Acetic anhydride

Endpoint summary

Description of key information

Local effects at the site of first entry dominate the acute oral and inhalation toxicity profiles of acetic anhydride. Following inhalation exposure, severe irritation of the respiratory tract has been reported, with oral administration ulceration of the stomach. Although there is little quantitative information available on the acute effects of a single exposure to acetic anhydride in humans, there is evidence from accidental exposure that, qualitatively, similar effects are likely to occur in humans. A dermal acute toxicity study with acetic anhydride in rabbits reported low toxicity by this route of exposure.

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records

Reference

Endpoint:

acute toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP compliant, near guideline study, available as unpublished report, adequate for assessment.

Principles of method if other than guideline:

5 animals per gender per group
Starved for 16 hours before administration of the test material.
Single oral gavage administration
Seven dose levels.
Animals monitored over 14 days.
Autopsy of animals that died during study
Survivors sacrificed at study termination, then autopsy.

GLP compliance:

no

Test type:

standard acute method

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

SPF-bred: WIGA, Sulzfeld
mean staring weight males = 254g
mean starting weight females = 190g

Route of administration:

oral: gavage

Vehicle:

olive oil

Remarks:

Emulsion in olive oil

Details on oral exposure:

formulated from 3.16 - 31.6 % in olive oil.

Doses:

316, 464, 681, 1000, 1470, 2150, 3160 mg/kg bodyweight

No. of animals per sex per dose:

5

Control animals:

no

Details on study design:

5 animals per gender per group. Single oral dose using 7 dose levels .
Animals monitored over 14 days and symtoms and deaths recorded at 1 hour, 24 hours, 48 hours, 7 days and 14 days post dose.
At the end of the 14 days the animals were killed following exposure to CO2 prior to examination of major internal organs.
Animals that died during the study were autopsied.

Sex:

male/female

Dose descriptor:

LD50

Effect level:

630 mg/kg bw

Mortality:

Death usually occurred within 24 hours of dosing.

Clinical signs:

other: Toxic signs included dyspnoea. apathy, lying down, staggering, shaking, trembling, diarrhoea, hypertension, arched back and general poor condition.

Gross pathology:

Animals that died during the study - heart: acute dilation; acute inflamation. Stomach: hardened lining and bloody ulceration. GI tract with redenned membranes.
Surviving animals - Stomach: ulcerative spots. Adhesions of the forestomach, liver, spleen, diaphram and peritoneum.

Mortality

Dose	Concentration	Number of Animals	Mortality within
mg/kg	%		1 hour	24 hours	48 hours	7 days	14 days
3160	31.6	5 male	0/5	5/5	5/5	5/5	5/5
		5 female	0/5	5/5	5/5	5/5	5/5
2150	21.5	5 male	0/5	5/5	5/5	5/5	5/5
		5 female	0/5	5/5	5/5	5/5	5/5
1470	14.7	5 male	0/5	5/5	5/5	5/5	5/5
		5 female	0/5	5/5	5/5	5/5	5/5
1000	10	5 male	0/5	3/5	3/5	3/5	3/5
		5 female	0/5	3/5	3/5	3/5	3/5
681	6.81	5 male	0/5	1/5	1/5	1/5	1/5
		5 female	0/5	5/5	5/5	5/5	5/5
464	4.64	5 male	0/5	0/5	0/5	0/5	0/5
		5 female	0/5	1/5	1/5	1/5	2/5
316	3.16	5 male	0/5	0/5	0/5	0/5	0/5
		5 female	0/5	0/5	0/5	0/5	0/5

Executive summary:

The LD50 of acetic anhydride in rats was estimated to be 630 mg/kg bodyweight following oral, gavage, administration of the test material.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LD50

Value:

630 mg/kg bw

Quality of whole database:

The key study is non-GLP but the design is similar to OECD test guidelines (Klimisch score = 2).

Acute toxicity: via inhalation route

Link to relevant study records

Reference

Endpoint:

acute toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP compliant, near guideline study, available as unpublished report. Minor restrictions in design and/or reporting but otherwise adequate for assessment.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

other: OECD guideline 412

Deviations:

yes

Remarks:

- No clinical pathology, limited pathology (males only)

Principles of method if other than guideline:

Preliminary range findings study in 5 male and 5 time-mated females per group, exposed to vapours of acetic anhydride for 6h/day for 5 days/week for 2 weeks (males) or from days 6-15 post coitum (females).

