Registration Dossier

Diss Factsheets

Administrative data

Description of key information

Oral
2 years, rat, drinking water: NOAEL >= 2000 ppm/day (corresponding to 124.1 mg/kg bw/day and 164 mg/kg bw/day, for males and females, respectively, on the basis of treatment specific fluid consumption rates and body weights; Borzelleca et al. 1964)

Inhalation
For systemic effects:
NOAEC rat, 2yr: 500 ppm (2028 mg/m³; NTP 1986) in absence of adverse effects
For local effects:
NOAEC rat, 2yr: 25 ppm (104 mg/m3; Lomax et al. 1997) due to nasal lesions in higher doses

The EU ESR (2002) and SCOEL review (2005) recognised differences between rodents and humans regarding the physiology of the nasal passages, metabolic activity result in the greater susceptibility of rodents compared with humans to inhaled esters. Consequently, a value of 50 ppm (SCOEL, 2005) is regarded as being the NOAEC(=DNEL) in humans.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records
Reference
Endpoint:
chronic toxicity: oral
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
equivalent or similar to guideline
Guideline:
other: not known
Principles of method if other than guideline:
Chronic, repeated dose study with exposure via drinking water
GLP compliance:
no
Limit test:
no
Specific details on test material used for the study:
source: Rohm & Haas company, Philadelphia
stabilized with 10 ppm monomethylether of t-butylhydroquinone
Species:
rat
Strain:
Wistar
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Age at study initiation: "young" (unspecified)
The  animals were individually housed and provided food (finely ground Purina Dog Chow Kibbled Meal; questionable information in the publication) ad libitum
- rats were individually caged and weighed once a week
Route of administration:
oral: drinking water
Vehicle:
unchanged (no vehicle)
Details on oral exposure:
The rats were individually caged and weighed once a week. The diet consisted of finely ground Purina Dog Chow Kibbled Meal consumed ad libitum. Fluid consumption values were determined over a 3-day period at the end of 1 and 4 weeks,
monthly through 6 months, and on even months thereafter. Food consumptions were measuered over 3-day periods at the same intervals.
The low and medium concentrations in the water were selected with the expectation that the diet equivalents would approximate 10 and 100 ppm. The high concentration was selected following preliminary tests that indicated
that this level would significantly depress fluid consumption.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Polarographic analysis of monomer content
Duration of treatment / exposure:
104 weeks (2 years)
Frequency of treatment:
Daily, ad libitum
Dose / conc.:
6 ppm
Remarks:
raised after 5 months to 7 ppm
Dose / conc.:
60 ppm
Remarks:
raised after 5 months to 70 ppm
Dose / conc.:
2 000 ppm
Dose / conc.:
12 other: ppm (on the basis of fluid and food consumption observations)
Remarks:
corresponding to roughly 0.6 mg/kg/bw (based on a conversion factor of 20 (Derelanko, M.J.,
2000)corresponding to roughly 0.6, 6 and 165 mg/kg/bw (based on a conversion factor of 20
(Derelanko, M.J., 2000)
Dose / conc.:
120 other: ppm (on the basis of fluid and food consumption observations)
Remarks:
corresponding to roughly 6 mg/kg/bw (based on a conversion factor of 20 (Derelanko, M.J., 2000)
Dose / conc.:
3 000 other: ppm (on the basis of fluid and food consumption observations)
Remarks:
corresponding to roughly 165 mg/kg/bw (based on a conversion factor of 20 (Derelanko, M.J., 2000)
No. of animals per sex per dose:
25
Control animals:
yes, concurrent no treatment
Details on study design:
Twenty-five male and female albino (Wistar) rats were administered 6, 60 or 2000 ppm of methyl methacrylate in the drinking water. The concentrations of the low- and mid-dose groups were increased to 7 and 70 ppm at the beginning of the fifth month of the study. The animals were individually housed and provided food ad libitum.  
Prior to the start of the study, it was apparent that methyl methacrylate was volatilizing at the tip of the water bottles. A special design was employed to reduce the volatilization and measurements showed that the methyl methacrylate concentrations remained within 15% of nominal for 72 hours.
The low and medium concentrations in the water were selected with the expectation that the diet equivalents would approximate 10 and 100 ppm. The high concentration was selected following preliminary tests that indicated that this level would significantly depress fluid consumption.

Observations and examinations performed and frequency:
Body weights were measured prior to study initiation, at weeks 1, 3, 6, 13, 26, 52, 78 and 104. Food and water consumption was measured over a three day period at the end of one and four weeks, monthly through month six and during even months thereafter. Hematological measurements, including hematocrit, hemoglobin, total white and differential white cell counts, were obtained from five rats from each sex in each treatment level at three month intervals. Pooled urine samples were collected from five rats per sex from each treatment group every three months to evaluate urinary concentrations of reducing substances and proteins.
Sacrifice and pathology:
Semiquantitative tests for urinary concentrations of reducing substances and protein were performed on urines pooled from 5 rats/sex per group at three month intervals. At two years, survivors were sacrificed and organ to body weight measurements were made for heart, spleen, kidney, liver and testes. Tissues preserved from all animals on study included heart, lung, kidney, liver, urinary bladder, spleen, gastrointeric, skeletal muscle, bone marrow, skin, brain, thyroid, adrenal, pancreas, pituitary and gonad. Histopathology was conducted on all tissues collected except from animals in the low dose group.
Haematological findings:
no effects observed
Description (incidence and severity):
Hematologic values varied within normal ranges in ali' groups of rats throughout the study
Urinalysis findings:
no effects observed
Description (incidence and severity):
Urine concentrations of protein and reducing substances showed no trends that appeared relatable to treatment.
Organ weight findings including organ / body weight ratios:
effects observed, non-treatment-related
Description (incidence and severity):
Organ to body weight ratios obtained at sacrifice of 2-year survivors differed from the controls only in significantly increased kidney ratios in female rats receiving 2000 ppm of methyl methacrylatc (controls 0.0082 ± 0.0019; treated 0.0094 ± 0.0011).
Histopathological findings: non-neoplastic:
no effects observed
Description (incidence and severity):
Histopathologic findings showed no abnormalities or lesions, in kind or incidence, not explicable on the basis of naturally occurring ones in this strain of rat at this age.
Details on results:
Body weight depression observed at 2000 ppm did not persist beyond the first few weeks of the study. Significant depression of fluid consumption was observed at 2000 ppm, although this tended to regress at the end of the study. Individual observations of depressed food consumption tended to parallel periods of depressed growth. These effects were considered as temporary non-adverse effects.
There were significantly increased kidney weight ratios for female rats at 2000 ppm. Since no substance-related effects were reported from histopathologic examinations in the kidneys, this effect is not considered as biologically relevant.
Dose descriptor:
NOAEL
Effect level:
>= 124.1 mg/kg bw/day (actual dose received)
Sex:
male
Basis for effect level:
other: based on fluid consumption and body weight (see attached document)
Dose descriptor:
NOAEL
Effect level:
>= 164 mg/kg bw/day (actual dose received)
Sex:
female
Basis for effect level:
other: based on fluid consumption and body weight (see attached document)
Dose descriptor:
NOAEL
Effect level:
>= 2 000 other: ppm nominal
Sex:
male/female
Basis for effect level:
other: corresponding to ca. 3300 ppm in the diet on the basis of fluid and food consumption observations
Critical effects observed:
not specified

Mortality:

A summary of the mortality data for methyl methacrylate is presented below.

Dose group (ppm)            Male           Female
Negative              (0)          12/25           9/25
                           6/7           7/25           7/25
          60/70          10/25           7/25
           2000          12/25          10/25

No statistical differences were noted in the mortality of the animals exposed to methyl methacrylate and those in the control group. A statistically significant decrease in body weight was observed in the first week for the female rats and in weeks one through three in the male rats administered 2000 ppm methyl methacrylate. Water consumption was reduced in the animals from the high-dose group; however, it was reported that this finding tended to regress towards the end of the study. Food consumption was not affected by the administration of methyl methacrylate in the drinking water. 

