174
Health Physics
of “7Cs, its contmuous movement mto coconuts and
other fruits via root uptake, as a result of low ““K
August 2010, Volume 99, Number 2
concentrations m the soil (Simon et al 2002), leads to
longest half-hfe bemg 51 days for “Sr Therefore, most
of the mternal dose resultmg from acute mtakes was
delivered during the year ofthetest
Absorbed doses
radionuchides with half-hves of about 1 y or longer
When the biological half-trme of residence in the body
was longer than I y, the dose from acute mtake was
much larger mtakes over the successive years after
fallout
Annual absorbed doses to RBM, thyroid, stomach
Among the radionuclides considered, there were six
delivered over several years This 1s, for example, the
wall, and colon were estimated for the 26 population
groups for the trme period from 1948 to 1970 Cumulative doses over that time period were estrmated as well
Four population groups have been selected to illustrate
the magmtude and the range of dose over the entire
terntory of the Marshall Islands Doses from acute and
chronic mtakes will be discussed m turn
case for Sr, with a physical half-hfe of 29 y and a
biological half-time of residence m the body of about
20 y Tables 12 and 13 present the absorbed dose
coefficients to age 70 y for a 1-y-old child and for an
adult for the six radionuchdes with long radioactive
Doses from acute intakes. Estimation of doses
from the acute intakes used dosecoefficients as described
that were derived from accepted mternational biokmetic
models and adjusted for f, values specific for radionuchdes mgested in fallout particles (see Ibrahim et al
both ages, about 100% of the dose 1s delivered to the
2010)
Annual doses from acute intakes at each atoll
varied primarily according to the amount of deposition
from the tests conducted m a given year Fig 3a to 3d
illustrates the armual organ dose (mGy) to two tissues
(RBM and thyroid) for three different birth years (1930
or before, 1953, and 1957) at Mayuro, Kwayalem, and for
half-lives as derived for the Bravo test (1 March 1954)
The tables also present the percentage of the dose
delivered m each ofthe first five years after mtake For
colon wall and to the stomach wall m the first year For
the systemic organs, RBM and thyroid,a large fraction of
the dose 1s delivered imthe first year, but a significant
fraction of the dose 1s also received in subsequent years
dueto the biological retention of the radionuchde m the
body
Doses from chronic intakes. Annual doses to
RBM, thyroid, stomach wall, and colon were calculated
the Utnk and Rongelap Island community members
(after accounting for their relocations) Similarly, Table
10 presents cumulative doses (mGy) to each of four
tissues for all birth years from 1931 (or before) through
1958 Since it 1s the mtent of this work to estimate doses
for representative persons, BCAD 1s reported for the
years m which tests occurred
The cumulative doses to mdividual organs are a sum
not only overall tests but a sum overall 63 radionuchdes
Table 11 presents a summaryof the radionuchdes which
were estimated to be the ten largest contributors to total
iternal dose from acute imtakes for each of the four
tissues and for each of the four population groups
for chromic intakes of long-hved radionuchdes for the 26
population groups over the years 1948 to 1970 Fig 4
compares annual doses to thyroid from chronic intakes
during the years 1948 through 1958 for three different
mity, and Rongelap Island commumty) For the dose to
from acute mtakes However, because of the absence of
(Majuro residents, Kwajalein residents, Utrk commu-
RBM,stomach wall, and colon wall, “Np wasoneofthe
five most important nuchdes regardless of the atoll
Other mportant nuclides for RBM were ‘Te, Ba and
°°Mfo For the stomach wall, the short-lived radioiodmes
and rachotellunums ‘I, “I, and *°Te were rmportantat
Mayuro and Kwajalem while “Y and °Y were most
important at Rongelap For the thyroid gland, the radiotodines and radiotelluriumseasily gave the largest doses
though ‘I was the largest contributor at Rongelap and
Utrik compared to "I at Kwayalem and Mayuro All of
the radionuchdes hsted in Table 11 are short-hved, the
birth years 1930 (and earher), 1953, and 1957
Cumulative doses were obtamed as sums of annual
doses Cumulative doses were a function of birth year
with the largest cumulative doses estimated for persons
bor m the years 1950 through 1956 The cumulative
dose estrmates for Majuro residents, Kwayalem residents,
the Utmk commumty, and the Rongelap Island commumity are presented m Table 14
The doses from chromc mtakes show the same
geographical and temporal pattern as the doses resulting
short-lived 1odime 1sotopes m the radionuclides that are
important to the thyroid doses from acute mtakes, the
thyroid doses from protracted intakes are not much
greater than the doses to other organs and tissues
Similar to the situation for acute mtakes, a few
radionuclides contributed most of the organ absorbed
dose from chrome mtakes Table 15 presents a rankimg of
thosefive radionuchdes (*Fe, “Co, “Zn, “Sr, and '°7Cs)
Forall organs and forall four of the atoll and population
groups discussed, ‘Cs was either the first or second
most important contributor to dose For the Rongelap