been documented by air and soil analyses (Hardy et al., 1972), or has 

 been inferred from records of other bomb wastes. 



Plutonium, similar to many metals, is enriched 1000-fold or more in 

 many plants and animals. It appears to be retained for many years 

 (Olafson and Larson, 1963; Miner, 1964) in larger terrestrial animals. 

 Plutonium appears in the food of the larger marine animals; however, 

 it has been found in much higher concentrations in members of the lower 

 trophic levels. It has not been estabUshed which organs and tissues are 

 involved in plutonium uptake by plankton. It may be that only surface 

 adsorption is involved at these levels. Suggestions of this have come 

 from findings of high plutonium concentrations on certain living and 

 dead surfaces. The highest concentrations so far have been found in 

 the outer 0.2mm layer of giant brown algae (Wong et al., 1972). 



In seawater, the present plutonium-239 radioactivities are only 

 roughly 2% of strontium-90 and cesium- 137 radioactivities. The radio- 

 activity of the shorter Hved nuclide plutonium-238 is at present only 

 2 or 3% of the longer hved nuclide. Dialysis studies in Russia (Zlobin 

 and Mokanu, 1970), suggest that plutonium may exist in seawater as 

 colloidal particles (less than 0.1 to 0.3 microns), unless attached to 

 larger particles. 



Vertical distributions need to be known for chemical budgeting and 

 other purposes, but the vertical distribution of plutonium is not well 

 known. Sensitivity and precision are so low that many earlier measure- 

 ments of deeper waters are suspect. However, there are several indirect 

 measurements that suggest a loss from the upper layers that is more 

 rapid than would occur with a completely passive material (one not 

 associating itself with particulate materials, living or dead). Budgeting 

 of concentrations in the Atlantic Ocean has yielded some scavenging 

 rate estimates (Noshkin and Bowen, 1972). Likewise, some model- 

 fitting of concentrations found by monitoring tissue concentrations in 

 large oceanic fish in the Pacific Ocean has suggested a loss from the 

 upper layers (where these fish live) of plutonium at the rate of half of 

 that present in about 4 years, in contrast with about 10 years suggested 

 for cesium (Folsom, 1972). 



One outcome of recent plutonium studies has been the establishment 

 of a large-scale turnover model for heavy metal nuclides in some special 

 regions of the ocean. These studies suggest that one could follow minute 

 changes for perhaps another decade in the upper layers of the Eastern 

 Pacific Ocean. One now has some idea where to sample in order to 

 detect a relatively small accidental increase of plutonium. The failure 

 of SNAP-9A (in outer space in 1964) introduced about one kilogram of 

 plutonium-238 into the ocean. This roughly tripled the amount already in 

 the ocean (Hardy et al., 1972), and the addition can be measured with 

 present methods. 



34 