  

Hematologic values varied within normal ranges in all groups of rats throughout the study, and urine concentrations of protein and reducing substances showed no trends that appeared relatable to treatment.

Organ to body weight ratios obtained at sacrifice of 2-year survivors differed from the controls only in significantly increased kidney ratios in female rats receiving 2000 ppm of methyl methacrylate (controls 0.0082 ± 0.0019; treated 0.0094 ± 0.0011).

Histopathologic findings showed no abnormalities or lesions, in kind or incidence, not explicable on the basis of naturally occurring ones in this strain of rat at this age.

  

Diet equivalents of the test materials were calculated from the fluid and food consumption data.

In these calculations, corrections were not made for evaporation losses of the test materials from the drinking water, the orders of magnitude of which are given under methods described above (maximum 15%). Allowing for such losses, it would appear that the concentrations of test materials in the drinking water were equivalent to approximately 10, 100, and 3000 ppm in the diet.

Conclusions:
No relevant effects were observed up to the highest dose tested (2000 ppm, limited by palatability) in a 2 years study in rats by oral administration in drinking water.
Executive summary:

A two years toxicity study was performend in 1964 to study the tolerance of animals to chronic ingestion of methyl methacrylate.

Twenty-five male and female Wistar rats were administered three doses of methyl methacrylate in the drinking water for two years (Borzelleca et al. 1964). Initial doses of 6, 60 or 2000 ppm were partially raised to 7, 70 and 2000 ppm after 5 months.

A special design was employed to reduce the volatilization and measurements which showed that the methyl methacrylate concentrations remained within 15% of the nominal concentration for 72 hours. Body weight depression was also observed at 2000 ppm but it did not persist beyond the first few weeks of the study. Significant depression of fluid consumption was observed at 2000 ppm, although this tended to regress at the end of the study. Individual observations of depressed food consumption tended to parallel periods of depressed growth. There were significantly increased kidney ratios for female rats at 2000 ppm. These effects were believed to be a consequence of reduced food intake and reduced body weights, and in the absence of any histopathology, were considered as not biologically relevant. Therefore the NOAEL is considered to be >= 2000 ppm, corresponding to 90.3 mg/kg bw/day and 193.8 mg/kg bw/day, for males and females, respectively, on the basis of treatment specific fluid consumption rates and body weights.

No relevant effects were observed after exposure of rats in drinking water up to the highest dose tested (2000 ppm, limited by palatability).

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
NOAEL
124 mg/kg bw/day
Study duration:
chronic
Species:
rat
Quality of whole database:
reliable with acceptable restrictions
System:
other: no adverse effects observed (stand-alone observation of increased kidney weights in high-dosed females)

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records
Reference
Endpoint:
chronic toxicity: inhalation
Remarks:
combined repeated dose and carcinogenicity
Type of information:
experimental study
Adequacy of study:
key study
Study period:
0981-01-28 to 1983-01-14
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
test procedure in accordance with national standard methods
Remarks:
NTP standard protocol, cancer bioassay with limited dose range
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)
GLP compliance:
yes
Limit test:
no
Specific details on test material used for the study:
- Name of test material (as cited in study report): methyl methacrylate
- Molecular weight (if other than submission substance): 100.1
- Smiles notation (if other than submission substance):
- Physical state: liquid
- Analytical purity: > 99.8 %
- Purity test date: several times throughout the test
- Stability under test conditions: stable
- Other: stabilised commercila grad material
Species:
rat
Strain:
Fischer 344
Sex:
male/female
Details on test animals or test system and environmental conditions:
Feed:
NIH 07 Rat and Mouse Ration (Zeigler Bros., Gardners, PA); until 4/23/81 and aft.er 5/8/81.
Wayne LAB BLOX" from 4/23/81 to 5/8/81. Available ad libitum except during exposure

Bedding: None
Water: Automatie wate ring system (Edstrom Industries, Waterford, Wll; available ad libitum

Cages: Stainless steel wire cages (Lab Products, Inc., Rochelle Park, NJ)

Animals per cage: 1

Animal room envoronment:
Temp: 72° -79° F;
humidity: 45%-65%;
fluorescent light: 12 h/d;
20 room air changes/h

Route of administration:
inhalation: vapour
Type of inhalation exposure:
whole body
Vehicle:
air
Remarks on MMAD:
MMAD / GSD: vapour
Details on inhalation exposure:
Methyl methacrylate was pumped from a stainless steel reservoir to a vaporizer by a stable micrometering pump with adjustable drift-free pump rates. The vaporizer was heated to 50° ± 2° C, and the
study material vapor, along with an air stream, entered thetest chamber.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Methyl methacrylate concentrations were monitored on-line twice during each exposure hour, initially by a photoionization detector and later by gas chromatographic analysis
Duration of treatment / exposure:
2 years
Frequency of treatment:
6 h / day, 5 d / wk
Dose / conc.:
0 ppm
Remarks:
males/females
Dose / conc.:
250 ppm
Remarks:
females
Dose / conc.:
500 ppm
Remarks:
males/females
Dose / conc.:
1 000 ppm
Remarks:
males
No. of animals per sex per dose:
50
Control animals:
yes, concurrent vehicle
Details on study design:
- Dose selection rationale: random (table)
- Dose selection rationale: Based on the results of several preliminary studies up to 90 d duration
Positive control:
no
Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: 2/d

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: at weighing

BODY WEIGHT: Yes
- Time schedule for examinations: weekly for the first 13 weeks, monthly afterwards

FOOD CONSUMPTION, FOOD EFFICIENCY and WATER CONSUMPTION: no data
HAEMATOLOGY, CLINICAL CHEMISTRY, URINALYSIS, NEUROBEHAVIOURAL EXAMINATION: No data
Sacrifice and pathology:
Grosspathology (necropsy) and histologic examination:
Necropsy and histologic examination performed on all animals; the following tissues were examined:
- gross lesions and tissue masses
- regional lymph nodes
- mandibular lymph node
- sternebrae including marrow,
- thyroid gland, parathyroids
- small intestine
- rectum
- colon
- liver
- mammary gland
- prostate/testes/epididymis or ovaries/uterus
- Iungs and mainstem bronchi
- nasal cavity and turbinates
- skin
- heart,
- esophagus
- stomach
- salivary gland,
- brain,
- hymus
- trachea
- pancreas
- spleen
- kidneys
- adrenal glands
- urinary bladder
- pituitary gland
- preputial or clitoral gland
- tracheobronchial lymph nodes
Statistics:
Data Recording: Data were recorded in the Carcinogenesis Bioassay Data System (Linhart et al., 1974). The data elements include descriptive information on the chemicals, animals, experimental design, survival, body weight, and individual pathologic results, as recommended by the International Union Against Cancer (Berenblum, 1969).

Survival Analyses: The probability of survival was estimated by the product-limit procedure of Kaplan and Meier (1958).
Statistical analyses for a possible dose-related effect on survival used the method of Cox (1972) for testing two groups for equality and Tarone's (1975) life table test for a dose-related trend.

