Acute and chronic intakes of fallout radionuclides @ S. L. SIMoNn ET AL. 10 0 T T T T T T T T T T 169 significant bias (1.e., without significant under- or T over-estimation), it 1s necessary to estimate organ Fraction Transferred doses without significant bias. Because actual persons might have been born on any dayof the year, assuming any single DOB cannot adequately represent all persons. To eliminate potential bias in doses due to choosing a single DOB, we define a metric of dose to best represent an entire birth cohort, 1.e., all persons born within a single year at one atoll. This dose would, in effect, be an average over all the possible birth dates. While a birth-cohort averaged dose would not represent the dose to any single real person,it is the least biased estimator of dose to the cohort as a whole and, 0 0.2 0.4 0.6 0.8 1 f, mother Fig. 2. Relationship between the fractions of elements ingested that are transferred to infants in breast milk (CRP 2004) and f, values for the mother (ICRP 1996). Solid line is regression fit of eqn (10): F,,, = 0.0854 x (f,)'°S! (R? = 0.48). Table 6. Predicted fraction of stable elements transferred to the infant in breast milk following maternal ingestion (prediction based on eqn 10, see Fig. 2). Element Cu As Br Rb Y Rh Pd Cd In Sn La Pr Nd Pm Sm J, Gnother) 5.0 5.0 1.0 1.0 1.0 5.0 5.0 5.0 2.0 2.0 5.0 5.0 5.0 5.0 5.0 X X x x x x x x X X x x x x x 107! 107! 10° 10° 107+ 10°? 1073 10°? 107? 107? 107+ 107+ 107+ 107+ 107+ Fraction transferred from mother to infant through breast milk 4.06 4.02 8.54 8.50 4.05 3.35 2.77 3.33 1.24 1.24 2.31 2.30 2.30 2.30 2.30 X X xX X X X X x x x x X X X X 107? 107°? 10°? 10°? 107° 107 1074 107 107 107 10> 1075 1075 1075 1075 hence, is the best single predictor of total cancer risk among that group. Hence, we define a quantity termed the “birth-cohort average dose,” BCAD,for the infant age category (1.e., birth to | y of age). To estimate the BCAD,it is necessary to determine three quantities: (1) the dose (by organ, nuclide, age, location) for a person born before the estimated date of fallout deposition, (2) the proportion of a birth cohort on a single atoll that is born before the date of deposition, and (3) the proportion born afterwards. Assuming that people are equally likely to have been born on every day of the year, the proportions born before and after the date of deposition are easily computed. The proportion born before the date of deposition, termed P,, can be estimated as equal to the numberof days from beginningof the year to the date of deposition divided by 365. Conversely, the proportion born after the date of deposition (termed P,) would equal | — P,. Using these concepts, the BCAD is simply defined: BCAD = P,, X (Dosereceived if born before) + P, X (Dosereceived if born after) = P,, X (Dosereceived if born before) + P, X 0 e The consumption rate of breast milk by infants was taken to 0.8 L d' (ICRP 2004) duringthefirst year of age and to cease afterwards (Levy et al. 1988; WHO2009). (2) For infants born in the year of a nucleartest, any definition of a “representative person” based on a single assumed date-of-birth (DOB) can lead to a biased dose estimate, depending on whether it is assumed the representative individual was born before or after fallout from the test occurred. Because the primary purposeof this dose and risk assessmentis to predict the numberof cancers that might occur among exposed Marshallese (Land et al. 2010), but without = P,, X (Dosereceived if born before). (11) It is important to note that for the years following the year of intake after a given test, the age of the representative person increased by increments of one year with each calendar year (for example, a person born at any time in 1954 was considered to be one year old from | January to 31 December 1955, two years old duringall of 1956, and so on). However, in the calculation of the annual dose coefficients, we assumed that the metabolic and anatomic characteristics of the person did not change with time after intake. Annual doses from chronic intakes. In this work, annual doses to RBM, thyroid, stomach, and