Butyric acid

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

In a frog embryo teratogenesis assay (FETAX) performed according to a standard guide of ASTM (E1439-91) using butyric acid as test substance, a LC50 of 3559 mg/L and an EC50 (malformation) of 421 mg/L was determined.

Effect on fertility: via inhalation route

Dose descriptor:

NOAEC

7 320 mg/m³

Additional information

For butyric acid, no valid studies concerning reproductive toxicity could be identified.

 

Endpoint information originating from n-butyl acetate as supporting substance will be used for read across based on following reasons.

 

After administration, n-butyl acetate will be rapidly metabolized in vivo in blood and various tissues by ubiquitous esterases. Half-life of this transformation is short resulting in complete cleavage of the ester. n-Butanol is formed which is rapidly metabolized in vivo to n-butyraldehyde by alcohol dehydrogenases and subsequently to n-butyric acid by aldehyde dehydrogenases. Thus, in the course of metabolic transformation of n-butyl acetate, butyric acid is generated rapidly and predominant as intermediary metabolite. Thus, it is justified to use n-butyl acetate as supporting substance in the evaluation of the systemic toxic effects of butyric acid.

 

Effect levels derived for the supporting substance n-butyl acetate will be transformed to effect levels for butyric acid using the respective molecular weights. These values are used to evaluate the toxic potential of butyric acid.

 

The reproductive toxicity of n-butyl acetate has been investigated in a valid inhalation GLP-study according to OECD TG 416 (Two-Generation Reproduction Toxicity Study). This will be the key study (Nemec, 2010).

 

A reliable (RL1) two generation inhalation study was performed with Sprague-Dawley rats (whole body exposure, 6 h/d, 7 d/w, 30/sex/group) which were exposed to 0, 750, 1500 or 2000 ppm test substance. Exposure was suspended from gestation day 21 through lactation day 4 to avoid the confounding effects on nesting and nursing behavior caused by separation of dams from their litters. Therefore, on lactation days 1-4, the F0 and F1 maternal animals received deionized water or the test article via oral gavage at dosage levels of 0, 1125, 2250 or 3000 mg/kg/day. F0 males and females were exposed for 113-114 and 121-127 consecutive days, respectively, and F1 males and females were exposed for 134-135 and 140-153 consecutive days, respectively. F2 males and females were exposed for 47-50 consecutive days.

 

There were no functional effects on reproduction (estrous cycles, mating and fertility indices, number of days between pairing and coitus, spermatogenic endpoints and gestation length) in any test article exposed group in the F0 or F1generations. The exposure level of 2000 ppm (9650 mg/m³) was considered to be the no-observed-adverse-effect concentration (NOAEC) for reproductive toxicity (fertility).

 

General systemic toxicity was evident in the 1500 and 2000 ppm group F0, F1and F2 adult males and females. Decrements in mean body weights, body weight gains and food consumption were observed at 1500 and 2000 ppm. Although body weights, body weight gains and food consumption were reduced in the 750 ppm males of the F1 generation, direct inhalation exposure of F2 animals on a comparable regimen did not reproduce this response. Additionally, the magnitude and temporal pattern of the reductions in the F1males at 750 ppm were not noted in the F0 generation. Therefore, mean body weights, body weight gains and food consumption at 750 ppm were considered to be unaffected by test article exposure. Degeneration of the olfactory epithelium in the nasal cavity was noted at 750 and 2000 ppm in F0 and F1 males and females (1500 ppm group not investigated). This finding was considered to be a site-of-contact irritant effect and not indicative of systemic toxicity. Statistically significantly higher mean lung weights (relative to final body weight) in F0 males at 1500 and 2000 ppm, in F1 males and females at 750, 1500 and 2000 ppm and in F0 females at 2000 ppm and adrenal weights (absolute, relative to brain and/or body weight) in F0 females at 1500 and 2000 ppm were noted; all were observed without correlating histologic findings and were considered a stress-related response (adrenal weights) or not adverse (lung weights). Therefore, the NOAEC for systemic toxicity in adult rats was considered to be 750 ppm under the conditions of this study (Nemec, 2010).

 

In the range finding study for the two generation study, the NOAEC for maternal toxicity was 500 ppm and for developmental toxicity 1500 ppm (Nemec, 2006).

 

In conclusion, no effects on fertility were observed in a two generation study (highest exposure concentration: 2000 ppm) with n-butyl acetate. Thus the NOAEC for reproductive toxicity of n-butyl acetate is 2000 ppm (9650 mg/m³) (Nemec, 2010).

 

Deduction of the NOAEC (inhalation) for Butyric acid

 

The NOAEC of butyric acid will be calculated on basis of the NOAEC of n-butyl acetate (Nemec, 2010) using the mass concentration/m³ and the respective molecular weights (88.11 and 116.11).

 

The deduced NOAEC (effects on fertility) for butyric acid is 7320 mg/m³ (2000 ppm).

