MIGRATION OF PLUTONIUM FROM FRESHWATER ECOSYSTEMS 639 



along with a mean weight for each taxon of bird suggest that approximately 5 x 10^ kg 

 of bird biomass moves through the air mass around U-Pond each year. Greater resolution 

 of this annual biomass quantity is limited by the lack of information on the magnitude of 

 bird activity in the pond region. 



Samples of sparrow, swallows, and killdeer (total of 6) were analyzed for whole-body 

 content of plutonium (including gut and contents). Plutonium concentrations ranged 

 from less than 1 X 10~^ to 5 x 10° pCi/g, with swallows showing the highest 

 concentrations. This may be associated with their mud-gathering activities involved in 

 nest construction. The mean of these samples is approximately 2 x 10~* pCi/g. 



An estimation of plutonium exported by birds suggests that approximately 1 X 10^ 

 nCi is removed from the pond each year. The maximum export is approximately 2 X 10^ 

 nCi of plutonium, whereas a minimum annual export is less than detectable. These export 

 quantities are below the estimated amounts of plutonium exported by waterfowl. They 

 also represent less than 1 X 10~^% of the total plutonium inventory for U-Pond. 



Mammals. Mammals (other than man) that contact U-Pond are mice, rabbits, coyotes, 

 and deer. Only mice were sampled from the mammal population and were collected 

 within 10 m of the pond's shoreline. 



The mouse population density around U-Pond is estimated to be not greater than 1 

 per 10 m^, or <6 X 10^ mice in a region around U-Pond that is equivalent to the pond's 

 surface area (~6 X 10^ m^). Since one mouse weighs approximately 2 g (dry), the mass 

 of this population is about 1 X 10^ kg. Whole-body samples of seven mice analyzed for 

 total plutonium showed a range of concentrations from 1 X 10~^ to about 1 X 10° pCi/g 

 (mean, ~5 x 10~^ pCi/g). This suggests that the mouse population may contain a 

 maximum of 1 X 10~^ nCi of plutonium, or a mean of about 5 X 10° nCi. It is not 

 known if all the plutonium found in mice came from U-Pond since there are regions 

 adjacent to the pond that have plutonium concentrations above background levels. 



The coyote population on tlie Hanford Site (600 mi^) has been estimated to be 

 around 300 following spring breeding (Rickard et al., 1977). Occasionally coyotes are 

 observed feeding on goldfish at U-Pond. A contact frequency by coyotes is estimated to 

 be not greater than about 1 per day, or about 4x10^ coyote visits per year. If we 

 assume that each coyote removes 1 goldfish (3 g, dry weight) with each visit, the dry 

 weight of goldfish removed by coyotes each year is about 1 x 10^ g. The maximum 

 concentration of plutonium in goldfish is about 3 X 10^ pCi/g (Table 2), which suggests 

 that as much as 3 x 10^ nCi of plutonium might be exported by coyotes each year. 



Rabbits and deer are seldom observed at U-Pond; less than 50 sightings of either 

 mammal have been made by the study team in over 3 yr. It is hkely that these mammals 

 visit U-Pond to drink water only; therefore we will consider their annual export of 

 plutonium to be negligible. 



It is interesting to note that the largest plutonium export route among mammals is 

 the researcher. During a normal study year, approximately 2 x 10^ kg of samples are 

 taken from the pond, which contains about 2x10^ pCi Pu/g. This "export" quantity of 

 4 X 10'* nCi/yr as research samples appears to be greater than that caused by all other 

 mammals combined. 



Wind. Attempts to quantify the export of airborne particulate plutonium from U-Pond 

 via wind were not made. It would be desirable to have data that express the rate of 

 plutonium movement away from the pond and its shore as airborne particles, but there 

 are many Umitations to this assessment. Sehmel (1977) reports that airborne plutonium 



