Is hafnium a valid surrogate for plutonium for biochemical and biokinetic studies in vivo?

The MINTEQA2 computer code was used to simulate and compare the speciation profiles of hafnium (Hf4+) and plutonium (Pu4+) with citrate, oxalate, ethylenediaminetetraacetate (EDTA(4-)) and diethylenetriaminepentaacatate (DTPA(5-)) over the pH range 2-10. The results show that the speciation patterns of the two metals are similar at the physiological pH of 7.4. The results are discussed in the light of the results of in vivo and in vitro biochemical studies with the two metals. It is concluded that, although the biological behaviour of hafnium does not mimic that of plutonium under all conditions, hafnium could be a useful surrogate for plutonium in studies of gastrointestinal absorption and of clearance from the blood; however, it appears to be less suitable as a general surrogate for biodistribution studies.