Analysis of Tumor lncidence: Three statistical methods are used to analyze tumor incidence data. The two that adjust for intercurrent mortality employ the classical method for combining
contingency tables developed by Mantel and Haenszel (1959). Tests of significance included pairwise comparisons of high dose and low dose groups with controls and tests for overall doseresponse trends.
Clinical signs:
not specified
Mortality:
mortality observed, non-treatment-related
Description (incidence):
No significant differences in survival were observed between any groups of either sex.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
Mean body weights of 1000-ppm male rats were 5%-10% lower than those of the controls after week 81. Mean body weights of 500-ppm female rats were 6%-11%l ower than those of the controls after week 73.
Food consumption and compound intake (if feeding study):
not examined
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
not examined
Haematological findings:
effects observed, non-treatment-related
Description (incidence and severity):
A statistically significant positive trend in the incidence of mononuclear cell leukemia occurred in female rats exposed to 500-ppm (incidence of 22%, 26% and 40% for the control, 250 ppm and 500 ppm groups, respectively). However, life table analysis, which can be regarded as more appropriate for life-threatening lesions, showed no difference. The incidence of mononuclear cell leukemia in the three groups of male rats was not statistically different by life table analysis.
Clinical biochemistry findings:
not examined
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
not examined
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Nasal Cavity and Olfactory Sensory Epithelium:
Serious and suppurative inflammation and degeneration of the olfactory epithelium in the nasal cavity were observed at increased incidences in exposed male and female rats relative to controls. Serous inflammation was characterized by noncellular mucus in the lumen of the posterior region of the nasal cavity.
Suppurative inflammation was characterized by an infiltration of neutrophils and varying numbers of mononuclear cells into the mucosa and submucosa of the nasal turbinates and wall of the nasal cavity. Degeneration of the olfactory epithelium was characterized by a loss of sensory neuroepithelial cells from the epithelium (atrophy) and, in the most severely affected areas, replacement by respiratory epithelium (metaplasia). This degeneration was accompanied by variable atrophy of the nerve bundles in the submucosa.

Lung: Alveolar macrophages were observed at increased incidences in exposed male and female rats. The severity in all groups was considered minimal. Focal or multifocal fibrosis was observed at an increased incidence in 500- ppm female rats.
Histopathological findings: neoplastic:
no effects observed
Description (incidence and severity):
Pituitary Gland: Pituitary gland adenomas or carcinomas (combined) in male rats occurred with a significant negative trend, and the incidence in the 1,000 ppm group was significantly lower than that in the controls . The
incidences of pituitary gland adenomas in the three groups of female rats were not different statistically.
Preputial Gland: Preputial gland adenomas and carcinomas occurred in male rats with a significant negative trend, and the incidence in the high dose group was significantly lower than that in the controls .

Hematopoietic System: Mononuclear cell leukemia in female rats occurred with a significant positive trend, and the incidence in the 500-ppm group was significantly greater than that in the controls by the incidental tumor test but not by life table analysis. The latter test procedure is generally considered more appropriate for life-threatening lesions. The incidences of mononuclear cell leukemia in the three groups of male rats were not statistically different by life table analysis.

The mononuclear cell leukemia in female rats in the control and dosed groups was classified according to the extent of involvement of the spleen and its advancement to other organs. The following criteria were used:
Stage 1. Spleen not enlarged or only slightly enlarged with small numbers of neoplastic mononuclear cells in the red pulp; no or very few mononuclear cells in the liver sinusoids. No identifiable neoplastic cells in other organs.
Stage 2. Spleen moderately enlarged with moderate to large numbers of mononuclear cells in the red pulp; architectural features including lymphoid follicles and periarteriolar lymphocytic sheaths remain intact. Minimal to moderate involvement of the liver. Mononuclear cells may be evident in blood vessels in other organs, but aggregates/masses of neoplastic cells generally limited to spleen and liver.

Stage 3. Advance disease with multiple organ involvement. Spleen usually markedly enlarged with effacement of normal architectural features by accumulated neoplastic cells. Liver moderately to markedly enlarged and nodular; hepatic parenchyma shows variable degenerative changes associated with the accumulation of neoplastic cells. Accumulations of neoplastic mononuclear cells in other organs including
lung, lymph nodes, kidney, brain, and adrenal gland.

According to these criteria, there were no differences in the character of the mononuclear cell leukemia found in the dosed female rats and the controls.
Dose descriptor:
LOAEC
Remarks:
for local effects in the URT (no NOAEC identified)
Effect level:
250 ppm
Based on:
test mat.
Sex:
female
Basis for effect level:
other: Histopathology (Irritation)
Key result
Dose descriptor:
NOAEC
Remarks:
for systemic effects
Effect level:
500 ppm
Based on:
test mat.
Sex:
female
Basis for effect level:
other: Gross pathology, Histopathology (organ effects)
Dose descriptor:
NOAEC
Effect level:
1 000 ppm
Based on:
test mat.
Sex:
male
Basis for effect level:
other: Gross pathology, Histopathology (organs)
Critical effects observed:
not specified

Mortality: No difference in survival between treated and untreated groups.

Histopathology:

Site / Lesion

Males

Control

[0 ppm]

Low. Conc.

[500 ppm]

High Conc.

[1000 ppm]

Nasal Cavity /

           Serous inflammation

           Suppurative inflammation

 

 0/50

11/50

 

37/50

21/50

 

44/50

30/50

Olfactory sensory epithelium /

           Degeneration

 

 7/50

 

39/50

 

42/50

Lung /

           Alveolar macrophages

           Focal or multifocal fibrosis

 

 6/49

 6/49

 

20/49

 6/49

 

16/50

 5/50

 

 

 

 

Site / Lesion

Females

Control

[0 ppm]

Low. Conc.

[250 ppm]

High Conc.

[500 ppm]

Nasal Cavity /

           Serous inflammation

           Suppurative inflammation

 

4/50

7/50

 

17/50

12/50

 

32/50

12/50

Olfactory sensory epithelium /

           Degeneration

 

2/50

 

39/50

 

44/50

Lung /

           Alveolar macrophages

           Focal or multifocal fibrosis

 

9/50

1/50

 

14/50

 2/50

 

16/50

 7/50

 

No histopathological findings other than local findings in the respiratory tract. Systemic histopathological effects, as for example in the brain in females particularly at 2000 ppm and above in the subchronic range finding study (Batelle, 1980), are absent in this 104 week study.

Body weight: Mean body weight gain was reduced in females at 500 ppm resulting in 6 -11% lower body weights after week 73 and in males at 1000 ppm which were 5 -10 % lower than controls after week 81.

There was no treatment-related increase in tumour incidence.

Conclusions:
The primary finding in this study was inflammation of rat nasal cavity as well as olfactory epithelial degeneration at all exposure levels in male and female rats. For local effects the LOAEC was 250 ppm in this study while a NOAEC could not be found. 
In contrast to the 90 d range finding study with histopathological changes in females at exposures of 1000 ppm and above (Battelle, 1980), no other significant histopathological changes were reported in male and female rats after 104-week exposures to MMA vapour in this study. Based on this a NOEC for systemic effects of 500 ppm is derived.
Executive summary:

In this104-week study with groups of 50 animals each, male rats were treated with MMA vapour by whole-body exposure to 500 or 1000 ppm while female rats were exposed to 250 or 500 ppm. Control animals were only treated with air.

The primary finding was inflammation of rat nasal cavity as well as olfactory epithelial degeneration at all exposure levels in male and female rats. For local effects the LOAEC was 250 ppm in this study while a NOAEC could not be found. 

No other significant histopathological changes were reported in male and female rats after 104-week exposures to MMA vapour in this study. Based on this a NOEC for systemic effects of 500 ppm is derived.

