Butyl methacrylate

Endpoint summary

Description of key information

The NOAE(C)L for systemic effects of n-butyl methacrylate was 120 mg/kg bw/d in a 90-day subchronic oral toxicity study in rats and 1891 ppm (11175 mg/m³) in a 28-day subacute inhalation toxicity study in rats. The NOAE(C)L for local effects was 1832 mg/m³ (310 ppm) in a 28-day subacute inhalation toxicity study in rats.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study.

Qualifier:

according to guideline

Guideline:

OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity Study in Rodents)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Research Models and Services, Germany GmbH
- Age at study initiation: 34 ± 1 day
- Weight at study initiation:
- Fasting period before study: No
- Housing: in groups of 5 animals per cage (Polysulfonate cages supplied by TECNIPLAST, Hohenpeißenberg, Germany; floor area about 2065 cm²)
- Diet: ground Kliba maintenance diet mouse/rat “GLP”, meal, ad libitum (Provimi Kliba SA, Kaiseraugst, Switzerland)
- Water: ad libitum
- Acclimation period: 8 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20-24
- Humidity (%): 30-70
- Photoperiod (hrs dark / hrs light): 12 / 12 (6.00 pm - 6.00 am dark; 6.00 am - 6.00 pm light)

Route of administration:

oral: gavage

Vehicle:

CMC (carboxymethyl cellulose)

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:
The test substance was administered as an emulsion. The appropriate amount of test substance was weighed out depending on the desired concentration. Thereafter, the vehicle (drinking water containing 1% carboxymethyl cellulose) was filled up to the desired volume + Cremophor EL + one drop Hydrochloric Acid (1mol/L) and subsequently mixed using a magnetic stirrer. The test-substance preparations were produced daily.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Concentration control analyses of the test-substance preparations in samples of all concentrations were performed at the start of the administration period and thereafter weekly.

Duration of treatment / exposure:

about three months

Frequency of treatment:

daily

Remarks:

Doses / Concentrations:
60, 120 and 360 mg/kg/day
Basis:
other: nominal in vehicle

No. of animals per sex per dose:

Control and high dose groups: 15 animals per sex per group (thereof 5 animals per sex per group for 28-day recovery)
Low and mid dose groups: 10 animals per sex per group.

Control animals:

yes, concurrent vehicle

Details on study design:

- Post-exposure recovery period in satellite groups: 28 days (5 rats/sex of control and high dose groups only)

Observations and examinations performed and frequency:

MORTALITY
A check for moribund and dead animals was made twice daily on working days and once daily on Saturdays, Sundays and public holidays. If animals were in a moribund state, they were sacrificed and necropsied.

CLINICAL OBSERVATIONS
All animals were checked daily for any clinically abnormal signs. Abnormalities and changes were documented for each animal.

DETAILED CLINICAL OBSERVATIONS (DCO)
Detailed clinical observations were performed in all animals prior to the administration period and thereafter at weekly intervals. The findings were ranked according to the degree of severity, if applicable. The animals were transferred to a standard arena (50 x 37.5 cm with sides of 25 cm high).The following parameters were examined: abnormal behavior during “handling”, fur, skin, posture, salivation, respiration, activity/arousal level, tremors, convulsions, abnormal movements, impairment of gait, lacrimation, palpebral closure, exophthalmus, feces (appearance/consistency), urine, pupil size

FOOD CONSUMPTION
Group food consumption was determined weekly for each cage. The average food consumption/cage was used to estimate the mean food consumption in grams per animal per day.

FOOD EFFICIENCY
Food efficiency (group means) was calculated based upon individual values for body weight and food consumption:
[(BWx - BWy)/FCy to x] x 100 = Food efficiency for day x,
with BWx = body weight on day x (g), BWy = body weight on day y (last weighing date before day x) (g), FCy to x = mean food consumption from day y to day x; calculated as mean daily food consumption on day x, multiplied with the number of days from day y to day x (g).

WATER CONSUMPTION
Water consumption was observed daily by visual inspection of the water bottles for any overt changes in volume.

BODY WEIGHT DATA
Body weight was determined before the start of the administration period in order to randomize the animals. During the administration period the body weight was determined on day 0 (start of the administration period) and thereafter at weekly intervals. The difference between the body weight on the respective day of weighing and the body weight on day 0 was calculated as body weight change.

FUNCTIONAL OBSERVATION BATTERY (FOB)
A functional observational battery was performed in all animals at the end of the administration period starting at about 10.00 am. At least one hour before the start of the FOB the animals were transferred singly to cages. Drinking water was provided ad libitum whereas no food was offered during the measurements. The FOB started with passive observations without disturbing the animals, followed by removal from the home cage, open field observations in a standard arena and sensorimotor tests as well as reflex tests. The findings were ranked according to the degree of severity, if applicable. The observations were performed at random.
Home cage observations: The animals were observed in their closed home cages; any disturbing activities (touch¬ing the cage or rack, noise) were avoided during these examinations in order not to in¬fluence the behavior of the animals. Attention was paid to posture, tremor, convulsions, abnormal movements, impairment of gait, other findings
Open field observations: The animals were transferred to a standard arena (50 x 50 cm with sides of 25 cm high) and observed for at least 2 minutes. Following parameters were examined: behavior when removed from cage, fur, skin, salivation, nose discharge, lacrimation, eyes/pupil size, posture, palpebral closure, respiration, tremors, convulsions, abnormal movements, impairment of gait, activity/arousal level, feces (number of fecal pellets/appearance/consistency) within two minutes, urine (appearance/quantity) within two minutes, number of rearings within two minutes.
Sensorimotor Tests/Reflexes: The animals were removed from the open field and subjected to following sensorimotor or reflex tests: approach response, touch response, vision ("visual placing response"), pupillary reflex, pinna reflex, audition ("startle response"), coordination of movements ("righting response"), behavior during "handling", vocalization, pain perception ("tail pinch"), grip strength of forelimbs, grip strength of hindlimbs, landing foot-splay test, other findings.

MOTOR ACTIVITY (MA) ASSESSMENT
MA measurements were carried out in all animals toward the end of the administration period. The examinations were performed using the TSE Labmaster System supplied by TSE Systems GmbH, Bad Homburg, Germany. For this purpose, the animals were placed in new clean polycarbonate cages for the time of measurement. 18 beams were allocated per cage. The numbers of beam interrupts were counted over 12 intervals for 5 minutes in each case. The animals were randomly placed in the cages. Motor activity measurements were carried out from 2.00 pm onwards. On account of the measuring variant "staggered", the starting time varied by the time which is needed to place the animals in the cages. For each animal, measurement was started individually when the 1st beam was interrupted and finished exactly 1 hour later. No food or water was given to the animals during measurements. After the transfer of the last animal in each case, the room of measurement was darkened. The program requires a file name for the measured data to be stored. This name consists of the reference number and a serial number.

OPHTHALMOSCOPY
Prior to the administration period, the eyes of all animals were examined using an ophthalmoscope (HEINE OPTOTECHNIK, Herrsching, Germany) after application of a mydriatic (Mydrum, Chauvin ankerpharm GmbH, Rudolstadt, Germany). At the end of the administration period the eyes of the control (0 mg/kg bw/day) and high dose animals (360 mg/kg bw/day) were examined for any changes, again.

