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DIETARY RADIOACTIVITY INTAKE
FROMBIOASSAY DATA: A MODEL
APPLIED TO "Cs INTAKE BY
BIKINI ISLAND RESIDENTS*
E. T. LESSARD. R. P. MILTENBERGER and \. 4. GREENHOUSE
Safety and Environmental Protection Division. Brookhaven National Laboratory, Upton
NY 11973
(Received | Mav 1979. accepted 10 December 1979)
Abstract—Several publications of the ICRP and NCRP (IiCRPS9: [ICRP68. ICRP7I;
NCRP77) describe mathematical models relating total radionuclide bodv burden. urinary
activity excretion rate and uptake interval. This paper presents an equation with which
the constant daily uctevity ingestion rate mav be calculated from sequentiaily obtained
whole body counting and urine bioassay data. The mode! was developed to reiate whole
body counting results to urmury activity excretion data for '"Cs in the Marshailese
population at Bikini [sland for whom accurate dietary intake and residence interval
informution were not avaiable, The technique is applicable to radioactivie matertal whose
brolugical and physical removal mechanisms are linear first order processes described by
uppropiate rute constants which give the instantaneous fraction of atoms transferred from
compartments in the body to urine per unit time, und the instantaneous fraction of atoms
decaying per unit time.
(ICRP65). Previous diet studies (Mu5S4; No77)
[INTRODUCTION
ICRP Pvstication LOA (ICRP71) specifically
describes the mathematical modelling used
for several radionuclides. In these models,
the constant continuous uptake of radioactive
material has been assumed to cease during
the acquisition of the bioassay sample. A
problem arises in the case of enviromental
exposures, such as those which occur in the
contaminated atolls of the Northern Marshall
Islands, where activity uptake continues during the sampling period.
Forat least the past 4 years, the "Cs body
burdens of people living on Bikini Island,
Bikini Atoll have been rising (Figs. | and 2) to
levels which have~approached and in some
cases exceeded the nonoccupational maximum
permissible body burden of [10 kBq (3.0 nCi)
*Research carried out under the auspices of the
U.S. Dept. of Energy under Contract DE-AC0276C H00016.
and '’Cs dose estimates performed by Robison (Ro77) assume a 'Cs dietary intake rate
of 1073-1850 Bqd™' (29-SO0nCid"'). Current
metabolic information for '°’Cs predicts that an
equilibrium '’Cs body burden would be
reachedat sufficient time ( ~ 2 yr) post onset of
constant continuous dietary intake (NCRP77).
Figures | and 2 depict the 1974-78 male
and female '’Cs mean body burdens (Coh75:
Coh77, M179). The data suggests that the
population mean ”’Cs body burdens may not
have attained an equilibrium value. The food
product presumedresponsible for the dramatic
rise in body burdens. namely, coconut, became
available in significant quantities in 1976. Prior
to this time, the individual body burdens should
have assumedrelatively low equilibrium value
for residents whose stay time on Bikini was
greater than two years. During the April 1978
field trip to Bikini Atoll, whole body counting
and urine sampling were performed on 68 adult
177
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