Isopentyl acetate

Endpoint summary

Description of key information

oral:

7.5.1.001 (BG RCI (1990/91), Schilling et al. (1997)):

At the highest dose of 1846.11 mg/kg bw/d (target substance) no effects were found for female animals wheras for male animals slight effects on haematology could be detected at the end of the 3-month test period. These were: Red blood cells: increase in the erythrocyte values, decrease in the mean corpuscular volume and decrease in the mean corpuscular hemoglobin content.

The next lower dose was therefore pointed out to cause no adverse effects: NOAEL = ca. 435.68 mg/kg bw/d (actually received) (target substance).

Effective concentrations of the source substance 3-Methylbutan-1-ol were re-calculated for the target substance isopentyl acetate using the MW.

7.5.1.002: range-finder study OECD TG 422, rat, 14 d. NOAEL = 369.22 mg/kg bw/d (sedation and mortality was found at 1476.9 mg/kg bw/d of target test substance (source substance:3-Methylbutan-1-ol) which was the highest dose tested). Effective concentrations of the source substance 3-Methylbutan-1-ol were re-calculated for the target substance isopentyl acetate using the MW.

7.5.1.003: OECD TG 422 study, rat, 42 d (m), 41-53 d (f), NOAEL =  443.07 mg/kg bw/d (target substance), NOEL = 147.69 mg/kg bw/d (target substance) (at the highest dose of 443.07 mg/kg bw/d (target substance) the body weight gain decreased in males; findings/changes evaluated to have no toxicological significance because of lack in dose-response relationship, for the following examinations: haematology, clinical chemistry, organ weights (thymus, rel. & absol. wt). Effective concentrations of the source substance 3-Methylbutan-1-ol were re-calculated for the target substance isopentyl acetate using the MW.

7.5.1.004 (Carpanini et al. (1973)):

In a published subchronic toxicity study, 10 male and 10 female Ash/CSE rats were treated for 3 and 6 weeks with doses of  738.44 and 1476.9 mg/kg bw /day of the target substance (source substance 3-methylbutan-1-ol) by gavage (Carpanini et al. 1973). In addition, 30 male and 30 female Ash/CSE rats were treated for 17 weeks with doses of  221.53,  738.44 and 1476.9 mg/kg bw /day. Body weights were determined initially, at day 5 and then weekly. Food and water consumption were determined over a 24-hr period preceding the day of weighing. Urine was collected during week 3, 6, and 13. After sacrifice, haematological examinations, serum analyses, gross and histopathological examinations were performed. There were no effects associated with 17 weeks of treatment in the results of the haematological examinations, serum analyses, urinary cell counts, renal concentration tests or organ weights. The slightly reduced rate of body-weight gain (9%) observed at week 17 in the males at the highest dose level was shown to be due to a reduced food intake. Although two rats given 1476.9 mg/kg bw/day died, the histopathological examination showed that these deaths were due to dosing into the lungs and not to any toxic effects. NOEL =  738.44 mg/kg bw/d (effect on body weight of males at highest dose of 1476.9 mg/kg bw/d) of target source isopentyl acetate. Effective concentrations of the source substance isoamyl alcohol were re-calculated for the target substance isopentyl acetate using the MW.

7.5.1.005 (Gibel et al., Geschwulstforsch. 45/1: 19-24 (1975); Z Exper Chir 7: 235-239 (1974): rat, oral gav., A LOAEL of 34.11 mg/kg bw/d (target substance) could therefore be defined.  

Effective concentrations of the source substance 3-Methylbutan-1-ol were re-calculated for the target substance isopentyl acetate using the MW.

However, this LOAEL is eventually disregarded, adapting to the official opinion of MAK (1996) where the data of Gibel et al. (1974/1975) were disqualified. MAK evaluated the data quality to be questionable. In the study report of "Study on the oral toxicity of 3-methylbutanol-1 in rats - Administration via the drinking water over 3 months", Project No.: 33S0056/88020, performed by BASF (1990) and owned by BG RCI, was also referred to Gibel et al. (1974/1975). In the report is pointed out that the suspicion of carcinogenicity cannot be ruled out under consideration of the information in Gibel et al. (1974/1975) and that carcinogenity studies may therefore follow in the future. The German MAK Commission evaluated the data apparently different.

Additional information

No key study is available for isopentyl acetate, however data from the metabolically related substance, i.e. 3-methyl-1-butanol has been taken into account via read across. Based on the available and adequate data on the metabolism of isopentyl acetate in the body (see under 7.1 Toxicokinetics, metabolism and distribution) it is assumed that the ingestion of isopentyl acetate leads to the rapid formation of 3-methyl-1-butanol and acetic acid in the gut and/or after becoming bioavailable due to esterase activities. Acetic acid is not regarded as toxicologically relevant compared to 3-methyl-1-butanol. Repeated dose effects of isopentyl acetate should therefore be found to be the same or similar to the effects of 3-methyl-1-butanol. The data on repeated dose toxicity of 3-methyl-1-butanol is therefore regarded as meaningful for the description of repeated dose effects of isopentyl acetate.

