Radiocesiums (134Cs, 137Cs) in zooplankton in the waters of Miyagi, Fukushima and Ibaraki Prefectures

Concentrations of radiocesium (134Cs and 137Cs) were measured in zooplankton in the waters of Miyagi, Fukushima, and Ibaraki Prefectures from May 2012 to January 2013. They varied from 0.1 to 9.1 Bq/kg-wet, and from 0.1 to 12.8 Bq/kg-wet for 134Cs and 137Cs, respectively. The zooplankton-to-water concentration ratio (CR) of 137Cs was calculated to be 20–1410 L/kg. Export fluxes of 137Cs by zooplankton were estimated to be 13–165 mBq/m2/y. The contribution of zooplankton for the downward transport of 137Cs was at most 18 % of the previously reported export fluxes of 137Cs by sinking particles as obtained from sediment trap observations.