GLP compliance:

yes

Test type:

other: 2 week repeat dose study

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 (UK) Ltd, Manston Road, Margate, Kent
- Age at study initiation: approximately 8 weeks (males), 9-11 weeks (females)
- Housing: 5/cage in suspended cages with stainless steel mesh floors. The cages of each group were housed on a rack in a separate ventilated chamber to avoid cross contamination following exposures
- Diet: SDS Rat and Mouse No. 1 SQC modified maintenance diet ad libitum. Available in home cages.
- Water: Tap water available from polypropylene bottles ad libitum in home cages.
- Acclimation period:12 days (males), 5 days (females)

ENVIRONMENTAL CONDITIONS
- Temperature:18-24°C
- Humidity: 40-70%
- Air changes (per hr): no data
- Photoperiod: 12 hrs dark / 12 hrs light

IN-LIFE DATES: From: 5 January 1994 To: 1 February 1994

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Stainless steel and glass 0.75m3 whole body chambers
- Method of holding animals in test chamber: singly housed in compartmented stainless steel mesh cages.
- Source and rate of air: Compressed, filtered air, air flow rate not reported.
- Method of conditioning air: Chamber air was pre-warmed by passage through a copper coil immersed in a water bath at 60°C.
- Temperature, humidity, pressure in air chamber: 22.5 - 23.2°C , 23-33% humidity (study mean data), internal pressure of 10mm H2O below ambient.
- Air flow rate: approximately 150L/min.
- Air change rate: Not reported
- Treatment of exhaust air: Drawn through an activated charcoal scrubbing system by an extract fan before being vented to atmosphere.

TEST ATMOSPHERE
- Brief description of analytical method used: Gas chromatography.
- Samples taken from breathing zone: yes


Acetic anhydride concentration was determined 6 times during each exposure (approximately hourly intervals), using gas chromatography. Samples were also analysed for acetic acid.
The absence of test substance aerosol was confirmed on one occasion during the study using a Royco Particle Monitor.

Analytical verification of test atmosphere concentrations:

yes

Duration of exposure:

6 h

Concentrations:

0, 24, 103, 407 ppm (males) Analytical
0, 24, 104 ppm (females) Analytical
0, 25, 100, 400 ppm Target

No. of animals per sex per dose:

5

Control animals:

yes

Details on study design:

Rats were exposed to the vapour of acetic anhydride using whole-body inhalation exposure chambers for 6 hours per day.
For males the planned exposure period was 5 days a week (Monday - Friday) for two consecutive weeks. This was only possible at the low exposure level, since, due to treatment-related findings, exposure occurred on only 6 occasions at the intermediate exposure level (100 ppm) and 1 occasion at the high exposure level (400 ppm).
Time-mated female rats were exposed on 10 consecutive days (Days 6 to 15 post coitum inclusive), although restricted to only 7 occasions for females in the intermediate group (100 ppm), again due to treatment-related findings. Due to the adverse effect of exposure at 400 ppm, in males, females allocated to this group were not exposed but retained as concurrent controls.

- Frequency of observations and weighing: Twice daily observations. body weights : Males - week -1, day 1 (pre-exposure) and then daily thereafter. Females - day 1 of pregnancy and then on days 2, 3, 6, 8, 10, 12, 14, 16, 18 & 20 post coitum.
- Necropsy of survivors performed: yes
- Other examinations performed: clinical signs, body weight, food consumption, water consumption, organ weights, histopathology, litter data and foetal examinations

Statistics:

Not appropriate due to small group size.

Sex:

male

Dose descriptor:

LC100

Effect level:

1 670 mg/m³ air

Exp. duration:

6 h

Remarks on result:

other: 400 ppm (2 died, 3 killed. Clinical signs indicative of respiratory irritation)

Mortality:

400 ppm - 2 males were found dead on day 2 and the other 3 were sacrificed due to their poor clinical condition. Consequently, no females were exposed at this level.