Short description of key information:
For butyric acid, no valid data on toxicity to reproduction could be located.
Endpoint information resulting from n-butyl acetate as supporting substance will be used as substitute. Data are available for inhalation exposure.
Supporting substance n-butyl acetate
In a two generation inhalation reproductive toxicity study (highest exposure concentration: 2000 ppm), no effects on fertility were observed.
Butyric acid
For butyric acid, the NOAEC (reproductive toxicity) can be calculated using the respective molecular weight and molar volume.
Butyric acid: NOAEC = 2000 ppm (7320 mg/m³).

Effects on developmental toxicity

Description of key information

For butyric acid, no valid data on developmental toxicity/teratogenicity could be located.
To compensate for this lack of data, information resulting from n-butyl acetate as supporting substance will be used as substitute. Data are available for inhalation exposure.
Supporting substance n-butyl acetate
In a developmental inhalation toxicity study in rats, n-butyl acetate did exhibit slight treatment-related effects on maternal toxicity as well as on developmental toxicity at an exposure level of 1500 ppm (only dose tested.). The LOAEC for maternal and developmental toxicity of n-butyl acetate in rats was 1500 ppm (7240 mg/m³). (Hackett/Battelle, 1982).
In a test with similar protocol using rabbits, a NOAEC of 1500 ppm for maternal and developmental toxicity was observed (Hackett/Batelle, 1982).
For butyric acid, the LOAEC / NOAEC for rat and rabbit respectively can be calculated using the respective molecular weight and molar volume.
Butyric acid: LOAEL rat / NOAEC rabbit: 1500 ppm (5490 mg/m³).

Effect on developmental toxicity: via inhalation route

Dose descriptor:

LOAEC

5 490 mg/m³

Additional information

Regarding the developmental toxicity/teratogenicity of butyric acid, only one study was identified (Narotsky, 1989/1994). Reliability is low due to o several shortcomings of the study.

 

To compensate for this lack of data, information originating from n-butyl acetate as supporting substance will be used based on following reasons.

 

After administration, n-butyl acetate will be rapidly metabolized in vivo in blood and various tissues by ubiquitous esterases. Half-life of this transformation is short resulting in complete cleavage of the ester. n-Butanol is formed which is rapidly metabolized in vivo to n-butyraldehyde by alcohol dehydrogenases and subsequently to n-butyric acid by aldehyde dehydrogenases. Thus, in the course of metabolic transformation of n-butyl acetate, butyric acid is generated rapidly and predominant as intermediary metabolite. Thus, it is justified to use n-butyl acetate as supporting substance in the evaluation of the systemic toxic effects of butyric acid.

 

Effect levels derived for the supporting substance n-butyl acetate will be transformed to effects levels for butyric acid using the molar volume and the respective molecular weights. These values are used to evaluate the toxic potential of butyric acid.

 

The effect of n-butyl acetate on developmental toxicity/teratogenicity was investigated in three inhalation studies. In two studies, rats were used as test animals (Hackett/Battelle 1982; Saillenfait 2007). A third study was done with rabbits (Hackett/Battelle, 1982).

 

Hackett/Batelle 1982, rat

 

Maternal toxicity, reproductive performance, and developmental toxicity were evaluated in Sprague-Dawley rats following 7 h/d inhalation exposure to 1500 ppm (7230 mg/m³) n-butyl acetate (37 - 43 animals/group). Four different exposure regimens were used: Group 1(control): filtered air; Group 2: test item exposure from gestation day 7 through 16; Group 3: test item exposure from gestation day 1 to 16; Group 4: test item exposure for 5 days/week for 3 weeks prior to mating and daily from gestation day 1 through 16. Unexposed males were used in mating (Hackett et al., 1982; RL1).

 

Necropsies were performed on rats at gestation day 21. Pregnant animals were examined for toxic changes, including altered food consumption, body weight, tissue weights and histopathology. Reproductive measures included the determination of numbers of corpora lutea, implantation sites, resorptions, dead fetuses and live fetuses. Live fetuses were weighed, measured, and subjected to external, visceral and skeletal examinations to detect morphologic anomalies.

 

Food consumption, body weight and liver weight was reduced in maternal rats exposed to n-butyl acetate. Fetal size was reduced in all n-butyl acetate exposed litters. Increased incidences of fetal rib dysmorphology were observed in rats exposed from gestation day 7 through 16, and more numerous hydroureters in fetuses from rats exposed prior to mating and from gestation day 1 through 16. There was no evidence of teratogenic effects following exposure of rats to 1500 ppm of n-butyl acetate. The LOAEC for maternal toxicity and developmental toxicity in this study was 1500 ppm.

