The Toxicology of Radioactive Substances. Volume 3.59

192 Pages·1967·9.19 MB·English

by  A. A. Letavet and E. B. Kurlyandskaya (Eds.)

THE TOXICOLOGY OF
RADIOACTIVE
SUBSTANCES
VOLUME 3
Iron-59
Edited by
A.A.LETAVET
and
E. B. KURLYANDSKAYA
Translated by
R.E. TRAVERS
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Library of Congress Catalog Card No. 61-9783
This is a translation of the original Russian
Toksikologiya radioaktivnykh veshchestv published in 1962 by Medgiz, Moscow
2691/67
TOXICOLOGY OF RADIOACTIVE
IRON-59
E. B. KURLYANDSKAYA
THIS volume contains experimental results obtained by the Radiotoxicology
Laboratory of the Institute of Occupational Hygiene and Disease, Academy
of Medical Sciences, U.S.S.R., in studying the toxicology of radioactive iron.
In accordance with the general direction of the Laboratory's work the data
presented here stem from the further development of investigations chiefly
concerned with the long-term effect of small doses of radioactive substances
close to permitted maxima.
We chose to study the toxicology of 59Fe for two reasons. Firstly 59Fe has
been used in various branches of science and technology. Thus, in the metal
industry, it is used to study the movement of metal and distribution of alloy
elements in the open-hearth furnace and pouring ladle (N. G. Bogdanova,
1958). It is also used to study the movement of charging materials in blast
furnaces and open-hearth furnaces, the blending of pig iron in the furnace
(M.T.Bul'skii et al., 1958), the hydrodynamics and crystallization of ingots
of melted and cold steel (A. A. Zborovskii and L. K. Strelkov, 1958), and
so on. , ■ ■ ■
In engineering 59Fe is used to study friction mechanisms, wear of machine
parts, metal fatigue, etc.
In biology it is employed in the study of haemoglobin metabolism in the
red cells, bone marrow, etc.
The above techniques far from exhaust all the possible uses of 59Fe in
scientific investigation. But its employment in industry and the laboratory
entails the possibility of intake by workers of very small quantities of 59Fe
close to the maximum permissible. Moreover, the existing maximum per­
missible concentrations of radioactive iron in air and water are based solely
on calculation and require biological verification. This was shown convinc­
ingly in our previous work on other radioisotopes and is one of the practical
purposes of the present investigations (see The Toxicology of Radioactive
Substances, vol. 1, 1957; vol. 2, 1960).
But the study of the long-term effect of 59Fe is also of theoretical impor­
tance. In recent years evidence has accumulated in the laboratory which in­
dicates the great significance of the chemical and biological properties of
radioactive elements in the picture of chronic radiation sickness produced by
intake of these substances. This applies especially to those elements whose
stable analogues are essential to normal body function (45Ca, 60Co, 59Fe,
1
2 Toxicology of Radioactive Substances
65Zn, and others). It is suggested that the direction of the pathological process
and the early signs of radiation sickness produced by these radioéléments will
differ from the effect of other radioéléments in accordance with the functional
background which these elements create as chemical substances, as in fact
was shown by our earlier work on 60Co (vol. 2, 1960).
Consequently, it might be expected that 59Fe, which plays an important
role in haemopoiesis and in the activity of the respiratory enzymes, should
also manifest its own characteristic effects. Study of these peculiarities of the
effect of 59Fe was the second aspect of our investigations.
There is a fair volume of literature on the behaviour of 59Fe in the normal
and anaemic animals following the administration of trace amounts (Aus-
toni and Greenberg, 1940; Copp and Greenberg, 1946; Hahn, 1948; and
others). The effect of small doses of 59Fe (single dose) has been studied by
R. E. Kavetskii, L.B.Stolyarova, R. D. Nikitenko and P.M.Amdurskaya.
These authors have established that the body reacts even to trace quantities
of 59Fe. But the literature which has reached us contains no references to the
long-term effect of 59Fe, administered in different ways and in amounts close
to the maximum permissible.
Not wishing to overburden the reader with information of a general nature
we shall summarize the physical, chemical and biological properties of iron
briefly.
59Fe has a half-life (Γ±) of 45^ days and a complex β- (Ε = 0-26 and
β
0-46 MeV) and y-spectrum (1-025 y-quanta on decay; E = 1-1-1-3 MeV).
y
In the human and mammalian body stable iron is an essential component
of haemoglobin and the respiratory enzymes. The human body normally
absorbs, daily, according to some data, from 6 to 8 mg iron (L.A.Klyu-
charev, 1953; Ts.D.Savve, 1954; and others) and according to other results,
8-12 mg (Granick and Hahn, 1944). In iron deficiency, the absorption may
increase greatly. On entering the blood, iron passes to the cells and takes part
in the metabolic processes and is also utilised by the bone marrow cells for
formation of haemoglobin. All these aspects were taken into consideration
when interpreting our results.
