Tracking Fukushima radionuclides: A research cruise in Japanese waters

Nicholas S. Fisher and Ken O. Bueseller report in the Bulletin of the Atomic Scientists

"...Without direct measurements of radionuclides in the ocean waters east of Japan, it is impossible to assess which isotopes are most abundant and which may pose risks to marine life or human consumers. Based on studies of previous releases into other coastal waters -- for example, intentional discharges from the Sellafield nuclear reprocessing plant in the United Kingdom, and accidental releases associated with the Chernobyl disaster -- it is likely that naturally occurring radionuclides, such as potassium 40 and carbon 14, will dominate the radioactivity in marine organisms. For example, fish muscle tissue normally contains potassium 40 levels of about 93 millibecquerels per gram (wet weight), carbon 14 of about 15 millibecquerels per gram, polonium 210 up to 5.2 millibecquerels per gram, and about 1 millibecquerels per gram each of uranium 238 and rubidium 87. By comparison, fish exposed to Sellafield effluent in the Irish Sea display cesium 137 concentrations of less than 2 millibecquerels per gram. Among the anthropogenic radionuclides of interest, cesium concentrates principally in muscle, while strontium and transuranic elements (such as plutonium and americium) concentrate in bone.

It is anticipated that for most locations the doses to humans from naturally occurring radionuclides, even for avid seafood consumers, will exceed those from the radionuclides released by the Fukushima accident. Near Sellafield, for example, doses to humans from naturally occurring radionuclides in seafood caught in the Irish Sea are about an order of magnitude higher than doses from artificial radionuclides. Total collective dose rates from natural radionuclides via marine pathways on a global basis are four orders of magnitude higher than collective doses from Chernobyl radionuclides. Even in the Baltic and Black Seas, the marine waters most contaminated by Chernobyl fallout, natural radionuclides provide a much larger collective dose to seafood consumers than do Chernobyl radionuclides..."

~ Source: Fukushima: What don't we know? ~