The Time of Intake to Be Assumed for Calculating DILs and DRLs

DOE-STD-1121-98

(12)

This value, T/2, is used by the ICRP (1982, 1988) and has been used by DOE contractors (Johnson

1991).

The expectation value of dose, however, is not the dose that would occur from an intake at time T/2.

Given a certain bioassay result (activity retained or activity excreted), X (known to arbitrary precision)

and a fractional retention or excretion estimate, R, the intake I (to which dose is linearly proportional) is

(13)

where T-ti is the interval between intake and bioassay measurement. The expectation value of the intake,

<I>, is

(14)

For the simple case when X is the activity retained, and the retention function is a simple

exponential,

(15)

Eq. (13) then becomes

(16)

The intake calculated from the assumption that it occurred at <ti> = T/2 is

(17)

The ratio of Equations (15) and (16) is