PRDIT § (Vou. 91 1964] MARTIN : RADIOECOLOGY AND STUDY OF ENVIRONMENTAL RADIATION 303 d that most lave a mean retain more emitters which have short half-lives and (b) the long-term hazards associated arfaces. SHORT-TERM ASPECTS OF REDISTRIBUTION AND CYCLING, 1. Soil. Fallout particles deposited on the surface of bare sandy soil or desert pavement may be redistributed by wind or water. In somesituations (Bellamy et al. 1949) erosional processes may result in the concentration of radioactive materials etween fallvity of fall: percentage mechanieal ‘tation, e.g., ie tends to ‘ing time of ion of vegaunit area is | activity is jing on the llout, maxiro or at disIts of small observed to h those ani1957) have » inhalation ja Test Site activity of mes normal. imals living ternal emitiminishes in 1 a general period that har absorpar and may © of animals, 7 be said to 1 body econ\ation levels e useful in ; associated to internal with lowlevels of exposure to external and internal emitters which haverelatively longer half-lives, on surfaces of deposition. Detailed studies made during and following Oper- ation Plumbbob (Larson et al. 196?) provided no evidence to support a general hypothesis of fallout dilution by erosion or concentration by deposition. The results of these studies indicate that the surface materials in small study areas (100 ft.x 100 ft.) were shifted about in a random fashion so that the variability of surface contamination was increased, but mean values showed no significant change. For periods of 1 to 5 years, the average fission product activity of bare soil surfaces remained higher than that of surfaces such as dunelets under shrubs and slight depressions in the desert pavement on which eroded materials were deposited. Of the airborne materials which were redistributed duringthefirst three weeks after fallout 9.7% to 21% of the total was composed of particles from 44 to 884 in diameter, and 68.3% to 85.4% of the total was composed of particles < 44, in diameter. From D +2 to D +16 days there was a steady deerease in the amount of redistributed fallout. A severe rain storm on D+17 resulted in the redistribution of particles < 100, ‘‘in quantities almost as high as the original levels of contamination’’ (Larson et al. 1967). Since the levels of soil contamination 6 months after fallout were consistent with predictions based on the decay rate of mixedfission products, it seems reasonable to conelude that redistribution had no effect on average, unit-area levels of environmental contamination. The local fallout deposited in a given area seemed to be mechanically trapped in the soil; and in spite of wind and rain action, the amount of fallout debris available for redistribution tended to decrease with time. 2. Plants. The loss of radioactivity from plants directly contaminated by fallout may depend not only upon the radioactive decay of the fallout retained but also upon the loss (or gain) of radioactive particles. Decontamination experiments (Lindberg et al. 1959, Romney et al. 1962) have shown that more than half of the activity deposited on leaves can be removed by washing with distilled water, 0.1N HCI, or 5% versene (EDTA). These results suggest that a significant fraction of the fallout particles deposited on leaves can be retained at least for the life of the foliage. A few observations (Romney et al. 1962) have indicated that the mechanical action of wind and rain mayresult, in a period of 1 or 2 days, ina loss of 20% to 25% of the activity deposited on alfalfa plants, but the gen-