HAEMATOLOGY
- Time schedule for collection of blood: at the end of the administration period
- Anaesthetic used for blood collection: Yes (Isoba, Essex GmbH Munich, Germany)
- Animals fasted: Yes
- How many animals: All animals per test group and sex. At the end of the recovery period only clotting analyses were examined in the remaining animals of the control and high dose group.
- The following parameters were determined in blood with EDTA-K3 as anticoagulant using a particle counter (Advia 120 model; Bayer, Fernwald, Germany): leukocyte count (WBC), erythrocyte count (RBC), haemoglobin (HGB), haematocrit (HCT), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), platelet count (PLT), differential blood count, reticulocytes, prothrombin time (Hepato Quick’s test; HQT). The clotting analyses were carried out using a ball coagulometer (AMAX destiny plus model; Trinity biotech, Lemgo, Germany). Furthermore differential blood smears were prepared and stained according to Wright without being evaluated.

CLINICAL CHEMISTRY
- Time schedule for collection of blood: at the end of the administration period
- Anaesthetic used for blood collection: Yes (Isoba, Essex GmbH Munich, Germany)
- Animals fasted: Yes
- How many animals: All animals per test group and sex. At the end of the recovery period only blood chemistry parameters were examined in the remaining animals of the control and high dose group.
- An automatic analyzer (Hitachi 917; Roche, Mannheim, Germany) was used to examine the clinicochemical parameters. The activities of the following enzymes were determined: alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), gamma-Glutamyltransferase (GGT). The following blood chemistry parameters were determined: sodium (NA), potassium (K), chloride (CL), inorganic phosphate (INP), calcium (CA), urea (UREA), creatinine (CREA), glucose (GLUC), total bilirubin (TBIL), total protein (TPROT), albumin (ALB), globulins (GLOB), triglycerides (TRIG), cholesterol (CHOL), magnesium (MG).

URINALYSIS
- Time schedule for collection of urine: at the end of the administration period overnight
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes
- Investigated parameters: pH, protein, glucose, ketones, urobilinogen, bilirubin, blood, specific gravity, sediment, color, turbidity, volume. With the exception of volume, color, turbidity, sediment examination and the specific gravity, all the urine constituents were determined semiquantitatively using test strips (Combur 9 test M, Roche, Mannheim, Germany) and a reflection photometer (Miditron M; Roche, Mannheim, Germany).

Sacrifice and pathology:

NECROPSY
All animals were sacrificed by decapitation under Isoflurane anesthesia. The exsanguinated animals were necropsied and assessed by gross pathology.

WEIGHT PARAMETERS
The following weight determinations were carried out on all animals: anesthetized animals, liver, kidneys, adrenal glands, testes, epididymides, ovaries, uterus, spleen, brain, heart, thymus, thyroid glands.

HISTOPATHOLOGY
After the organs were fixed, processing, examination by light microscopy and evaluation of findings in the following tissues of all control and high-dose animals of the main groups were performed: salivary glands (mandibular and sublingual glands), esophagus, stomach (forestomach and glandular stomach), duodenum, ileum, jejunum (with Peyer’s plaques), cecum, colon and rectum, liver, pancreas, brain, pituitary gland, sciatic nerve, spinal cord (cervical, thoracic and lumbar cords), eyes, adrenal glands, thyroid glands, parathyroid glands, trachea, lungs, nose (nasal cavity/level III), aorta, heart, bone marrow (femur), lymph nodes (mesenteric and axillary lymph nodes), spleen, thymus, kidneys, urinary bladder, testes, ovaries, oviducts, uterus and vagina, prostate, seminal vesicle and epididymides, female mammary gland, skin.
Additionally, nose tissue (nasal cavity/level III) was examined in all low- and mid-dose animals of the main groups and in all control and high-dose animals of the recovery groups. Furthermore, all gross lesions were examined in all affected animals of all groups.

Statistics:

Statistics of clinical examinations: Means and standard deviations of each test group were calculated for several parameters. Further statistical analyses were DUNNETT's test (two-sided) for body weight and body weight change, and KRUSKAL-WALLIS test (two-sided)/Wilcoxon-test (two-sided) for feces, rearing, grip strength forelimbs, grip strength hindlimbs, foot-splay test, and motor activity.
Statistics of clinical pathology: Means, medians and standard deviations of each test group were calculated for several parameters. Further statistical analyses were KRUSKAL-WALLIS test (two-sided)/Wilcoxon-test (two-sided) for clinical pathology parameters, urine volume, and urine specific gravity, and FISHER's exact test for urinalysis, except color, turbidity, volume and specific gravity.
Statistics of pathology: KRUSKAL-WALLIS test (two-sided)/Wilcoxon-test (two-sided) for weight parameters.

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

no effects observed

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

no effects observed

Haematological findings:

effects observed, treatment-related

Clinical biochemistry findings:

effects observed, treatment-related

Urinalysis findings:

effects observed, treatment-related

Behaviour (functional findings):

no effects observed

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

not examined

Details on results:

ANALYSES
Stability analyses: The stability of the test substance in drinking water containing 1% Carboxymethylcellulose + Cremophor EL + one drop Hydrochloric Acid (1mol/L) was demonstrated over a period of 4 h at room temperature. As the mixtures were stored no longer than this time period, the stability was guaranteed.

Homogeneity control analyses: Considering the standard deviation in the homogeneity analysis, it can be concluded that n-Butyl Methacrylate was distributed homogeneously in 1% Carboxymethylcellulose + Cremophor EL under the addition of one drop Hydrochloric Acid (1 mol/L).

Concentration control analyses: Due to the physical-chemical properties of the test article (esp. volatility), concentration control analyses were performed weekly. Thus, 13 analytical results were obtained for each dose group throughout the entire study. Taken together these results of the low dose group, the measured concentration was 85.2% of the nominal value. For the mid dose group, the corresponding value was 87.0% and for the high dose group 91.8% of the nominal concentration were determined.
Independently from the obtained variations of the analytical series, these mean values are assessed to demonstrate the correctness of the test-substance preparations within the current study.

CLINICAL EXAMINATIONS
- Mortality: No animal died prematurely in the present study.
- Clinical examinations: During clinical examinations, only Microphthalmia left was observed in 1 female of test group 2 (120 mg/kg bw/day).
This isolated finding only observed in one mid dose female animal was assessed as spontaneous in nature and therefore not substance related.
- Food consumption: Food consumption was significantly increased in males of group 1 (60 mg/kg bw/day) on day 91. This finding, which occurred only once in low dose males, was assessed as incidental in nature and therefore not substance related.
- Water consumption: No substance-related overt changes in water consumption were observed.
- Body weight data: The body weight was significantly decreased in male animals of test group 3 (360 mg/kg bw/day) towards the end of the study (-7% on days 84 and 91). The corresponding body weight change was also significantly decreased in these animals from day 77 till the end of the administration period (-12.1% on day 84 and 91). This impairment of body weight data in high dose males was assessed as related to treatment with the test substance and indicates general systemic toxicity. During the recovery period, no significant influence on body weight data was measured anymore. The body weight of the female animals in all test groups was not significantly influenced by the test article during the administration period. However, in female animals of test group 3 (360 mg/kg bw/day) a significantly lower (-7.8%) weight was noted on day 98, at the beginning of the recovery period, only. This significant difference evolved from an apparent above-average "increase" (by 9 grams) of the mean control body weights in the recovery animals, right after cessation of the treatment. The control group rats designated at the start of the study for recovery, by chance, weighed more than the control group rats sacrificed at the end of the administration period. Because of this, the body weight of the test group 3 (360 mg/kg bw/day) recovery rats appeared to be significantly decreased compared to the control group recovery rats at the beginning of the recovery period. Thus, the apparent weight decrease in the high-dose recovery females is not related to the test article and is considered to be toxicologically irrelevant.
- Food efficiency: No substance-related findings were observed.
- Functional observational battery (FOB): Deviations from "zero values" were obtained in several animals. However, as all findings were equally distributed between treated groups and controls, were without a dose-response relationship or occurred in single animals only, these observations were considered to have been incidental. Besides this, during functional observational battery the following examinations were carried out and have to be assessed individually: Home cage observations: No substance-related findings were observed. Open field observations: No substance-related findings were observed. Sensorimotor tests/reflexes: No substance-related findings were observed. Quantitative parameters: No substance-related findings were observed.
- Motor activity (MA) measurement: Regarding the overall motor activity, no substance-related findings were observed. Comparing the single intervals, the motor activity was significantly decreased in female animals of group 3 at interval 10, compared to the control value. This single occurrence only observed towards the end of the period of measurement was without any significant influence on the overall motor activity and therefore assessed as toxicologically irrelevant.
- Ophthalmological examinations: The observed corneal stipplings and remainders of the pupillary membrane were equally distributed between the dosed animals and the controls. Therefore, these findings were clearly not related to treatment and were without any toxicological relevance.

