Page 535
hs
Distribution of the Rare Eart
—————
soil and plants (Lowman and Palumbo, unpublished
data). These data indicate that very little of
rare earth nue ee od
ewe orincipal source of
4
Se
als, also, 158
fist aed terrestrial anim
nuclide iB
The physical state of the
t ytegen
organism.— In ia
eed governs its fate 10 the
rption of cerium
re appears to be some abso
tion
indicating that at least a por
ae
treestion.
Chipman
form.
nucaide ts in the soluble
um-144 was
(or example, found that ceri
liver
tn small amounts by the bone and
In addition, Rudakov (1958) reported
foicroaners.
the rare earth nuclides ingested under natural conditions is retained in the tissues of terrestrial
animals.
The inhalation of particulate matter is also
a factor to be considered. This process could be
important, especially during periods of ,heavy fallout from nuclear tests and accidental discharge of
were absorbed by
wign amounts of Ce'44-prl44
hour immersion in a
radioactive materials from reactor stacks.
initial concentration of these nuclides in their
gastrointestinal tracts and low concentrations in
other tissues.
rsity of
-Prl44 is incorporated in small
$1955).
Washington,
soluble form.
Uni-
Seymour et al., 1957;
Rinehart et al.,
1955;
As in other animals, the rare earth elements
enter man during the ingestion of food and the inhalation of air and dust. Based on the data of J.
G. Hamilton and co-workers, Morgan (1960) estimated
In terrestrial animals there appears to be
ry
that less than 0.01 per cent of the rare earth ele-
littie absorption of the rare earth nuclides
rom the digestive tract. The results of Durbin et
1. (1956) showed that cerium-144, europlum-152 and
puropium-154, terbium-160, and thulium-170 adminisfered orally to rats were not absorbed significantly.
Bowsver. parenteral injection of several radiolanphar ides: complexed with an organic acid to increase
their solubility. showed that absorption from the
gite of injection was almost complete within four
@ays.
The primary sites of deposition initially
@Were the liver and skeleton.
After ten months,
however, the site of greatest concentration was the
bone ; other tissues contained only very small
Bmounts of the rare earth nuclides (see also Kyker
and Anderson, 1956). Similarly, in samples of rats
gollected at Eniwetok Atol] shortly after a nuclear
detonation, the rare earth activity was highest in
he skeleton and liver (Thomas et al., 1958).
Samles of rat
tissues collected approximately two and
one-half years after the last test series in 1958
Operation HARDTACK I) contained no detectable rare
@arth radioactivity although there was some in the
é
Table 4.
Nuciide
BioPhysical logteal
Lanthanum 140
BCoriumm ia. 4
;
Prometniim. 47
:é
1.68
Maximum
Fe.
BR
i
Rus
ao
290
293
243
146
4
Eos
.
.
a
$ lat
7x10
GI-(s)
Liver-(s)
Lung- (1)
GI-(i)
GI~(s)
3=Bone-(s)
1500 1442
GI-(i
GI-(s)
Bune-(s)
6
the
1480 1125)
tract
water
The last biological factor to be considered
here is the selectivity and concentration of the
rare earths by different species. Organisms in the
lower trophic levels concentrate them to a greater
degree than do organisms in the higher trophic
levels.
For example, Krumholz and Foster (1957)
estimated that the concentration factor was 1,000
for phytoplankton, 500 for filamentous algae, and
100 for fish.
Also,
it has been shown by Spooner
(1949), Rice (1956), and Rice and Willis (1959)
in
Maximum permissible concentration
for 40-hour week
GI-(s)
Kidney-(s)
Lung-(1)
lar RE
intesti
2x 1077
0.2 4
3 x 10
10-8
8 x 10/3
-4
3 x 10 3
6 x 1073
6 x 10 6
3
10/6
6 x 10°
0.6
210.
100
107
fraction reaching
organ
;
mens
-
:
Soluble;
=
10_
6x 10-8
3.x 107°
0.09
107
1076
é x 10-8
3.5x1075
0.09
10-7
107
1078
2x 107°
1073
1
0.075
5 x 1077
0.3
2x
3 x 10 5
2x
2x 109
20
_
By
inhalation
10
0.01
GI-(i}
lower
'
food.
7x 10-4
6 x 10°
1.0
60
Lung-{i)
;
These and similar data have been considered in
establishing for man the maximum permissible concentrations in air, water, and food.
The values
for some of the rare earth nuclides are presented
in Table 4,
0.3
GI-(1)
4 tio!
7e10
in by inhalation reaches the critical organs for
these nuclides.
7 x 10
5
pang” (4)
As Sointemtina4s
‘Jee
GI-(i)
Bone-(s)
570
1500
——— a
7
burden in
GI -(s)
1500
; =.
eee
)
tion of the longer-lived rare earth nuclides taken
Effec- Critica] total body
(microcuries per cubic centimeter)
By
tive
organ*
(microcuries)
Wateré
Air
ingestion
290
4#20
ments pass from the gastrointestinal tract to the
blood.
It was found also that only a small frac-
Maximum permissible concentrations of some rare earth radionuclides in
air and in water for occupational exposure (Frou: K.Z. Morgan, 1960).
Half-life (days)
,
increased in
the liver. The relatively rapid uptake by the
liver suggested that some of the cerium was in the
Mmuunts tn muscle, liver, kidney, lung, gills,
od ukeletai tassues of fish (Thomas et al., 1958;
Morouxhs et al., 1956;
Cerium-144 was eliminated rapidly
from the gastrointestinal tract but
Baemples collydged at the Eniwetok Proving Ground
how that Ce
Experi-
ments have shown that rats subjected to aerosols
containing lanthanum-140 (Cohn et al., 1957) and
cerium-144 (Hennacy, 1961) had a relatively high
farcer ings after a onepassage of
diva tise solution, and that with the
es in
rsere was a redistribution of the nuclid
At one day they were found mainly in
Lissues
At one month the radioactivity in the
liser
he
ene was twice as high as that in the liver.
from
Mther results, including those obtained
4x
,
.
3 x 107°° 7.5 x 1077
107"
j
insoluble,
ad } i
‘
La
Yan