V-/EPA
United States
Environmental Protection
Agency
Health Effects Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S1-81-011 Mar. 1981
Project Summary
Sensitive Biochemical and
Behavioral Indicators of Trace
Substance Exposure:
Part 1. Cerium
Edward J. Massaro, John B. Morganti, Bradley A. Lown, Carl H. Stineman,
and Rosemary B. D'Agostino
The overall objective of this project
was to investigate potential toxic
effects of acute and chronic exposure
to Ce with the mouse as a model
mammalian system. In the adult mouse,
the tissue/organ distribution of Ce
was determined at various times after
exposure to a single dose or repeated
(multiple) doses of CeC13. In addition,
the effects of Ce exposure on selected
behavioral parameters were also ex-
amined along with open-field and
exploratory behaviors, passive and
active avoidance learning, and an
aspect of social behavior. Statistical
correlations between tissue/organ Ce
levels and various behavioral measures
were also examined in the adult
studies to gain insight into the basis of
the relationships between the two sets
of data. Another major focus of this
research examined the effects of Ce.
on the gravid female mouse and on the
embryonic, fetal and postnatal devel-
opment of the offspring of Ce exposed
dams. Cerium tissue/organ distribu-
tion and various maternal and offspring
developmental behaviors were investi-
gated.
This Project Summary was develop-
ed by EPA's Health Effects Research
Laboratory. Research Triangle Park,
NC, to announce key findings of the
research project which is fully docu-
mented in a separate report of the
same title (see Project Report ordering
information at bach).
Discussion
Subcutaneous administration of 136
mg Ce/kg (LD5) was found to induce
fatty infiltration of the liver. However,
this effect was transient: the fatty infil-
tration regressed with time while the
liver Ce levels remained elevated. The
nature of this phenomenon was probed
in studies of the subcellular distribution
of Ce in the liver as a function of time.
Lethality parameters were established
for Ce (citrate) administered intragas-
trically (i.g.) and subcutaneously (s.c.).
The i.g. route was selected for its
environmental relevance and the s.c.
route for better dosage control and for
its relation to the transdermal route.
For males, the LD5o, LDa5 and LD5
(with 95% confidence intervals) levels
were: 1291 (1198-1449), 1163(1017-
1250) and 1000(743-1104) mg Ce/kg,
respectively, for the i.g. route of admin-
istration and 205 (181-241), 173(140-
195) and 136 (86-160) mg Ce/kg,
respectively, for the s.c. route.
Nongravid and gravid (day 12 of
gestation) females received 68 to 318
mg Ce/kg. Day seven viability and
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Lethal dose levels (calculated by probit
analysis) for the s.c. route of administra-
tion are summarized in Tables 1 and 2,
respectively.
The tissue distribution of Ce was
investigated in adult males andfemales,
in the developing fetus and in offspring
of Ce exposed dams. Male mice were
exposed either to a single, acute dose or
to a multiple dose sequence.
For single dose exposure, all tissues/
organs exhibited significant main effects
of time and/or route. The liver, kidney,
lung, muscle, cerebrum and brain stem
also showed an effect of dose but only
within the s.c. route. Many tissues
exhibited a time-by-route interaction
but only lung exhibited a dose-by-time
interaction and-only-via the s.c. route.
The strongest effect by far was that of
route. This was anticipated and largely
reflects the poor uptake of Ce via the i.g.
route as well as quantitative differences
in the actual doses administered via
each route. The time effects were due to
the time dependent decrease in tissue
Ce (except in the spleen where Ce peaks
between one and three days post ad-
ministration). The significant dose effects
via the s.c. route were due to higher
tissue/organ Ce levels in animals re-
ceiving the higher Ce dose. The absence
of such effects in some tissues may be
accounted for by the high variability
encountered at the doses employed.
The time-by-route andtime-by-dose
interactions within the s.c. route may be
attributed to route/dose pharmacoki-
netic differences.
The tissue/organ Ce levels for the
multiple dose exposure are presented in
Table 3. The multivariate ANOVAshowed
that, across all tissues, there was a
significant difference in Ce concentra-
tion across exposures (F = 2.27, d.f. =
126/510.92, p 0.001). The univariate F-
ratios showed that this was also true (p
0.05) for all individual tissues except
blood, cerebellum and brain stem. For
the most part, the effect was one of in-
creasing Ce tissue/organ Levels with
the increasing number of exposures.
