Bromomethane

Repeated dose toxicity: inhalation

Administrative data

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1994

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 412 (Subacute Inhalation Toxicity: 28-Day Study)

Deviations:

yes

Principles of method if other than guideline:

The method used differs from the prescribed method (EC B8) in the following respects:
Test animals were exposed for seven hours per day for five days per week, however the test method specifies exposure for six hours per day for seven days a week.
Four animals per sex were used for each test group; however, the test methods specify that five animals per sex per group should be used.

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Bromomethane

EC Number:

200-813-2

EC Name:

Bromomethane

Cas Number:

74-83-9

Molecular formula:

CH3Br

IUPAC Name:

bromomethane

Details on test material:

Methyl Bromide: Batch no.: SLV; purity: 100%.

Test animals

Species:

dog

Administration / exposure

Details on study design:

Six groups of 4 dogs/sex/group were exposed to 0, 5, 10, 25, 50 and 100 ppm (equivalent to 0, 4.3, 8.6, 21.6, 43.2 or 86.4 mg/kg bw). The 10 ppm group was increased to 150 ppm for weeks 5 and 6. Methyl Bromide was administered for 7 hours/day, 5 days/week for 4 weeks. Body weights and food consumption were recorded. Physical observations and opthalmoscopic and neurologic examinations were carried out. Haematology, clinical chemistry, serum bromide and urinalysis examinations were conducted. A post-mortem examination and necropsy were performed on all animals. Tissues were preserved and examined histopathologically. Statistical analyses were carried out.

While decreased activity during the actual exposures and weight losses were seen in the 100 ppm animals during the initial 4 weeks of exposure, no neurologic deficits were seen. In order to determine if neurological deficits could be produced at a higher exposure level, an additional 2 weeks of exposure was planned for three groups. Half of the control animals were sacrificed after 4 weeks of exposure and the remaining animals continued to be sham exposed to clean air during the 2 week extended period. All of the 5 ppm animals continued to be exposed at 5 ppm to assess the potential for a cumulative effect after repeated exposures as suggested during the initial 4 weeks of exposure at higher exposure levels. The exposure level for the 10 ppm animals was increased to 150 ppm beginning with the fifth and last day of exposure in the fifth week.

Results and discussion

Results of examinations

Details on results:

Mortality:
No spontaneous deaths occurred as a result of exposure.

Physical observation:
In-chamber observations: There were no remarkable observations during the actual exposures to 5, 10 or 25 ppm Methyl Bromide. However, decreased activity during exposure was noted in two of the dogs in the 50 ppm group on exposure day 14 and during almost all exposures thereafter. The decreased activity was primarily seen as a diminution or total lack of an excited response, which is normally seen when the chambers are approached for observation. In the 100 ppm group, decreased activity was seen in three of the eight dogs beginning on the exposure day 9 and was subsequently seen in all dogs at various intervals. In the 150 ppm group, decreased activity was seen in all dogs beginning with the second exposure. Therefore, Methyl Bromide produced a dose-related decrease in activity, and the apparent prerequisite of several Methyl Bromide exposures prior to observation of decreased activity suggested a cumulative response. On the sixth day of exposure to 150 ppm, poor condition was seen in all of the dogs and prostration and tremors were seen in one male.

Weekly detailed observations:
During the first four weeks of exposure to Methyl Bromide there were no observations attributable to Methyl Bromide. During the two week extension of the study, irregular gait was noted in 4 females and 1 male dog exposed to the 150 ppm dose. This was considered to be Methyl Bromide related. Other observations were noted sporadically and all the reactions noted were considered not to be Methyl Bromide related.

Clinical veterinarian examination:
On the day following the sixth exposure, opisthotonos, paddling gait of both fore- and hindlimbs, opening and closing of the jaws and convulsions were recorded in 3 male dogs exposed to 150 ppm. The surviving 5 dogs (1 male, 4 females) in this exposure group received no further exposure to Methyl Bromide.

Neurological examination:
After four weeks of exposure there was no evidence of any neurologic deficit. After the study extension no neurological abnormalities were observed in the 0 or 5 ppm groups. All of the dogs from the 150 ppm group, examined 2 days after their sixth and last exposure, showed evidence of ataxia, a base-wide stance, intention tremor, nystagmus, marked depression and inability to stand and perform postural responses. The dominant signs of these suggest posterior fossa (cerebellar/ vestibular) dysfunction.