Clinical signs:

other: 400 ppm - During exposure all males showed prone posture, half-closed eyees, lachrymation and exaggerated breathing. After exposure all showed noisy respiration. On day 2, pre-exposure, 2 males were found dead. Of the 3 survivors, all had gasping respi

Body weight:

400 ppm - All animals showed weight loss of approximately 50 g following the first exposure.
100 ppm - Marked bodyweight loss was seen in all animals following the first exposure.
25 ppm - No effects on body weight following the first exposure .

Gross pathology:

400 ppm - All males showed gaseous distension in the gastrointestinal tract, particularly in the stomach. In addition most animals showed brown perinasal staining.
100 ppm - All males and two females had gaseous distension at one or more levels of the gastrointestinal tract. All males had enlarged cervical and/or tracheobronchial lymph nodes and most showed minimal adipose tissue.
25 ppm - All males had enlarged cervical and/or tracheobronchial lymph nodes and two had congestion in the anterior lobe of the right lung.
There were no treatment related macroscopic abnormalities in females.

Other findings:

- Food consumption - At 400 ppm, the group mean cage value was almost zero after the first exposure and at 100 ppm, a marked reductions in food consumption were seen in both sexes following the first exposure. At 25 ppm , group mean food consumption was slightly lower than controls tfollowing the first exposure

- Water consumption - At 400 ppm, the group mean cage value was almost zero after the first exposure and at 100 ppm, marked reductions in water consumption were seen in both sexes following the first exposure. At 25 ppm , group mean water consumption was slightly lower than controls following the first exposure.

Organ weights: At 25 ppm, lung weight was higher and liver and kidney weights were lower in males compared to controls. Organs were not weighed in females.

- Histopathology:
- Potential target organs: Respiratory tract.
- Other observations: HISTOPATHOLOGY: NON-NEOPLASTIC
400ppm - severe degenerative changes were seen in nasal passages, larynx, trachea and tracheal bifurcation and lungs, comprising rhinitis, epithelial ulceration/ degeneration with associated inflammatory exudate and/or epithelial hyperplasia/squamous metaplasia.
100 ppm - severe/slightly less severe degenerative changes were seen in nasal passages, larynx, trachea and tracheal bifurcation and lungs, comprising rhinitis, epithelial ulceration/ degeneration with associated inflammatory exudate and/or epithelial hyperplasia/squamous metaplasia. There was evidence of regenerative hyperplasia and hypertrophy in the lungs. Lymphoid proliferation was seen in macroscopically abnormal lymph nodes.
25 ppm - changes were less severe and comprised rhinitis and hyperplasia in the nasal passages, epithelial hyperplasia and squamous metaplasia in the larynx, slight epithelial hyperplasia in the trachea, epithelial hypertrophy with goblet cells in the lungs and lymphoid proliferation in macroscopically abnormal lymph nodes.

Conclusions:

Marked acute toxicity, indicative of respiratory irritation, was seen in males at 400 ppm acetic anhydride.

Executive summary:

In a 2 week preliminary toxicity study in rats, marked acute toxic treatment-related effects, indicative of respiratory irritation, were seen in males exposed to 407 ppm acetic anhydride for 6 hours on day 1. On day 2, pre-exposure, 2 males were found dead and the remaining 3 males were killed due to their clinical condition. Females were not exposed to this concentration of acetic anhydride. Clinical signs during exposure included half closed/closed eyes, lachrymation, prone posture and exaggerated respiration. Immediately after exposure all animals showed noisy respiration. Bodyweight loss after exposure was marked with food and water consumption almost zero. Surviving animals showed gasping respiration and two were lethargic and they were therefore killed for humane reasons. Microscopic effects included severe epithelial hyperplasia and/or ulceration in the respiratory tract (nasal paassages, larynx, trachea/tracheal bifurcation and lungs).

At 100 ppm, similar, though less severe clinical signs were seen after the first exposure.

At 25 ppm, half-closed eyes in females was the only clinical abnormality seen during exposure, there were no clinical signs in males and no effects on bodyweight after the first exposure.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LC50

Value:

1 670 mg/m³ air

Quality of whole database:

The key study is a GLP compliant, guideline study of high quality (Klimisch score=1). Value for LC50 is approximate.

