Radiocesium indicator

The half-period for decrease of muscle cesium-137 concentration in NTS animals after the cessation of atmospheric nuclear weapons testing in 1959 appears anomalous (Table I and Figure 2). In addition to being considerably greater (2.3 years) than the other half-periods found, its standard deviation was larger than the value. If one considers only the initial rate of decrease of radiocesium in these muscle samples, one finds a half-period of 0.9 year which is quite consistent with other data. Examination of these data, in comparison with data from liver (Figures 2 and 3), indicates that only muscle decreased its rate of decline in 1960. It should also be noted that the values during 1960 were only about twice the standard error of analysis. Thus, analytical error alone is not an improbable cause of these anomalous values. 

Radiocesium is an excellent indicator for the behavior of inactive cesium in the biosphere because its radiation can be detected rather quickly, its passage through the compartments of biosystems can be studied much more easily than by direct estimation of the inactive cesium content. Thus, the behavior of radiocesium in ecosystems supplies much information relating to cesium transport in the atmosphere, soil, plants, and animals. 

The effect of the topography on a microscale level (m) to the radiocesium distribution in a cultivated field was investigated by Kachanoski et al. (1985). They reported that the spatial distribution was significantly related to the past surface curvature. Nyhan et al. (1983) described a decreasing trend in the spatial variance component with increasing field sampling volume for Trinity soils (25 ml with a coefficient of variance (CV) of 64% to 1500 ml with a CV of 17%, N = 10), which indicates a small scale spatial dependence of Cs. 

Slow (reverse) migration of radiocesium from clay-mineral interlayers into solution. In the kinetic models discussed above, a reverse process of radiocesium remobilization from fixed edge-interlayer sites was not considered. The equilibration times of up to 4-weeks were too short for the reverse process to become apparent. Nevertheless, the fact that radiocesium in sediments is still exchangeable to a certain extent after more than 20 years of contact with sediments (3), indicates that such a reverse process must exist. 

Table II shows the average fraction of exchangeable- Cs in sediments after 3 sequential 24-hr Nlij-extractions and the additional fraction mobilized after the fourth, long-term (400-842 days) extraction. Assuming (1) that all (rapidly) exchangeable radiocesium had been removed by the three prior extractions, and (2) a first order remobilization process, we can roughly calculate the reverse rate constant that describes the slow remobilization of Cs from the sediments. Table II indicates that the half-life of this reaction, which is interpreted as slow release from the edge-...

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