Male and female rat body weights were lower at the 1000 ppm (5-10%) and 500 ppm (6-11%) exposure levels, respectively, presumably due to reduced food consumption due to nasal irritation and damage of olfactory epithelium. While food consumption was not recorded in this study this association is confirmed by two other studies, the developmental toxicity study with MMA with reduced food consumption and reduced body weight gain at concentrations higher than 99 ppm (Solomon, 1993) and a subchronic inhalation study with methacrylic acid where there was also an association of irritative effects in the nose and reduced food consumption and reduced body weight gain (BASF, 2008). Consequently, reduced body weight gain, while clearly treatment-related - is considered to be secondary to the local effects in the nose and not the result of true systemic toxicity.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
NOAEC
2 080 mg/m³
Study duration:
chronic
Experimental exposure time per week (hours/week):
30
Species:
rat
Quality of whole database:
reliable with acceptable restrictions
System:
other: no adverse effects observed (stand-alone observation of a reduced body weight in females at 2080 mg/m3 = 500 ppm = highest dose considered as secondary to local effects (consequence of the local nasal lesion and effects on smell and behaviour/appetite))

Repeated dose toxicity: inhalation - local effects

Link to relevant study records
Reference
Endpoint:
chronic toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1975-10-23 - 1977-10-23
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study
Remarks:
Method and results sufficiently described, similar to OECD-guideline 453.
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)
GLP compliance:
no
Limit test:
no
Species:
rat
Strain:
Fischer 344
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories, Inc. (Wilmington, USA)
- Housing: group-housed by sex in wire mesh cages (seven per cage)
- Diet (e.g. ad libitum): Purina Laboratory Chow
- Water (e.g. ad libitum): water unspecified
- Acclimation period: 19 d


ENVIRONMENTAL CONDITIONS
not reported
Route of administration:
inhalation
Type of inhalation exposure:
whole body
Vehicle:
air
Details on inhalation exposure:
1. Original study (Reno FE, 1979):  The test substance was administered in 6000-liter inhalation chambers with pyramidal tops and bottoms, under  dynamic conditions of 1000 liters/minute of airflow. Control animals were exposed to filtered room air in the same manner as the treated animals. 
2. Re-Evaluation of the study (Lomax LG et al., 1997):  Animals were exposed to the test substance vapor in 6000 liter inhalation chambers under dynamic conditions of 1000  liters/minute of air flow. The control animals were exposed to filtered room air in a chamber with similar air-flow characteristics.  
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
The concentration of MMA in each chamber was monitored, when possible, at hourly intervals during each 6-hr exposure using an Infrared 6-Station Analyzer (Wilks-Miran, Foxboro, MA, USA).
Duration of treatment / exposure:
2 years (104 weeks)
Frequency of treatment:
6 hr/day, 5 days / week
Dose / conc.:
25 ppm
Remarks:
corresponding to approx. 104 mg/m3 or 0.10 mg/l; confirmed by analytical reassessment (1992)
Dose / conc.:
100 ppm
Remarks:
corresponding to approx. 416 mg/m3 or 0.41 mg/l; analytical reassessment (1992): 99.8 ppm
Dose / conc.:
400 ppm
Remarks:
corresponding to approx. 1640 mg/m3 or 1.64 mg/l; analytical reassessment (1992): 396.1 ppm
No. of animals per sex per dose:
70 males and 70 females were assigned to each of the four exposure groups (including control). 
Control animals:
yes, concurrent vehicle
Details on study design:
Post-exposure period: Not applicable
Observations and examinations performed and frequency:
1. Original study (Reno FE, 1979):
-NOTE: This study is also summarized with further evaluation of nasal passage microscopy in Lomax et al. (1997).
Methods: Groups of 70 male and 70 female (total animals = 280 males and 280 females) rats were randomly assigned to either a control or one of three test groups. The animals were group housed (7/cage) and provided food and water ad libitum, except during the exposure period. The animals were exposed to the test substance six hours a day five days per week for a total of 104 - 106 weeks. The test substance was administered in 6000-liter inhalation chambers with pyramidal tops and bottoms, under dynamic conditions of 1000 liters/minute of airflow. Control animals were exposed to filtered room air in the same manner as the treated animals. Concentrations of the test substance in each chamber were measured hourly during each exposure period using an infrared analyzer. Animals were observed daily for mortality and moribundity. Body weights and clinical observations were recorded prior to study initiation, weekly during weeks 1 though 12, biweekly from week 14 through 24, every fourth week from week 28 through 78 and biweekly from week 80 through 104. Ophthalmoscopic exams were performed on all rats prior to treatment using an indirect ophthalmoscope at weeks 13, 52 and 102.
2. Re-Evaluation of the study (Lomax LG et al., 1997): Animals: Three hundred male and 300 female rats were received from Charles River Breeding Laboratories, Inc. (Wilmington, MA, USA). Animals were maintained under quarantine for 19 days, during such time all rats were evaluated for clinical signs of disease and an ophthalmoscopic examination. Following the quarantine period, 70 males and 70 females were assigned to each of the four exposure groups (including the control). The animals were housed by sex in wire mesh cages (seven/cage). Animals were provided feed and water ad libitum, except during the exposure period. Exposure conditions: Animals were exposed to the test substance vapor in 6000 liter inhalation chambers under dynamic conditions of 1000 liters/minute of air flow. The control animals were exposed to filtered room air in a chamber with similar air-flow characteristics. Observations: All animals were observed for mortality and morbidity daily. Individual body weight data were collected at the start of the study, weekly for the first twelve weeks and biweekly to week 24, every fourth week to week 78 and biweekly until study termination (week 104). At such time, a more detailed evaluation of gross toxicity and tissue masses was performed. Ophthalmoscopic evaluations were conducted at weeks 13, 52 and 102.
Sacrifice and pathology:
1. Original study (Reno FE, 1979):
Blood samples were collected from ten males and ten females in each group at weeks 13, 52 and 102 and from ten males and ten females in the control and high-exposure group at weeks 26 and 78 for hematological evaluation via segmental amputation of the tail. The following parameters were examined: hematocrit, hemoglobin, erythrocyte count, erythrocyte morphology, total leukocyte count and differential leukocyte count. In addition, coagulation and prothrombin times were determined from all blood samples taken at 13, 52 and 104 weeks and from the samples collected from the control and high-exposure groups at week 78. Femoral bone samples were collected from all sacrificed animals at weeks 13 and 52 and from 10 animals/sex/group at termination. The number of myeloid and erythroid cells and the myeloid/erythroid ratios were determined. Blood samples were collected for clinical chemistry evaluations from the abdominal aorta of all animals sacrificed at weeks 13 and 51 and from ten males and ten females per group at study termination. The following parameters were evaluated: fasting glucose, blood urea nitrogen, serum glutamic pyruvic transaminase, alkaline phosphatase, total protein, total albumin, albumin/globulin ratio. In addition, total cholesterol and triglycerides were also determined from blood samples taken from all animals sacrificed at week 52 and from ten animals/sex/group at week 104. Twenty-four hour urine samples were collected from 10 animals/sex/group at weeks 13, 52 and 104 by individually housing the rats overnight in stainless steel cages. The following parameters were evaluated: appearance, pH, ketones, total protein, specific gravity, bilirubin, glucose and occult blood. Necropsy: Ten rats/sex/group were sacrificed by exsanguination after 13 and 52 weeks of exposure. Animals found moribund during the course of the study were sacrificed at the time of the observation. The remaining animals were sacrificed after 102-104 weeks of exposure to the test substance. A gross necropsy was performed on all animals that were sacrificed and most of the animals that died during the study. Brain, kidneys, lungs, spleen, thyroids, adrenals and testes/ovaries from each animal were weighed and the organ to body weight ratio was calculated. The following tissues were collected and preserved in formalin or Bouin's solution: brain, pituitary, thoracic spinal chord, esophagus, salivary glands, thyroids, lungs, thymus, heart, spleen, kidneys, adrenals, stomach, duodenum, ileum, jejunum, colon, skin, mesenteric lymph nodes, urinary bladder, ovaries, uterus, mammary gland costochondral junction, liver, sciatic nerve, skeletal muscle, pancreas, nasal turbinates, unusual lesions, eyes and the testes with epididymides. Intraperitoneal body fat was recorded without exception at week 52 and by exception at all subsequent intervals. Histopathology was performed on the brain, spinal cord, pituitary, thyroid, adrenal, heart, lung, spleen, liver kidney, and ovaries/testes from 10/animals/sex in the low- and mid-exposure groups; and the nasal turbinates of all low- and mid-level animals. Also, the adrenals, ovaries/testes, heart (with coronary vessels), kidneys, liver, lungs, nasal turbinates, pituitary and thyroid were evaluated from 10 animals/sex/group from the control and high-exposure groups sacrificed at weeks 13 and 52.