Acute toxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Oral

Non-human data

An LD50 value of 630 is reported for the rat (BASF, 1980a). Rats were administered the material by the oral, gavage, route of exposure. Death usually occurred within 24 hours of administration, following clinical signs of dyspnoea, apathy, staggering, shaking, diarrhoea and arched back. There was evidence of bloody ulceration in the stomach post mortem, indicating significant local effects of the material.

In general agreement with the above study earlier investigators (Smyth et al., 1951) reported an LD50 value of 1780 mg/kg for a combined group of male and female rats.

For acetic anhydride, an oral LD50 value of 630 mg/kg (BASF, 1980a) is considered appropriate.

Human data

No human (oral) information available.

Inhalation

Non-human data

The key inhalation information is taken from a well-conducted sighting study, compliant with GLP (HRC, 1994). The aim was to determine appropriate repeat-dose exposure concentrations of acetic anhydride for a subsequent OECD screening study and in this sighting study a number of animals died within the first 24 hours.

Five male rats per group were to be exposed, daily for 6 hours, to acetic anhydride vapour (0, 25, 100, 400ppm; 0, 104, 418, 1670 mg/m3) using whole-body inhalation exposure chambers. The planned exposure period for male rats was 5 days per week for 2 weeks. Only 1 exposure was included at 400 ppm (1670 mg/m3) due to severe acute reaction to treatment: clinical signs reported during exposure were eyes closed/half closed, lachrymation, prone posture and exaggerated respiration. Immediately after exposure all animals exhibited noisy respiration. Within 24 hours 2/5 animals died, survivors had gasping respiration and lethargy and were sacrificed the following day. Macroscopic changes at necropsy included gaseous distension of gastrointestinal tract, consistent with gasping. Irritation of the respiratory tract, usually in the epithelium (hyperplasia and/or ulceration) was often severe. Earlier, a briefly reported range-finding study reported acetic anhydride as having moderate toxicity (Smyth et al., 1951). A single 4-hour exposure to 2000 ppm (8400 mg/m3) caused all six rats to die within 14 days whereas at 1000 ppm (4200 mg/m3) all animals survived.

From the above information, the LC50 (4 hour exposure) of acetic anhydride vapour is approximately 1670 mg/m3 (400 ppm).

Human data

Sinclair et al. (1994) reported a fatal accident involving acetic anhydride when a young man was exposed to acetic anhydride when a drum containing the substance exploded beside him. He may have been exposed to liquid and/or vapour and/or aerosol forms of acetic anhydride but no reliable dose information is available. He died 2 months later with severe lung damage. Haemorrhagic congestion and fibrous adhesions within the pleural cavity were reported following autopsy. Histology revealed widespread ulceration of the bronchial mucosa.

Dermal

Non-human data

Secondary sources report a LD50 (rabbit) value of 4000 mg/kg (RTECS, 1987). No further information available.

Human data

No human dermal information available.

Citations:

Smyth HF, Carpenter CP & Weil C (1951). Range-findings toxicity data: list IV. Arch. Ind. Hyg. Vol 4, pp119-122.

Justification for selection of acute toxicity – oral endpoint
The key study is the only study available.

Justification for selection of acute toxicity – inhalation endpoint
The key study is the only study available.

Justification for selection of acute toxicity – dermal endpoint
According to Annex VII Column 2 adaptation the physicochemical properties of the substance, which is corrosive, precludes the need to conduct a dermal acute toxicity study. Data are available via oral and inhalation routes.

Justification for classification or non-classification

The rat oral LD50 value of 630 mg/kg means that acetic anhydride warrants classification under CLP, as Cat 4, H302, Harmful if swallowed.

A well-conducted 6-hour inhalation study in rats reported that 2/5 animals died within the first 24 hours of administration of 400 ppm (1670 mg/m3) and the remaining 3 animals were sacrificed the following day, due to severe clinical signs. The findings indicate severe local effects at the site of contact. According to the guidance such cytotoxic irritant effects induce tissue changes at the site of contact which can be detected by clinico-pathological or pathological methods (see repeat dose studies section 7.5). Such effects may induce long lasting functional impairment of the respiratory system.

For the inhalation route, the relevant CLP category is STOT-SE, H335 Category 3 which only includes narcotic effects and respiratory tract irritation.