Assessment of radiocaesium accumulation by hatchery-reared salmonids after the Fukushima nuclear accident

Abstract

To understand the process of radiocaesium uptake in salmonids after the Fukushima Dai-ichi Nuclear Power Plant accident, a lake caging experiment and two captive-rearing experiments with controlled radiocaesium concentrations of water and feed were conducted in and around Lake Chuzenji, central Honshu Island, Japan (160 km from the station). Substantial accumulations of radiocaesium were confirmed in muscle of hatchery-reared kokanee (Oncorhynchus nerka) and masu salmon (Oncorhynchus masou) after release into the cages, indicating that radionuclide contamination of fish is an ongoing process, 1.5 years after the nuclear accident. Two captive experiments, controlling water and feed radiocaesium levels, showed that direct radiocaesium transfer from water (43 mBq·L–1) in Lake Chuzenji to muscle tissue was undetected, at least during the ∼90-day experimental period, whereas a rapid increase in radiocaesium levels was observed when fish were cultured using radiocaesium-contaminated pellets. The results revealed that radiocaesium contamination in salmonids is mainly via the food chain and that direct intake from water via the skin, gut, and (or) gills has no major direct impact on muscle tissue concentrations.