CHICAGO — More companies are recalling tens of thousands of packages of imported shrimp sold at Mariano’s, Kroger and other U.S. stores, including in Illinois and Indiana, because they may contain radioactive contamination, according to federal notices.

AquaStar USA Corp. of Seattle is recalling more than 26,000 packages of refrigerated cocktail shrimp sold at Walmart stores in 27 states between July 31 and Aug. 16.

The company is also recalling about 18,000 bags of Kroger-branded cooked, medium peeled, tail-off shrimp sold at stores in 17 states between July 24 and Aug. 11. The affected shrimp was sold at Baker’s, Gerbes, Jay C, Kroger, Mariano’s, Metro Market, Pay Less Supermarkets, and Pick ‘n Save in Alabama, Arkansas, Georgia, Illinois, Indiana, Kansas, Kentucky, Michigan, Missouri, Mississippi, Nebraska, Ohio, South Carolina, Tennessee, Virginia, Wisconsin and West Virginia.

At the same time, H&N Group Inc., a wholesale seafood distributor in Vernon, California, is recalling more than 17,000 cases of frozen shrimp sold to grocery stores on the East Coast, according to a notice from the U.S. Food and Drug Administration. That recall began on Aug. 12.

The products have been pulled because they may be contaminated with Cesium-137, a radioactive isotope that is a byproduct of nuclear reactions. The risk appears to be small, but the shrimp could pose a “potential health concern” for people exposed to low levels of Cesium-137 over time, FDA officials said.

The FDA issued a safety alert this month warning consumers not to eat certain frozen shrimp imported from PT. Bahari Makmur Sejati, an Indonesian company doing business as BMS Foods. Cesium-137 was detected in shipping containers from the company sent to U.S. ports and in a sample of frozen breaded shrimp.

FDA has also added PT. Bahari Makmur Sejati to a new import alert for chemical contamination to stop products from this firm from coming into the U.S.

It remains unclear how the containers or the shrimp became contaminated. Federal officials said they are investigating and declined to respond to detailed questions from The Associated Press about the source or extent of the contamination.

None of the shrimp that triggered alerts or tested positive for Cesium-137 was released for sale, the FDA said. But other shipments sent to stores may have been manufactured under conditions that allowed the products to become contaminated, the agency said.

Officials with U.S. Customs and Border Protection first detected the potential radioactive contamination in shipping containers sent to U.S. ports in Los Angeles, Houston, Miami and Savannah, Georgia. Customs officials alerted the FDA, which conducted tests of packaged shrimp and confirmed Cesium-137 in a single sample.

Experts in nuclear radiation agreed that the health risk is low, but said it’s important to determine the source of the contamination and share that information with the public.

The level of Cesium-137 detected in the frozen shrimp was about 68 becquerels per kilogram, a measure of radioactivity. That is far below the FDA’s level of 1,200 becquerels per kilogram that could trigger the need for health protections.

It is unusual to see this concentration of Cesium-137 in shrimp, said Steve Biegalski, who chairs the Nuclear and Radiological Engineering and Medical Physics program at the Georgia Institute of Technology. Routine levels detected in shrimp from the Pacific Ocean are about 100 times lower than those found in the BMS shrimp, according to the American Nuclear Society.

“We sometimes can see Cesium-137 from historic nuclear weapons fallout, nuclear accidents such as Fukushima or Chernobyl, but the levels in the environment are super, super, super low right now and cannot explain what’s going on here,” Biegalski said.

___ The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education and the Robert Wood Johnson Foundation. The AP is solely responsible for all content.

ABC7 Chicago contributed to this report.