Dibromomethane

Repeated dose toxicity: inhalation

Administrative data

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Not performed according to known TG or GLP, but the study was well documented and scientifically accepted

Data source

Reference

Reference Type:

other: published data accessed

Title:

UNNAMED

Author:

US EPA

Year:

2010

Bibliographic source:

EPA Doc. No. 86-870001205, Fiche No. OTS0516108).

Materials and methods

Principles of method if other than guideline:

study was conducted using groups of 115 male and 15 female Sprague-Dawley rats and three male Beagle dogs exposed to 0, 25, 75, or 150 ppm (0, 178, 533, or 1066 mg/m3) of methylene bromide for 6 hours/day, 5 days/week, for a total of 62 or 63 exposures (rats) or 70 exposures (dogs) in approximately 90 days . After 58 exposure days, five rats/sex/level were sacrificed for cytogenetic analysis of bone marrow.
On the day after the last exposures, 10 rats/sex/level and all dogs were necropsied. The 100 remaining male rats were observed for up to 2 years following exposure.

GLP compliance:

not specified

Test material

Test material information

1

Reference substance name:

Dibromomethane

EC Number:

200-824-2

EC Name:

Dibromomethane

Cas Number:

74-95-3

Molecular formula:

CH2Br2

IUPAC Name:

dibromomethane

Test animals

Species:

other: rats and dogs

Strain:

other: Sprague Dowley and Beagles

Sex:

male/female

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure:

not specified

Vehicle:

not specified

Duration of treatment / exposure:

90 days

Frequency of treatment:

6hours/day 5 day/week

Doses / concentrations

Remarks:

0 (control),25,75,150 ppm

No. of animals per sex per dose:

115 males/group and 15 females/group

Control animals:

yes

Details on study design:

Treatment-related effects observed at the 90-day sacrifice were limited to the 0.53 and 1.07 mg/L exposure groups
A 2-year post-exposure holding period was implemented for 100 males/group. Endpoints included clinical signs, body weights, organ weights, hematology, urinalysis, clinical chemistry, cytogenetics, gross pathology, and histopathology

Examinations

Observations and examinations performed and frequency:

Endpoints that were evaluated during the exposure and observation parts of the study include clinical signs, body weight, hematology, and urinalysis indices (7 rats/sex/level, all dogs at termination of exposure, and 7 male rats/level after 1 year ofobservation) and clinical chemistry indices (10 rats/sex/level, all dogs at termination of exposure, and 10 male rats/level after 1 year of observation). The hematology determinations included red blood cell counts, hemoglobin concentration, packed
cell volume , and total and differential white blood cell counts. The urinalysis determinations included pH, protein, ketones, bilirubin, urobilinogen, and occult blood. The clinical chemistry determinations included blood urea nitrogen, alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase. Cytogenetic analyses were not performed because of inadequate slide preparation. Additional endpoints included plasma bromine/bromide levels at various time points and
blood carboxyhemoglobin (COHb) percentages. COHb was measured using an optical method. For each of these endpoints three rats/sex/level were evaluated preexposure and at 1, 3, 30, 41, 51, and 61 days of exposure. The authors did not specify whether the same or different animals were used for each measurement. All dogs were evaluated at similar time points. Complete gross necropsies and organ weight measurements (brain, heart, liver, kidneys, and testes) were performed on 10 rats/sex/level after 61or 62 exposures and all dogs after 70 exposures. Complete gross necropsies were also performed on 10 male rats/level at 1 and 2 years postexposure. Comprehensive histological examinations were performed in the 0- and
150-ppm groups after 90 days of exposure (Five rats/sex/level and all dogs) and at 1 year postexposure (five male rats/level). No histological examinations were performed during the observation period on male rats that died spontaneously, were killed in moribund condition, or were sacrificed after 2years. Histological examinations in the 25- and 75-ppm exposure groups were limited to the lungs, trachea, and bronchial lymph nodes in dogs after 90 days of exposure.

Results and discussion

Results of examinations

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

body weight decrease beginning on day 121 at the 1.07 mg/L exposure level.
(2 years post exposure group)

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

increased blood percent carboxyhemoglobin saturations in both sexes.
Increased blood percent carboxyhemoglobin saturations were also seen in both sexes at 0.53 and 1.07 mg/L throughout the exposure period.

