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SOME ASPECTS OF THE BIOLOGY
OF ZIRCONIUM-95
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the filtering capacity of appropriate aquatic
Following
intramuscular administration
of
zirc onium-95 Rstate not given) to eels kept in
both fresh and sea water, Tomiyama and Kobayashi
(1957) found a different distribution of the nuclide than has just been described fo. the mouse
and rabbit. Twenty-five hours after administration the nuclide was widely distributed among the
Laboratory of Radiation Riology.
University of Washington, Seattle, 1 oashington
Zirconium-95 with a sixty-five day half life
has become of biological interest primarily because of its relatively high yield in nuclear fis15 per cent of the total radioactivity 90
days after fission and 7.3 per cent one year after
fission (Hunter and Ballou, 1951).1
“
organisms,
EDWARD E. HELD
sion,
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Stable zircon-
ium has no known biological function although it
has been found in trace amounts in plants (Rankama
and Sahama, 1950),
Vinogradov (1959), states that
there have been very few quantitative determinations of zirconium in soils; om the basis of about
900 determinations the average content is at most
0.04 per cent. Two thirds of the zirconium is
found as Zircon (Zirconium oxide), a stable mineral (Rankama and Sahama, 1950). It does not seem
likely, therefore, that isotopic dilution need be
tissues and organs but found in the largest amount
in the blood, kidney, and spleen, It is stated
that the excretion was very slow, When zirconium95 was added to the water about 70 per cent of
that in the eel was found in the gills and most of
the remainder in external portions such as the
surface mucus. The authors interpret the high
level in the gills as indicating uptake through
the gills.
Various organic acids influence the distribution of zirconium-95 in the rat regardless of the
route of entry (Hamilton, 1949), Zirconium
citrate was first used to replace plutonium and
yttrium in skeleton by Schubert (1949),
This and
subsequent work of this kind has been reviewed by
of Zirconium-95 by organisms under ordinary condi-
Rosenthal (1960), These metals are concentrated
in the osteoid matrix rather than being deposited
in the mineral structure as are the alkaline
earths,
The only published review of the radicchemistry of zirconium is that by Steinberg, (1960).
Confusion exists as to the behavior of zirconium
Langham (1960) has reviewed the significance
of the portals of entry of fission products,
Gastrointestinal absorption of zirconium-95 is
very low, 0,01 per cent, Pulmonary deposition of
of any great concern when considering the uptake
ions,
in solutions because of the formation of colloids
and extensive hydrolysis and polymerization of
zirconium ions.
Zirconium tracer is strongly co-
precipitated with most precipitates in the absence
of complex-forming ions. In evaluating biologi-
cal uptake,
particularly in aqueous media, an im-
portant point made by Steinberg should be kept in
mind, i.e., Zirconium is easily carried on
foreign matter and adheres to glassware.
Thus,
in studies of the uptake of zirconium-95 by organisms it is more than usually important to know
the chemical state of the zirconium both at the
time of administration and at the conclusion of
the experiment.
It should also be especially per-
tinent to establish a “balance sheet,”for the
total system, including such portions as the sides
of containers used,
Unfortunately,
such informa-
tion is not always available in the literature,
Gofman (1949) has described the preparation
of colloids of zirconium isotopes for use in the
selective localization of radioisotopes in tissues, Dobson et al., (1949), using these preparations in the mouse and rabbit by intravenous injection,
found that colloids of zirconium of rela-
tively large particle size ("Sedimentible in large
part with ordinary centrifuges,..") rapidly disappeared from the blood (half time was 30 seconds to
one minute) and were deposited mainly in the liver
and spleen, Colloids of smaller particle size
disappeared from the blood more slowly (half time
was 30 to 80 minutes) and were deposited mainly in
the bone marrow and spleen and secondarily in the
liver. Once deposited, both types of colloids retained their distribution patterns for the dura-
tion of the experiments, two to four weeks. The
objective of these experiments was to establish
methods for radiotherapy.
Similar preparations
could also be useful in studies of the uptake of
colloids by various organisms and in studies
of
since the reading of this paper Collins et al, have reported that zirconium-95 in accurnulated fallout during 1958 and 1959
in New York City produced gamma doses comparable to dosea
from cesium-137.
R.S. Morse, 1961,
series.
(Colling, W.R., Jr.; G.A. Welford, and
Fallout from 1957 and 1958 nuclear test
Science 134 (3484): 980-984. )
the oxide is similar to that of other oxides and
nitrates. Material remaining in the lungs remains in the pulmonary lymph nodes. Under most
circumstances ingestion is probably the primary
portal of entry.
In plants zirconium-95 is found mainly in
the roots if supplied in the soil or in aqueous
solution (Klechkovskii and Gulyakin, 1958;
Nishita et al., 1960).
If foliar application is
made the zirconium remains near the site of application,
In experiments with the alga Porphyra sp.,
Foreman and Templeton (1958) have reported con-
centration factors between 200 and 470 and comparatively rapid loss of the zirconium-95, 50
per cent in six days, 96 per cent in 65 days,
Only the abstract was available and the authors’
conclusions were not given but it seems most
likely that a surface adsorption phenomenon is
involved.
Timofeeva-Resovskaya and Timofeeva~-Resovskii
(1958) have reported a concentration factor for
zirconium-95 of 315 by the snail, Limnea
stagnalis. Again only the abstract was available and experimental details were not given,
Zirconium-95 in environmental contamination has been found in a wide variety of organ-
isms2 but always appears to be associated with
adsorption, surface contamination, or the itnges-
tion of particulate matter.
Although still de-
tectable in soil several years after contamination by local fallout from nuclear tests, zir-
conium-95 does not appear in the food web in
Significant amounts after less than a year.
Summing up, the biological half-life of
zirconium-95 is much longer than its 65-day physical half-life, Uptake from environmental contamination is mainly by the oral route in animals and
“A large number of reports have appeared and will not be
cited individually. Those available at this writing are included
in the reference cited and can be identified by their titles.
CLEY
DOF AR
(p77