Muscle levels were highly variable and
may reflect some direct absorption of Ce
via migration from the injection sites.
Distribution of Ce in the tissue of
mother, fetus, and offspring was also
determined. Cerium levels were highest
in all maternal tissues one to two days
after Ce administration and then declined
through the remainder of the gestation
period. The highest Ce level observed
was in liver (333 ± 23 ppm) two day post
administration. The Ce levels in mater-
nal tissues were of the order: liver >
spleen > lung > kidney. Maternal brain
Ce levels were low (less than 0.3 ppm) at
all times of observation. Cerium levels
in the developing organism were highest
one day post administration (5.71 ±
1.22 ppm) and then declined six fold
over the succeeding four days. Cerium
was below the level of detectability
(limit of detection < 0.05 ppm) in the
individual tissues selected for examina-
tion of offspring of all treatment groups
from parturition up to 21 days post
partum. Neonates had measurable
whole body Ce levels up to three days
post maternal Ce administration. How-
ever, Ce was undetectable in fetal blood,
liver, kidney, cerebrum and cerebellum
even though mean whole body content
measured 0.12 ppm ± 0.02 ppm.
Effects of exposure to acute and
repeated doses of Ce, via the i.g. or s.c.
routes, on selected behavioral parame-
ters were also investigated. These data
were correlated with those of the tissue
distribution study in an attempt to gain
insight into the mode of toxic action of
Ce. These studies included both single
(acute) and multiple dose exposures.
Acute exposure studies included mea-
sures of open-field behavior, exploratory
behavior, wheel usage, passive and
active avoidance, and social behavior.
Significant effects were found for all
measures.
The effects of repeated exposure to Ce
on open-field and exploratory behavior
were studied and correlated with tissue
levels of Ce. A significant multivariate
effect was found for number of expo-
sures, and significant univariate effects
were found for rearings and exploration.
Developmental studies included neo-
natal, maternal, and adult offspring
Table 1. Effect of Increasing Ce
Dose* on Seven Day
Viability or Gravid" and
Nongravid Animals
Seven Day Viability
Dose Level Nongravid Gravid
68
86
104
122
140
157
175
192
210
228
246
264
282
300
318
—
—
10/10C
10/10
8/10
7/10
4/10
6/10
6/10
2/10
1/10
1/10
0/10
0/10
10/10
10/10
9/10
8/10
8/10
5/10
5/10
3/10
1/10
1/10
0/10
0/10
—
—
—
*The Ce dose administered was based
on maternal weight at time of injection.
hAII mice were injected on day 12 of
gestation.
^Numerator - number surviving;
denominator - total N.
Table 2. Ce Lethal Dose Levels as Determined by Linear Regression Analysis
of Seven Day Viability
Nongravid
Gravid6
Lethality*
Dose"
Rangec
Dose
Range
/.Di
LD5
LD^
LD25
LD*o
LDSO
LD60
LD75
LD90
LD95
LD99
117
138
151
174
193
205
218
241
280
305
360
71.6-142
95.8-161
112-172
143-193
168-212
183-226
198-244
220-283
249-360
266-419
300-559
80.2
94.4
108
131
150
166
179
199
226
254
301
43.6-103
55.8-119
73.1-129
100-153
127-172
147-189
160-204
181-237
198-280
218-361
251-497
"Lethality levels are expressed as the percent mortality expected within seven days
after Ce administration.
bCe dose, in ppm administered on the basis of maternal weight, calculated to produce
the corresponding lethality.
cThe p<0.05 probability range of the corresponding dose. {
"All mice were injected on day 12 of gestation.