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

increased liver weight in females

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

Gross pathological examination of males exposed to 1.07 mg/L at the end of the 2-year post-exposure period revealed liver atrophy, decreased incidence of small red foci, and dark red foci visible in the liver; the study authors considered these lesions to be the result of spontaneous age-related processes.. All gross pathological (2-year observation) and histopathological (1-year observation) neoplastic and non-neoplastic observations were considered to be spontaneous in nature and unrelated to exposure.

Histopathological findings: non-neoplastic:

no effects observed

Description (incidence and severity):

No treatment-related histopathological effects were observed.(after 90 days)

Effect levels

1

Dose descriptor:

NOAEL

Remarks:

rats

Effect level:

0.18 mg/L air

Sex:

male/female

Basis for effect level:

other: increased blood percent carboxyhemoglobin saturations in both sexes during exposure and at termination of exposure

2

Dose descriptor:

LOAEL

Remarks:

rats

Effect level:

0.53 mg/L air

Sex:

male/female

Basis for effect level:

other: increased blood percent carboxyhemoglobin saturations in both sexes during exposure and at termination of exposure

3

Dose descriptor:

NOAEL

Remarks:

dogs

Effect level:

0.53 mg/L air

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: increased blood percent carboxyhemoglobin saturations in both sexes during exposure and at termination of exposure

Remarks on result:

other:

4

Dose descriptor:

LOAEL

Remarks:

dogs

Effect level:

1.07 mg/L air

Sex:

male/female

Basis for effect level:

other: increased blood percent carboxyhemoglobin saturations in both sexes during exposure and at termination of exposure

Target system / organ toxicity

Critical effects observed:

not specified

Any other information on results incl. tables

There were no exposure-related changes in most of the endpoints in either species.

Dose-related increases in serum levels of free bromide ion and total bromine occurred at ≥25 ppm in the rats and dogs at all times of evaluation. There were no clinical signs of intoxication and no histopathological changes in both species. There was a slight increase in relative liver weight at the termination of the exposure period in female rats exposed to 75 pp(8.9% higher than controls,

p< 0.05) and 150 ppm (6.1% higher than controls, not statistically significant). Male rats that were exposedto ≥75 ppm showed an equivocal decrease in

body-weight gain during Study Days 121−361 in the postexposure observation period, but the decrease is not considered biologically significant.

Exposure to methylene bromide also caused increased blood COHb levels in both species as shown in Table 1. Increases in mean COHb percentages that were statistically significant (p< 0.05 compared to control group) occurred at ≥7

5 ppm methylene bromide; there was only one statistically significant increase at 25 ppm (after 61 exposures in females). However, due to the small group sizes (n= 2 or 3 rats/sex/level at each time point), the statistical tests performed

by the researchers had little power to detect an effect. Dogs were less sensitive than the rats, as

indicated by a small increase in percent COHb saturation relative to controls detectable only at 150 ppm (mean 6.0% increase at the only sampling time where the difference from the control mean was statistically significant). Regression analysis was performed by the researchers to

quantitatively assess the effect of increasing exposure concentration on percent COHb saturation. The analysis used pooled percentage COHb saturation values after 30 to 61 exposures; data for each concentration were pooled to improve the precision of analysis and because COHb percentages did not increase appreciably after more than 30 exposures. The slopes of the regression lines predicted that the average increase in percent COHb saturation (relative to

controls) in the animals repeatedly exposed to 25, 75, and 150 ppm would be 0.4, 1.2, and2.4%, respectively,in dogs, 2.6, 8.3, and16.5% in male rats , and 2.3, 6.8, and 13.5% in female rats.

Baseline COHb in untreated control animals was 2.8%.

Applicant's summary and conclusion

Conclusions:

Exposure related effects were not observed at any exposure level during the study. Body weights on all dogs were comparable to those of controls during the study. At necropsy, terminal body weights, organ weights, and organ to body weights ratio were comparable to controls. Haematological values in treated dogs were comparable to those of controls. Clinical chemistry values of exposed dogs were comparable to control dogs. All gross and histopathologic observations on control and treated dogs were considered spontaneous in nature, and not as a result of treatment. Among spontaneous lesions was a frequent occurrence of chronic inflammatory lesions of the lungs that varied in severity. In some animals, the lesions were clearly related to aspiration of food material, and in others typical of a parasitic infestation common in dogs. There was some discrepancy in values for bromide ions and for total bromides. The NOAEL was determined to be 75 ppm (based on elevatedcarboxyhemoglobin), and the LOAEL was set to 150 ppm.