Ophthalmoscopic examination:
No observation of any Methyl Bromide related ocular disease was found.

Body weight and food consumption:
A decrease in body weight from pre-test weights was seen during the first week of exposure in both the males and females in all groups, including control. The maximum decrease of weight (0.5kg) was seen in the females in the 50 and 100 ppm groups and in the males in the 100 ppm group. In the same group (100 ppm) after 4 weeks of exposure, both male and female group mean weights were about 0.6 kg less than their respective pre-test weights. Among the animals whose exposure level was increased from 10 ppm to 150 ppm, the females lost approximately 1 kg of body weight each, and one male lost 2.6 kg, within 1 week.

In terms of food consumption measurements, no significant differences were seen between Methyl Bromide exposed animals and air control animals at any exposure level during the first 4 weeks of the study. However, when the exposure level in the 10 ppm group was increased to 150 ppm, their food consumption dropped by approximately 40%.

Changes in mean body weights (in kilograms) in males and females are expressed in Figures 5.3.3-1 and 5.3.3-2 respectively.

Effect levels

Dose descriptor:

NOEL

Effect level:

21.6 mg/kg bw/day (actual dose received)

Basis for effect level:

other: see 'Remark'

Target system / organ toxicity

Critical effects observed:

not specified

Any other information on results incl. tables

Figure 5.3.3-1 Mean body weight values- males

see attachment

 

Figure 5.3.3-2 Mean body weight values- females

see attachment

 

Clinical laboratory studies:

No effects related to Methyl Bromide exposure were seen in any of the haemathology parameters.

 

The only apparent Methyl Bromide related effects seen during clinical chemistry evaluations were a decrease in creatine kinase and increase in chloride seen in the 100 ppm group after four weeks of exposure. This decrease is of uncertain toxicological significance.

 

A dose-related and cumulative build-up in serum bromide was seen in all groups exposed to more than 10 ppm Methyl Bromide. The cumulative build-up appeared to have essentially reached a plateau in both males and females after 4 weeks of exposure. Increasing the exposure level of Methyl Bromide from 10 ppm to 150 ppm on the last day of the fifth week of exposure produced a dramatic increase in the serum bromide level.

 

Analysis of urine showed that increased levels of bilirubin and protein were seen in the animals exposed to 150 ppm Methyl Bromide.

 

Terminal organ and body weights and organ/body and organ/brain ratios:

Methyl Bromide exposure produced no effects on absolute or relative organ weights. When heart-to-brain weight ratio and the variation among groups were considered, there were no clear Methyl Bromide treatment effects noted.

 

Macroscopic and microscopic findings:

There were no macroscopic findings observed at necroscopy, relative to the Methyl Bromide exposures. Microscopic findings, which appear to be related to Methyl Bromide, included: vacuoles in the granular layer of the cerebellum which were seen in all males and females from the 10/150 ppm group and in 1 male each from the control and 100 ppm groups. Intracytoplasmic vacuoles were observed in the cells of the zona fasiculata of the adrenal glands of 4 males and 1 female from the 150 ppm group and in one female each from the control and 50 ppm groups. Degradation of the olfactory epithelium was noted in all males and females from the 150 ppm group. There were no macroscopic or microscopic changes seen in the eye or optic nerve.

 

Repeated 7 h our/day inhalation exposure to 150 ppm of Methyl Bromide produced neurologic deficits, thereforethis exposure level could not be tolerated for a chronic exposure. Repeated exposure to 100 ppm produced toxic effects such as decreased body weight, decreased serum creatine kinase, and increased chloride, but the only neurologic effect was decreased activity. Repeated exposure to 50 ppm only produced decreased activity.

Applicant's summary and conclusion

Conclusions:

NOEL (No Observed Effect Level): 25 ppm (equivalent to 21.6 mg/kg bw/day) based on findings of decreased body weight, decreased serum creatine kinase, and increased chloride and decreased activity at higher dose levels. (Calculation reference: McMahon, 1977)