Maleic anhydride

Repeated dose toxicity: inhalation

Administrative data

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1981

Report date:

1981

Reference 2

Reference Type:

publication

Title:

A 6-month multispecies inhalation study with maleic anhydride

Author:

Short D.R.et al.

Year:

1988

Bibliographic source:

Fundamental and Applied Toxicology 10, 517-524

Reference 3

Reference Type:

review article or handbook

Title:

Maleic Anhydride and Maleic Acid, SIDS Initial Assessment Report For SIAM 18

Author:

OECD SIDS

Year:

2004

Bibliographic source:

OECD SIDS Initial Assessment Report For SIAM 18, Paris, France, 20-23 April 2004

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Evaluation of maleic anhydride toxicity in rats, hamsters and monkeys after 6 months of inhalation administration.

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Maleic anhydride

EC Number:

203-571-6

EC Name:

Maleic anhydride

Cas Number:

108-31-6

Molecular formula:

C4H2O3

IUPAC Name:

2,5-dihydrofuran-2,5-dione

Details on test material:

- Name of test material (as cited in study report): Maleic anhydride
- Physical state: white briquettes
- Analytical purity: > 99%

Test animals

Species:

rat

Strain:

other: CD

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River
- Weight at study initiation: 230-310 g (males); 174-200 g (females)
- Age at study initiation: about 8 weeks
- Housing: single
- Diet: ad libitum (except during exposure)
- Water: ad libitum (except during exposure)
- Acclimation period: at least 2 weeks

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

air

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: 15 m² cubical stainless-steel and glass chambers with pyramidal tops
- System of generating particulates/aerosols: Atmospheres containing the test material were generated by heating maleic anhydride, which has a melting point of 53°C, and by transporting vapors from the melt to the chambers with a stream of nitrogen gas. The overall quantity af maleic anhydride vaporized was determined by weighing the "boat" containing maleic anhydride prior to exposure and upon recrystallization of the compound after exposure.


TEST ATMOSPHERE
- Brief description of analytical method used: Chamber concentrations were sampled at least three times per day
- Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Concentrations in the chamber (total maleic; i .e ., maleic anhydride plus maleic acid) were monitored by drawing samples through Tenax columns and by quantifying the retained material, after thermal desorption into a nitrogen steam, using a gas chromatograph equipped with a flame ionization detector and a stainless-steel column packed with 1 .5% OV-l01 on 100-120 Chromosorb G-HP. The range of column and detector temperatures was 115 to 150°C and 205 to 220°C, respectively.

Duration of treatment / exposure:

6-months / 132 or 133 exposures

Frequency of treatment:

6 hours per day, 5 days per week

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0 mg/m³ air (analytical)

Doses / concentrations 2

Dose / conc.:

1.1 mg/m³ air (analytical)

Doses / concentrations 3

Dose / conc.:

3.3 mg/m³ air (analytical)

Doses / concentrations 4

Dose / conc.:

9.8 mg/m³ air (analytical)

No. of animals per sex per dose:

15

Control animals:

yes, concurrent no treatment

Details on study design:

- Fasting period before blood sampling for clinical biochemistry: 16- hour fasting period

Positive control:

no

Examinations

Observations and examinations performed and frequency:

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: before and after each exposure

BODY WEIGHT: Yes
- Time schedule for examinations: twice a week for the initial 2 months and weekly thereafter

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: monthly intervals
- Dose groups that were examined: on all test animals.

HAEMATOLOGY: Yes
- Animals fasted: Yes
- How many animals: 5 rats/sex/group from the control and high-exposure groups at 3 months and 5 rats/sex/group at 6 months
- Parameters checked: hemoglobin, hematocrit, total erythrocyte count, and total and differential leucocyts count

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: at 3 and 6 months
- How many animals: 5 rats/sex/group from the control and high-exposure groups at 3 months and 5 rats/sex/group at 6 months
- Parameters checked: glucose, urea nitrogen, serum glutamic pyruvic transaminase activity, serum alkaline phosphatase activity, carbon dioxide, erythrocyte and plasma cholinesterase activity, and terminal brain cholinesterase activity

URINALYSIS: Yes
- Time schedule for collection of urine: 5 rats/sex/group from the control and high-exposure groups at 3 months and 5 rats/sex/group at 6 months
- Metabolism cages used for collection of urine: Yes
- Parameters checked: volume, pH, specific gravity, description of color and appearance, qualitative tests for albumin, glucose, bilirubin, ketones and occult blood and microscopic examination of the sediment

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes (on the control and high-exposure groups)

Statistics:

All statistical analyses compared the treatmant groups with the control group, by sex. Not all parameters were statistically evaluated at all intervals. Some parameters at some intervals were evaluated statistically after a review of the data indicated that a possible exposure related effec may have been present. The hematological, biochemical and urinalysis parameters (terminal) and absolute and relative organ weights (terminal) were compared by analysis of variance (one-way classification), Bartlett's test for homogeneity of variances and the appropriate t-test (for equal or unequal variances) as described by Steel and Torrie using Dunnett's multiple comparison tables to judge significance of differences.