Our investigations into the long term effect of 59Fe consisted of two main
series of experiments.
The first series was carried out on 103 rabbits divided into 4 groups. In the
first group (20 rabbits), iron was administered orally at a dose rate of 1 μο
ferric chloride (59FeCl ) per kg weight per day, the radioactivity of which
3
exceeded by 10 times the international maximum permissible concentration
for water. The animals of the second group (42 rabbits) received 10 μc/kg,
the third group (24 rabbits) received stable iron in an amount equivalent to
that administered to the second group, from 1 to 4 mg/kg, and the fourth
group (17 rabbits) constituted a physiological control.
In the second series of experiments, 45 rats were used. In some, 0-03 μο of
59Fe oxide (the maximum permissible dose for a single administration) was
injected intratracheally on three occasions. The others received a single
intratracheal injection of 106, 3-36 and 27-5 [LC per rat, which are respectively
Toxicology of Radioactive Iron-59 3
10, 30 and 250 times the maximum permissible dose for a single administra­
tion. Nine rats were given a single dose of 20 Resoluble 59Fe citrate per rat,
which exceeded by 100 times the maximum permissible concentration for
soluble iron compounds. This series of experiments was made to examine the
effect of soluble and insoluble compounds of radioactive iron, the significance
of local doses of insoluble compounds in the development of tumours, and
also to verify the maximum permissible concentrations of soluble and in­
soluble compounds. The animals were maintained on a constant standard
diet.
In the first series of experiments on the long-term effects of 59Fe the follow­
ing factors were studied :
(1) metabolism of orally administered 59Fe in the body (absorption, dis­
tribution and excretion) ;
(2) tissue doses in individual organs and in the whole body;
(3) the electrical activity of the brain as shown by encephalograms;
(4) the electrical activity of the heart under normal conditions and against
a background of pharmacological stresses ;
(5) haemopoiesis under normal conditions and during functional stresses
(parturition, bloodloss) ;
(6) certain biochemical changes (proteins and protein fractions, sugar un­
der normal conditions and with sugar loading);
(7) morphological changes in organs and tissues at different intervals dur­
ing administration;
(8) means of stimulating excretion of 59Fe from the body.
In the second series (intratracheal injection) the following factors were in­
vestigated:
(1) effect of 59Fe on the central nervous system (stimulation threshold,
summation of subliminal impulses) ;
(2) peripheral blood;
(3) long-term effects of intratracheal injection of soluble and insoluble
59Fe compounds with calculation of tissue doses in the lungs and whole body
(morphological investigation).
Such complex investigations on the same animals over a period of up to
21 months enabled the detection of peculiarities in the behaviour and bio­
logical effect of 59Fe in the long-term experiment, distinguishing it from the
effects of other isotopes studied by us (cf. E.B.Kurlyandskaya: Toxicology
of Radioactive Substances, vol. 1, 1957 and vol. 2, 1960) and also the formu­
lation of maximum permissible concentrations of 59Fe based on biological
results.
In studies on the metabolism of 59Fe after oral administration (G. A. Avru-
nina) it was established that on a normal diet, without iron deficiency in the
body, only about 5 per cent of soluble ferric chloride is absorbed by the
gastro-intestinal tract. The unabsorbed portion is almost entirely excreted
with the faeces in the course of a week. At the same time, however, the half-
4 Toxicology of Radioactive Substances
life of iron in the blood is fairly long, about 200 days, and is due to its fixa­
tion in the bone marrow and utilization in haemoglobin synthesis.
In the earlier published work of the Laboratory, it was shown that with
daily administration of radioisotopes (89Sr, 134Cs, 60Co) an equilibrium level
of body content is reached. The time taken to reach this equilibrium and the
level of activity attained depend on the character of the isotope, the amount
of carrier, the animal's diet and other factors. Similar principles were found
to apply also to 59Fe (G.A. Avrunina). After 45-65 days, according to the
amount of carrier, a fairly constant level of 59Fe is maintained in the blood,
bone marrow, liver and other organs, and varies insignificantly throughout
21 months. However, it is significant that no such constancy obtains in the
gastro-intestinal tract of animals dying at different stages, and the amount of
59Fe found there is from 5 to 8 times the amount of the daily administered
dose. As a result, fairly heavy doses of irradiation may occur in the abdomi­
nal cavity, and can be detected by systematic in vivo measurement of external
y-radiation from the animals submitted to chronic 59Fe intoxication. This
factor is not sufficiently considered by physicists in calculating maximum
permissible concentrations, and it confirms the necessity for their experi­
mental verification.
