Young blades of the giant brown marine alga Macrocystis, are shown to be potential monitors of rapid changes in coastal sea water plutonium concentrations. Choosing blades of the same age, and normalizing their activities to unit surface area, rather than weight, provide a method for monitoring plutonium trends with time. When greatest sensitivity is required, a factor of 4 may be gained by choosing the oldest blades. Polonium and plutonium accumulate on surfaces of several algae in a ratio of about 200. Small surface living animals, bryozoans, build up polonium with preference to plutonium by 1000, and have activity concentrations only 50 times less than the 75,000 pCi/kg typically found in the pyloric caeca of large marine fish.
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