Plutonium in Rocky Flats Freshwater Systems 



D. PAINE 



This study was initiated to determine the behavior of plutonium in the freshwater aquatic 

 environs at the Rocky Flats Dow Chemical plutonium fabrication plant. Golden, Colo. 

 The principal study area included four holding ponds for waste solutions generated at the 

 plant complex. 



Samples of biotic and abiotic components were collected from the spring of 1971 

 through the summer of 1973. These components consisted of sediment, water, seston, 

 zooplankton, fish, vegetation, and small mammals in close proximity to the aquatic 

 systems. Laboratory experiments were performed to quantify field results. Owing to the 

 high variability of plutonium concentrations in the environment, numerous samples were 

 collected and analyzed by a modified solvent-extraction liquid-scintillation counting 

 procedure. 



Sediments were the major site of^^^'^^^Pu deposition. Coring analysis revealed the 

 largest concentrations at subsurface-sediment depths, and thus depth-profile data were 

 used in calculating total inventory. A retention function determined in the laboratory 

 demonstrated a rapid transfer of plutonium from water to sediment. Pond reconstruction 

 during the study period resulted in significant increases in mean-surfaceftop 5 

 cmj-sedimerit concentrations. 



Seston contained 30 to 80% of the '^^^''^^^Pu in an unfiltered water sample. 

 Concentration ratios in seston, ranging from 10^ to 10^ , were higher than those found in 

 marine studies. No vertical distribution of '^^^'^'^'^Pu was noted in pond water. 

 Laboratory experiments suggested active uptake by algae rather than by simple surface 

 adsorption. Zooplankton showed a discrimination against plutonium concentration along 

 the simple phytoplankton-to-zooplankton food chain. Fish flesh and bone showed no 

 levels above minimum detectable activity (MDA, 0.03 d/min per 10-g sample for a 

 100-min count). Vegetation associated with pond sediments contained higher concentra- 

 tion ratios from sediment to aerial portions of plants than previously observed, ranging 

 fromlO"^ to 10-\ 



Although plutonium in the biosphere presently exists at very low concentrations, trophic 

 biomagnification and possible locaUzed contamination may result in increased plutonium 

 concentrations in organisms of higher trophic levels. CycHng processes and biological 

 uptake of plutonium must be understood before environmental releases so that rational 

 assessment of its potential hazard can be performed. The major concern with plutonium 

 is its potential hazard to man. Plutonium could enter man either directly through 

 inhalation of atmospherically suspended material or indirectly through incorporation into 

 his food chain. The inhalation route is considered the most hazardous mode of entry to 

 man (Taylor, 1973). However, the concentration of plutonium in sediments or in aquatic 



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