Interaction of Airborne Plutonium 

 with Plant Foliage 



D. A. CATALDO and B. E. VAUGHAN 



The interaction of airborne pollutants with the foliage of terrestrial plants has been 

 investigated from many aspects, including interception, retention, and absorption. 

 Although interception parameters for both gaseous and particulate pollutants have been 

 effectively modeled, the behavior and fate of pollutants, especially particulates, after 

 foliar interception are not known. Particles with diameters of 10 to 200 pm exhibit 

 retention half-times of 10 to 24 days. Direct and indirect data, however, suggest that 

 submicronic particles are more effectively retained on plant foliage than are larger 

 particles. Studies are presented to describe the retention behavior of sub micron-size 

 particles deposited on foliage of bush bean and sugar beet plants. Simulated rainfall \yus 

 used to evaluate retention efficiency. These studies showed submicronic particles to be 

 increasingly less available for leaching with increasing residence time on the leaf; e.g., 

 more than 90% of the foliar plutonium deposits were firmly held to the leaf surface. 

 Retention mechanisms are discussed in terms of leaf morphology and the leaching regimes 

 used. The absorption of foliar plutonium and its subsequent translocation to seed and 

 root tissues were dependent on a number of parameters, including chemical form and the 

 presence or absence of a solution vector. 



The behavior of the transuranic elements in the environment and their potential for 

 transfer in the food chain have been the subject of extensive study over the past 25 years. 

 Although there is a general understanding of many problems concerning atmospheric 

 transport (Slinn, 1975; 1976) and of the behavior of plutonium in specific ecosystems 

 (Nevada Test Site), little is known of the controlling mechanisms that influence the 

 bioavailability of plutonium and the other transuranic elements and their subsequent 

 transfers along the food web to man. With the current stratospheric depletion of fallout 

 plutonium (Bennett, 1976), the importance of the inhalation route to man is greatly 

 reduced. This then suggests that the major sources of transuranic elements in the future 

 will result from resuspension of fallout-contaminated soils on a global basis, resuspension 

 from highly contaminated local sources, accident situations, and low-level releases from 

 nuclear facilities. 



Present radiological safety estimations frequently discount foliar sorption and 

 emphasize the soil-to-root pathway for the entry of transuranic and other radioelements 

 to the food chain (Vaughan, Wildung, and Fuquay, 1976). Typical dose-assessment codes 

 assume a rapidly declining exponential loss of material from leaves (Soldat, 1971). This is 

 certainly not a general situation. It does not apply to the behavior of plutonium aerosols 

 described here and probably applies only to very large particles and to certain gaseous 



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