Japanese baby milk powder manufacturer Meiji is recalling over 400,000 cans of “Meiji Step” powdered milk after traces of radioactive cesium were detected.

The products were made 3 days after the March 11 9.0 earthquake off the coast of Japan that triggered a devastating tsunami and resulted in one of the worst nuclear disasters in the past 25 years: Fukushima. 

Meiji says it doesn’t know how the cesium got into the powdered milk, but suspects the accident is the source. The cans were packaged in April and distributed in May, before strict restrictions on food and exports were instituted as a result of the radiation disaster. The affected cans expire in October 2012.

In a nuclear accident, radioactive isotopes, which are normally contained inside the fuel rods, may be released into the atmosphere as gases or particulates if the rods are damaged. These can be inhaled or ingested through contaminated food or water. After the accident, radioactive materials like iodine-131, cesium-137 and 29 others contaminated the water, soil, forests and crops for miles around with recent studies suggesting cesium-137 emissions were double initial governmental estimates. Cesium-137 is distributed through the body’s soft tissues, including muscle, but is eliminated faster from the body than other isotopes.

What is concerning for parents is infants are especially susceptible to radiation, as cellular activity is more pronounced and cells are dividing more rapidly. Damaged RNA could be passed down through generations of cells. The length of exposure and contamination determines the risk; prolonged exposure to radiation can damage DNA and cause various cancers including leukemia. Estimates put a few days of consuming contaminated milk powder requires a month to be eliminated from a baby’s system.

Tests conducted on the baby milk powder on Dec. 3 and 4 found Cesium-134 at levels as high as 15.2 Bq/kg, while cesium-137 reached 16.5 Bq/kg. The maximum permissible level for milk and dairy products for infants is 200 Bq/kg in Japan.

The raw milk used in the powder had been produced before March 11 and the water used in the production process wasn’t found to be contaminated, Meiji said. The factory where the baby milk powder is made is about 124 miles southwest of the Fukushima plant. Radioactive barium, cesium, iodine and tellurium were detected March 16 in a radiation plume that was released at Fukushima.

The company says the levels are within safe limits and don’t pose a health risk.