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

For further details, see section below "Details on results".

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

For further details, see section below "Details on results".

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:

no effects observed

Haematological findings:

effects observed, non-treatment-related

Description (incidence and severity):

For further details, see section below "Details on results".

Clinical biochemistry findings:

effects observed, non-treatment-related

Description (incidence and severity):

For further details, see section below "Details on results".

Urinalysis findings:

effects observed, non-treatment-related

Description (incidence and severity):

For further details, see section below "Details on results".

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, non-treatment-related

Description (incidence and severity):

For further details, see section below "Details on results".

Gross pathological findings:

no effects observed

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

For further details, see section below "Details on results".

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY: Survival was >90% in all groups. Nasal and ocular irritations were observed at all maleic anhydride-exposed animals during the study. High-exposure rats exhibited a red-tinged nasal discharge, isolated cases of ocular discharge and sneezing. These effects were less severe in animals from the low- and mid-exposure groups.

BODY WEIGHT AND WEIGHT GAIN: Statistically significant reductions in body weights were observed in the male rats in the mid-exposure group on days 78, 92, 106, and 127; and in the high-exposure group on days 40 through 189 (p<0.05). Statistically significant reductions in body weights were observed in the female rats in the mid-exposure groups on days 54, 127, 141, 148, 155, an 156; and in the high-exposure group on days 37, 47, 57, 71, 85-176, and 189 [<10%, (p<0.05)]. However, at the end of the treatment period, terminal body weights were reduced only for male rats from the high-exposure group. There were no statistically significant effect on body weight at the low-exposure group for either sex of rat.

HAEMATOLOGY: significant decrease in monocyte count in high dose male rats; no biological significance was attributed to these values since they were within the normal range af variation

CLINICAL CHEMISTRY: Clinical chemistry results indicated a few differences which were statistically different from the control values; however, none of these differences were considered to be treatment related or consistent in both sexes. These differences were:
- glucose was reduced in males (- 9%) and increased in females (+ 17%) of the mid dose group after 6 months while both sexes of the high dose group had reduced values after 3 months (-18% and -21%, respectively);
- serum CO2 levels were slightly elevated in the high dose males after 6 months (+ 11%);
- urea nitrogen was slighly increased in high dose females after 6 months (+ 26%);
- red blood cell cholinesterase activity was reduced in mid dose males at 6 months (-17%) and brain cholinesterase was increased in mid (+ 27%) and high dose males (+ 21%) at 6 months

URINALYSIS: Female rats in the low-dose group had a significantly reduced urine volume (- 59%) with an increased specific gravity (+ 3%). These observations were not dose related and thus not considered related to treatment.

ORGAN WEIGHTS: Organ weight changes were observed in rats (8 of 9 tissues weighed). The only changes present in both the mid- and high-exposure groups were increased relative pituitary weight in female rats (+ 23%/+ 30%), increased relative adrenal weight (females: + 28%/36%; males: + 19% in the high-exposure group) and reduced absolute (- 26%/- 28%) and relative thyroid weight (- 24%/- 20%) in male rats. Since the histopathology data did not provide evidence of tissue damage, these changes were not considered to be related to treatment.

HISTOPATHOLOGY: NON-NEOPLASTIC: Hyperplastic changes in the nasal tissues, which ranged in grade of severity from trace to mild, were present in all maleic anhydride exposed rats. Both the incidence and grade appeared to be exposure-related. Metaplastic changes in the nasal tissues were present in rats at all exposure levels and the incidence increased in a nonlinear fashion. Rats at all exposure levels exhibited a focal to multifocal infiltration of the nasal epithelium with neutrophils and eosinophils graded as trace to mild. A luminal exudate was present only on one and three males from the mid and high exposure groups, respectively. These changes in the nasal passages were indicative of irritation and judged to be reversible.
The only other histopathological change that was statistically significant (p < 0.05) relative to control animals was an increased amount of hemosiderin pigment in the red pulp from spleens of female rats in the high-exposure group.

