Acute and chromic mtakesof fallout radionuclides @ SL Simow er av
intakerates of "Cs by children compared to adults were
167
3 to7 y, and 0 for other children We assumedthatthe
thyroid does not occur until the end of the 11” week
followmg conception when the fetal thyroid begms to
function (ICRP 2001) This mmphesthat the thyroid dose to
intakes of Sr, which are, as for '°’Cs, mamly dueto the
fraction of the dose the fant would receive per umt intake
18 for children aged less than 3 y, 1 4 for children aged
same age dependency was applicable for estrmating
consumption of internally contammated terrestrial food-
stuffs However, the mtakes of ®Zn, ™Fe, and “Co were
due to the consumption offish and other seafood Using
the consumption estimates for fish and other seafood
provided by Robison and Phillips (1989) and the assumption that the activity mtake was proportional to the
amounts of seafood consumed, the age-dependent rela-
tive mtakes of Zn, “Fe, and “Co were | for adults, 0 9
for 15-y-old, 08 for 10-y-old, 06 for 5-y-old, 03 for
1-y-old, and 01 for newborn
the fetus per umt mtake of “I by the mother 1s a small
after bnth ~0 001% at 5 wk development, 0 03% at 10 wk,
2% at 15 wk, 6% at 25 wk, and about 10% at 35 wk In this
work,the doses to the embryo and fetus are assumed to be
very small and taken to be equal to zero
Forall age groups andall radionuclides considered,
with the exception of the "I mtakes by adults, the dose
coefficients are based on the biokinetic models recommended by ICRP (1996, 2004) The only parameter
values that have been changed are those of the alimentary
tract absorption fractions (f,), which have been taken
from the review by Ibrahim et al
Dosecalculations
Annual absorbed doses to RBM, thyroid, colon, and
stomach wall have been estimated for the time period
from 1948 through 1970 for representative mdividuals
who were assumed to bealive in 1970 The methods used
to estimate doses resultmg from acute mtakes and from
chronic mtakes will be considered m turn
Annual doses from acute intakes. The method for
calculatmg annual doses from acute mtakes1s stmply the
product of the acute average mtake, @ (Bq), of radionuchde z and the dose coefficient (Gy Bq"') for that
radionuclide where the dose coefficient was specific to
an imterval of time after mtake either the remainder of
the calendar year m which the intake occurred,or the full
year M successive years
Dio, 1, y) = Olt) X DC(o, 1, age, y),
(9)
where
(2010), that are
specifically related to the mtakes of radionuclides in
particulate fallout An established computer code (Eck-
erman et al 2006) was usedto solve the ICRP biokmetic
models and to provide annual dose coefficients for all
organs and age groups Foranytest, the first year armual
dose coefficient was the dose per umt intake received
from the date of the mtake until the end of the calendar
year (e g , 365 dif the date of intake was | January, 306d
if the date of mtake was 1 March, and 61 dif the date of
intake was | November) The annual dose coefficients
for the subsequent years were the doses per umt mtake
received durmg the full calendar years This deriva-
tion, which mfluences the first year’s estrmated dose
as well as estrmated doses m subsequent years for
radionuchdes with long radioactive half-lives, 1s 1lus-
trated m Fig 1, takmg °°Sr as an example The annual
dose for the first year was highest for an mtake
assumed to have taken place on | January, was 15%
less 1f the mtake occurred on | March, and about 78%
D(o,t, y) =the dose (Gy) for organ o from
radionuchde zm a specific year,
y, after mtake,
OG) =the average acute mtake (Bq) of
radionuchde 2, and
DC(o, t, age, y) =the amual dose coefficient (mGy
Bq"') for organ o from radionuchde 1, for age in a specific year,
y, after mtake
The armual dose coefficients, which are the absorbed
doses per umt activity mtakes (mGy Bqu'), have been
estimated for six age groups (<I y, 1-2 y, 3-7 y, 8-I2y,
13-17 y, 18+ y) Dosesto the embryo and fetus have not
been calculated as they are expected to have been much
smaller than those received during thefirst year oflife For
example, m the case of 1odme, which has been relatively
well studied, selective uptake of that element by the fetal
less 1f the mtake occurred on I November For the
subsequent years, m comparison, the armual dose coefficient
for 1 January mtake was lower compared to the other dates
(4% lower compared to 1 March and about 15% lower
compared to 1 November)
For intakes of ‘I by adults, the dose coefficients
were derived based on the parameters of the biokmetic
model presented m Fig Al for an average of the two
preferred data sets of physiologic parameters (Table Al)
The set of physiological parameters assigned as 2b
(Table Al) assumed a fractional thyroid uptake about
one-third greater than 1s usually assumed for populations
with typical western diets (42% compared to 30%) In
orderto correct the thyroid mass for a greater than typical
thyroid uptake (Zvonova 1989), we assumed the thyroid
massto be larger than the usual default assumptions by
the same proportion Hence, for our purposes, we assumed the adult thyroid mass to be 26 g compared to the