CLINICAL PATHOLOGY
- Hematology: At the end of the administration period no treatment-related adverse changes were found in the rats of both sexes concerning the complete blood cell counts. In the male rats of the 360 mg/kg bw/d dose group the relative reticulocyte counts were significantly lower compared to the controls. This change was not regarded as toxicological relevant, because no other red blood cell parameter were affected. After substance administration, the prothrombin time (Hepatoquick’s time) was significantly prolonged in male and female rats of the 360 mg/kg bw/d dose group. This change was no longer present after the 4 weeks recovery period.
- Clinical chemistry: At the end of the administration period in rats of both sexes of the 360 mg/kg bw/d dose group the inorganic phosphate levels were significantly increased and the calcium levels were significantly decreased. The changes were no longer present after the recovery period apart from weakly significantly increased inorganic phosphate levels in males. The urea levels were significantly increased in male and female rats of the 360 mg/kg bw/d dose group, and additionally in males of the 120 mg/kg bw/d dose group. This increased urea level was the only clinical pathology value affected in the mid dose group. Therefore, it was regarded as treatment-related but not adverse. After the recovery period, the urea level was still slightly significantly increased in female rats of the high dose group. After the last administration day, the triglyceride concentrations were significantly decreased in rats of both sexes of the 360 mg/kg bw/d dose group. Additionally, in rats of the high dose group the total bilirubin levels in males as well as the glucose levels in females were significantly increased and the globulin values were significantly decreased in females. All these changes were not present after the recovery period, anymore. But in male rats of the high dose group the glucose levels were weakly significantly decreased after the recovery period. These lower glucose levels were regarded as incidentally, because in these animals the glucose levels were not changed at the end of the administration period, and in female rats the glucose levels were increased during the substance administration. At the end of the administration period, the inorganic phosphate and urea levels were statistically significantly higher in females of the 60 mg/kg bw/d dose group. These were the only findings in this dose group, and they were not dose-dependent. Therefore, theses changes were regarded as incidentally rather than treatment-related. At the end of the administration period, the sodium levels were significantly lower in males of the 360 mg/kg bw/d dose group. This change was not accompanied by any other electrolyte level change, and was not present in females. Therefore, this deviation was regarded as incidentally rather than treatment-related.
- Urinalyses: At the end of the administration period no treatment-related adverse effects were found in the dosed rats regarding the urinalysis parameters. In the males of the 360 mg/kg bw/d dose group there were found less phosphate crystals in the urine sediment compared to the controls. Regarding the individual pH values of the urine samples, there appeared to be slightly lower pH values in the dosed rats. Therefore, it was assumed, that the phosphate crystals were dissolved in the urine of the dosed males. Nevertheless, this effect was regarded as treatment-related, but not adverse.

PATHOLOGY
- Absolute organ weights: The increased kidney weights (+ 11%) in female animals of the 360 mg/kg body weight group are regarded as treatment-related, although there was no histopathologic correlate which could explain this weight increase. The decrease in adrenal gland weights in males of the mid-dose (- 11%) and high-dose (- 10%) groups is regarded as a consequence of the decreased terminal body weights, although these decreases were not statistically significant. It is therefore not regarded as a treatment-related effect. All other mean absolute weight parameters did not show significant differences when compared to the control group. The significant increase in kidney weights of the male animals of the recovery group (+ 17%) is not treatment-related, as the kidney weights of the main group males of the 360 mg/kg dose group were within the range of the control group. All other mean absolute weight parameters did not show significant differences when compared to the control group.
- Relative organ weights: The increased relative brain, kidney, and liver weights in the 360 mg/kg body weight group of male animals are regarded as a consequence of the reduction in terminal body weight. In females, the significant increase in relative kidney and liver weights are regarded as treatment-related. Due to the fact that the terminal body weight was not changed in treated animals and the absolute liver weight was increased up to +9%, although not statistically significant, a substance relationship can not be excluded. This effect is not regarded to be adverse in nature as no histopathologic finding were observed. The decrease in the uterus weight of the 60 mg/kg body weight group is assessed as incidental, because there is no dose-response relationship and the uterus weights in the higher dose groups were greatly than that of the control level. All other mean relative weight parameters of the main groups and the recovery groups did not show significant differences when compared to the control groups.
- Gross lesions: All gross lesions occurred singly or they were biologically equally distributed between control and treatment groups.
- Histopathology: In males and females of the 360 mg/kg body weight group degeneration and regeneration of the olfactory epithelium was observed. The nasal cavities of animals of the recovery groups (control and 360 mg/kg body weight) were examined. There were no abnormalities detected. Mainly the nasal septum and the ethmoid turbinates were affected. In the more severe cases, there was extension to almost all parts of the nasal cavity. The finding was always observed at the transition of the respiratory to the olfactory epithelium at the nasal septum and extended upwards until up to 2/3 of the septum was affected. There was a mixture between degenerative findings (loss of epithelial cells, reduction in epithelium height, irregular architecture, apoptosis) and regenerative findings (hyperplasia/hypertrophy of basal cells, nest-like accumulation of basal cells, occasionally extending into the submucosa, mitotic figures). In animals diagnosed with grade 1, the hyperplasia/hypertrophy was often the most evident finding. All other findings noted were either single observations or they were biologically equally distributed between control and treatment group. All of them are considered to be incidental or spontaneous in origin and without any relation to treatment.

