106 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



(0.002 iiCxjm^). Biological measurements were made, including vegetation-community 

 structure and biomass; litter mass; arthropod community structure and biomass; and 

 small mammal species occurrence, population density, biomass, reproduction, and whole 

 carcass and organ masses. In addition, small mammals were examined by X ray for 

 skeletal sarcomas, microscopy for lung tumors, and necropsy for general pathology and 

 parasite occurrence. 



Although minor differences in certain biological attributes between study areas were 

 observed, none could be related to plutonium levels. Pathological conditions and parasites 

 were found in some rodents, but occurrence frequencies between control and 

 contaminated areas were similar. No evidence of cancers or other radiogenic disease was 

 found. Tliese observations and measurements, combined with intensive field observations 

 over a period of 5 years, led to the conclusion that plutonium contamination at Rocky 

 Flats has not produced demonstrable ecological changes. Furthermore, the levels of 

 plutonium observed in tissues of plants and animals in contaminated areas were 

 insufficient to produce the doses that would be required to produce obvious biological 

 changes. 



Subcellular biological changes, such as chromosome aberrations, cannot be ruled out 

 at Rocky Flats. Even if chromosome aberration frequencies were increased in the more 

 highly contaminated areas, however, population-level changes would likely not persist 

 because of the surrounding reservoir of normal genetic information. The possibility of 

 long-term biological effects cannot be discounted either, although this would appear 

 highly unlikely, nor can we conclude that a similar level of plutonium contamination 

 spread over a much larger area would be without ecological consequence. The latter idea, 

 discussed by Odum (1963), stems from the fact that population effects in a highly 

 localized area can be readily masked by immigration of unaffected individuals and 

 propagules from the surrounding area, emigration of affected individuals, and gene pool 

 mixing between the contaminated and surrounding areas. Such masking might not 

 operate, at least to the same degree, for a large area. The validity of any future studies of 

 animals in small-size contaminated areas might be increased if a barrier were erected to 

 prevent the animals from moving into or out of the study area. 



Extensive searches for ecological changes in contaminated areas have been carried out 

 at the Nevada Test Site (Wallace and Romney, 1972; Allred, Beck, and Jorgensen, 1965; 

 and Rhoads and Piatt, 1971). In the majority of these studies, however, the 

 contamination consisted principally of mixed fission products, and, except for the work 

 reported by Rhoads and Piatt, the more dramatic ecological effects were generally 

 attributed to nonradiological perturbations. The best opportunities for searching for 

 ecological effects from plutonium alone exist in a number of areas on or adjacent to the 

 Nevada Test Site which have been used for "safety shot" tests. These tests involved 

 detonation by conventional explosives of plutonium in various containment configura- 

 tions. Some 300 acres containing on the order of 10 iiC\ Pu/m^ exist, and a few acres 

 have levels exceeding 6000 wCi Pu/m^ (Wallace and Romney, 1975; Martin and Bloom, 

 1976). Studies of small mammals and grazing cattle in these areas have failed to discover 

 any evidence of radiogenic pathology (Romney and Davis, 1972; Smith, Barth, and 

 Patzer, 1976). Varney and Rhoads (1977) have examined shrubs in areas assumed to have 

 been contaminated primarily with plutonium. Although their data implied that such 

 shrubs had increased frequencies of chromosomal aberrations in comparison to controls, 

 the evidence was not conclusive. 



