Acrylic acid

Repeated dose toxicity: oral

Administrative data

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

22 Aug 1983 - 22 Nov 1983

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1987

Report date:

1987

Reference 2

Reference Type:

publication

Title:

SUBCHRONIC AND CHRONIC STUDIES OF THE EFFECTS OF ORAL ADMINISTRATION OF ACRYLIC ACID TO RATS.

Author:

Hellwig J et al.

Year:

1993

Bibliographic source:

Fd. Chem. Toxicol. 31: 1-18

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Acrylic acid was administered by gavage to 50 Wistar rats (20 males, 20 females) for 3 months. For comparison a group of untreated animals (10 males, 10 females) was used as a control. Doses were 150 and 375 mg test substance per kg body weight/day.

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Acrylic acid

EC Number:

201-177-9

EC Name:

Acrylic acid

Cas Number:

79-10-7

Molecular formula:

C3H4O2

IUPAC Name:

prop-2-enoic acid

Specific details on test material used for the study:

- Name of test material (as cited in study report): Acrylic acid, pure
- Analytical purity: > 99 %
- Impurities (identity and concentrations): stabilized with 200 ppm MEHQ
- Test Substance No.: 82/380

Test animals

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Karl THOMAE, Biberach an der Riss, Germany
- Age at study initiation: 42 days old
- Weight at study initiation:
- male animals: 183 .3 (166 - 202) g
- female animals: 146.9 (133 - 162) g
- Fasting period before study: no
- Housing: singly in Type DK III stainless steel wire cages
- Diet (ad libitum): ground Kliba 343 rat/mouse/hamster "A" food supplied by KLINGENTALMUHLE AG, CH-4303, Kaiseraugst, Switzerland
- Water (ad libitum): tap water
- Acclimation period: 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 - 24°C
- Humidity (%): 30 - 70 % (80 % only for short periods)
- Photoperiod (hrs dark / hrs light): 12 hours

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

water

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:
For preparation of the test substance preparations the substance was weighed in a measuring flask in a varying amount according to dose group, the flask made up to the mark with doubly distilled water, and then shaken. The solutions were prepared in such a way that 5 mL of solution contained 150 or 375 mg of acrylic acid. The animals of the control group received the solvent doubly distilled water as a control, also by gavage.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

In order to check the correctness of the amounts of acrylic acid weighed, control analyses of the concentrations of each dose were carried out before the beginning of the study, after 4 and 8 weeks of the study, and toward the end of the study. The corresponding determinations were effected by gas chromatography.
Results of analytical dose verification: 147.5 - 151.21 mg/5 mL water and 359.3 - 375.21 mg/5 mL water were determined.

Duration of treatment / exposure:

90 days

Frequency of treatment:

5 days/week

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

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

Doses / concentrations 2

Dose / conc.:

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

No. of animals per sex per dose:

10

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale:
In a parallel study (Project No. 74C0380/8239) in connection with the testing for chronic toxicity, Wistar rats received the substance with the drinking water in various doses (0, 120, 800, 2000 and 5000 ppm) over a period of 3 months (satellite groups) or 12 months (main groups).
The present study was intended to be able to compare between continuous administration with the drinking water and single (bolus) administration by gavage on working days, the study being designed in particular to investigate the extend of the irritating effect of acrylic acid on the digestive tract. For this study, therefore, doses were chosen which roughly corresponded to the two highest doses in the drinking water study. At 150 mg/kg body weight (= approx. 2000 ppm - factor 13.3) effects on the body weight gain and on the feed and drinking water consumption were expected. 375 mg/kg body weight (= approx. 5000 ppm - factor 13.3) should additionally lead to organ alterations (among others kidney and digestive tract).

Positive control:

no

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily

BODY WEIGHT: Yes
- Time schedule for examinations: weekly

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

WATER CONSUMPTION: Yes
- Time schedule for examinations: weekly

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: No

CLINICAL CHEMISTRY: No

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
After sacrifice, the animals were weighed, necropsied, assessed by gross pathology, and the organs weighed.
In addition to the weight of the exsanguinated animal bodies the absolute and relative weights (organ weight/100 g body weight) of the following organs were determined:
liver, kidneys, spleen, testes, ovaries, adrenals, brain.

