Radiocecology
434
um-id1 4 and
uclides. praseodymi
te
ur in the particula
occ
y
abl
rob
e
ea
ey,
ber rare
sea water (Carritt and Harl
'
elements of this group,
: 37) ree eee of the characteristics, probably
ical
chem
lar
sati
oo ine
and Willis (1959) found
let to this form. Rice
um-144 proceeded at a
ceri
t the precipitation of
in water
d water than it did
ster rate in distille
cation also that
indi
an
es,
niti
sali
her
‘
fresh
in the p articulate ,form im
Big
ts
centage of stable
per
ly
low
eme
xtr
tee
Cx
a
er
lution in the
trium, and lanthanum in solu
ius
total amount that has been
: Fie. apared with the that
has been designated
elationship
‘
ts
PP) tee fer percentage’ by Goldschmidt, reflec
The soluts.
elemen
these
of
lity
low solubi
elements as
diities in water of some rare earth
the
Retersined by Moeller and Kremers (1945)ts and
are given
Peransfer percentages
n
Table 3.
.
Solubility product’
Table 3.
5
"
j :
for these elemen
1
and transfer per-
centage of some rare earth elesents.
Hydroxide
Sw
Amount
solubility
is
product (at
Total
present
in
Transfer
perceng
tage
ppt
supplied
ycoan
ocea
5.2 x 10°~“
16.9
.0003
.002
0.8-1.5 x 10719
97.7
0004
.001
i
Elemont
2
tigrade)
25° o centig
W¥ttriue
‘Eceriua’?§
Planthanua i x 10°)?
il
0003-003
AoFrom: Moeller, T., and H.E. Kremers (1945).
“From: Goldschmidt, V.M.,
fT.G. Sahama (1950).
+
quoted in Rankama, £., and
As stated by Carritt and Harley (1957) "...it
mould appear...that marine waters are saturated
‘Meith respect to these elements and that a major
mortion of the rare earth elements are dispersed
fin the sea as solids.”
From the above data it can
‘pe concluded that any radioactive rare earth nu@lide added to the sea or to fresh water will exist
gmostly in the particulate state.
£
In the hydrosphere the spatial distribution of
ihe particulate rare earth nuclides is governed by
«physical factors such as gravity, turbulence, and
qmdsorption to other matter.
Rare earths adsorbed
that less than 12 per cent of the cerium-144 and
yttrium-9] added to seven different types of soil
was removed with distilled water. More than 90 per
cent of these radionuclides remained fixed to four
of the soils after leaching with neutral ammonium
acetate.
If the pH of the leaching solution was
raised above 5.5 the extractability of cerium-144
and yttrium-9]1 decreased sharply.
adsorbed cerium-144 was released more readily.
The low availability of these nuclides under normal soil conditions is also demonstrated by the
sm@]] amount in the tissues of land plants.
Pr
,
cel44.
yttrium-91 and promethium-147 are taken up
in about the same order of magnitude and usually in
much Smaller amounts than radiostrontium or radio-
cesiym and usually in lesser amounts than Rul 06-
Rh
(Nishita and Larson, 1957:
Jacobson and
Overstreet, 1948; Rediske et al., 1955).
Also,
Seiders et al. (1953) found that although the rare
earths comprised most of the radioactivity in Nevada Test Site soil, they were not preferentially
absorbed by plants growing in this soil.
The presence of rare earth radionuclides in
leaf samples collected at Eniwetok Atoll during and
immediately following the nuclear test series in
1956 (Operation REDWING) was reported by Thomas et
al. (1958). The high levels of rare earths found
in these samples can be explained only on the basis
of surface adsorption, a mechanism believed to be
of major importance in the accumulation of these
nuclides by land plants.
The presence of stable isotopes of elements in
the environment is also known to affect the uptake
of various nuclides by organisms. Rediske et al.
(1955) found that the addition of stable yttrium to
the substrate caused a significant increase in
radioyttrium in the plant tissues.
It is probable
that addition of the stable isotope of yttrium displaced the radioisotope from the soil and increased
its availability to the plant.
BIOLOGICAL FACTORS
In discussing the factors involved in the
ability of an organism to absorb rare earth nu-clides, it is essential to consider the type of or-
geo large particulate matter will tend to sink to
ganism as well as the method by which the organism
obtains nutrients. The particulate nature of the
lanthanides in the aquatic environment makes dif-
4(1958), for example, found relatively high amounts
Rice (1956), Rice and Willis (1959), and Chipman
(1958) have shown that many species of planktonic
w#the bottom or to the appropriate density layer, and
q@xcept for bottom-feeding organisms will be removed,
yessentially, from further distribution. Martin
of cerium-144
(189 micromicrocuries per square
ficult their absorption by autotrophic organisms.
algae adsorb particulate lanthanum-140, cerium-144,
and yttrium-91 rapidly.
j
However, when
bentonite, a clay mineral, was pretreated with acid,
Bowen and Sugihara (1958)
epowed chat the cerium-144 and promethium-I47 conanes. deeper waters of the Atlantic Ocean in some
Phey
ine higher than that of the shallow waters.
a rec les in the water are "sweeping down
rare
taining th
aster
: ‘i partaerened these data as indicating
that the
Flo remove!
rate than the microplankton are
em in the surface waters.
In contrast
he rthebee by sedimentation, Part
of the rare
ide debris ome adsorbed to small organic and
inorgan-~
it he
turbulencemoog in the water, and,
because
of
febie parciculace matten by wind and ocean
currents,
;
ow layers for
some ti me and event
@esoc lated with living
organisms Naily may be
F c
In the land enviro
nme nt a lso the physico-chemi betrieen a the lan
thanides Bovern their
spatial
thoes nucle
For example, in the soi
l solution
do nor os!
es are insoluble and
con
seq
uen
tly they
tions
@ readily through the
s01l.
Investiga|
onducted by Nishit
a and Larson (1957) showed
However, Rice and Willis
(1959) showed that a diatom (Nitzschia closterium)
absorbed ionic cerium-144, although at a slower,
rate than particulate cerium-144, and Spooner (1949)
suggested that yttrium-90 uptake by sessile algae
might be an ion-exchange process.
Although the filter~feeding zooplankton remove
radioactive particles from water by surface adsorp-
tion, the primary source of these rare earth: nuclides is ingested organic and inorganic particulate matter.
Chipman (1958) showed that marine copepods and other filter-feeding zooplankton exposed
to sea water containing phytoplankton cells and
other cerium-144-bearing particles ingested this
material rapidly. Similar studies by Chipman
(1958) and Boroughs et al. (1957) with filterfeeding invertebrates,
such as oysters, scallops,
and clams, showed that particulate radionuclides,
including cerium-144, were concentrated mark-
edly but were not accumulated in the body tissues.
Apparently the insolubility of these particles at
the physiological pH of the digertive tract makes
their absorption difficult.