Tissue doses were calculated by G.A.Avrunina from the results of mea­
surement in particular organs and also in the whole body, obtained by sys­
tematic in vivo measurement of external y-radiation of the animals. Doses of
ß- and y-radiation in the liver in rabbits of the first and second groups were
0-133 and 1-35 rads per day, in the spleen 0-173 and 1-56 rads, in the bone
marrow 0-109 and 0-55 rads, and in the blood 0-145 and 0-91 rads per day
respectively. In the remaining organs doses were considerably lower (cf.
Avrunina's paper in the present volume).
The mean whole body dose (mean of the in vivo measurements) was in the
first group about 0-040 rads per day, and in the second about 0-3 rads per
day. Thus, mean doses under our experimental conditions were either close
to the maximum permissible or, when the administered amounts were in­
creased by 10 and 100 times, exceeded maximum permissible by 15 times,
which again underlines the absence of a complete correlation between cal­
culated results and the data obtained experimentally.
The picture of chronic radiation sickness produced by administration of
59Fe bore peculiarities characteristic for iron.
Three to five weeks after beginning daily administration of a dose of 10 μc
per kg weight to rabbits of the second group changes appeared in the re­
sponse of the brain currents to rhythmic photostimulation (D. A. Ginsburg),
manifested by the appearance of evoked rhythm at higher stimulation fre­
quencies. In most animals trace rhythms were detected in the motor-sensory
regions which were not found in the control animals.
It must be emphasized that resting E.E.G. activity was unchanged and
current disturbance was manifested only on application of functional stress,
such as rhythmic photostimulation. This indicates a functional rather than an
organic impairment of the brain at these stages.
Toxicology of Radioactive Iron-59 5
Earlier, even in the first month of administration of 10 [/.c/kg 59Fe, changes
in the haemopoiesis occurs (N.L.Beloborodova, V. L. Ponomareva, E.K.
Red'kina). In our previous volume (The Toxicology of Radioactive Substan­
ces, vol. 2, 1960) detailed results concerning the chronic effect of 60Co on
haemopoiesis were given. The specific effect of 60Co on red blood formation,
connected with the role of the stable isotope of cobalt in these processes, was
dealt with. Taking into consideration the importance of iron in erythropoie-
sis, and also differences in the mechanisms of action of Co and Fe, a com­
parison was made between the effects of these two elements on the red blood.
The number, form, diameter and osmotic fragility of the red cells were in­
vestigated, along with the size and character of the red cell precursors in the
bone marrow (V.L.Ponomareva).
It transpired that the very early changes in erythropoiesis caused by admini­
stration of 60Co and 59Fe were quite different.With prolonged oral administra­
tion of 60Co the main change was an initial increase, followed by a reduction in
the number of red cells. After 16 months of administration pronounced anae­
mia had developed in the rabbits. The colour index was virtually unchanged.
With administration of 59Fe, the haemoglobin level begins to rise from the
first month, reaching its highest point by the 6th month (1-7 g per cent).
There was no significant change in the number of red cells, and consequently
the colour index was considerably increased. This increase became statis­
tically significant after the first month of administration of 59Fe (data from
62 experimental and 35 control animals). The question arises as to whether
the rise in the haemoglobin level was associated with the administration of
iron as a component part of haemoglobin. And indeed, by the end of the
first month a statistically significant short-term increase in the haemoglobin
level and colour index was detected in rabbits receiving an equivalent
amount of stable iron. Thus, there is a basis for supposing that, as in the
60Co experiments, micro-quantities of the element iron change the functional
condition of the haemopoietic system, giving specific changes in the patho­
logical process in the haemopoietic organs.
In view of the particularly important role of iron in erythropoiesis changes
in size and shape of the red cells were studied (V.L.Ponomareva). It was
shown that administration of 59Fe produces an increased mean red cell dia­
meter, which becomes statistically significant from the 3rd, and reaches a
maximum by the 6th, month of administration. It should be emphasized
that the number of reticulocytes in the peripheral blood, which normally have
a larger diameter, did not increase. The diameter distribution curves of both
peripheral blood red cells and of their nuclear precursors in the bone marrow
(erythroblasts and normoblasts) were shifted to the right, i.e. towards larger
diameters. Red cell volume was also increased, but to a lesser degree than dia­
meter. In this connection increased numbers of leptocytes were observed in
the experimental rabbits, earlier in the second group (ΙΟμ/kg) and somewhat
later in animals of the first group. It may be supposed that the increased dia­
meter of the red cell precursors in the bone marrow is linked with develop­
mental abnormalities.
