cesium, and is used in a variety of industrial gauges, Geiger-Muller counters, and radiation therapy devices. But it’s also a byproduct of nuclear fission, and traces of the isotope remain in the environment due to past nuclear weapons testing. The 1986 Chernobyl Nuclear Disaster, for instance, caused widespread distribution of cesium-137 throughout Europe.

The U.S. Centers for Disease Control and Prevention (CDC) says that the isotope is so common that people are actually exposed to it every day at safe levels. However, if you were to ingest a particular package of shrimp sold at Walmart in several (mostly southern) U.S. states—including Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Missouri, Mississippi, Ohio, Oklahoma, Texas, and West Virginia—you’d likely exceed those safe levels after repeated exposure. The FDA is advising customers to throw away any Great Value brand frozen raw shrimp with the expiration date of 3/15/2027.

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.

“FDA has not detected Cs-137 in any product above the current derived intervention levels for Cs-137 (1200 Bq/kg),” the agency wrote. “However, FDA has concluded that the level detected in the breaded shrimp sample could represent a potential health concern for those exposed to this level of Cs-137 from consumption of the shrimp over an extended period of time combined with radiation that exists in the environment and from other sources such as medical procedures.”

Exposure to large amounts of cesium-137 can cause severe burns, radiation sickness, and even death. While exposure to low-level radiation isn’t nearly as dire, it’s not an experience you want to repeat over a long period of time. According to the CDC, the ingestion or inhalation of cesium-137 can distribute the radioactive material to soft tissues, such as muscles. This exposes them to both beta and gamma radiation that can increase cancer risk.

In other words, a bit bigger deal than eating a banana.