The Bioaccumulation of contamination in plankton, US Armed Forces, 1955

Quote (emphasis added) “Page 59. The problem of radioactive particles falling into the ocean raises the question of their availability to this portion of the biosphere. Plankton normally found in sea water are consumed in large quantities by fish.

These plankton concentrate mineral elements from the water, and it has been found that radioactivity may be concentrated (Page 60) in this manner by as much as a thousand fold. Thus, for example, one gram of plankton could contain a thousand times as much radioactivity as a gram of water adjacent to it. The radioactivity from these plankton which form a portion of fish diet tends to concentrate in the liver of the fish, and, if sufficiently high levels of contamination are encountered, could have a marked effect upon the ecology of an ocean area.

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