RELATIONSHIP OF MICROBIAL PROCESSES 317 



TABLE 4 Effects of Plutonium at Several Soil Concentration Levels 

 on the Distribution of Microorsanisms in Soil Relative to Controls* 



•*From Wildung, Garland, and Drucker (1973; 1974). 



tPositive sign denotes significant effect. Zero indicates that there was no significant 



effect. 



soil solubility as well as to toxicity. It should also be noted, however, that the effect on 

 respiration rate was dependent on the magnitude of the soil respiration rate in 

 plutonium-treated soil relative to untreated controls, which, in turn, was dependent on 

 the initial level of microorganisms in soil. In soils exhibiting a higher CO2 evolution rate, 

 the reduction of respiration rate due to plutonium amendment was more pronounced. 

 Studies of the toxicity of other transuranic elements to soil microflora have not been 

 conducted. 



Mechanism of Effect. It is important to distinguish, where possible, chemical and 

 radiation effects of the transuranic elements on soil microorganisms to understand the 

 long-term effects of microorganisms on transuranic-element form. Pronounced initial 

 chemical toxicity can result in the development of special pathways of detoxification 

 leading to alteration of transuranic-element form. The lack of chemical toxicity may 

 imply chemical moditlcations of the transuranic elements through interaction with cell 

 metabolites. In contrast, radiation resistance is associated with an enhanced ability to 

 repair radiation damage to key macromolecules without development of new biochemical 

 pathways leading to alteration of transuranic-element form. However, the possibilities for 

 indirect alteration of transuranic-element form would be higher for a radiation-resistant 

 organism than for an organism that did not exhibit either radiation or chemical resistance 

 since, due to competitive advantage, these resistant organisms may be expected to be 

 present in larger numbers than less-resistant organisms where transuranic elements are 

 concentrated, such as in the vicinity of colloids. 



The effects of plutonium on soil microorganisms may be due largely to radiation 

 damage. Schneiderman et al. (1974) measured the effects of plutonium form and 

 solubility on soil metabolic activity and on the types, numbers, and resistance of soil 

 fungi and actinomycetes in soil separately amended with ^.^^Pu (1 to 144jUg/g) and 