2. Re-Evaluation of the study (Lomax LG et al., 1997):
Blood samples were collected from 10 males and 10 females per dose group at weeks 13, 52 and 104 and 10 males and 10 females in the control and the high-dose group at weeks 26 and 78. The following hematological parameters were evaluated at each sampling interval: hematocrit, hemoglobin, red blood cells counts, erythrocyte counts, total white blood cell counts, erythrocyte morphology and prothrombin time. Bone marrow samples were collected from the femurs of all rats killed at week 13 and 52 and from 10 males and 10 females from each group at study termination. Blood also was obtained from the abdominal aorta of all rats killed at week 13, 52 and study termination. The following clinical chemistry parameters were evaluated: glucose, blood urea nitrogen, serum glutamic-pyruvic transaminase, alkaline phosphatase, total protein, total albumin, total cholesterol (except for week 13) and triglycerides (except for week 13). Twenty-four hour urine samples were collected from 10 animals per sex per group at weeks 13, 52 and 104. The following parameters were evaluated: appearance, pH, specific gravity, glucose, ketones, total protein, bilirubin, and occult blood. Necropsy: Ten rats per sex per group were sacrificed after 13 and 52 weeks of exposure. The remaining animals were sacrificed after 104 - 106 weeks of exposure. Necropsies were performed on all decedents. The brain, kidneys, lungs spleen, adrenal and thyroid glands and the testis or ovaries were weighed and the organ to body weight ratios were calculated. The following tissues were preserved in buffered 10% formalin: brain, pituitary, spinal cord, esophagus, salivary glands, thyroid glands with parathyroid, lungs, mediastinal lymph nodes, thymus, heart, aorta, larynx, spleen, kidneys, adrenals, stomach, duodenum, ileum, jejunum, colon, skin, mesenteric lymph nodes, urinary bladder, uterus, mammary gland, prostate, seminal vesicles, costochondral junction, liver, sciatic nerve, skeletal muscle, pancreas, nasal cavity and gross lesions. The eyes from all rats and the testes with epididymides were preserved in Bouin's fixative. Microscopic evaluations were made using the tissue listed above in the control and the high-dose groups at study termination. The brain, spinal cord, pituitary, thyroid, adrenal, heart, lung, liver, spleen, kidney, and ovaries/testes from 10 animals per sex in the low- and mid-dose groups and the nasal cavities from all animals in the low- and mid-dose groups were evaluated microscopically. Sections from the adrenals, testes or ovaries, heart, kidneys, pituitary, thyroids, liver, nasal cavities and lungs of control and high-dose animals were examined microscopically after the week 13 and 52 interim sacrifices. Following the issuance of the original report, tissue blocks of the nasal cavities from the animals killed at the terminal sacrifice and the control and high-dose group at week 13, were obtained and a composite cross-sectional map of representative nasal cavity lesions with the approximate distribution was prepared for the mid- and high-dose groups.
Statistics:
1. Original study (Reno FE, 1979): Data Analysis: Pairwise comparisons of the mean body weights from weeks 12, 24, 36, 48, 52, 60, 72, 78, 90 and 104 were conducted using the F test for equality of two variances and Student's t-test. Clinical laboratory data (except urinalysis and leukocyte differentials), terminal body weights and absolute and relative organ weights (organ/body weight) of all animals sacrificed at weeks 13, 52 and term were subjected to a preliminary test for equality of variance followed by one-way analysis using Bartlett's test for homogeneity and Snedecor and Cochran, respectively. When statistical significances were observed, an additional set of analyses was conducted using Scheffe's method for judging all contrast in analysis of variance.
2. Re-Evaluation of the study (Lomax LG et al., 1997): Data analysis: Pair-wise comparisons of the mean body weights were performed. Clinical laboratory data, with the exception of urinalysis and leukocyte differentials, terminal body weights and absolute and relative organ weights of all animals killed at weeks 13 and 52 and at study termination were subjected to a preliminary test for the equality of variance. To evaluate tumor incidence, Fisher's one-sided exact test was conducted between the control and high-dose groups. For all analyses, statistical significance was determined by a p value < 0.05.
Clinical signs:
no effects observed
Description (incidence and severity):
No signs of test substance-related toxicity were observed in any of the treated animals throughout the 104-week exposure period. The most frequent observations included cloudy eye(s) and bloody crust
around one or both eyes. The author reported that these findings occurred with approximately the same frequencies in treated and control groups.

Re-Evaluation (1997)
No signs of treatment-related
toxicity were observed. At the 13, 52 and 104-week observation intervals, cloudy eyes and bloody crusts
around one or both eyes were noted in all of the treatment groups, as well as the control animals. Body
weights for males were lower than the control at various intervals but overall were considered equivalent
over the 104-week period. Mean body weights for females were lower than the controls at ca. 1.64 mg/L
(400 ppm) after week 52. Haematology, clinical chemistry and urinalyses did not indicate any treatmentrelated
effects in any of the parameters evaluated.
Mortality:
mortality observed, non-treatment-related
Description (incidence):
Mortality rates for the treated animals were similar to those of the controls
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
Male body weights were significantly higher in the mid-level exposure group at week 24, lower weights in the low-level exposure group at week 104, and lower weights of the high-level exposure group at weeks
28 and 78. In the females, the low-level exposure groups showed a significant decrease in body weight at weeks 60, 72 and 78 and an increase at weeks 12 and 24. The females in the mid-level exposure
group showed a significant decrease at weeks 52, 60 and 78 and in the high-level exposure group at weeks 28, 36, 52, 60, 72, 78 and 90. The author concluded, the body weight reduction observed in the
females exposed to ca. 1.64 mg/L (400 ppm) MMA was test substance-related.
Ophthalmological findings:
effects observed, non-treatment-related
Description (incidence and severity):
Ophthalmoscopic observations were noted at weeks 13, 52 and 102. The author reports that no consistent ocular abnormalities were noted at weeks 13 and 52. Ocular findings noted at week 102
included cataracts, pale coloration, corneal cloudiness and red discharge. The cataract findings were considered to be caused by aging.
Haematological findings:
no effects observed
Description (incidence and severity):
Evaluation of the haematology and clinical chemistry data did not reveal any remarkable trends. Statistical analyses showed numerous significant differences between the treated and the control groups; however, these differences were considered sporadic and were considered by the author a reflection of sampling and biological variability. A transitory appearance of occult blood was observed in all groups at week 52. All remaining intervals were generally unremarkable.
Organ weight findings including organ / body weight ratios:
effects observed, non-treatment-related
Description (incidence and severity):
A statistically significant increase in absolute and relative organ weights of the females exposed to ca. 1.64 mg/L (400 ppm) MMA was observed in the lungs, liver, kidneys, and ovaries at week 13. A
statistically significant decrease in absolute and relative thyroid and adrenal weights were observed in both males and females in the high-level exposure group at week 52. Absolute thyroid and adrenal
weights were significantly higher in the males exposed to ca. 0.41 mg/L (100 ppm), MMA for 52 weeks. Other significant differences were noted at weeks 52 and 104; however, the author concluded that no
consistent dose-related pattern was established.
Gross pathological findings:
effects observed, non-treatment-related
Description (incidence and severity):
Findings noted in animals that were sacrificed at weeks 13 and 52 were mainly discolorations of the lung and liver. None of the findings were considered treatment-related. Tissue mass findings for animals
sacrificed at week 104 were typical for the age and the species of rats. No treatment-related differences with respect to the frequency were observed.