-------
Table 3. Tissue/Organ Ce Concentrations in fig Ce/g (Wet Weight) Tissue (PPM) - Repeated Exposure
Cumulative dose (mg Ce/kg) ppm" N (subjects per cell)
Time (days) after
first exposure
20
40
60
80
100
120
140
160
180
200
200
200
3
6
9
12
15
18
21
24
27
30
69
125
10
10
10
10
10
8
7
9
7
7
9
6
Blood*
Mean
0.04
0.03
0.04
0.05
0.06
0.04
0.03
0.04
0.03
0.04
0.09
0.18
SD
0.03
0.03
0.04
0.06
0.05
0.02
0.03
0.03
0.03
0.02
0.23
0.16
Stomach
20
40
60
80
100
120
140
160
180
200
200
200
3
6
9
12
15
18
21
24
27
30
69
125
10
10
10
10
10
8
7
9
7
7
9
6
Mean
0.68
0.87
1.67
2.21
2.92
3.29
2.99
4.05
3.69
4.65
4.51
4.03
SD
2.27
0.37
0.61
0.55
1.35
1.28
1.56
1.46
1.60
2.27
2.05
2.91
Bone
20
40
60
80
100
120
140
160
180
200
200
200
3
6
9
12
15
18
21
24
27
30
69
125
10
1O
10
10
10
8
7
9
7
7
9
6
Mean
3.71
6.69
12.70
16.48
22.02
26.62
15.74
21.02
34.01
27.60
30.91
39.17
SD
1.14
5.41
3.74
10.69
12.98
11.70
5.82
9.81
29.18
13.38
9.04
9.01
Liver
Mean
28.80
47.53
73.36
81.93
111.02
130.59
118.38
147.31
151.61
155.27
157.06
152.78
SD
7.14
3.32
16.72
16.50
19.76
29.46
11.60
24.97
19.24
37.32
57.51
44.73
Duodenum
Mean
0.78
0.96
2.11
2.40
3.59
4.31
2.87
3.80
4.49
3.59
3.77
2.63
SD
0.37
0.41
0.75
1.22
1.98
1.86
0.43
1.18
1.82
1.53
3.93
1.11
Cerebrum*
Mean
0.09
O.O5
0.13
0.07
0.08
0.16
0.11
0.13
0.13
0.12
0.13
0.77
SD
0.05
0.05
0.11
0.03
0.03
0.08
0.06
0.06
0.05
0.06
0.11
0.65
Kidney
Mean
1.09
3.18
3.23
3.63
5.08
6.23
5.50
6.18
6.23
6.55
7.56
6.01
SD
0.38
5.17
1.17
0.90
1.28
1.13
0.95
2.63
2.57
2.15
3.10
1.57
Testes
Mean
0.37
0.54
0.82
1.14
1.38
7.72
1.51
1.84
1.83
1.84
1.85
2.09
SD
0.12
0.24
0.17
0.75
0.35
0.46
0.35
0.25
0.33
0.54
0.68
0.67
Cerebellum*
Mean
0.2
0.2
0.3
0.2
0.2
0.3
0.3
0.2
0.3
0.3
0.2
1.3
SD
0.2
0.2
0.3
0.2
0.2
0.3
0.3
0.1
0.2
0.2
0.3
1.2
Spleen Pancreas Lung
Mean
27.34
38.21
83.65
94.54
133.74
175.98
160.55
195.25
227.88
228.50
315.83
341.32
SD Mean
10.25 0. 19
15.36 0.24
43.43 0.59
44.76 0.60
33.61 0.94
64.62 0.86
35.99 0.82
46.02 1.10
96.71 0.98
118.61 1.08
217.35 1.16
124.05 1.84
SD Mean SD
0.09 2.59 0.45
0.07 3.71 1.08
0.56 11.32 12.46
0.21 9.07 2.86
0.78 9.07 1.12
0.27 12.42 3.58
0.42 13.19 1.65
0.48 14.67 2.85
0.18 15.95 5.10
0.37 16.27 5.01
1.47 14.24 4.83
1.20 13.49 2.38
Skeletal Muscle
Mean
0.11
32.04
24.53
23.12
89.54
32.62
35.91
47.71
30.18
26.90
37.80
54.25
Brain
Mean
0.09
0.06
0.08
0.10
0.12
0.16
0.14
0.12
0.16
0.13
0.19
1.13
SD
0.07
44.46
26.53
28.25
114.56
26.89
56.17
42.37
29.18
17.90
44.57
50.94
Stem*
SD
0.07
0.06
0.08
0.08
0.07
0.10
0.08
0.10
0.07
0.12
0.25
0.47
'Each dose (s.c.) contained 20 mg Ce/kg body weight as the CeCI* sodium citrate, 1:3 complex, pH 7.4. Animals were sacrificed
three days after their last injection except for the fast two groups which were sacrificed 42 and 98 days after their last
injection.