HISTOPATHOLOGY: Yes
All the organs listed below were fixed in toto or in representative parts depending on their size in a 4 % buffered formaldehyde solution at room temperature:
all gross lesions, head, heart, thoracic aorta, trachea (with larynx), lung with stem bronchi (right and left), esophagus, stomach (forestomach and glandular stomach), small intestines (duodenum, jejunum, ileum), large intestines (cecum, colon, rectum), salivary glands, liver, pancreas, spleen, thymus, sternum with sternal marrow, kidney, urinary bladder, testes, prostate, seminal vesicle, ovaries, uterus in toto, pituitary, adrenals, thyroids (with parathyroids), brain, skeletal muscle (m. massetor), eye with optic nerve, skin, mesenteric lymph nodes, mammary gland, tongue, buccal mucosa, nasal mucosa.

In the case of the tongue a medial longitudinal section was examined.
The buccal mucosa was removed from the region of the molars and examined as longitudinal section.
In the case of the esophagus a cross-section from the segment in the vicinity of the stomach was examined.
In the case of the liver and kidneys a slide for fat demonstration was prepared in extension of the study protocol. After decalcification of the facial part of the skull a section was removed at the level of the 2nd crista palatinae and the 1st molar. The side facing the molar was intended to be the area of section. This level contains ectoturbinals, endoturbinals with nasal septum, maxillary sinus, nasopharyngeal duct, and to some extent also sections of the molars.

Statistics:

Clinical examinations and pathology: The statistical significance of body and organ weights was carried out using a t-test generalized by Williams for simultaneous comparison of several dose groups with a control group.

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Whereas the control animals did not exhibit any clinically evident signs, severe findings attributable to the administration of the test substance were caused in many but not all of the animals that received 150 or 375 mg of test substance/kg body weight. In a number of animals a premature death was the result. From about the 3rd week of the study onward, an increasing number of animals manifested pronounced tympania (gaseous distention of the stomach or abdomen), frequently accompanied by dyspnoea and cyanosis. In addition, several animals began as early as in the first week of the study to make unphysiological utterances, which most closely resembled those made by ducklings. Finally, in some animals - usually shortly before
death occurred - appearances typical of agony, such as hypothermia, apathy and piloerection, were seen; moreover, numerous rats that died prematurely showed a reduced general state of health. Overall, the clinical signs in the animals of test group 2 (375 mg/kg bw) were considerably more pronounced than in those in test group 1 (150 mg/kg bw), as was also shown by a comparison of the respective mortality rates. However, in test group 2 (375 mg/kg bw) one female animal was to be found which was free from clinical signs for the whole period of the study, and furthermore in 4 male rats of this group only temporary signs were observed, which had disappeared by the end of the study.

Mortality:

mortality observed, treatment-related

Description (incidence):

Numerous animals of test groups 1 and 2 (150 and 375 mg/kg bw) died before the end of the period planned for the study. The mortality rate was between 50 and 90 % depending on group and sex, and the intercurrent deaths occurred between the 14th and 81st day of the study.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Whereas the change in body weight in the animals of test group 1 (150 mg/kg bw) took a similar course to that of the corresponding control animals, the male animals of test group 2 (375 mg/kg bw) exhibited a slightly or moderately retarded weight gain. In the female animals of the latter group a corresponding trend was only barely perceptible during the first 3 weeks of the study. Therefore an evaluation of the parameter is no longer rational
because of the intercurrent deaths (see Mortality).

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

Neither the male nor the female rats of test groups 1 and 2 (150 and 375 mg/kg bw) exhibited any marked differences with respect to the mean daily feed consumption in comparison with the corresponding control groups.