Effect levels

1

Dose descriptor:

NOAEC

Remarks:

(systemic)

Effect level:

3.3 mg/m³ air

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: temporarily reduced body weight in both sexes, not considered as adverse effect

2

Dose descriptor:

LOAEC

Remarks:

(systemic)

Effect level:

9.8 mg/m³ air

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: reduced body weight in both sexes, increased amount of hemosiderin pigment in the red pulp from spleens of female rats

3

Dose descriptor:

LOAEC

Remarks:

(local)

Effect level:

1.1 mg/m³ air

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: nasal and ocular irritations, discharges, hyperplastic and metaplastic changes in the nasal tissue, focal to-multiofocal infiltration of the nasal epithelium

Target system / organ toxicity

Critical effects observed:

not specified

Any other information on results incl. tables

Table 1: Body weights of male and female rats exposed to atmospheres containing maleic anhydride

Total maleic (mg/m³)
	0		1.1		3.3		9.8
Month	M	F	M	F	M	F	M	F
0	268a	188	269	187	267	187	269	185
1	385	252	374	250	372	247	371	251
2	423	279	416	275	400	265	395b	263b
3	467	300	446	293	437b	285	417b	276b
4	480	312	471	303	456	293	430b	286b
5	500	326	495	318	480	302b	448b	294b
6	526	342	524	332	510	320	482b	320

a Mean gram/rat for rats/group

b Significantly different from control.

Table 2: Histopathological observations in nasal tissue from rats exposed to atmospheres containing maleic anhydride

Total maleic (mg/m³)
Histopathological observation	0	1.1	3.3	9.8
Mucosa epithelial hyperplasia focal/multifocal, septum/ turbinates
M	0/0a	13/40	7/93	0/80
F	0/0	40/33	27/67	0/93
Mucosa, squamous metaplasia focal/ multifocal, septum/turbinates
M	0b	13	13	73
F	0	0	13	87

a Perrcentage of animals with trace grade/percentage of animals with mild grade . Tissues from 15 rats/sex/group were examined .

b Percentage of animals with observation . Tissues from 15 rats/sex/group were examined.

Applicant's summary and conclusion

Conclusions:

In a 6-month inhalation study performed with rats, test item related effects on body weight and local effects in the respiratory tract were observed. Based on the results, the NOAEC (systemic) is considered to be 3.3 mg/m³ air and the LOAEC (local) 1.1 mg/m³ air.

Executive summary:

In a 6 -month inhalation toxicity study maleic anhydride was administered to 15 rats/sex/concentration by whole body exposure at concentrations of 0, 1.1, 3.3 or 9.8 mg/m³ air (analytical) for 6 hours per day, 5 days/week for a total of 6 months.

Nasal and ocular irritations were observed at all maleic anhydride-exposed animals during the study. High-exposure rats exhibited a red-tinged nasal discharge, isolated cases of ocular discharge and sneezing. These effects were less severe in animals from the low- and mid-exposure groups.Then, statistically significant reductions in body weights were observed in the male rats in the mid-exposure group on days 78, 92, 106, and 127; and in the high-exposure group on days 40 through 189 (p<0.05). Statistically significant reductions in body weights were observed in the female rats in the mid-exposure groups on days 54, 127, 141, 148, 155, an 156; and in the high-exposure group on days 37, 47, 57, 71, 85-176, and 189 [<10%, (p<0.05)]. However, at the end of the treatment period, terminal body weights were reduced only for male rats from the high-exposure group. There were no statistically significant effect on body weight at the low-exposure group for either sex of rat. Significant decrease in monocyte count in high dose male rats; however, no biological significance was attributed to these values since they were within the normal range af variation. Furthermore, clinical chemistry results indicated a few differences which were statistically different from the control values; however, none of these differences were considered to be treatment related or consistent in both sexes. Female rats in the low-dose group had a significantly reduced urine volume (- 59%) with an increased specific gravity (+ 3%). These observations were not dose related and thus not considered related to treatment.

Organ weight changes were observed in rats (8 of 9 tissues weighed). The only changes present in both the mid- and high-exposure groups were increased relative pituitary weight in female rats (+ 23%/+ 30%), increased relative adrenal weight (females: + 28%/36%; males: + 19% in  the high-exposure group) and reduced absolute (- 26%/- 28%) and relative thyroid weight (- 24%/- 20%) in male rats. Since the histopathology data did not provide evidence of tissue damage, these changes were not considered to be related to treatment.

Hyperplastic changes in the nasal tissues, which ranged in grade of severity from trace to mild, were present in all maleic anhydride exposed rats. Both the incidence and grade appeared to be exposure-related. Metaplastic changes in the nasal tissues were present in rats at all exposure levels and the incidence increased in a nonlinear fashion. Rats at all exposure levels exhibited a focal to multifocal infiltration of the nasal epithelium with neutrophils and eosinophils graded as trace to mild. A luminal exudate was present only on one and three males from the mid and high exposure groups, respectively. These changes in the nasal passages were indicative of irritation and judged to be reversible. The only other histopathological change that was statistically significant (p < 0.05) relative to control animals was an increased amount of hemosiderin pigment in the red pulp from spleens of female rats in the high-exposure group.

The NOAEC (systemic) is 3.3 mg/m³ based on the transient reduced body weight. The LOAEC (local) is 1.1 mg/m³ air based on the local effects in the respiratory tract observed at all applied concentration levels.