Freshwater fish in Japan contaminated with cesium, implications for US

More than a year after it was received by the journal, a paper examining the contamination of Eastern Japan's freshwater fish (data taken from the Fisheries Agency of the Japanese government and measured between May and September 2011) was published by Nature.com. Meat-eating fish, classified as Salmonidae, were found to have almost twice the level of radioactive cesium compared to fish classified as Plecoglossidae or plant-eating.

The contamination of freshwater fish was found as far as 400 km south-west from the plant. Japan is characterized by high-density irrigation and canal waterways, ponds, and urban water systems. These conditions could support widespread and entrenched contamination although the researchers say they will have to further investigate how bioaccumulation affects cesium concentration, espcially since the data were gathered under emergency conditions to prevent ingestion of highly radioactive foodstuffs.Figure 3: The isogram map shows average active cesium (quasi-Cs137) contamination level of the Ayu (Plecoglossus) captured in between May and September 2011 on each prefectures in eastern Japan.

"Quasi-Cs137" means that both cesium 134 and cesium 137 are included in this measurement. This isogram represents only contamination in the plant-eating fish. Cesium contamination of meat-eating fish would be about twice as high.

Although some of this fish is too contaminated to be imported directly to the United States or European countries, much of it could be imported, even though it would not be consumed in Japan since their radioactive cesium limit is 100 Bq/kg. This points to the need for proper food testing in the US, lowering of allowable contamination limits, and labeling of food.