Dose descriptor:

NOAEL

Effect level:

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

Sex:

male/female

Basis for effect level:

other: Effects on the liver activity (increased liver weight, prolonged prothrombin time, lower serum globulin and triglyceride levels in males and/or females) and kidneys weight (increased absolute weight in females)

Critical effects observed:

not specified

ABSOLUTE ORGAN WEIGHTS:

Main groups:

	Male animals			Female animals
Group (mg/kg bw)	60	120	360	60	120	360
Adrenal glands	- 4%	- 11%*	- 10%*
Kidneys				+ 4%	+ 3%	+ 11%**

*: p ≤ 0.05, **: p ≤ 0.01; Kruskal-Wallis H and Wilcoxon test, two-sided

 

Recovery groups:

	Male animals
Group (mg/kg bw)	360
Kidneys	+ 17%*

*: p ≤ 0.05, **: p ≤ 0.01; Wilcoxon test, two-sided

 

 

RELATIVE ORGAN WEIGHTS:

Main groups:

	Male animals			Female animals
Group (mg/kg bw)	60	120	360	60	120	360
Brain	+ 1%	+ 1%	+ 11%**
Kidneys	0%	- 2%	+ 13%**	+ 1%	+ 2%	+ 13%**
Liver	+ 4%	+ 7%	+ 9%**	- 3%	+ 4%	+ 11%**
Uterus				- 23%*	+ 3%	+ 9%

*: p ≤ 0.05, **: p ≤ 0.01; Kruskal-Wallis H and Wilcoxon test, two-sided

 

 

INCIDENCE AND GRADING OF THE OBSERVED DEGENERATION AND REGENERATION OF THE OLFACTORY EPITHELIUM:

 

Nasal cavity level III	Male animals				Female animals
Dosemg/kg bw	0	60	120	360	0	60	120	360
Organs examined	10	10	10	10	10	10	10	10
Degeneration/regen-eration olf. epithelium	0	0	4	5	0	0	2	7
Grade 1			3	3				2
Grade 2				1			1	3
Grade 3			1				1	2
Grade 4				1

 

Executive summary:

In a study conducted according to OECD TG 408 in compliance with GLP, n-butyl methacrylate was administered daily to male and female Wistar rats by gavage at dose levels of 0, 60, 120 and 360 mg/kg body weight per day over a period of 3 consecutive months (BASF, 2009). Control and high dose groups consisted of 15 animals per sex per group, whereas low and mid dose groups consisted of 10 animals per sex per group. After 3 months of treatment, 10 animals per sex of all dose groups were sacrificed (main groups). The remaining 5 animals per sex of control and high dose groups were maintained for another 28 days without administration of the test substance (recovery groups).

At 360 mg/kg bw/day, body weight change significantly decreased in male animals from day 77 onwards (-12.1% on days 84 and 91). Prothrombin time was significantly prolonged (+10% males; +12% females) and inorganic phosphate (+14% males; +30% females), total bilirubin levels (+17% in males), glucose levels (+13% in females) as well as urea levels (+36% males; 21% females) significantly increased. Calcium (-3% in males and females), globulin levels (-4% in females) and triglyceride levels (-24% in males and females) significantly decreased. Absolute kidney weight (+11% in females), relative kidney weight (+13% males and females) and liver weight (+9% males; +11% females) significantly increased. Multifocal degeneration/regeneration of olfactory epithelium was observed in males (5 out of 10) and females (7 out of 10). After the recovery period, phosphate levels (+7% in males) and urea concentrations (+22% in females) were significantly increased.

At 120 mg/kg bw/day, multifocal degeneration/regeneration of olfactory epithelium was observed in males (4 out of 10) and females (2 out of 10).

At 60 mg/kg bw/day, no substance-related adverse findings were observed.

Multifocal degenerative and regenerative olfactory epithelium of the nasal cavity was observed in high dose (360 mg/kg bw/day) and mid dose (120 mg/kg bw/day) (4 out of 10 males and 2 out of 10 females). At 60 mg/kg bw/day, no substance-related adverse findings in the olfactory tissues were observed. Considering the short half life of n-BMA in blood (99.7 % removed in first pass by the liver, Jones 2002) it is unlikely that these effects were of systemic origin, but were rather local effects as a consequence of the dosing technique. This substance-related effect was completely reversible, as no animal of the recovery group showed any finding in the nose after 28 days after cessation of exposure.

In conclusion, the oral administration of n-butyl methacrylate by gavage over a period of 3 months with a recovery period of 28 days revealed toxicologically relevant signs of systemic toxicity at the high dose level of 360 mg/kg bw/day, limited to effects on the liver activity (increased liver weight, prolonged prothrombin time, lower serum globulin and triglyceride levels in males and/or females) and kidneys weight (increased absolute weight in females). The NOAEL for these effects was 120 mg/kg body weight/day in both males and female Wistar rats.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

120 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Study was conducted in accordance with a recognized scientific procedure for determining the toxicity of a test substance when administered repeatedly via inhalation for 4 weeks to experimental animals. Study was conducted in compliance with GLP regulations. The study meets national and international scientific standards (OECD 412) and provides sufficient information to support the conclusions regarding the NOAEC and the LOAEC demonstrated from the study data.

Qualifier:

according to guideline

Guideline:

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

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

other: Crl:CD BR

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River, Kingston, Stone Ridge, NY, USA
- Age at study initiation: 35-day old
- Weight at study initiation: ca 260 g for males and ca 195 g for females
- Housing: individually in suspended wire-mesh cage in the inhalation chamber rooms
- Diet (e.g. ad libitum): Purina certified rodent chow 5002 (excepted during exposure)
- Water (e.g. ad libitum): tap water (excepted during exposure)
- Acclimation period: two weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21 - 27
- Humidity (%): 40 - 60
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Details on inhalation exposure:

All chambers were operated  at an air flow rate of 400 L/min, resulting in a calculated 99% aerosol  equilibrium time of 23 minutes or 6.4% of the exposure time. Vapors of the test material were generated  from the liquid form, introduced at a constant flow into heated flasks  (approx. 102-105 degrees C) through which a constant flow of air was  metered.  The inhalation chambers were stainless steel, approximately  2000 L. Chamber temperature was 22.8-25.5 degrees C; chamber relative  humidity was 62.5-67.6%.  Fresh air was mixed with the test chemical  vapors to achieve the desired concentration. 
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: The animals received a whole-body inhalation exposure under dynamic conditions in 2000-L stainless steel, glass, and Plexiglas® chambers.
- Method of holding animals in test chamber: Each animal was individually housed in a suspended wire-mesh cage without food or water during the exposure. Cage positions within the chambers were rotated each day to insure that the animals were exposed at several different locations within each chamber.
- Source and rate of air: Calibrated flowmeters (Fisher-Porter Inc., Warminster, PA) delivered compressed air at a rate of 30 L/min into the air inlet of each flask
- Temperature, humidity, pressure in air chamber: The mean temperatures and relative humidities for all four chambers ranged from 22.8 to 25.5°C and 62.5 to 67.6%, respectively.
- Air flow rate: The chamber volume and air flow rate were adjusted to reach 99% of the maximum vapor concentration (t99) within 30 minutes of the total exposure time (Silver, 1946). The volume of animais loaded into the chamber was Iess than 7% of the total chamber volume.
- Air change rate: no data
- Generation of the Test Atmosphere: The test material vapor concentrations were generated by metering the test material with calibrated Fluid Metering Pumps into 500 or 5000 ml three-necked round bottom flasks. The flasks were located in hemispherical heating mantles.
- Method of particle size determination: not appropriate, only vapors were generated
- Treatment of exhaust air: no data

TEST ATMOSPHERE
- Brief description of analytical method used: The concentration of butyl methacrylate in the chambers was determined using a Miran 1A gas analyzer attached to a strip chart recorder. Before the initiation of the exposure, the Miran 1A gas analyzer was callbrated using precisely measured amounts of butyl methacrylate delivered into a dynamic vapor generator. A calibration curve was generated to convert the readings obtained from the Miran 1A gas analyzer into parts-per-million (ppm) butyl methacrylate.
- Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analytical  concentrations only of test material were determined throughout the  study.  Test concentrations were measured during each daily exposure  period (every 80 minutes) and the vapors analyzed by GC to confirm  purity. 

