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EC number: 239-594-3
CAS number: 15546-11-9
Among mice killed 24 hours after treatment, the mean incidence of
micronucleated polychromatic erythrocytes (per 1000 polychromatic cells
scored) was 1.6 for the vehicle control group, with a range of 0.0-3.9.
Corresponding values for animals given DBTC at 2, 10 or 50 mg/kg were
closely similar: 1.8, 1.7 or 1.0 with ranges of 0.0-4.2, 0.0-4.6 and
Thus, mean values for DBTC treated groups were closely similar to mean
control group values at the 24 hour termination time, and statistical
analysis confirmed that there was no significant difference between the
vehicle control group and any DBTC treated group (p>0.05).
Among mice killed after 48 or 72 hours, the mean incidences of
micronucleated polychromatic erythrocytes in vehicle controls were 0.6
(range 0.0-2.0) and 1.4 (range 0.0-2.9) respectively. Corresponding
values for animals given DBTC at 50 mg/kg were 3.5 (range 0.0-17.1) and
5.3 (range 0.0-17.5) respectively.
Thus marked increases in the mean frequency of micronucleated
polychromatic cells were apparent in animals dosed with DBTC at 50 mg/kg
at both termination times. It should be noted that these increases were
principally due to data from female mice at both 48 and 72 hours, and
only one male at the 72 hour termination showed a marked increase in
micronucleated polychromatic cells (although this animal also showed
marked bone marrow toxicity). However, statistical analysis showed no
significant differences between sexes in the frequency of micronucleated
polychromatic cells at either termination time, and data were pooled for
comparison to concurrent vehicle control data, which showed the observed
increases at both termination times to be statistically significant
(0.05>p>0.01 in both cases).
Chlorambucil treatment produced a range of micronucleated cells per 1000
polychromatic erythrocytes from 34.0 to 75.8 with a mean of 49.7.
Statistical analysis showed that animals treated with chlorambucil had
significantly more micronucleated polychromatic cells than vehicle
controls (p<0.01). This increase in chromosomal damage after exposure to
a known mutagen demonstrates the sensitivity of the test system.
The recorded incidence of micronuclei per 1000 mature erythrocytes
varied between 0.0 and 2.9 throughout all groups.
The ratio of polychromatic to mature erythrocytes was 1.0 in the vehicle
control group at 24 hours. Ratios for groups given DBTC at 2, 10 or 50
mg/kg and terminated 24 hours later were 1.1, 1.1 or 1.0 respectively.
Forty-eight hours after treatment, the ratio of the vehicle control
group and the group given DBTC at 50 mg/kg was 0.8. Seventy-two hours
after treatment, the ratio of polychromatic to mature erythrocytes in
the vehicle control group was 0.7, and in DBTC treated animals it was
Thus no evidence of bone marrow toxicity was observed in animals treated
with DBTC and killed 24 or 48 hours later; at 72 hours, although the
vehicle control group ratio was slightly reduced (0.7), a marked
reduction was observed in animals treated with DBTC at 50 mg/kg (0.5).
In animals treated with chlorambucil, the ratio between polychromatic
and mature erythrocytes was 0.8.
In an assessment of clastogenic action on bone marrow erythrocytes in
the micronucleus test (Life Science Research Limited project number:
91/0357) the test material showed evidence of induced chromosomal or
other damage leading to micronucleus formation in polychromatic
erythrocytes of mice treated orally with DBTC at 50 mg/kg and sacrificed
48 or 72 hours later.
The procedures and experimental design employed complied with the
recommendations of the relevant toxicity testing guideline of the OECD
(Guideline 474, 1983), the US EPA Guidelines (1985) and EEC Annex V
A biologically and statistically significant increase in the incidence
of micronucleated polychromatic cells was observed in the bone marrow of
mice treated with DBTC at 50 mg/kg and killed 48 and 72 hours later
(0.01<p<0.05): this effect was seen more clearly in females than in
males. No such effect was apparent for any group treated with DBTC and
killed 24 hours later (p>0.05). Statistically significant increases over
controls were also seen in positive control group animals given
chlorambucil at 30 mg/kg (p<0.01).
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