6 Toxicology of Radioactive Substances
These results show that the appearance in the peripheral blood of macro-
cytic leptocytes with increased haemoglobin content, due to increased volume
of the red cells, must be considered one of the early reactions of the haemo-
poietic organs to administration of 59Fe. Increased haemoglobin and red
cell volume is a peculiarity of the effect of 59Fe, whereas leptocytosis was also
observed with administration of 60Co.
Qualitative and quantitative analysis of the morphological composition of
the bone marrow showed that, in the experimental animals, the total number
of nucleated bone marrow cells increases from the first months of adminis­
tration, and, in most, also the number of cells of the red series, especially in
animals of the first group (1 μό).
Analysis of the experimental results shows that during the first year of
administration of 59Fe definite changes in erythropoiesis occur, apparently
of a compensatory character. It may be supposed that one of the causes of
erythroid hyperplasia, during daily administration of small amounts of 59Fe,
is concealed anoxia, associated with, on the one hand, formation of physio­
logically sub-standard haemoglobin, and on the other, with reduced ef­
ficiency of the respiratory enzymes, the molecules of which include radio­
active iron. Evidence for this supposition is provided by the fact that, despite
the raised level of haemoglobin, when a significant stress is placed upon the
haemopoietic organs, such as bloodloss, the haemoglobin level is restored
more slowly in the experimental animals than in the controls. It would seem
that this can be considered a symptom of defective haemoglobin synthesis,
and is shown by the condition of the haemopoietic processes in pregnant
animals after prolonged administration of 59Fe (N.L.Beloborodova, V.L.
Ponomareva, E.K.Red'kina). As the results of these authors in the present
volume show, anaemia, developed earlier during pregnancy in the experi­
mental animals than in the controls, and was accompanied by signs of
pathological erythropoiesis. Post-partum anaemia in the former was marked
by its duration and by the formation of defective erythrocytes.
It is of interest to note that with all the specificity of the effect of 59Fe on
red blood formation, changes in leuco- and lymphopoiesis in no way differed
from those observed with other isotopes, especially 60Co. With administra­
tion of both isotopes, transitory lymphopenia was observed from the first
month, together with a fall in the absolute number of lymphocytes. Further
investigation showed that the fall in the absolute lymphocyte number was a
consequence of impaired lymphopoiesis, which during the first 12-14 months
was of a functional character (A. S. Kaplanskii, E.S.Gaidova) without the
morphological changes which occurred at later periods.
In analysing the results obtained on the effect of 59Fe on the haemopoietic
processes, the suggestion can be made that changes in erythropoiesis during
prolonged administration of this isotope are the result of the combined ra­
diation and chemical effect of the element, which plays a very important part
in erythropoiesis.
Although 59Fe has specific effects on haemopoiesis, changes in cardiac
responses, as shown by electrocardiograms, differ little from those produced
Toxicology of Radioactive Iron-59 1
by 60Co (A.O.Saitanov). As in the latter case, daily administration of 59Fe
in an amount of 10 and 1 μc per kg body weight produced a change in the
terminal part of the ventricular complex, chiefly of the T wave, which ap­
peared during the 10th—11th month and was especially pronounced from the
14th to the 20th months of administration, i.e. during the period when paral­
lel histological investigations were revealing dystrophic lesions in the cardiac
muscle. At approximately the same period changes in certain biochemical
processes occur. Thus, serial estimations of the fractional composition of the
serum proteins by R. L. Orlyanskaya revealed a reduction of albumin, de­
tected by paper electrophoresis, and an increase of y-globulin in the serum
of animals of the first and second groups, which may be associated with a
disturbance of the liver's synthesizing function. This is also shown by
changes in the sugar curve in experimental animals following oral adminis­
tration of glucose.