Re-Evaluation (1997)
Gross necropsy of the rats sacrificed at weeks 13 and 52 did not show any treatment-related effects.
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Histopathology
Week 13
No treatment-related histopathological findings were noted in the rats exposed to ca. 1.64 mg/L (400 ppm) MMA for 13 weeks. Findings were consistent among groups and were typical for rats of this age and strain.
Week 52
No treatment-related histopathological findings were noted in the rats exposed to ca. 1.64 mg/L (400 ppm) MMA for 13 weeks. Findings were consistent among groups and were typical for rats of this age
and strain.
Week 104
Treatment-related histopathological findings were limited to a very slight increase in the lesions of mild rhinitis observed in the mucosal lining of the nasal turbinates. A summary of the lesions is provided below.
Incidence of Lesions in Nasal Mucosa
No clear treatment-related effect could be established. Although lesions of mild rhinitis occurred more often in treated rats than control rats, it could not be determined if the rhinitis was a result of direct
chemical insult to the turbinate area or whether the presence of MMA vapors predisposed the rats to an increase in spontaneous disease. [NOTE - Subsequent evaluation of the nasal lesions (Lomax et
al., 1997) indicated that there were exposure related nasal lesions at ca. 0.10 and 0.41 mg/L (100 and 400 ppm)]. Neoplasms and spontaneous disease lesions were observed with comparable frequency in
control and treated rats. Chronic nephritis was observed in most rats; however, it was more pronounced in males.


Re-Evaluation:
The following information was obtained from the reevaluation of the nasal tissues from this study originally conducted by Reno et al.(1979) - see also summary for this study in this Dossier. Microscopic
evaluation of the nasal cavity sections obtained from the animals exposed to the test substance for 13 weeks showed degeneration of the neuroepithelial cell lining of the dorsal meatus in conjunction with
atrophy of Bowman's glands and focal basal cell hyperplasia. Lesions were identified on the tips of the maxilloturbinates and nasoturbinates and focally along the nasal septum in the more anterior regions
of the nose. These lesions were characterized by chronic active inflammation, respiratory epithelial hyperplasia and squamous metaplasia. No microscopic findings were identified in the ocular tissue or
the lungs or other tissues. Blocks of the nasal cavities of animals from the 52-week sacrifice were unable to be located and, therefore, were not evaluated. No new findings were identified in the tissues that
were available for animals exposed to the test substance for 52 weeks. Spontaneous disease lesions included early respiratory disease in both the control animals and the animals exposed to 400 ppm of
the test substance. Also focal areas of pneumonitis were observed in two females in the control group.
Gross necropsy after two years of exposure to the test substance showed no treatment-related effects.
The nasal cavity was the target organ for chronic toxicity. Rats exposed to the 100 and 400 ppm dose group had dose-dependent lesions in the anterior portions of the nasal cavity. The olfactory
epithelium lining the dorsal meatus in the anterior region of the nasal cavity was affected by exposure to higher concentrations of the test substance. The microscopic changes consisted of degeneration of
the olfactory epithelium and underlying Bowman's glands, hyperplasia of basal cells, replacement of olfactory epithelium by ciliated epithelium and inflammation of
the mucosa and/or submucosa. Lesions tended to be bilateral in distribution. The olfactory lesions in rats exposed to 100 ppm were localized in the more posterior (level 3) portion of the dorsal meatus,
while those in animals exposed to ca. 1.64 mg/L (400 ppm) were found in levels 2 and 3. Hyperplasia of glands in the lamina propria and/or goblet cells and inflammation of the mucosa/lamina propria were
observed in the respiratory epithelium in the high exposure group animals. No effects were seen in nasal epithelium of rats exposed to ca. 0.10 mg/L (25 ppm) MMA.
Histopathological findings: neoplastic:
no effects observed
Description (incidence and severity):
No statistically significant differences were observed in the frequency of tumours between the rats exposed to ca. 1.64 mg/L (400 ppm) of the test substance and that of the controls. In female rats exposed to ca. 1.64 mg/L (400 ppm) of the
test substance, a statistically significant decrease in pituitary adenoma/carcinomas and mammary gland fibroadenomas was recorded. In male rats, a decreased incidence of pheochromocytoma was observed.
Dose descriptor:
NOAEC
Remarks:
systemic (gross pathology histopathology, clinical effects)
Effect level:
ca. 1 640 mg/m³ air
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: corresponding to 400 ppm
Dose descriptor:
LOAEC
Remarks:
local effects (Histopathology, olfactory epithelium)
Effect level:
ca. 416 mg/m³ air
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: nasal lesions; corresponding to 100 ppm
Key result
Dose descriptor:
NOAEC
Remarks:
local effects (Histopathology, olfactory epithelium)
Effect level:
ca. 104 mg/m³ air
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: corresponding to 25 ppm
Critical effects observed:
not specified

The mean analytical concentration was evaluated. The overall mean concentrations of MMA vapour were 25.0, 99.8 and 396.1 ppm for the 25, 100 and 400 ppm exposure groups, respectively.

 

Mortality: Mortality rates were relatively low through week 78. High mortality was observed through week 104. The author indicates that the increase in mortality was probably due to aging, not related to test substance exposure. The mortality rates for treated groups were comparable to the control group. A summary of the mortality rates (%) is provided below.

 

 

Dose group (ppm)

Week 0-13

Week 0-52

Week 0-104

MALES

 

 

 

Negative Control (0)

0

0

16

25

0

1.7

20

100

0

1.7

16

400

0

0

20

FEMALES

 

 

 

Negative Control (0)

0

0

24

25

0

3.3

36

100

1.4

3.3

26

400

0

5.0

30

Incidence of Lesions in Nasal Mucosa

 

 

Males

 

 

 

Females

 

 

 

Group No.*

1

2

3

4

1

2

3

4

No. of Nasal Turbinates Examined

48

49

49

48

44

48

45

46

Serous Exudate

3

11

12

16

15

8

17

23

Purulent Exudate

2

6

4

8

2

9

6

6

Pleocellular Infiltrate

1

4

6

19

3

14

9

11

Distended Submucosal Glands

5

21

21

12

3

14

12

9

Squamous Metaplasia (focal)

2

3

1

5

0

5

1

2

Inflammatory Polyp

0

0

1

2

0

0

0

0

*Groups 1, 2, 3 and 4 were exposed to ca. 0, 0.10, 0.41 and 1.64 mg/L (0, 25, 100 and 400 ppm) MMA, respectively.

 

No clear treatment-related effect could be established. Although lesions of mild rhinitis occurred more often in treated rats than control rats, it could not be determined if the rhinitis was a result of direct chemical insult to the turbinate area or whether the presence of MMA vapors predisposed the rats to an increase in spontaneous disease. [NOTE - Subsequent evaluation of the nasal lesions (Lomax et al., 1997) indicated that there were exposure related nasal lesions at ca. 0.10 and 0.41 mg/L (100 and 400 ppm)]. Neoplasms and spontaneous disease lesions were observed with comparable frequency in control and treated rats. Chronic nephritis was observed in most rats; however, it was more pronounced in males.

 

2. Re-Evaluation of the study (Lomax LG et al. (1997)):

-------------------------------------------------------

 

The mean analytical concentrations of the test substance in the exposure chambers were 25.0, 99.8 and 396.1 ppm less than 10% per dose level.

 

Mortality rates for the treated animals were similar to those of the controls. No signs of treatment-related toxicity were observed. At the 13, 52 and 104-week observation intervals, cloudy eyes and bloody crusts around one or both eyes were noted in all of the treatment groups, as well as the control animals. Body weights for males were lower than the control at various intervals but overall were considered equivalent over the 104-week period. Mean body weights for females were lower than the controls at ca. 1.64 mg/L (400 ppm) after week 52. Haematology, clinical chemistry and urinalyses did not indicate any treatment-related effects in any of the parameters evaluated.

