Americium in the marine environment-relationships to plutonium

The behavior of 241Am in the marine environment, and by analogy other transplutonium nuclides, is compared and contrasted with that of 239,240Pu. Radiochemical data for these nuclides in seawater, sediments, and organisms contaminated mostly by global fallout, are used to generate the ratio 241Am/239,240Pu. It is used as an index of fractionation between Pu and Am. The average value for this ratio (0.20) found in shallow nearshore sediments is proposed as representative by mid-73 of integrated, unfractionated fallout at mid-latitudes in the Northern Hemisphere. No fractionation between Am and Pu has been found in these sediments even under conditions when they are being lost from the sediment following upward vertical migration. Higher ratios in deep ocean water and sediments suggest that Am sinks more quickly than Pu in the water column. Data for some marine organisms, mostly algae, suggest that while Am may frequently be concentrated to a degree similar to that for Pu, some organisms may discriminate against, others in favor of, Am relative to Pu