Observations on the condition of rabbits subjected to prolonged adminis­
tration of radioisotopes showed great variation in individual sensitivity both
to 59Fe and other isotopes. The most sensitive animals die during the early
stages of the experiment (chiefly during the first few months), mainly from
pneumonia. Examination of animals dying at this stage revealed a diffuse
suppurative process with leucocytic reaction in the lungs, and foci of myeloid
haemopoiesis were found. The animals which survived for a fairly long period
(up to 11-12 months) were in good condition and gained weight. At this
stage, no gross morphological lesions were found (E. S. Gaidova). The latter
arise chiefly during the period from 10 to 17 months and are most pro­
nounced in second group animals. These rabbits show adiposis, sluggish in­
flammatory reactions, diffuse and focal sclerosis of the pulmonary tissue, and
atypical bronchial epithelium; areas of adenomatosis appear, blood vessel
walls become softened and oedematous and the amount of lymphoid tissue
in the spleen decreases. Dystrophic and sclerotic lesions are found in the liver
and kidneys. In some animals, the thyroid gland showed a reduction in
follicle size, and a reduction and even complete disappearance of colloid. The
gonads showed atrophie lesions (E. S. Gaidova). These morphological fea­
tures are in complete agreement with the functional disturbances in the dif­
ferent systems and organs. It must be emphasized that the lesions observed
were little different from those previously found with other isotopes.
Analysis of the results obtained showed that even with a ten-fold increase
of the maximum permissible concentration recommended by ICRP* for
59Fe and with a relatively small (2-3 times) excess of the radiation dose
in the body and "critical" organs, the changes characteristic of radioactive
iron occur. This led us to question the level of the existing international
maximum permissible concentrations of 59Fe for water (4 x 10"6 c/1). The
permissible concentrations proposed by us (according to our results they
should not exceed 1 x 10~8 c/1) have been incorporated into the U.S.S.R.
* Recommendation of the International Commission on Radiological Protection. Re­
port of Committee II on Permissible Dose for Internal Radiation, p. 45. Pergamon Press,
1960.
8 Toxicology of Radioactive Substances
Rules of Hygiene for work with radioactive substances and sources of ioniz­
ing radiation (No. 333-66 of 26 June 1960).
Further work in the field of soluble and insoluble radioactive compounds
included investigation into the effects of intratracheal injection of a soluble
iron citrate compound and insoluble iron oxide (N. D. Sagaidak). By this
method of administration virtually all the insoluble iron compound remains
in the lungs for a prolonged period, only negligible amounts being found in
other organs. Distribution of iron citrate after intratracheal injection is
similar to that obtained in G.A.Avrunina's experiments (cf. the present
volume. Body dose in rabbits receiving daily oral administration of 59FeCl ,
3
and some data on accumulation and excretion of 59Fe). A peculiarity of the
behaviour of iron citrate in the lungs is of interest. Although most is ab­
sorbed from the lungs during the first day after injection, nevertheless by the
end of a month after a single injection about 9 per cent of the injected quantity
has become fixed in the lungs for a prolonged period, probably in the form
of a compound of 59Fe with proteins. The possibility of formation in the
lungs of insoluble radioactive compounds, which may create a rather large
total radiation dose, our lack of knowledge concerning conversion of soluble
compounds in the lungs, and the gravity of the possible consequences, lead
us to suggest that work on radioactive aerosols for inhalation must be car­
ried out under the most strict conditions, i.e. as though for insoluble com­
pounds, which would make human contact with radioactive aerosols safe. The
necessity for this is dictated by the following facts. N.D. Sagaidak, studying
the long-term effects of intratracheal injection of 59Fe oxide in amounts ex­
ceeding the maximum permissible concentrations by 10 and 30 times, found
bronchial cancer in 6 of 25 rats (25 per cent). Total radiation dose in the
lungs during the 15 months of the experiment was 484-1296 rads, and on the
first day 8*5-26 rads. With injection of permissible quantities of iron oxide
for 15 months no cancer was observed. It is noteworthy that the threshold
for the carcinogenic effect with iron was significantly lower than with the
other insoluble isotope compounds we have studied (32P and 198Au). This
has enabled us to suggest that there is apparently no single threshold for the
carcinogenic action of radioactive isotopes, and the value of the threshold
may be affected by many factors, including the chemical and biological
properties of the element, in this case 59Fe. It can also be assumed that for
isotopes with short half-lives, the amount of radiation and the total energy
absorbed are the main factors, which for these isotopes (24Na, 198Au, 32P)
must be large (thousands of rads), as T. A. Kochetkova and G.A.Avrunina's
investigations have shown. The time factor is of primary importance for
isotopes with long half-lives, i.e. the duration of the prolonged effect of
small doses. This proposition requires further experimental verification and
in fact forms one of this laboratory's current research problems.
But the data already available are enough to indicate the necessity for the
strict standardization of radioactive aerosols, the prolonged inhalation of
which either creates large local doses at the sites of deposition or has an ir­
ritant effect in these areas, leading to the occurrence of neoplasms in the