SYNTHtJJS OF THE RESEARCH LITERATURE 25 



wind transport of soil is highly seasonal and is relatively more important in dry, sparsely 

 vegetated areas than in mesic, heavily vegetated areas. 



In the arid western United States, wind erosion of soil occurs primarily in the spring 

 and late summer months, coinciding with periods of high wind and low surface soil 

 moisture. Studies in the humid soutlieast United States suggest that wind is a minor cause 

 of transport of plutonium in soil (Dahlman, Bondietti, and Eyman, 1976) because of the 

 low incidence of high winds and the heavy cover of vegetation. 



Soil particle sizes and plutonium concentrations in soil affect the importance of wind 

 as a plutonium transport vector. Plutonium concentrations of various soil size fractions 

 can differ by several orders of magnitude and, depending on source characteristics, are 

 generally highest in the smaller size fractions (Nyhan, Miera, and Neher, 1976; Nyhan, 

 Miera. and Peters, 1976; Tamura, 1975; Little and Whicker, 1977). Furthermore, wind 

 preferentially moves certain sizes of soil particles, depending on the physical characteris- 

 tics of soil, the wind speed, and the soil moisture (Beasley, 1972). The relationship of 

 some of these factors to plutonium transport by wind is illustrated for a 1-month 

 sampling period at two locations in the fallout zone at Trinity Site, New Mexico, in 

 Table 1 1. Within 1 km of ground zero, very Uttle of the plutonium activity was present in 



TABLE 1 1 Mass and Plutonium Content of Dust and Soil 



Samples from Two Locations in the Trinity Fallout 



Zone for the Period 7-14-76 to 8-10-76 



*Saltated dust collected in the zone to 15 cm above the ground 

 surface with accumulative Bagnold dust sampler. 



the silt— clay (<53 /jm) size fraction of dust or soil samples. However, about 45 km from 

 the crater along the fallout pathway, a much higher percentage of the plutonium in dust 

 and soil samples was present in this size fraction. These differences demonstrate the 

 potential importance of the relationship of soil particle sizes to plutonium concentration 

 in understanding plutonium transport within ecosystems. Sih-clay particles may be 

 transported farther and are more likely to remain attached to biological surfaces than are 

 larger size particles (Romney and Wallace, 1977; Romney et al., 1963; Little, 1976; this 

 volume). 



Plutonium suspended by wind can be redeposited on soil or intercepted by biological 

 surfaces. Redeposition of plutonium on soils can lead to major changes in the distribution 

 of the element within an ecosystem, as shown by work at the Nevada Test Site (Romney 

 et al., 1963; Essington et al., 1976). These studies showed that plutonium associated with 

 blown sand accumulates around the bases of shrubs where many of the desert life 

 processes function (Romney and Wallace, 1977). Our understanding of soil plutonium in 

 otlier areas and cUmates is Umited. However, the accumulation of plutonium around 

 vegetation clumps (or other natural or man-made obstacles) may be common to all 

 regions where wind is a major soil-erosion agent. 