Food efficiency:

not examined

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

no effects observed

Description (incidence and severity):

The altogether greatly varying mean daily drinking water consumption of the rats used did not reveal any clearly dose-dependent trend; moreover, opposing trends were at times detectable in the male and female animals. Thus, for example, after 21 days of the study the male rats of the control group exhibited a markedly higher drinking water consumption than those of test groups 1 and 2 (150 and 375 mg/kg bw), whereas at this point the female rats of the two test groups consumed more water than the corresponding control group. Hence, all in all no clear effect of the test substance on the drinking water consumption was observed.

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

not specified

Description (incidence and severity):

Of the organ weights of the animals sacrificed at the end of the study only the relative liver weight of the female animals of group 1 (150 mg/kg bw) was significantly increased (level of significance 5%). The increase was very slight and without relevance, the more so as a similar change was not observed in the male animals in group 2 (375 mg/kg bw). Also due to the small number of weights available for evaluation (group 1: 5 males, 5 females; group 2: 4 males, 1 female) no clear statement on adverse effects can be made.

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

Of the animals of dose groups 1 and 2 sacrificed at the end of the study, only 1 male and 3 female animals of group 1 did not exhibit any pathological changes. In the remaining animals, including those from group 2, there were findings suggesting an irritation of the stomach; in several animals the plica marginata was slightly or markedly thickened, in 2 animals the gastric mucosa was hyperemic, and 1 animal had hemorrhagic erosions/ulcerations in the glandular stomach. The other findings in the animals sacrificed are to be assessed as isolated findings independent of the administration of the test substance.
The gastrointestinal tracts of the animals that died intercurrently were usually empty or, in a few instances, exhibited a minimal content of feed or fluid. In all of the animals, the stomach and the entire or parts of the intestinal tract were distended with tympania. Since tympania had been observed clinically and intra vitam before, a postmortal genesis is to be excluded so that in the animals that died prematurely tympania has to be assumed as the cause of death in connection with the clinical signs.
The findings in the lungs (emphysema, edema, etc.) are also to be regarded as a consequence of the tympania and a resulting elevation of the diaphragm (Roehmheld's syndrome). The findings in the stomachs of the animals that died intercurrently corresponded to those in the animals sacrificed at the end of the study, but the cases with hemorrhagic erosions/ulcerations in the glandular stomach were relatively more frequent. Involutions of the spleen were seen in 6 animals and sharp liver margins in one animal, indicating the poor nutritional state of these animals that died intercurrently.

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

The gross-pathological findings were largely confirmed on histopathological evaluation of the animals sacrificed and those that died intercurrently, and additional cases usually diagnosed; in the stomach a pronounced hyperemia of the mucosal apices and erosions in the glandular stomach with/without cellular reactions were frequently observed. Under the microscope, the thickening of the plica marginata represented a submucosal edema or a slight degree of epithelial hyperplasia in this region. The fact that, particularly in the case of the male animals, the slight thickenings of the plica marginata seen on grosspathological inspection could not always be confirmed histopathologically, may be due to a shrinking process as a result of the fixation. On the other hand, thickenings which are perhaps still to be regarded as physiological borderline cases were noticed before during gross pathology.

For the tympania in the gastrointestinal tract, there was no histopathological equivalent suggesting a bacterial participation with morphological changes. The histopathological findings in the lungs were also equivalent to those in gross pathology (alveolar hyperemia, alveolar edema, alveolar emphysema, dystelectases). Unexpected findings were observed at examination of the nasal mucosa. Catarrhal and/or catarrhal- purulent rhinites were found in the nasal cavities and/or in the naso-pharyngeal duct of more than half of the animals of the dose groups and in individual animals also in the sinus maxillaris; in four of the animals they were even of a necrotizing character. In many animals there was in addition atrophy/metaplasia of the
mucosa in the ventral region of the nasopharyngeal duct and, in isolated cases, also in the regions of the respiratory epithelium of the nasal cavities. In 2 animals the submucosa of the nasal mucosa was thickened or fibrosed, and an increased goblet cell activity was determined in 3 animals. It must therefore be assumed that the changes are associated with the administration of the test substance, since a corresponding state of inflammation was not seen in any of the control animals. However, it may be said that it is rather improbable that these findings were due to a systemic effect of the substance. It is more likely that they are directly related to the administration by gavage because portions of the test substance were regurgitated during introduction into or withdrawal of the tube from the stomach, or drops adhering to the tube got into the pharyngeal duct on withdrawal. The ventral localization of the changes and the purulent mucus in the pharynx of one animal, diagnosed during gross pathology, also support this assumption.

