Radiocesium monitoring in Indonesian waters of the Indian Ocean after the Fukushima nuclear accident

As data on anthropogenic radionuclide concentrations (i.e., 134Cs and 137Cs) in Indonesian marine environments including the Indian Ocean are scarce, offshore monitoring has been performed in the West Sumatra and South Java Seas. The activity concentration of 137Cs ranges from below minimum detectable activity (MDA) to 0.13 Bq m−3 in the surface seawater of the South Java Sea and from lower than MDA to 0.28 Bq m−3 in the surface seawater of the West Sumatra Sea. The concentrations of 137Cs in the surface seawater of the West Sumatra and South Java Seas are lower than the estimation of 137Cs concentration in the subsurface waters owing to the input of the North Pacific Ocean via the Indonesian Throughflow (ITF). The concentrations of 134Cs in the sampling locations were lower than MDA. These results have indicated that these Indonesian marine waters have not yet been influenced by the Fukushima radioactive release.