Concentrations near detection limit and should be regarded as upper limits rather than accurate values.
-------
observations. Significant effects were
found in all cases.
To obtain information on the relation-
ship of the subcellular distribution of Ce
to the genesis and rapid disappearance
of Ce induced fatty infiltration of the
liver, the subcellular distribution of Ce
was investigated.
One day post administration, the
livers of the Ce exposed animals exhib-
ited signs of fatty infiltration. They were
mottled and light in color and, following
centrif ugation of the homogenates to
obtain the nuclear pellet, the super-
natants displayed evidence of lipid
levels considerably higher than those
found in control liver homogenates.
A representative subcellular distribu-
tion of Ce in the liver (obtained utilizing
density gradient procedure B described
above) at one, three and seven days post
administration is presented in Table 4.
The ANOVA of the distribution, as a
function of time, is presented in Table 5.
Two animals in the one day group had
extraordinarily high percentages of Ce
in their nuclear fractions and low per-
centages in their pellets. (Other than
evoking individual variability, there is, at
present, no explanation for this finding).
Thus, the means and standard deviations
for the nuclear and "Pellet" fractions
are presented, both including and ex-
cluding these animals.
The highest percentages of recovered
Ce was found in the "Pellet." This
fraction is comprised of the materials
having a density greater than that of the
nuclear fraction. The percentage of Ce
in the "Pellet" increased from 45 to 53
from one to seven days post exposure.
The nuclear fraction contained the
second highest percentage of Ce. How-
ever, in contrast to the "Pellet" fraction,
the percentage of Ce in this fraction
decreased from 28 to 14 from one to
seven days post administration. The
mitochondria contained the third highest
percentage of Ce which remained rela-
tively invarient throughout the period of
observation. As in the "Pellet," the
percentages of Ce in both the micro-
somes and the cytosol increased across
time, while the peroxisome content
decreased to a constant level at three
days. The differences in Ce content
across time were significant for all
fractions except the mitochondrial.
Conclusions
The Tissue/Organ Distribution and
Alterations in Open-Field and Exploratory
Table 4.
Liver Subcellular Ce Distribution at One, Three and Seven Days Post
Administration (Percent of Ce Recovered}
Time post administration (days)
Fraction
Mean
SD
Mean
SD Mean
SD
Cytosol
Microsomes
Mitochondria
Peroxisomes
Nuclei
'•Pellet""
2.34
7.32
10.33
6.37
36.70
(28.16)"
37.47
(45. 73)"
0.39
1.29
1.80
1.40
14.31
(4.22)"
13.32
(4.05)*
4.40
12.49
10.09
3.64
17.49
51.88
0.73
0.88
2.21
0.73
4.95
2.89
7.17
13.92
8.28
3.18
14.14
53.29
0.53
1.52
1.30
0.73
2.01
1.60
% of Ce Recovered
96.34
1.73
90.64 2.82 88.49 3.55
"Values obtained omitting two animals with extraordinarily high nuclei and low pellet
values.
tiThis term denotes all materials with a density greater than that of the nuclear fraction.
Behavior Following Accute Exposure to
Ce. Between four hours and seven days
post administration, Ce administered
via the i.g. route at a level as high as the
LD2s, had no significant effect on open-
field (ambulations and rearings) or
"hole-in-board" exploratory behaviors
of the adult mouse. Apparently, this was
due to the fact that little Ce is absorbed
from the gut. Despite low uptake, the
doses employed were toxic to the mouse.
Gastritis and enteritis were demonstrated
histologically in these animals. How-
ever, it is not known if Ce was directly
responsible for such lesions. It is possible
that osmotic phenomena may have
been involved in view of the high solute
concentrations employed.
A different situation prevailed when
Ce was administered via the s.c. route.
At short times post administration,
open-field and exploratory behaviors
were significantly depressed, systemic
distribution of Ce was substantial and
behavioral alterations were correlated
with tissue/organ Ce levels.