Duration of treatment / exposure:

4 weeks

Frequency of treatment:

6 hr/day, 5 days/week

Remarks:

Doses / Concentrations:
0, 310, 952 and 1891 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

5

Control animals:

yes, concurrent vehicle

Positive control:

not appropriate

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: All animals were observed before and after each daily exposure for general condition and signs of toxicity, and once during the post-exposure observation period.

DETAILED CLINICAL OBSERVATIONS: No

BODY WEIGHT: Yes
- Time schedule for examinations: Each animal was weighed weekly.

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
Food consumption was measured weekly

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No

WATER CONSUMPTION: No

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: during necropsy at conclusion of study
- Anaesthetic used for blood collection: Yes
- Animals fasted: Yes
- How many animals: all animals
- Parameters examined: hematocrit, platelet count, hemoglobin, mean ceil volume, red blood cell, mean ceil hemoglobin, white blood cell count, mean cell hemoglobin conc.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: during necropsy at conclusion of study
- Anaesthetic used for blood collection: Yes
- Animals fasted: Yes
- Parameters examined:
triglyceride globuiin
cholesterol albumin : globulin ratio
blood urea nitrogen creatinine
glucose bilirubin (total)
alkaline phosphatase calcium
total protein inorganic phosphorus albumin
chloride sodium
potassium
glutamic pyruvic transaminase/alanine aminotransferase activity
glutamic oxaloacetic transaminase/aspartate aminotransferase activity
gamma-glutamyl transferase activity

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

ORGAN WEIGHTS: Absolute and relative organ weights (organ-body), measured at necropsy, included: adrenals, brain, kidneys, liver, lungs, and testes.

GROSS PATHOLOGY: Full compliment of tissues, including all male and female reproductive organs, were fixed and examined in all animals.

HISTOPATHOLOGY: The following tissues and organs were examined histologically in the high dose and control groups only: adrenals, gross lesions, heart, kidneys, larynx, liver, lungs, nasal cavity, spleen and trachea. Only identified target organs were to be examined in mid and low dose groups. Slides were stained with hematoxylin and eosin

Statistics:

Distribution of body weight, body weight changes,  and organ weight were inspected for normality and homogeneity of variance  across all dose groups.  Analysis of variance models were used to assess  the presence or absence of an overall compound effect. Separate one-way  models were used within the male and female data to assess overall  treatment group effects.  Two-way models were used for treatment group,  sex and interaction between groups. Pairwise comparisons of least square  means between control and treated groups were evaluated using  Dunnett'st-test.  Hematology and clinical chemistry values were inspected  for normality and homogeneity using ANOVA. Statistical significance was  demonstrated at the p < 0.05. 

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

effects observed, treatment-related

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

not specified

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
No deaths were noted at any concentration tested. The only treatment-related signs of toxicity observed were inactivity, lacrymation, eye squinting, and labored breathing. These signs were seen only during the six-hour exposure. Slight inactivity occurred in all butyl methacrylate exposed groups on days 1, 2, and 3. Inactivity to slight inactivity occurred at concentrations of 952 and 1891 ppm on days 4 through 20. Lacrymation was observed only twice during the first three days, once at 952 ppm and once at 1891 ppm. Eye squinting occurred only at the highest concentration from day 3 to day 20, with the exception of day 4, were no eye squinting was observed. Labored breathing occurred once during day 1, at 1891 ppm.

BODY WEIGHT AND WEIGHT GAIN
A statistically significant increase in the body weight for the 310 ppm females was observed during Week 3. However, because this was an isolated finding, and no concentration-related trend was observed, it was judged not to be treatment-related.

FOOD CONSUMPTION
A statistically significant decrease in the feed consumption for the 1891 ppm females was observed during Week 1. However, because this was an isolated finding, and no effect on body weight was observed, it was judged not to be treatment-related.

HAEMATOLOGY
No treatment-related differences in hematology parameters were observed.

CLINICAL CHEMISTRY
The clinical chemistry data showed two parameters with statistically significant findings. A decrease in the alkaline phosphatase concentration for 310, 952, and 1891 ppm female animals, was observed. A statistically significant decrease in the triglyceride concentration for 952 ppm and 1891 ppm female animals, was also observed. Although these parameters were statistically different from the controls in a concentration-related trend, these findings were judged not to be of toxicological significance.

ORGAN WEIGHTS
The organ weight data showed a statistically significant increase in kidney weight to body weight ratio in males and females exposed at 1891 ppm. Absolute kidney weights for this group were not statistically different from the controls.

GROSS PATHOLOGY
no data

HISTOPATHOLOGY: NON-NEOPLASTIC
Histopathologic evaluation revealed treatment-related observations in the nasal cavities. Microscopic examination of the nasal cavities of male and female rats exposed to 1891 ppm had slight and localized bilateral degeneration of olfactory epithelium lining the dorsal meati. One male rat and one female rat exposed to 952 ppm had similar changes in the olfactory epithelium. Rats exposed to 310 ppm had no exposure related nasal cavity microscopic changes.

Dose descriptor:

NOAEC

Effect level:

310 ppm

Sex:

male/female

Basis for effect level:

other: 1801 mg/m3 for local effects in the nasal olfactory epithelium

Dose descriptor:

NOAEC

Effect level:

1 891 ppm

Sex:

male/female

Basis for effect level:

other: systemic effects

Dose descriptor:

LOAEC

Effect level:

952 ppm

Sex:

male/female

Basis for effect level:

other: 5531 mg/m3, for local effects in the nasal olfactory epithelium

Critical effects observed:

not specified

Conclusions:

The no-observable adverse effect concentration (NOAEC) for systemic effects was 1891ppm. Based on histopathological changes seen in the nasal cavities, the no-observable adverse effect concentration (NOAEC) for local effects was 310 ppm.

Executive summary:

In an OECD Guideline 412 Repeated Dose 28-day inhalation study, 10 male and 10 female rats were exposed by whole body to 0, 310, 952 and 1891 ppm (0,1832, 5626, 11175 mg/m³) n-BMA for 6 hr/day, 5 days/week for 4 weeks. Treatment-related effects included lacrimation, eye squinting, and laboured breathing in the 952 and 1891 ppm (5626 and 11175 mg/m³) concentration groups throughout the study. There were no treatment-related effects on body weight or feed consumption, and no deaths occurred. Haematological measurements and clinical chemistry values generally were unaffected by treatment. Despite increased relative kidney weights at the high concentration (1891 ppm/11175 mg/m³) in both sexes, and slight increases in serum BUN values (resulting in increased BUN:creatinine ratio), histopathology of the kidneys was normal. The only treatment-related histopathological finding was localised bilateral degeneration of olfactory epithelium lining the dorsal meatus of the nasal cavity at 952 and 1891 ppm (5626 and 11175 mg/m³) in both sexes.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

11 175 mg/m³

Study duration:

subacute

Species:

rat

Repeated dose toxicity: inhalation - local effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Study was conducted in accordance with a recognized scientific procedure for determining the toxicity of a test substance when administered repeatedly via inhalation for 4 weeks to experimental animals. Study was conducted in compliance with GLP regulations. The study meets national and international scientific standards (OECD 412) and provides sufficient information to support the conclusions regarding the NOAEC and the LOAEC demonstrated from the study data.

