As we will attempt to demonstrate, many of these factors are likely to be important in restricting the distribution of Pu and slowing its movement into food chains. PRESENT CONDITIONS IN PU-CONTAMINATED AREAS There is at present a large amount of information describing the extent of contaminated areas, concentrations of Pu present, its distribution within the soil profile, and the nature of the Pu There have been extensive studies concern- particles themselves. ing the movement of Pu by wind (Phelps and Anspaugh, 1975; Shinn and Anspaugh, 1975), and although there have been no formal studies on the subject, there is some indication of movement of Pu by surface water. For example, radiological surveys of Area 11 have shown a finger of Pu activity toward the south, beginning to follow a drainage channel from the Pu-valley site. In general, however, these studies have shown that Pu is not evenly distributed in and on the soils but is likely to be concen- trated about the bases of clumps of shrubs, a distribution attributed to movement by wind and entrapment where there is a reduced wind velocity under and around shrubs. It should be pointed out that these conditions have developed over a period of 10 to 20 yrs, depending on the time of initial Pu distribution; these conditions are therefore indicative of what is likely to continue to occur in the future. Tamura (1975) has noted that Pu in the NTS area is probably in the oxide form, that it is associated with the silt fraction of the soils, and that its solubility was very low, less than 0.5%. Its occurrence in the top five cm was shown by Essington et al. (1975). Tamura also noted that the fraction of Pu moved by wind might be tightly bonded with silicate particles rather than as separate Pu oxide particles. 170