An inverse relationship between be-
havior, brain and lung Ce levels was
found. Of all tissues studied, the brain
correlated most strongly with behavior.
This is of particular interest in that the
same treatment groups which had
exhibited depressed open-field behavior
(which occurred at four hour and one
day post s.c. administration of Ce at the
LD25 level and at four hour post ad-
ministration of the LDs dose) also exhib-
ited detectable brain Ce levels. In con-
trast, the brain Ce levels of all other
groups were essentially at or below the
detection limit. Moreover, there are
numerous reports in the literature of
lanthanum interfering with "calcium
sites" on nerve cells. Cerium, the next
element in the lanthanide series, may
have a similar effect which, in this
study, was expressed as depressed
open-field and exploratory behavior.
After the brain regions, the strongest
behavioral correlation involved the'
lung. The lung accumulated substantial
quantities of Ce. However, histological
examination revealed no abnormalities
attributable to Ce. Thus, the relationship
Table 5. Analysis of Variance of Liver
Subcellular Ce Distribution
Variable Time Effect
Multivariate d. f.
F-ratio
Univariate d. f.
F -ratios
Cytosol
Microsomes
Mitochondria
Peroxisomes
Nuclei
Pellet
% Ce Recovered0
12/20
13.67"
2/15
118.72"
45.66"
2.01
17.75"
11.08*
(16.26)"
7.23*
(9.22)M
11.22*
"P<0.001.
bp
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between lung Ce levels and behavior
remains unclear. These data suggest
that inhalation of Ce may be a consider-
ably greater hazard than ingestion.
The spleen is of interest in that it
contained the highest Ce concentration
of any tissue examined. Its Ce level was
the only one positively correlated with
behavior. The spleen may have acquired
its Ce load from damaged erythrocytes
and leucocytes. The high Ce concentra-
tion in the spleen and the positive
correlation with behavior suggest that
sequestration of Ce by the spleen may
function to spare more sensitive poten-
tial target tissues, such as the brain,
from perturbation. Indeed, the small
negative correlations which were ob-
served between Ce levels in the spleen
and brain regions are consistent with
such a "protective" function.
It is possible, of course, that the
hypoactivity observed in the open-field
behavioral measures of animals receiv-
ing Ce via the s.c. route was mediated by
a secondary effect of Ce, namely, that it
made the animals physically ill and
lethargic. However, it should be noted
that no behavioral effects were observed
in animals receiving Ce via the i.g. route,
even though histopathological analysis
provided evidence of acute gastritis and
enteritis with a duration of at least
seven days post administration.
If the animals were hypoactive simply
because they were physically ill, it
would be anticipated that the i.g. dosed
animals would certainly have been
physically ill at least through day seven
post administration. The s.c. dosed
animals which showed no evidence of
gastritis or enteritis exhibited significant
open-field behavioral alterations which
were strongly correlated with brain Ce
levels. Furthermore, s.c. dosed animals
also exhibited alterations in exploratory
behavior. The exploratory task employed
was substantially less dependent on the
gross activity level of the animals and,
therefore, suggests that the effects of
Ce were not limited toa simple decrease
in the general activity level.
In summary, Ce administered via the
s.c. route achieves general systemic
distribution and depressed open-field
and exploratory behavior up to 24 hours
post administration, possibly by inter-
action with the CNS.
High Ce doses administered i.g.,
while toxic, did not effect either ambula-
tions or rearings m the open-field nor
exploratory behavior. Probably, this was
due to the poor uptake of Ce from the gut
which consequently limited systemic
distribution. Peroral exposure to Ce
would appear to present little danger of
acute toxicity, since the doses used in
these studies were considerably greater
than any anticipated to occur from
environmental exposure.
If Ce compounds are incorporated into
fuels, inhalation will constitute another
route of environmental exposure. A
much higher percentage of Ce appears
to be retained following inhalation than
ingestion. However, even via s.c. ad-
ministration, the lung accumulates Ce
and lung Ce levels are inversely cor-
related with open-field activity. These
findings suggest that inhalation of Ce
may be a considerably greater acute
hazard than ingestion and must be
investigated before Ce (compounds) can
be considered "safe" for widespread
environmental dispersion
Activity Wheel Study The results of
this study indicate that a single dose of
Ce at the s.c. LD5 level can significantly
depress general activity and that this
effect is persistent. This relative depres-
sion was maintained, along with a
monotonic increase in performance, for
all groups (LD5, LD25 and controls) over
time. The most depressed scores for the
Ce exposed groups occurred during the
24 hour period following Ce administra-
tion. It is difficult to interpret this effect,
since the animals did not exhibit any
obvious signs of illness or incapacitation.
