436 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



TABLE 8 Median Isotopic Ratios 



(" ^ Pu pCi/g ^ " « Pu pCi/g) in 



Rocky Flats Environmental Samples* 



*Only data in which both ^^'Pu and ^"*Pu were 

 above detectable Umits were included. 



tThe median and confidence limits were calculated by 

 method R^ of Doctor and Gilbert (1977). 



relatively enhanced assimilation of ^^^Pu, compared to ■^^^Pu,into these compartments 

 than into soil. 



Obviously, there are some physical reasons for skepticism regarding data wliich 

 suggest that two isotopes of the same element behave differently in biological systems. 

 The difference in mass between '^■'^Pu and ^^^Pu is less than that between ^^"^U and 

 ^^*U, on which millions of dollars have been spent for enrichment. Alpha-recoil energy 

 from ^^^Pu and ■^^^Pu could displace other atoms from near the surface of a particle of 

 plutonium metal. However, unless the particle is composed of either pure ^^^Pu or pure 

 '^^Pu, there would probably be no preferential displacement of either nuclide relative to 

 their ratio in the original metal. Rocky Flats plutonium metal probably did not contain 

 either pure ^ -^ ^ Pu or ^ ■^ ^ Pu particles . 



However, if a particle of pure "•'^Pu were in some way introduced into an organism, 

 autoradiolysis by this high-specific-activity nuclide might allow relatively fast biological 

 transport compared to ^•'^Pu. This idea is not unprecedented. Rats that inhaled ^^*Pu02 

 and ^"'^Pu02 of the same particle size and crystalline form translocated up to seven times 

 as much ^^^Pu as ^"'^Pu to systemic organs at times up to a year postinhalation (Stuart, 

 1970). Ballou et al. (1973) allowed rats and beagle dogs to inhale Pu02 aerosols of 