Qualifier:

according to guideline

Guideline:

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

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

other: Crl:CD BR

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River, Kingston, Stone Ridge, NY, USA
- Age at study initiation: 35-day old
- Weight at study initiation: ca 260 g for males and ca 195 g for females
- Housing: individually in suspended wire-mesh cage in the inhalation chamber rooms
- Diet (e.g. ad libitum): Purina certified rodent chow 5002 (excepted during exposure)
- Water (e.g. ad libitum): tap water (excepted during exposure)
- Acclimation period: two weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21 - 27
- Humidity (%): 40 - 60
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Details on inhalation exposure:

All chambers were operated  at an air flow rate of 400 L/min, resulting in a calculated 99% aerosol  equilibrium time of 23 minutes or 6.4% of the exposure time. Vapors of the test material were generated  from the liquid form, introduced at a constant flow into heated flasks  (approx. 102-105 degrees C) through which a constant flow of air was  metered.  The inhalation chambers were stainless steel, approximately  2000 L. Chamber temperature was 22.8-25.5 degrees C; chamber relative  humidity was 62.5-67.6%.  Fresh air was mixed with the test chemical  vapors to achieve the desired concentration. 
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: The animals received a whole-body inhalation exposure under dynamic conditions in 2000-L stainless steel, glass, and Plexiglas® chambers.
- Method of holding animals in test chamber: Each animal was individually housed in a suspended wire-mesh cage without food or water during the exposure. Cage positions within the chambers were rotated each day to insure that the animals were exposed at several different locations within each chamber.
- Source and rate of air: Calibrated flowmeters (Fisher-Porter Inc., Warminster, PA) delivered compressed air at a rate of 30 L/min into the air inlet of each flask
- Temperature, humidity, pressure in air chamber: The mean temperatures and relative humidities for all four chambers ranged from 22.8 to 25.5°C and 62.5 to 67.6%, respectively.
- Air flow rate: The chamber volume and air flow rate were adjusted to reach 99% of the maximum vapor concentration (t99) within 30 minutes of the total exposure time (Silver, 1946). The volume of animais loaded into the chamber was Iess than 7% of the total chamber volume.
- Air change rate: no data
- Generation of the Test Atmosphere: The test material vapor concentrations were generated by metering the test material with calibrated Fluid Metering Pumps into 500 or 5000 ml three-necked round bottom flasks. The flasks were located in hemispherical heating mantles.
- Method of particle size determination: not appropriate, only vapors were generated
- Treatment of exhaust air: no data

TEST ATMOSPHERE
- Brief description of analytical method used: The concentration of butyl methacrylate in the chambers was determined using a Miran 1A gas analyzer attached to a strip chart recorder. Before the initiation of the exposure, the Miran 1A gas analyzer was callbrated using precisely measured amounts of butyl methacrylate delivered into a dynamic vapor generator. A calibration curve was generated to convert the readings obtained from the Miran 1A gas analyzer into parts-per-million (ppm) butyl methacrylate.
- Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analytical  concentrations only of test material were determined throughout the  study.  Test concentrations were measured during each daily exposure  period (every 80 minutes) and the vapors analyzed by GC to confirm  purity. 

Duration of treatment / exposure:

4 weeks

Frequency of treatment:

6 hr/day, 5 days/week

Remarks:

Doses / Concentrations:
0, 310, 952 and 1891 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

5

Control animals:

yes, concurrent vehicle

Positive control:

not appropriate

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: All animals were observed before and after each daily exposure for general condition and signs of toxicity, and once during the post-exposure observation period.

DETAILED CLINICAL OBSERVATIONS: No

BODY WEIGHT: Yes
- Time schedule for examinations: Each animal was weighed weekly.

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
Food consumption was measured weekly

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No

WATER CONSUMPTION: No

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: during necropsy at conclusion of study
- Anaesthetic used for blood collection: Yes
- Animals fasted: Yes
- How many animals: all animals
- Parameters examined: hematocrit, platelet count, hemoglobin, mean ceil volume, red blood cell, mean ceil hemoglobin, white blood cell count, mean cell hemoglobin conc.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: during necropsy at conclusion of study
- Anaesthetic used for blood collection: Yes
- Animals fasted: Yes
- Parameters examined:
triglyceride globuiin
cholesterol albumin : globulin ratio
blood urea nitrogen creatinine
glucose bilirubin (total)
alkaline phosphatase calcium
total protein inorganic phosphorus albumin
chloride sodium
potassium
glutamic pyruvic transaminase/alanine aminotransferase activity
glutamic oxaloacetic transaminase/aspartate aminotransferase activity
gamma-glutamyl transferase activity

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

ORGAN WEIGHTS: Absolute and relative organ weights (organ-body), measured at necropsy, included: adrenals, brain, kidneys, liver, lungs, and testes.

GROSS PATHOLOGY: Full compliment of tissues, including all male and female reproductive organs, were fixed and examined in all animals.

HISTOPATHOLOGY: The following tissues and organs were examined histologically in the high dose and control groups only: adrenals, gross lesions, heart, kidneys, larynx, liver, lungs, nasal cavity, spleen and trachea. Only identified target organs were to be examined in mid and low dose groups. Slides were stained with hematoxylin and eosin

Statistics:

Distribution of body weight, body weight changes,  and organ weight were inspected for normality and homogeneity of variance  across all dose groups.  Analysis of variance models were used to assess  the presence or absence of an overall compound effect. Separate one-way  models were used within the male and female data to assess overall  treatment group effects.  Two-way models were used for treatment group,  sex and interaction between groups. Pairwise comparisons of least square  means between control and treated groups were evaluated using  Dunnett'st-test.  Hematology and clinical chemistry values were inspected  for normality and homogeneity using ANOVA. Statistical significance was  demonstrated at the p < 0.05. 

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

effects observed, treatment-related

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

not specified

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
No deaths were noted at any concentration tested. The only treatment-related signs of toxicity observed were inactivity, lacrymation, eye squinting, and labored breathing. These signs were seen only during the six-hour exposure. Slight inactivity occurred in all butyl methacrylate exposed groups on days 1, 2, and 3. Inactivity to slight inactivity occurred at concentrations of 952 and 1891 ppm on days 4 through 20. Lacrymation was observed only twice during the first three days, once at 952 ppm and once at 1891 ppm. Eye squinting occurred only at the highest concentration from day 3 to day 20, with the exception of day 4, were no eye squinting was observed. Labored breathing occurred once during day 1, at 1891 ppm.

BODY WEIGHT AND WEIGHT GAIN
A statistically significant increase in the body weight for the 310 ppm females was observed during Week 3. However, because this was an isolated finding, and no concentration-related trend was observed, it was judged not to be treatment-related.

FOOD CONSUMPTION
A statistically significant decrease in the feed consumption for the 1891 ppm females was observed during Week 1. However, because this was an isolated finding, and no effect on body weight was observed, it was judged not to be treatment-related.

HAEMATOLOGY
No treatment-related differences in hematology parameters were observed.

CLINICAL CHEMISTRY
The clinical chemistry data showed two parameters with statistically significant findings. A decrease in the alkaline phosphatase concentration for 310, 952, and 1891 ppm female animals, was observed. A statistically significant decrease in the triglyceride concentration for 952 ppm and 1891 ppm female animals, was also observed. Although these parameters were statistically different from the controls in a concentration-related trend, these findings were judged not to be of toxicological significance.

ORGAN WEIGHTS
The organ weight data showed a statistically significant increase in kidney weight to body weight ratio in males and females exposed at 1891 ppm. Absolute kidney weights for this group were not statistically different from the controls.

