N = Number of persons in the U.S. in 1955;

NCF = Dose-conversion factor for the thyroid, rad mCi-1; and

λ = Effective rate of loss of 131I on pasture, day-1.

The amount, S, of 131I released by the tests at the Nevada Test Site was given in the NCI report from data derived by Hicks (1982, 1990). A reasonable estimate is 150 MCi, which may be considered as a geometric mean with a geometric standard deviation of 1.25. The latter value is based upon an estimate for a closely related parameter and is given by Ng et al. (1990).

The fraction, fd, of the 131I released by the tests that deposits within the continental United States is much more difficult to quantify. In a study to be published, Anspaugh and McArthur (1998) have determined that the amount of 137Cs remaining in the NTS and the Phase I and II areas of the ORERP study (see Church et al. 1990) is equivalent to 10 percent of that originally released. This may be considered as a lower bound on the amount deposited within the continental U.S. An upper bound could be considered as 1.00. Then, assuming that these bounds are the 5th and 95th percentile of a lognormal distribution, the geometric mean is 0.32 with a geometric standard deviation of 2.0. This value is also reasonably consistent with the independent estimate made by Beck et al. (1990) that 25-30 percent of 137Cs produced in the Nevada Tests was deposited within the continental U.S. The latter estimate was based upon drawing crude contours of deposition density as measured by gummed-film collectors and calculating that the fraction of 137Cs deposited within those contours was 21 percent (the estimates ranged from 5 percent for Operations Ranger and Hardtack II to 42 percent for Operation Tumbler-Snapper). An additional amount of about 10 percent was assumed to be deposited with local fallout; thus, the estimate of 25-30 percent of total fallout deposited within the continental U.S.

The area, A, of the continental U.S. according to data in Funk & Wagnalls (1994) is 3,119,963 square miles.

The mass-interception fraction, α, of 131I in fallout that is retained by pasture-type vegetation is taken to be 1.0 based on the article by Simon (1990). Further, the range is estimated to be from 0.5 to 2.0. This is approximately equivalent to a geometric mean of 1.0 with a geometric standard deviation of 1.52.

The dry mass consumption rate, MPD, for milk cows is based on the work by Koranda (1965), who reported an average value of 14 kg day-1. It is assumed here that this value can be characterized by a geometric standard deviation of 1.5; this would correspond to a geometric mean value of 13 kg day-1.

The classic value for the rate of secretion of 131I in milk, fm, is 0.005 day L-1 (Garner and Russell 1966). This value is assumed to be a geometric mean with a geometric standard deviation of 1.5.

The per capita consumption rate of milk, L, is taken from the NCI report. The value of 0.4 L day-1 is assumed to be a geometric mean with a geometric standard deviation of 1.5.



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