Bo = d|r n n LX Yy/K i=l on the grounds of a better linear regression fit through the origin for the latter. It is felt, however, that the general topic of ratio estimation for plutonium and other transuranics needs further consideration, particularly in view of the skewed nature of these environmental data. Some thought needs to be directed toward optimum methods of estimating ratios when both numerator and denominator are, say, lognormally distributed. For example, if both are lognormal, then the individual ratios Y,/Xy are also lognormally distributed, which Suggests a method efficient for estimating lognormal means might be considered (Aitchison and Brown, 1969, p. 44). A related problem is the bias that is known to be present to some extent in By and By when the 241 Am data are subject to error (Snedecor and Cochran, 1967, p. 164). 235 The new data from A site, Area 11, will permit the estimation of to 238) and 239-2405, to 241 an ratios in soil and vegetation. U The 2334 to 238y ratio will decrease with increasing distance from GZ 235 238 since the device was made up predominately of U. The Pu to 239-240 Pu ratios can also be computed for the soil samples analyzed by Los Alamos Scientific Laboratory (LASL). Some additional plutonium and americium data from TTR and Area 11 sites will also permit the update of estimated ratios given in Gilbert, et al. (1975). Some new analyses of the ratio data may also be useful. For example, there has been no attempt to explain the variability observed in vegetation to soil plutonium ratios. It would prove informative to investigate whether high Pu concentrations in vegetation tend to be associated with low Pu concentrations in soil. This is suggested by the Stratum 3 Double Track vegetation and soil data 1975, Fig. 32). (Gilbert et al., If so, this could be a reflection of the particulate nature of Pu in the soil samples versus the less variable (more homogenous) vegetation solutions from which aliquots for analysis are drawn. 108