It appears that a single exposure to Ce,
at relatively high levels (LD5, LDzs), has a
substantial effect on total (24 hour)
activity level. Perhaps total activity, as
assessed by the activity wheel, is a more
sensitive index of subtle effects induced
by Ce exposure than is the short time
sample obtained with such measures as
the open-field.
Passive Avoidance Compared to sodi-
um citrate, acute Ce citrate administra-
tion was associated with an increase in
latency in both trails of the passive
avoidance learning task. This was prob-
ably another manifestation of the de-
pressed activity observed in the acute
open-field and activity wheel studies.
Relative to the citrate controls, learning
of the passive avoidance task was not
adversely effected by Ce administration.
Active Avoidance Behavior Single
doses of Ce at the LD5 and LD25 levels
had no effect on two-way active avoidance
learning by the mouse. However,consis-
tent with the results of the open-field,
activity wheel, and passive avoidance
studies (see above), Ce at the s.c. LDas
level depressed activity. The depressed
activity did not influence the learning of
the task.
Social Behavior As in the open-field,
activity wheel, passive avoidance and
active avoidance studies, Ce (at the LD5
and LD2s levels) depressed gross activity.
Thus, the control (citrate) animals were
significantly more active than either
group of Ce exposed animals (which
were not significantly different). Al-
though mobility was depressed, Ce had
no dramatic effect on the social behav-
iors that were investigated. However,
multivariate ANOVAof the data revealed
a dosage by day of observation inter-
action. This interaction is difficult to
assess. Taken at face value, it would
appear that Ce, at high dose levels
(LDzs), does affect a measure of social
behavior (e.g., distance maintained be-
tween pairs of animals), but the effect
has a long latency period and does not
appear until 3 days post exposure The
absence of more consistent patterns of
effects on social behavior indicates that
further study is required before confident
conclusions can be generated.
The Tissue/Organ Distribution and
Alterations in Open-Field and Explora-
tory Behavior Following Exposure to
Repeated Doses of Ce Exposure to
repetitive s.c. doses of Ce citrate at the
LDi level resulted in the accumulation
of Ce mainly in the spleen, liver and
skeleton. No decrease in Ce levels was
observed in these tissues up to 98 days
after the last dose was admimsteied.
Cerium levels in the liver, kidneys,
pancreas and testes and, possibly, m the
stomach and duodenum appeared to
plateau following the fifth or sixth dose
However, spleen and bone continued to
accumulate Ce even after exposure was
ended. Blood and brain levels were very
low exhibiting counting rates (141Ce)
near background. It is of interest to note
that the blood Ce levels remained low
throughout the course of the experiment.
Similar results were found in the acute
s.c. study (see above). Cerium obviously
is cleared very efficiently from the blood
Judging from their Ce concentrations
across time, the spleen, liver and bone
appear to be involved in the clearance
mechanism.
Although Ce is rapidly cleared from
the blood, it is not rapidly excreted and
toxic effects could result from long-term
retention unless Ce is sequestered in
some non-toxic form.
Exposure to repetitive s.c. doses of Ce
significantly depressed ambulations in
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the open-field and marginally depressed
"hole-m-board" explorations across all
subjects. However, these behavioral
measures did not correlate with tissue/
organ Ce levels which indicate that the
depressive effect of Ce is not a one step
process depending directly on Ce levels
in some tissue(s). Rather, it probably
involves a chain of events culminating
in depressed activity. Such a process is
not uncommon in biological systems.