GROSS PATHOLOGY
no data

HISTOPATHOLOGY: NON-NEOPLASTIC
Histopathologic evaluation revealed treatment-related observations in the nasal cavities. Microscopic examination of the nasal cavities of male and female rats exposed to 1891 ppm had slight and localized bilateral degeneration of olfactory epithelium lining the dorsal meati. One male rat and one female rat exposed to 952 ppm had similar changes in the olfactory epithelium. Rats exposed to 310 ppm had no exposure related nasal cavity microscopic changes.

Dose descriptor:

NOAEC

Effect level:

310 ppm

Sex:

male/female

Basis for effect level:

other: 1801 mg/m3 for local effects in the nasal olfactory epithelium

Dose descriptor:

NOAEC

Effect level:

1 891 ppm

Sex:

male/female

Basis for effect level:

other: systemic effects

Dose descriptor:

LOAEC

Effect level:

952 ppm

Sex:

male/female

Basis for effect level:

other: 5531 mg/m3, for local effects in the nasal olfactory epithelium

Critical effects observed:

not specified

Conclusions:

The no-observable adverse effect concentration (NOAEC) for systemic effects was 1891ppm. Based on histopathological changes seen in the nasal cavities, the no-observable adverse effect concentration (NOAEC) for local effects was 310 ppm.

Executive summary:

In an OECD Guideline 412 Repeated Dose 28-day inhalation study, 10 male and 10 female rats were exposed by whole body to 0, 310, 952 and 1891 ppm (0,1832, 5626, 11175 mg/m³) n-BMA for 6 hr/day, 5 days/week for 4 weeks. Treatment-related effects included lacrimation, eye squinting, and laboured breathing in the 952 and 1891 ppm (5626 and 11175 mg/m³) concentration groups throughout the study. There were no treatment-related effects on body weight or feed consumption, and no deaths occurred. Haematological measurements and clinical chemistry values generally were unaffected by treatment. Despite increased relative kidney weights at the high concentration (1891 ppm/11175 mg/m³) in both sexes, and slight increases in serum BUN values (resulting in increased BUN:creatinine ratio), histopathology of the kidneys was normal. The only treatment-related histopathological finding was localised bilateral degeneration of olfactory epithelium lining the dorsal meatus of the nasal cavity at 952 and 1891 ppm (5626 and 11175 mg/m³) in both sexes.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

1 832 mg/m³

Study duration:

subacute

Species:

rat

Additional information

Data availability

For n-BMA a combined repeated dose and reproductive toxicity screening study (OECD 422) is available and a subchronic toxicity study (OECD 408), both by the oral route. In addition, n-BMA has been tested by inhalation in a subacute inhalation study (OECD 412). A chronic study does not have to be performed, because the substance is rapidly metabolised, and by analogy to MMA ultimately metabolised to carbon dioxide and water. Therefore, there is no concern for lesions due to accumulative toxicity. Since the esters of the category, including nBMA, are rapidly metabolised with relatively short half-lives in the body it is a strong possibility that the toxicity of the primary hydrolysis products to may contribute to the observed toxicity profile of the parent ester. For this reason repeated dose study data available for the acid and alcohol metabolites are presented in the form of a summary and discussed.

ORAL

n-Butyl methacrylate was studied for oral toxicity in rats in an OECD combined repeat dose and reproductive/developmental toxicity screening test at doses of 0, 30, 100, 300 and 1000 mg/kg/day (Ito, 1998).

Local effects

There were no local effects in the oral cavity or in the intestinal tract – the site of first contact on oral dosing or any other tissue investigated.

Systemic effects

At 1000 mg/kg relative kidney weights were increased. Urinary examination revealed increases in ketone bodies and occult blood, and haematological and blood chemical examinations showed increases in prothrombin time and urea nitrogen and atrophy of the red pulp in the spleen was also observed histopathologically.Absolute and relative weights of the spleen were decreased at a dose of 100 mg/kg or more, and relative kidney weights were increased at a dose of 1000 mg/kg. Histopathological examination revealed atrophy of the splenic red pulp at doses of 100 mg/kg or more. The kidney showed no histopathological abnormalities attributable to the test substance. The NOELs for repeat dose toxicity were considered to be 30 mg/kg/day for males and 300 mg/kg/day for females. This study has been independently reviewed (RSA, 2008). Based on published historical control data from the same test laboratory, effects seen at 100 and 300 mg/kg/d were not statistically significant when compared with historical controls. Hence, the NOAEL of this study is 300 mg/kg/d.

Body weight effects

In both males and females, there were weight gain depression and a decrease in food consumption at a dose of 1000 mg/kg. The NOAEL for body weight effects was 300 mg/kg.

Summary (OECD 422)

In conclusion, the oral administration of n-butyl methacrylate by gavage in an OECD 422 study revealed toxicologically relevant signs of systemic toxicity at the high dose level of 1000 mg/kg bw/day, The NOAEL in this study was 300 mg/kg body weight/day in both males and females.

In a more recent study conducted according to OECD TG 408 in compliance with GLP, n-butyl methacrylate was administered daily to male and female Wistar rats by gavage at dose levels of 0, 60, 120 and 360 mg/kg body weight per day over a period of 3 consecutive months (BASF, 2009). Control and high dose groups consisted of 15 animals per sex per group, whereas low and mid dose groups consisted of 10 animals per sex per group. After 3 months of treatment, 10 animals per sex of all dose groups were sacrificed (main groups). The remaining 5 animals per sex of control and high dose groups were maintained for another 28 days without administration of the test substance (recovery groups).

Local effects

There were no local effects in the oral cavity or in the intestinal tract – the site of first contact on oral dosing. On the other hand, multifocal degenerative and regenerative olfactory epithelium of the nasal cavity was observed in high dose (360 mg/kg bw/day) and mid dose (120 mg/kg bw/day) males and females. Multifocal degeneration/regeneration of olfactory epithelium was observed in males (5 out of 10) and females (7 out of 10). At 120 mg/kg bw/day, multifocal degeneration/regeneration of olfactory epithelium was observed in males (4 out of 10) and females (2 out of 10). At 60 mg/kg bw/day, no substance-related adverse findings were observed. However, considering the study design, it is not possible to determine if this effect is of a systemic or local origin. The NOAEL for these effects was 60 mg/kg body weight/day in both males and females. This substance-related effect was completely reversible, as no animal of the recovery group showed any finding in the nose after 28 days after cessation of exposure.

Systemic effects

At 360 mg/kg bw/day, prothrombin time was significantly prolonged (+10% males; +12% females) and inorganic phosphate (+14% males; +30% females), total bilirubin levels (+17% in males), glucose levels (+13% in females) as well as urea levels (+36% males; 21% females) significantly increased. Calcium (-3% in males and females), globulin levels (-4% in females) and triglyceride levels (-24% in males and females) significantly decreased. Absolute kidney weight (+11% in females), relative kidney weight (+13% males and females) and liver weight (+9% males; +11% females) significantly increased. After the recovery period, phosphate levels (+7% in males) and urea concentrations (+22% in females) were significantly increased. The NOAEL for systemic effects was 120 mg/kg body weight/day in both males and females.

Body weight effects

At 360 mg/kg bw/day, body weight change significantly decreased in male animals from day 77 onwards (-12.1% on days 84 and 91). The NOAEL for body weight effects was 360 mg/kg body weight/day in females and 120 mg/kg body weight/day in males.