The most noteworthy histopathological finding, however, was seen in the kidneys of the majority of the animals that died intercurrently. Thus, in 10 out of 11 male animals in the two dose groups a necrotizing tubular nephrosis on the basis of a ballooning degeneration with subsequent fragmentation of the epithelia in the cortical region was diagnosed. With the female animals this was the case in 11 out of 14. Wíth the animals of the dose groups sacrificed at the end of the study this finding was remarkably enough absent and not even suggested. The extent to which this finding is related to a
primary nephrotoxic effect of the substance, or whether it is of a secondary ischemic nature, was not to be derived from the morphological picture. However, a tubulonecrosis on the basis of an ischemia could be explained by the tympania, beginning with a respiratory hypoxidosis intra vitam (see clinical dyspnoea) and, with progressing tympania, by a direct compression of the afferent and/or efferent renal vessels. This is indicated by the fact
that the kidney findings were only obtained in animals that died intercurrently having tympania in the gastrointestinal tract. Out of the 4 animals that died and exhibited no tubulonecrosis, 2 animals showed pronounced cloudy swelling of the epithelia and the other 2 animals moderately increased tubular dilatation. These findings may similarly be interpreted as a consequence of ischemia. The pronounced fatty degeneration of tubular epithelia in individual female animals is a further indicator for damage. Although the degenerative renal changes were to some extent considerably masked by postmortal autolytic tissue alterations, they could still be distinguished from the latter relatively clearly as having occurred intra vitam.

In the liver no pathological differences between the control and the dose groups were seen, with the exception of one animal with vacuolar degeneration. In this connection, special mention is to be made of the fatty deposits; they were not increased in the sense of an ischemic fatty degeneration of liver cells. This, too, would substantiate the assumption that the kidney findings occurred within a relatively short time and mechanically as a result of a local compression ischemia and not as a result of a general hypoxidosis. A third possibility to be discussed would be the question of a slight nephrotoxic effect of the test substance being enhanced by the effect of the compression ischemia.

Histopathological findings: neoplastic:

no effects observed

Effect levels

Key result

Dose descriptor:

LOAEL

Effect level:

150 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: overall effects

Target system / organ toxicity

Key result

Critical effects observed:

no

Any other information on results incl. tables

Summary:

375 mg/kg body weight group:

Body weight change:

- slightly to moderately retarded growth of the male rats, also suggested in the female rats during the first 3 weeks of the study

Clinical signs:

- in most of the animals employed, from the 3rd week of administration onwards tympania of the gastrointestinal tract, frequently accompanied by cyanosis and dyspnoea

- in the case of individual animals unphysiological utterances

Mortality:

- premature death of 6 out of 10 male and 9 out of 10 female rats

Gross-pathological and histopathological findings:

- irritations of the stomach such as thickening of the plica marginata, hyperemia and hemorrhagic erosions/ ulcerations of the gastric mucosa

- elevation of the diaphragm (Roemheld syndrome), pulmonary edema/emphysema and alveolar hyperemia and dystelectases as a consequence of the already clinically evident tympania

- catarrhal or catarrhal purulent rhinites in some of the animals

- necrotizing tubular nephroses mostly in the animals that died prematurely

150 mg/kg body weight group:

Clinical signs:

- in some animals from the 3rd week of administration onward tympania of the gastrointestinal tract, accompanied in some animals by cyanoais and dyspnoea

Mortality:

- premature death of 5 out of 10 animals used per sex

Gross-pathological and histopathological findings:

- as for test group 2 (375 mg/kg body weight) but frequently less pronounced and in a smaller number of animals