In the acute study described previous-
ly, highly significant depressions of
ambulations, rearings and explorations
at four hours and one day post s.c.
administration occurred. The doses
employed in that study were much
higher (136 and 173mgCe/kg)thanthe
individual doses (20 mg Ce/kg) used in
the repeated dose study. This could
account for the differential behavioral
results. Detectable Ce levelswerefound
in the brain coincident with depressed
behavior in the acute study, whereas no
detectable brain Ce levels were found in
the repeated dose study. It may be that
the depression of ambulations and
exploratory behavior observed in the
repeated dose study was due to small
amounts of Ce in the central nervous
system. However, the magnitude of this
relationship was too small to detect
statistically given the sample size and
the sensitivity of the Ce assay.
Both the acute and repeated dose
studies demonstrated that exposure to
Ce can induce behavioral changes in the
mouse. It seems reasonable to conclude
that widespread environmental disper-
sion of Ce could be potentially hazardous
considering these findings and the long
biological residence time of Ce. How-
ever, much more information must be
accumulated before the risks of envi-
ronmental Ce dispersion can be accu-
rately assessed.
Neonatal and Adult Offspring Studies
Maternal administration of Ce on Day
12 of gestation affected the development
of certain offspring behaviors. Con-
versely, offspring of mothers receiving
Ce on Day seven of gestation did not
differ from control offspring in the
neonate and adult behavioral measures
investigated. Whether the differential
effects of day of exposure were due to
differences in the intrinsic sensitivity of
the developing organism at these stages
of gestation or to placenta! permeability
factors were not examined.
The, most consistent effect of Ce was
on offspring weight. Neonatal weight
was reduced in offspring-exposed to Ce
in utero via maternal administration and
in the offspring reared by mothers who
received Ce on Day two post partum:
during lactation/suckling. The signifi-
cant prenatal X postnatal interaction
indicates that the treatment the foster
mother receives can modify the rate of
weight gain of the offspring she rears.
Thus, exposure of pregnant females to a
single dose of Ce at the s.c. LDi level had
a relatively long-lived effect on the
mother which was reflected postnatally
in a decreased rate of offspring growth.
This effect may be direct, through
residual Ce in the milk of mothers
treated during gestation, or indirect,
through effects on maternal behavior
manifested, for example, as neglect of
offspring, and reflected in such factors
as ineffective suckling or lack of grooming.
The latter possibility appears reason-
able since laboratory studies revealed
that Ce is not transmitted to offspring
via the milk of mothers exposed during
gestation to the dose levels of Ce em-
ployed. However, the reduced weights
observed in offspring exposed to Ce
prenatally may indicate for example,
that the developing fetuses received
inadequate nutrition because of covert
maternal intoxication resulting in im-
paired transport of nutrients across the
placenta, Ce induced metabolic dys-
function in the offspring that resulted in
impaired ability to utilize nutrients, the
production of milk of inferior nutritional
quality or, perhaps, all, or combinations,
of these possibilities.
Maternal Behavior The offspring
retrieval data indicate that pups exposed
to Ce in utero are retrieved in preference
to control pups. Unfortunately, activity
was not tested on Day three post partum,
the day retrieval was tested. Conceivably,
Ce pups were preferentially retrieved
because they were less active and of
lighter weight.
Liver Subcellular Distribution of Ce
The highest percentages of Ce were
found in the pellet (about 50%) and the
nuclei (28% decreasing to 14%). About
half of the Ce found in the nuclei of cells
examined one day post exposure ap-
peared to have moved into the pellet,
microsomal and cytosolic fractions of
cells by three to seven days post expo-
sure. While no data are available on the
mechanism of this transfer, Ce may be
transported out of the nuclei bound to
mRNA produced in conjunction with re-
generative processes in the liver. Cerium
may exist in the pellet in the form of
insoluble phosphates and hydroxides.
Insoluble forms of Ce also may be
trapped within organelles or bound to
macromolecules (proteins, RNAorDNA)
that are normally associated with them.
Edward J. Massaro is with the Pennsylvania State University, University Park,
PA 16802, John B. Morganti, Bradley A. Lown, Carl H. Stineman. and
Rosemary B. D'Agostino are with the State University College at Buffalo,
Buffalo, NY 14222.
George M. Goldstein is the EPA Project Officer (see below).
The complete report, entitled "Sensitive Biochemical and Behavioral Indicators
of Trace Substance Exposure: Part 1. Cerium," (Order No. PB 81-150 765;
Cost: $8.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
> US GOVERNMENT PRINTING OFFICE 1901-757-064/0301
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