 

Gross necropsy of the rats sacrificed at weeks 13 and 52 did not show any treatment-related effects.

 

The following information was obtained from the reevaluation of the nasal tissues from this study originally conducted by Reno et al.(1979) - see also summary for this study in this Dossier. Microscopic evaluation of the nasal cavity sections obtained from the animals exposed to the test substance for 13 weeks showed degeneration of the neuroepithelial cell lining of the dorsal meatus in conjunction with atrophy of Bowman's glands and focal basal cell hyperplasia. Lesions were identified on the tips of the maxilloturbinates and nasoturbinates and focally along the nasal septum in the more anterior regions of the nose. These lesions were characterized by chronic active inflammation, respiratory epithelial hyperplasia and squamous metaplasia. No microscopic findings were identified in the ocular tissue or the lungs or other tissues. Blocks of the nasal cavities of animals from the 52-week sacrifice were unable to be located and, therefore, were not evaluated. No new findings were identified in the tissues that were available for animals exposed to the test substance for 52 weeks. Spontaneous disease lesions included early respiratory disease in both the control animals and the animals exposed to 400 ppm of the test substance. Also focal areas of pneumonitis were observed in two females in the control group.

Gross necropsy after two years of exposure to the test substance showed no treatment-related effects. The nasal cavity was the target organ for chronic toxicity. Rats exposed to the 100 and 400 ppm dose group had dose-dependent lesions in the anterior portions of the nasal cavity. The olfactory epithelium lining the dorsal meatus in the anterior region of the nasal cavity was affected by exposure to higher concentrations of the test substance. The microscopic changes consisted of degeneration of the olfactory epithelium and underlying Bowman's glands, hyperplasia of basal cells, replacement of olfactory epithelium by ciliated epithelium and inflammation of the mucosa and/or submucosa. Lesions tended to be bilateral in distribution. The olfactory lesions in rats exposed to 100 ppm were localized in the more posterior (level 3) portion of the dorsal meatus, while those in animals exposed to ca. 1.64 mg/L (400 ppm) were found in levels 2 and 3. Hyperplasia of glands in the lamina propria and/or goblet cells and inflammation of the mucosa/lamina propria were observed in the respiratory epithelium in the high exposure group animals. No effects were seen in nasal epithelium of rats exposed to ca. 0.10 mg/L (25 ppm) MMA. No statistically significant differences were observed in the frequency of tumours between the rats exposed to ca. 1.64 mg/L (400 ppm) of the test substance and that of the controls. In female rats exposed to ca. 1.64 mg/L (400 ppm) of the test substance, a statistically significant decrease in pituitary adenoma/carcinomas and mammary gland fibroadenomas was recorded. In male rats, a decreased incidence of pheochromocytoma was observed.

Conclusions:
In a two years repeated dose inhalation study no systemic effects nad no carconogenic effects were observed in concentrations up to 1640 mg/ (cooresponding to 400 ppm). NOAEC for local effects (histopahthology/olfactory effects) is 104 mg/l (corresponding with 25 ppm).
Executive summary:

In a two years chronic inhalation study to evaluate pharmacotoxic and carcinogenic effects of methyl methacrylate in rats animals were treated in test concentrations of 25, 100 and 400 ppm (corresponding to 0.1; 0.41 and 1.64 mg/l) by whole body exposure. No treatment related effects were observed regarding clinical signs, mortality, body weight, opthalmological and haematological findings, organ weight, grosspathology and neoplastic findings compared to the control animals.

Rats exposed to the 100 and 400 ppm dose group had dose-dependent lesions in the anterior portions of the nasal cavity. The olfactory epithelium lining the dorsal meatus in the anterior region of the nasal cavity was affected by exposure to higher concentrations of the test substance. The microscopic changes consisted of degeneration of the olfactory epithelium and underlying Bowman's glands, hyperplasia of basal cells, replacement of olfactory epithelium by ciliated epithelium and inflammation of the mucosa and/or submucosa. Lesions tended to be bilateral in distribution. The olfactory lesions in rats exposed to 100 ppm were localized in the more posterior (level 3) portion of the dorsal meatus, while those in animals exposed to ca. 1.64 mg/L (400 ppm) were found in levels 2 and 3. Hyperplasia of glands in the lamina propria and/or goblet cells and inflammation of the mucosa/lamina propria were observed in the respiratory epithelium in the high exposure group animals. No effects were seen in nasal epithelium of rats exposed to ca. 0.10 mg/L (25 ppm) MMA. NOAEC for local effects (histopahthology/olfactory effects) is 104 mg/l (corresponding with 25 ppm).

No systemic effects were observed in concentrations up to 1640 mg/l (corresponding to 400 ppm) methyl methacrylate (gross pathology, histopathology and clinical effects).

No carcinogenic effects were observed in this study.

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
NOAEC
104 mg/m³
Study duration:
chronic
Species:
rat
Quality of whole database:
reliable with acceptable restrictions

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion
Endpoint conclusion:
no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

There are reliable data available to assess the toxic potential of methyl methacrylate after repeated oral and inhalation exposure in studies up to a duration of 2 years.

 

ORAL

Twenty-five male and female Wistar rats were administered three doses of methyl methacrylate in the drinking water for two years (Borzelleca et al. 1964). Initial doses of 6, 60 or 2000 ppm were partially raised to 7, 70 and 2000 ppm after 5 months.

A special design was employed to reduce the volatilization of MMA; measurements showed that the methyl methacrylate concentrations remained within 15% of the nominal concentration for 72 hours. Body weight depression was observed at 2000 ppm but it did not persist beyond the first few weeks of the study. Significant depression of fluid consumption was observed at 2000 ppm, although this tended to regress at the end of the study. Individual observations of depressed food consumption tended to parallel periods of depressed growth. There were significantly increased kidney ratios for female rats at 2000 ppm. These effects were believed to be a consequence of reduced food intake and reduced body weights, and in the absence of any histopathology, were considered as not biologically relevant. Therefore the NOAEL is considered to be >= 2000 ppm, corresponding to 164 mg/kg bw/day and 124.1 mg/kg bw/day, for males and females, respectively, on the basis of treatment specific fluid consumption rates and body weights.

This assessment is supported by results of an OECD 416 2 generation reproductive toxicity study with oral gavage administration to rats (BASF, 2009). Here,

twenty-five male and female Wistar rats (P parental generation) were administered with MMA at 0; 50; 150 and 400 mg/kg body weight/day. At least 73 days after the beginning of treatment, P animals were mated to produce a litter (F1). Mating pairs were from the same dose group and F1 animals selected for breeding were continued in the same dose group as their parents. Groups of 25 males and 25 females, selected from F1 pups to become F1 parental generation, were treated with the test substance at dosages of 0; 50; 150 and 400 mg/kg body weight/day post weaning, and the breeding program was repeated to produce F2 litter. No signs of systemic toxicity were observed other than slightly reduced body-weight gain at 150 mg/kg bw/d and above. Reduced body weights were judged to be the direct result of reduced food intake and therefore not an adverse finding. Consequently, the NOAEL was confirmed at the highest dose studied (450 mg/kg/d).

 

DERMAL

There are no relevant dermal repeated dose studies. For assessment purposes the oral data are used with a route-to-route extrapolation factor of 1.

 

INHALATION

Methyl methacrylate (MMA) has been evaluated for toxicity in acute, sub-acute and chronic inhalation (Hext et al. (2000); [Battelle (1980), NTP (1986)], Reno FE (1979)). In subacute, subchronic and chronic inhalation studies on rats and mice, the predominant target organ was the respiratory tract.

