TRANS URANICS IN TERRESTRIAL ENVIRONMENT 703 



From field studies in plutonium-contaminated areas, most of the plutonium 

 associated with vegetation appears to be surficial and not incorporated within tissues. 

 Therefore critical tissues (meristem for growth and flower bud for reproduction) may 

 receive a widely variable dose from surface contamination, depending on the location of 

 the material and the thickness of epidermal tissue layers. I am not aware of any studies 

 designed to show the detailed histological distribution of transuranics in and on plant 

 tissues in contaminated-field environments. 



The effective dose to animal tissues is equally difficult to determine. The dose from 

 inhalation and ingestion of transuranics is subject to many variables. Absorption, 

 translocation, deposition, and retention are affected by the physical and chemical forms 

 of the nuclide and physiology of the animal (International Commission on Radiological 

 Protection, 1972). The environmental chemistry of plutonium is extremely complex 

 (Wildung et al., 1977), and our overall understanding is inadequate (Dahlman, Bondietti, 

 and Eyman, 1976). 



A few studies have been conducted in which simulated fallout particles containing 

 beta and beta— gamma emitters were administered to field plots. The studies by Murphy 

 and McCormick (1973) and Dahlman, Beauchamp, and Tanaka (1973) come closer to the 

 kind needed for transuranics in that the problems of dosimetry are circumvented by 

 simply relating effects to the level of fallout simulant applied. Murphy and McCormick 

 applied ^°Y-coated albite particles to experimental granite outcrop plant communities. 

 The effects on the reproductive potential of Viguiera porteri treated with 0, 205, and 526 

 mCi/m^ were measured. Dahlman, Beauchamp, and Tanaka applied ^ ^^Cs fused to silica 

 sand particles to 100-m^ plots in a fescue meadow. The levels applied (22 mCi/m^) 

 caused measurable decreases in seed production of Festuca arunduiacea. A similar study 

 using ^^ Y-tagged sand grains to produce effects on crop plants was conducted by Schulz 

 (1971). Fallout simulants containing ^ ^^Cs were also apphed to field plots at Oak Ridge, 

 Tenn., to study the effects on arthropods and small mammals (Auerbach and Dunaway, 

 1970). 



For research findings to be integrated and understood, however, it is highly desirable 

 to estimate the dose to critical tissues from the levels of simulants applied. In the studies 

 cited, beta-particle doses were estimated by thermoluminescent dosimeters and various 

 computations. The Stanford Research Institute developed fallout-particle simulants for 

 the field studies and measurement and computational techniques for beta dosimetry 

 (Lane, 1971; Brown, 1965; Mackin, Brown, and Lane, 1971). Similar technology could 

 probably be applied to alpha emitters for their use in field studies. 



I am not aware of any studies in which physically and/or chemically characterized 

 transuranics have been experimentally applied to field plots at levels sufficient to cause 

 measurable ecological effects. The safe conduct of such studies would require an area 

 remote from human habitation and stringent health physics practice and cleanup. Such a 

 study would be expensive, possibly hazardous, and difficult to justify. A greenhouse 

 study involving plants growing on soil that has been heavily contaminated with 

 transuranics is being conducted by A.Wallace and E.M. Romney at the University of 

 California at Los Angeles. One of the objectives of this study will be the effects of alpha 

 particles. 



Another investigation that bears on the problem of biological effects of transuranics 

 in the environment is under way at Battelle— Pacific Northwest Laboratories under the 

 direction of R. E. Wildung. Early results indicate radiafion toxicity from ^^^Pu and 

 ^^^Pu to some strains of soil actinomycetes and fungi at levels of 0.7 /jCi/g (soil) 



