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PLUTONIUM
3. HEALTH EFFECTS
excretion of
239+240
Pu to that of the excretion predicted to occur if absorption had been complete. The
latter was predicted using kinetic models of excretion of absorbed plutonium (Durbin 1972; Talbot et al.
1987, 1993). The reported mean absorption fraction was 1.7x10
-4
(range: 0.2x10
-4
–4.9x10
-4
) for subjects
who ingested winkles. The estimated mean absorption fraction for subjects who ingested cockles was
3.4x10
-4
(range up to 7x10
-4
) based on the kinetic model of Durbin (1972),
which predicts approximately
1.1% of the body burden eliminated in 7 days, or 1.9x10
-4
(range up to 3.9x10
-4
), based on the kinetic
model of Talbot et al. (1987, 1993), which predicts approximately 2% of the body burden eliminated in
7 days.
Gastrointestinal absorption was also measured in three adult male volunteers following ingestion of a
plutonium citrate solution along with food (Popplewell et al. 1994). Based on comparisons between
measured urinary plutonium excretion for 8 or 9 days postingestion and similar assessments following
intravenous injection of plutonium citrate 6 months later, calculated fractional absorption of ingested
plutonium ranged from 2x10
-4
to 9x10
-4
.
The gastrointestinal absorption fraction has also been estimated in
human populations, based on analyses
of inhalation and ingestion intakes, biological monitoring of plutonium excretion in urine or
measurements of body burdens at autopsy. These estimates rely on model-based assumptions regarding
the deposition of inhaled plutonium and the absorption fraction for plutonium deposited in the
respiratory
tract. Sun and Meinhold (1997) conducted an analysis of data on 34 residents of Rongelap Island who
were exposed to plutonium fallout during and following the nuclear bomb detonations in the Marshall
Islands. Based on measurements of urinary plutonium excretion and assumptions regarding the
deposition and absorption of inhaled plutonium, the gastrointestinal absorption fraction (for diet and soil,
combined) was estimated to be approximately 4.2x10
-4
(range: 1.7x10
-4
–7.1x10
-4
). Mussalo-Rauhamaa
et al. (1984) conducted an analysis of plutonium body
burdens in Finnish Lapps and, along with estimates
of inhalation and dietary intake of plutonium (primarily from consumption of reindeer), and assumptions
regarding elimination rate of plutonium, estimated the gastrointestinal absorption fraction to range from
approximately 8x10
-4
to 9x10
-4
.
The gastrointestinal absorption of plutonium has been studied in nonhuman primates, dogs, and a variety
of rodent species. Most of these studies have estimated absorbed plutonium as the sum of the plutonium
burden in major tissue depots (e.g., liver and skeleton), plus the plutonium excreted in urine.
Double
isotope techniques have also been used to estimate the gastrointestinal absorption of plutonium in
nonhuman primates (USNRC 1992). In this study,
239
Pu(VI) bicarbonate was administered orally and
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PLUTONIUM
3. HEALTH EFFECTS
236
Pu(VI) bicarbonate (or
238
Pu) was administered intravenously to baboons and the gastrointestinal
absorption fraction was estimated from the retention ratios for the two isotope ratios in tissues and
cumulative excretion ratio in urine. Absorption was estimated to be 0.22% of the oral dose in fasted
baboons and 0.011% in fed baboons. Gastrointestinal absorption of plutonium was measured in adult
marmosets that received single
gavage doses of either
239
Pu citrate or
239
Pu citrate added to powdered
potato, and was based on levels of activity measured in tissues (mainly liver and skeleton) following
sacrifice (Ham et al. 1994). Absorption was approximately 0.24% of the dose when administered as
plutonium citrate and 0.14% of the dose when administered in potato powder.
In addition to the above studies conducted in nonhuman primates, gastrointestinal absorption of
plutonium, in various isotopic and chemical forms,
has been measured in pigs, dogs, and various rodent
species. Results from these studies support the following general conclusions regarding factors that affect
absorption: (1) in general, absorption of plutonium citrate tends to be greater than nitrate, which is
greater than plutonium oxide (PuO
2
) (Sullivan 1980a); (2) most estimates of absorption of plutonium
citrate and nitrate in adult animals are <0.1% of the dose; (3) fasting tends to increase absorption
(Bhattacharyya et al. 1986; USNRC 1992); (4) absorption is 10–1,000 times greater in
neonates compared
to adults, depending on the animal species and chemical form of plutonium (Sullivan 1980a, 1980b;
Sullivan and Gorham 1983; Sullivan et al. 1985); (5) iron deficiency increases absorption in juvenile rats
and administration of ferric iron (Fe
3+
) to iron-deficient rats decreases absorption (Sullivan and Ruemmler
1988); and (6) absorption of plutonium in surface dusts (e.g., bomb test sites) in guinea pigs was <0.001%
of the dose (Harrison et al. 1994).
3.4.1.3 Dermal Exposure
Occupational accidents have resulted in dermal exposures and/or penetration of plutonium into skin
wounds and subsequent systemic absorption of plutonium (McInroy et al. 1989; Woodhouse and Shaw
1998). In one case,
postmortem measurements of
239
Pu levels in tissues, measured 17 years following the
incident, showed that liver contained approximately 41% of the body burden and skeleton contained 49%
of the body burden (McInroy et al. 1989). Woodhouse and Shaw (1998) reported urinary excretion of
plutonium during 20–30-year periods following various wound-related exposures to PuO
2
(oxalate),
Pu(NO
3
)
4
, or plutonium metal. Systemic absorption of
239
Pu was estimated to have
been approximately
0.001%. Plutonium absorption through the intact human palmar skin was estimated to have been
0.0002%/hour when applied as the nitrate (10 μg Pu) in a 0.4 N nitric acid solution for 8 hours (Langham