 

In a combined chronic toxicity/ carcinogenicity study, male and female Fischer 344 rats were exposed to methyl methacrylate monomer vapours at ca. 0, 0.10, 0.41 and 1.64 mg/L (0, 25, 100 and 400 ppm), 6 hr/day, 5 days/wk for 24 months (Reno et al. 1979; Lomax et al. 1997). Parameters monitored throughout the study included clinical signs, individual body weights, haematology, clinical chemistry and urinalyses. 10 rats per sex per exposure group were killed after 13 and 52 wk of exposure and all surviving rats were killed during wk 104-106. Mortality and haematological, clinical chemistry and urinalyses parameters were not affected by methyl methacrylate exposure.

 

The US National Toxicology Program conducted a series of repeat-exposure inhalation toxicity studies of increasing duration in male and female rats and mice. Effects on the nasal respiratory tract were seen in studies in rats and mice in studies of 14 weeks [Battelle Pacific Northwest Lab (1980a) and 104 weeks duration (NTP; 1986a). In the 14 week study 10 male and female rats and mice were exposed to MMA concentrations 0, 500, 1000, 2000, 3000 and 5000 ppm (6 hr/day, 5 days/wk for 97 d). In the 2 year study for 6 hr/day, 5 days/wk for 24 months 50 male and female rats and mice were treated with 2 concentrations of MMA: rats, male 500 and 1000 ppm; female 250 and 500 ppm; mice male and female, 500 and 1000 ppm.

Hext et al. (2000) exposed rats to 0, 110, or 400 ppm MMA, 6 hours/day, for 1, 2, 5, 10, or 28 consecutive days. Additional MMA-exposed rats were held for up to 36 weeks following exposure to assess reversibility of the nasal olfactory lesions. 

 

Local effects

The nasal cavity was identified as the target organ for chronic toxicity in male and female rats exposed to 416 and 1,640 mg/m3 (100 or 400 ppm). The microscopic nasal cavity changes occurred primarily in olfactory epithelium lining the dorsal meatus and consisted of degeneration of neuroepithelium, basal cell hyperplasia and atrophy of Bowman's glands. In the inhalation studies local degeneration of the olfactory epithelia was observed in acute (6hrs) at 100ppm, through to chronic (2-yr) studies at 100ppm (LOEL) with marked degeneration at 400ppm and above. The NOAEC for local effects was considered to be ca. 104 mg/m3, corresponding to 25 ppm.

 

In the non-rodent species dog and hamster, substance related effects on the respiratory tract were not observed after subchronic exposure to concentrations up to ca. 1,640 mg/m3 (400 ppm; Tansy et al. 1979, Lomax et al. 1997).

 

Relevance of animal data

The recognised differences between rodents and humans regarding the physiology of the nasal passages, metabolic activity result in the greater susceptibility of rodents compared with humans to inhaled esters. In the EU ESR (2002) these differences were disregarded and rodents were regarded being of comparable sensitivity to humans. Subsequently, in the SCOEL review (SCOEL, 2005) greater emphasis was placed on human data, showing the absence of adverse respiratory effects up to at least 50 ppm and this was considered to be consistent with rodents being at least three times more sensitive than humans based on PBPK considerations (Andersen et al. 2002, Mainwaring et al. 2001). Consequently, a value of 50 ppm is regarded as being the NOAEC (=DNEL) in humans.

 

Effects on body weight

Slightly reduced body-weight gain was observed in the inhalation studies at 400 ppm and above and at 150 mg/kg bw/d and above in the 2-gen study and transiently at 2000 ppm (124/164 mg/kg bw/d) in the drinking water study.

 

MMA has a pungent odour (odour threshold 0.5 – 1.5ppm) and can taint food and water as evidenced by the repeat dose oral studies. Reduced food consumption in the absence of any other clinical signs other than salivation was observed in the recent 2-gen study and transiently in the earlier 2 yr drinking study, is consistent with the pungent odour and tainting capacity of MMA and the likely reason for the reduced body-weight gain in these animals.

 

In an inhalation developmental toxicity study in rats, reduced maternal body weight or decreases in maternal body-weight gain and decreases in maternal feed consumption were noted at 99 ppm and above in the absence of any other signs of general systemic toxicity up to the highest concentrated tested (2,028 ppm) (Solomon, 1991) clearly establishing that the reduced body weight gain was a consequence of reduced feed consumption.

 

At the time that the chronic inhalation studies were performed, food consumption was not routinely recorded. Hence no such data is available to substantiate a link between reduced food consumption and reduced weight gain in these studies.

 

From the histopathology and from clinical observations in the sub-acute study it can be concluded that animals exposed to 400 ppm and above, MMA in the chronic studies had substantial nasal mucosal irritation, increased nasal secretions and some discomfort and that this would have likely been expressed as a diminished sense of smell/behavioural changes. By analogy to the developmental toxicity study by

Solomon it may be concluded that these changes would have the consequence of reducing appetite and have caused the decreased food consumption and depression of body-weight gain.

 

The association of olfactory epithelial injury and reduced feed consumption and decreased body-weight in high-level exposure groups recognized in the literature for other chemicals. For example, Dorman et al (2004) (Hirsch AR, and Zavala, 1999) reported that rats (F344 and Sprague-Dawley) and mice (B6C3F1) exposed to another olfactory epithelial toxicant, hydrogen sulphide (H2S), had exposure-related olfactory epithelial injury and rhinitis at exposure concentrations>= 30 ppm H2S. Rats exposed to 80 ppm ofH2S demonstrated reduced feed consumption and depressed terminal body weights.

 

In summary, the reduced body-weight gain observed in inhalation studies with MMA is the direct consequence of reduced food intake, as a consequence of severe nasal irritation and reduced olfactory function, and not of any true systemic toxicity. Hence, protecting against local effects (irritation and tissue damage in the respiratory tract) would protect against reduced body-weight gain in humans.

 

Systemic effects

 

Signs of general systemic toxicity including histopathological changes in liver, kidneys, spleen, bone marrow and brain were seen at concentrations of 2000ppm and above by inhalation but no effects by oral ingestion up to 400 mg/kg bw/d in the 2-Generation reproductive toxicity study (BASF, 2009) or 2000 ppm (c.a. 124/164 mg/kg bw/d) in the 2-yr drinking water (Borzelleca et al., 1964), other than increased relative kidneys weights which were considered to be a result of reduced body-weights and therefore not adverse findings.

 

After a 14-week inhalation, mice had cellular necrosis in liver and renal cortices > ca. 8,200 mg/mg3 (2,000 ppm) and rats showed splenic follicular atrophy and bone marrow atrophy at ca. 20,800 mg/m3 (5,000 ppm; Battelle 1980). Malacia and gliosis of the brain in the 14 week range finder to the NTP study (Battelle, 1980) is considered being the relevant systemic effect, which was seen in 5/9 female rats exposed at 2000 ppm and 1/8 females at 1000 ppm. Therefore, the absence of this effect at 500 ppm (2028 mg/m³) in the corresponding 2-year study (NTP) is considered representing the NOAEC for chronic systemic effects of MMA.

 

 

Other references:

Dorman, Struve MF, Gross EA, and Brenneman KA. Respiratory tract toxicity of inhaled hydrogen sulfide in Fischer-344 rats, Sprague-Dawley rats, and B6C3F1 mice following subchronic (90-day) exposure. Toxicol Appl Pharmacol 198: 29-39, 2004.

Hirsch, and Zavala G. Long term effects on the olfactory system of exposure to hydrogen sulfide. Occup. Environ. Med. 56:284-287, 1999.

Justification for classification or non-classification

Based on the available information, the potential of methyl methacrylate for systemic toxicity after repeated dosing is low. Hazards based on local effects were covered by the classification for the irritation potential on skin and respiratory tract (see chapter 7.3). Therefore, no additional classification is considered as justified.