Summary (OECD 408)

In conclusion, the oral administration of n-butyl methacrylate by gavage over a period of 3 months with a recovery period of 28 days revealed toxicologically relevant signs of systemic toxicity at the high dose level of 360 mg/kg bw/day, limited to effects on the liver activity (increased liver weight, prolonged prothrombin time, lower serum globulin and triglyceride levels in males and/or females) and kidneys weight (increased absolute weight in females). The NOAEL for systemic toxicity was 120 mg/kg body weight/day in both males and females.

Metabolites

MAA: no data available.

n-Butanol: Limited repeat dose data are available on nButanol (BA). CNS effects (ataxia and hypoactivity) were observed only during the final six weeks of a study in which CD rats (30/sex/dose group) were exposed to BA via gavage for 13 weeks (Toxicity Research Laboratories, 1986). The NOAEL in this study was 125 mg/kg/day and the LOAEL was 500 mg/kg/day. 

DERMAL

There are no relevant dermal repeated dose studies for systemic effects. For assessment purposes the oral data are used.

Metabolites

MAA: For methacrylic acid a limited, repeated dose skin irritation study exists, where dilutions of MAA in water (0, 5%/0.56mM) and acetone (0, 5%/0.56mM, 10%/1.12mM, 19%/2.24mM) have been applied (3/wk for 3 weeks) to the skin of male mice. Based on an average body weight of 32 g and an application volume of 100 µl/mouse, the dermal doses correspond to approx. 150, 300 and 600 mg/kg. 5% MAA in water produced and vehicle controls produced no irritation while 5% MAA in acetone produced only very slight irritation from the third application and 10 and 20% MAA in acetone produced moderate or severe irritation from the first application. Systemic effects other than clinical signs and changes in body weight have not been assessed.

n-Butanol: In a dermal study, 42 to 55 ml/kg applied to the skin of rabbits each day for 1 to 4 consecutive days resulted in 100% mortality; however, 30 applications of 20 ml/kg over a period of six weeks did not produce any fatalities (Patty, 1982). (OECD SIDS, 2001).

INHALATION

In an OECD Guideline 412 Repeated Dose 28-day inhalation study, 10 male and 10 female rats were exposed by whole body to 0, 310, 952 and 1891 ppm (0, 1832, 5626, 11175 mg/m³) n-BMA for 6 hr/day, 5 days/week for 4 weeks.

Local effects

Treatment-related effects included lacrimation, eye squinting, and laboured breathing in the 952 and 1891 ppm (5626 and 11175 mg/m³) concentration groups throughout the study. The only treatment-related histopathological finding was localised bilateral degeneration of olfactory epithelium lining the dorsal meatus of the nasal cavity at 952 and 1891 ppm (5626 and 11175 mg/m³) in both sexes. Based on histopathological changes seen in the nasal cavities, the no-observable adverse effect concentration (NOAEC) for local effects was 310 ppm (1832 mg/m³).

Systemic effects

Haematological measurements and clinical chemistry values generally were unaffected by treatment. Increased relative kidney weights were observed at the high concentration (1891 ppm/11175 mg/m³) in both sexes, and slight increases in serum BUN values (resulting in increased BUN: creatinine ratio). In the absence of corresponding histopathological changes this was not regarded as an adverse substance-related effect. The no-observable adverse effect concentration (NOAEC) for systemic effects was 1891 ppm.

Body weight effects

There were no treatment-related effects on body weight or feed consumption, and no deaths occurred.

Metabolites

MAA: In an OECD 413, 90-day vapour inhalation study in Sprague Dawley rats with MAA revealed general toxicity at 350 ppm (1253 mg/m3) in male animals. Local, marginal irritation of the respiratory epithelium in the nasal cavity was observed in two female animals. No changes in sexual organs or sperm mobility and sperm head counts were noted. The NOAEL was 100 ppm (358 mg/m3) for local irritation effects in male and females The NOAEL for systemic effects based upon reduced body weight gain in the presence of reduced feed intake but no other systemic effects was also 100 ppm (358 mg/m3) in male and females.

n-Butanol: Rats exposed to 4000 ppm BA (6 h/day x 5 days, N=10/group) had no impairment of hearing when tested using reflex modification audiometry (Crofton et al., 1994)(OECD SIDS, 2001). Read across to Butyl acetate (BaC) was made since BAc is rapidly hydrolysed in vivo to BA. Decreased body weight and feed consumption were observed in Sprague-Dawley rats exposed to 1,500 and 3,000 ppm BAc for 13 weeks. However, no systemic, organ-specific toxicity was observed. BAc during exposure only, but a cumulative effect on activity during the 13-week exposure was not observed (Bernard and David, 1996; David et al., 1996). There was no evidence of subchronic neurotoxicity based on functional observational battery (FOB) endpoints, quantitative motor activity, neuropathy and scheduled-controlled operant behavior endpoints. A NOAEL of 500 ppm was reported for systemic effects in rats, and a NOAEL of 3,000 ppm was reported for post exposure neurotoxicity in rats (Bernard et al., 1996; David et al.,1998). The equivalent values for BA, corrected for molecular weight, would be 223 ppm and 1338 ppm, respectively (OECD SIDS, 2001).This equates to a derived NOAEL of 500 ppm for local and systemic effects of n-butanol.

Human data

There are no relevant studies in humans.

Summary

Methacrylate esters, including nBMA, are hydrolysed to the potentially irritant and corrosive metabolite MAA and the corresponding alscohol, in this case n-butanol. NOAELs for local and systemic effects have the potential to be relevant to the repeat dose toxicity of nBMA.

Local effects

Local effects are only observed at very high doses in oral studies whereas they are the lead effect via the inhalation route - irritation of the nasal epithelium. This effect is observed with nBMA at correspondingly higher concentrations compared to e.g. methyl methacrylate.

Systemic effects

Systemic toxicity is limited to non-specific toxicity, i. e. effects on body weight gain etc., with no relevant specific target organ effects other than organ weight increases unsupported by corresponding changes in histopathology. Furthermore, there appears to be no marked increase in sensitivity for this non-specific toxicity with time. The NOAEL for systemic effects for n-BMA is 120 mg/kg/d in the subchronic oral study and 1891 ppm/11175 mg/m³ in the subacute inhalation study.

Discussion

Local effects

The available repeat dose toxicological data on LAME (low alkyl methacrylic esters) esters are consistent with the findings from acute studies indicating that local effects at the site of entry are predominantly due to a combination of the irritant action of the parent ester and the acid metabolite MAA. In the case of nBMA this effect occurs only at high concentrations near the saturated vapour density.

Local effects due to the irritant/corrosive acid metabolite are not important for the dermal and oral routes as absorption is slower and esterase activity within the barrier tissue lower and more diffuse.

Systemic effects

Systemically, n-BMA shows general signs of repeat-dose toxicity with no Specific Target Organ Toxicity (STOT). The lead systemic effect is reduced body weight gain and other organs systems are only involved at high doses. This is consistent with the metabolites where an equally non-specific toxicity is observed at comparable or higher doses.

Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:
Non specific effects at higher doses, no effects at specified NOAEL

Justification for selection of repeated dose toxicity inhalation - local effects endpoint:
Irritation of the nasal epithelium

Justification for classification or non-classification

According to the available data and CLP criteria for classification, no classification is warranted for specific target organ toxicity — repeated exposure. Based on the available information, the potential of n.butyl methacrylate for systemic toxicity after repeated dosing is low and no severe, irreversible organ effects have been observed in the relevant dose range. Hazards based on local effects were covered by the classification for the irritation potential on skin and respiratory tract (see chapter 5.3). Therefore, no additional classification is considered as justified.