In the most relevant study, according to OECD 408 and GLP, i.e. a drinking water study, ten Wistar rats per sex and dose received nominal concentrations of 1000, 4000 and 16000 ppm 3-methylbutan-1-ol corresponding to approx. 80, 340, 1250 mg/kg bw /day for 3 months. For comparison, one group of untreated animals (10 males, 10 females) was used as a control. There were no clinical signs in the sense of a toxic effect notable during the study period. Although an increased water consumption of males and females in the 1000 and 4000 ppm groups was observed, it was assessed as being no toxic effect since there was no clear dose response relationship apparent and it varied at different times in degrees of intensity.

In respect of haematology and clinical chemistry, the following observations were made:

Red blood cells: at the end of the 3-month administration period, there was in the blood of the males of test group 3 (16000 ppm) an increase in the erythrocyte values, a decrease in the mean corpuscular volume and a decrease in the mean corpuscular hemoglobin content. The authors of the study assumed that these changes might have been attributable to the test substance administration and could be an indication of a marginal hemotoxic potential of the test substance. In "Guidance on information requirements and chemical safety assessment Chapter R.7a: Endpoint specific guidance, Version 2.0, ECHA, November 2012", the following is stated under "R.7.5.4.1 Non-human data on repeated dose toxicity", "Testing data on repeated dose toxicity", "Animal data":

"...Indicators of immunotoxicity include changes in haematological parameters, serum globulin levels...". Therefore, the next lower dose level was pointed out as NOAEL for male animals (= 340 mg/kg bw/d (nominal) = ca. 295 mg/kg bw/d (actually ingested)).

Other haematology findings: By contrast, there was a slightly increased erythrocyte count of the males in test group 2 (4000 ppm) which was not considered to be related to the test substance, since this value is still within the range of biological variation and since there are otherwise no further findings in this test group which point to an effect on the red blood count.

No other relevant adverse effects were observed in this 90 d study.

In a published subchronic toxicity study, 10 male and 10 female Ash/CSE rats were treated for 3 and 6 weeks with doses of 500 and 1000 mg/kg bw /day 3-methylbutan-1-ol by gavage (Carpanini et al. 1973). In addition, 30 male and 30 female Ash/CSE rats were treated for 17 weeks with doses of 150, 500 and 1000 mg/kg bw /day. Body weights were determined initially, at day 5 and then weekly. Food and water consumption were determined over a 24-hr period preceding the day of weighing. Urine was collected during week 3, 6, and 13. After sacrifice, haematological examinations, serum analyses, gross and histopathological examinations were performed. There were no effects associated with 17 weeks of treatment in the results of the haematological examinations, serum analyses, urinary cell counts, renal concentration tests or organ weights. The slightly reduced rate of body-weight gain (9%) observed at week 17 in the males at the highest dose level was shown to be due to a reduced food intake. Although two rats given 1000 mg/kg bw/day died, the histopathological examination showed that these deaths were due to dosing into the lungs and not to any toxic effects. An NOEL of 500 mg/kg bw/d could be pointed out in this study as there was a reduced the body weight gain of males at the highest dose of 1000 mg/kg bw/d (not observed for females) and an overall NOAEL of 1000 mg/kg bw/d.

In addition, there are data available from a Combined repeated-dose / reproductive developmental toxicity study according to OECD TG 422 and in compliance with GLP regulations (Kuraray Co. Ltd. 2008). 3-methylbutan-1-ol was administered to male and female Sprague-Dawley strain SPF rats at dose levels of 0 (control group), 30, 100 or 300 mg/kg bw for a total of 42 days to males (for 14 days before mating throughout the mating period up to the day before necropsy) and for a total of 41 to 53 days to females (for 14 days before mating throughout the mating and gestation periods up to day 4 of lactation) to examine its repeated dose toxicity and reproductive and developmental toxicity. For the males and females in the 0 and 300 mg/kg bw groups, a 14-day recovery period was provided after administration for 42 days to examine reversibility of the toxic changes. The females in the recovery group were not subjected to mating. No deaths occurred in any group and there were no test article-related effects in clinical observation, detailed clinical observation, manipulative test, measurement of grip strength, measurement of motor activity, food consumption, urinalysis (including water intake), haematological examination, blood chemistry examination, organ weight, histopathological findings or gross pathological examination. In the measurement of body weight, a low value in body weight gain (from day 1 to day 42) during the administration period was observed in males in the main group of the 300 mg/kg bw group. During the 2-week recovery period, the body weight gain of males in the recovery group of the 300 mg/kg bw group was higher than that of the control group. Based on the results described above, it was judged that the no effect level for repeated dose toxicity of 3-methylbutan-1-ol was 100 mg/kg bw/day in males and the no adverse effect level 300 mg/kg bw /day in females.

