416 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



Studies were recently begun on wind transport of plutonium in the Trinity fallout 

 zone, where evidence of wind erosion of soil is readily apparent. Although these studies 

 are not complete, several important observations have been made. First, soil flux by 

 surface creep and saltation processes is highly seasonal and has peaked in the months of 

 July and August for two consecutive years of observation. Second, soil particle size 

 analyses on dust-collector samples show major differences in the amount of silt -clay 

 material between study sites. About half the dust material at Area 21 is in the silt— clay 

 size range, whereas less than 1% of collected dust at Area GZ is in the silt— clay size range. 

 These differences become important when coupled with the plutonium concentrations in 

 the various soil particle size fractions (from Table 5). For example, silt— clay material in 

 dust collectors at Area 21 contains over 200 times as much plutonium as the silt— clay 

 fraction of dust samples at Area GZ. 



Summary and Conclusions 



Despite differences in ecosystems and plutonium source, there are several similarities in 

 plutonium distribution between the Los Alamos and Trinity study areas. First, the 

 soils— sediment component contains virtually all the plutonium, with vegetation and 

 rodents containing less than 0.1% of the total. Plutonium has penetrated to considerable 

 soil depths at both locations, although it has occurred much more rapidly and to a greater 

 degree in the alluvial soil at Los Alamos than in the arid terrestrial soils at Trinity. At 

 both locations less than 50% of soil column plutonium inventories was found in the 

 surface 2.5 cm. 



The plutonium penetration depth appears to correspond to the moisture penetration 

 depth in the Trinity fallout zone. This is probably the governing factor at Los Alamos, 

 although storm runoff and accompanying turbulent mixing complicate the process. In 

 Acid— Pueblo Canyon, the bulk of the soil column inventory lies in the lower profiles, an 

 indication of the loss of plutonium from surface layers due to sediment transport. 



The plutonium in most cases was associated with relatively coarse soil size fractions. 

 The silt— clay (<53 /jm) fraction contained relatively little (<15%) of the plutonium, a 

 reflection of the small amounts of this size fraction in study area soils. An exception was 

 in Area 21 at Trinity, where the <53-iLtm soil size fraction contained about 73% of soil 

 plutonium inventories. The importance of these distributional differences stems from the 

 fact that silt— clay soil particles can be transported farther and are more likely to adhere 

 to biological surfaces than larger size fractions. 



Concentrations in herbaceous ground vegetation were generally related to those in 

 soils from all sites. Our data strongly indicate that external contamination of plant 

 surfaces is the major soil-to-plant transport mechanism in these arid systems. The 

 plutonium concentrations in pelt and Gl tissues were related to corresponding soil 

 concentrations at all sites. Over 95% of the plutonium body burden in rodents was 

 associated with pelt and GI tract samples, an indication of the dominance of physical 

 and/or biological processes as the contaminating mechanism. 



Horizontal transport in both areas is dominated by wind- and water-driven processes. 

 At Los Alamos surface runoff water governs the downstream transport of plutonium; 

 indications are that wind is a relatively more important transport vector at Trinity, 