In the publications of Gibel et al. (1974/1975), various effects were described upon oral administration of 3-methyl-1-butanol:

Pathological findings included toxic liver damage (steatosis, congestion, single cell and grouped cell necrosis, fibrosis, cirrhosis)

In some animals changes in the myokard with scar formation was observed, rarely also with slight perivascular inflammtory infiltrate.

In single cases, interstitial pancreatitis and fibrosis was found at the pancreas. An oral LOAEL of 23.1 mg/kg bw/d could be defined based on the data of Gibel et al. (1974/1975), mostly under consideration of the following aspects: the test substance plus its purity was sufficiently identified, it was administered over a long period (1.75 years) and the incidence of toxic effects from treatment versus no treatment was apparent even at the test group size of 15. Furthermore, toxic effects were also found by Gibel et al. (1974/1975) in a second independent experiment upon subcutaneous administration (see 7.5.4 Repeated dose toxicity: other routes).

However, there is also strong criticism on the data of Gibel et al. (1974/1975) by a toxicolgy expert, including the following aspects:

Not according to current standard protocols and GLP, limited documentation, low animal number used, low relevance of dose route used, i.e. subcutaneous, bolus, no characterization of test material used. Information on purity cannot be sufficiently derived by the info given, i.e. twofold  distillation., no info on gender specificity of effects, only single dose tested, no dose dependency established., no MTD determined for correct dose setting, control group showed no  tumours, which is unusual, no comparison with historical control data possible, findings after treatment with the estimated doses (limited doc, the assumed dose level of 23.1 cannot be verified and is not cited in e.g. MAK report) are in strong contradiction to the findings from e.g valid subchronic guideline GLP study, showing only very slight erythrocyte effects. This further questions the reliability of the GIBEL publication, no dose dependency of putative effects demonstrated no statistical analysis performed, acc. to MAK -> study cannot be used for assessment due to these limitations, carcinogenic potential of isopentylacetate/isoamylalcohol unlikely, since no structural alert for cancer, no effects in gentox. studies, no test substance related hyperplasia/preneoplastic lesions in guideline repeated dose studies observed, only slight haematology effects in the superior GLP-90-d study.

Furthermore, MAK (1996) criticised the data (epr 7.7.001):

- it would be unusual that no malignant tumours had developmed in the control animals

- liver damage and reduced survival would suggest that the doses given to the treated animals had been excessive

- the incidences of liver tumours were suspected to have been a result of massive cytotoxicity

- the leukaemia could not be explained but the incidence of about 8% after both oral and subcutaneous administration would not seem likely to be significantly different from the control values.

-The study would not meet the requirements for a valid carcinogenicity study because of the small numbers of animals, the lack of data for the purity of the substances, the fact that dose-dependency was not investigated and statistical analysis was not carried out.

The above stipulated LOAEL is therefore eventually disregarded, adapting to the official opinion of MAK (1996). In the study report of "Study on the oral toxicity of 3-methylbutanol-1 in rats - Administration via the drinking water over 3 months", Project No.: 33S0056/88020, performed by BASF (1990) and owned by BG RCI, was also referred to Gibel et al. (1974/1975). In the report is pointed out that the suspicion of carcinogenicity cannot be ruled out under consideration of the information in Gibel et al. (1974/1975) and that carcinogenity studies may therefore follow in the future. The German MAK Commission evaluated the data apparently different.

All available and adequate data from repeated dose studies was generated by the use of 3-methyl-1-butanol as test substance, administered orally and in one study via subcutaneous route (data entered under IUCLID 7.5.1 + 7.5.4). These data should be regarded together in a weight of evidence approach to evaluate possible toxic effects from the repeated exposure to isopentyl acetate.

Justification for classification or non-classification

According to the CLP regulation (Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures), pp. L353/124, L353/125, the following classification scheme generally applies to the endpoint of repated dose toxicity: Category 1: effects at <= 10 mg/kg bw/d; Category 2: effects at 10 -100 mg/kg bw/d; both for rat, oral gavage).

In a GLP-90-d study (rat, oral) only slight haematology effects were observed at the highest dose level in males (Schilling et al. (1997), BG RCI (1990)). A NOAEL of 295 mg/kg bw/d is pointed out from that study.

An oral LOAEL of 23.1 mg/kg bw/d could be defined if the data of Gibel et al. (1974/1975) would be taken into consideration. This would trigger the above mentioned classfication scheme (Category 2). However, as laid out under "Discussion" above, the data of Gibel et al. (1974/1975) was disqualified by MAK (1996) and other expert opinion.

This is the basis for non-classification.