 

Hackett/Batelle 1982, rabbit

 

A test with similar protocol was performed in New Zealand rabbits: Group 1(control): filtered air; Group

2: test item exposure from gestation day 7 through 19; Group 3: test item exposure from gestation day 1 to 19. Necropsies were performed on rabbits at gestation day 30. Unexposed males were used in artificial insemination procedure (Hackett et al., 1982; RL1).

 

Exposure of rabbits to 1500 ppm n-butyl acetate affected food consumption: food consumption was generally higher in rabbits exposed to n-butyl acetate than in rabbits exposed to filtered air; onset of n-butyl acetate exposure resulted in a decrease of food consumption. No related changes in body weights were observed. Reproductive performance was unaltered by n-butyl acetate exposure. Fetal effects of n-butyl acetate exposure included increased incidences of retinal folds, misaligned sternebrae, and morphologic variations of the gallbladder in litters of rabbits exposed from gestation day 1 trough 19. No major malformations were observed. The effects on food consumption were not regarded to be adverse. The NOAEC for maternal and developmental toxicity in this study was 1500 ppm.

 

Saillenfait 2007

 

Developmental toxicity of n-butyl acetate was investigated in Sprague-Dawley rats (19 -2 1 pregnant rats/dose group) which were exposed from day 6 to 20 of gestation to concentrations of 0, 500, 1000, 2000, 3000 ppm (6 h/d, whole body). Under the conditions tested, maternal toxicity was evident at concentrations of 1000 ppm or higher (significant decrease in body weight gain at 2000 and 3000 ppm; reduced food consumption at >/= 1000 ppm). The only effects on prenatal development observed was a significant decrease in fetal weight at 3000 ppm. The NOAEC for maternal toxicity is 500 ppm and for developmental toxicity 2000 ppm (Saillenfait et al., 2007; RL2).

 

Narotsky 1989/1994

 

After oral administration to pregnant rats, butyric acid did not exhibit distinct developmental toxicity or teratogenic effects. But results are considered inconclusive due to small samples sizes caused by pronounced maternal toxicity (mainly respiratory effects)

 

 

In a developmental toxicity screening study according to Chernoff and Kavlock (1982) butyric acid (> 99%) was administered by gavage to rats at two dose levels (100, and 133 mg/kg bw/day) from day 6 through day 15 of gestation. Dams were allowed to deliver and pups were observed until postnatal day (PD) 6 before sacrifice of dams and pups.

 

Pronounced maternal toxicity (respiratory tract) was observed in both the low- and high-dose group. Mortality was high (3/15 and 7/15, controls 0/20). Overall, maternal toxicity gave reason to low numbers of surviving pregnant rats and progeny.

 

Gestation lengths and litter sizes were comparable in all groups. Non-significant increases of prenatal mortality were observed in the high-dose group. A decrease in postnatal viability in the low-dose group as well as a reduction of pup weight in the high-dose group on postnatal day 6 was attributed to the severe respiratory effects on dams.

 

Gross and visceral examinations of the progeny revealed only sporadic alterations. Skeletal examinations demonstrated increased incidences of lumbar rips. But the number of specimens examined was limited due to the high mortality of dams and progeny.

 

In conclusion, butyric acid caused severe maternal respiratory toxicity at both dose levels. Regarding developmental toxicity, no clear evidence could be demonstrated. Litters with high pup mortality or reduced pup weights were related to high respiratory toxicity in dams. Non significant increases in prenatal mortality and lumbar ribs were inconclusive due to small sample sizes. Developmental effects on progeny seem to be related to the maternal toxicity (Narotski 1989).

 

In contrast to butyric acid, other short-chain aliphatic acids with proven developmental toxicity like valproic acid and 2-ethylhexanoic acid clearly delay parturition, reduce the growth and the viability of the offspring and cause skeletal malformations. These effects could not be observed with butyric acid. Butyric acid obviously does not induce valproic acid like developmental effects (Narotsky 1989, 1994).

 

This is supported by results of structure activity relationship investigations for developmental toxicity of short-chain carboxylic acids. To exhibit distinct developmental toxicity, a branching at the C-2 position of the acid seems to be necessary. Furthermore, the groups branching from the C-2 position are required to be longer than a methyl group (C1 chain). All this requirements do not apply to butyric acid (Narotsky 1994).

Toxicity to reproduction: other studies

Additional information

In a frog embryo teratogenesis assay performed according to a standard guide of ASTM (E1439 -91) using butyric acid as test substance, a LC50 of 3559 mg/L and an EC50 (malformation) of 421 mg/L was determined. The DHI (Developmental Hazard Index) calculated to 8.4 indicating that the effective dose of butyric acid causing malformation was about 8-fold lower than the dose causing lethality.

 

The test system used is not comparable to in vivo developmental toxicity tests with mammals. Exposure, intake, distribution and metabolism do not match. It may be used for screening. But to decide under REACH about developmental toxicity effects of a test substance in humans, test procedures laid down in OECD or EU test guidelines on developmental toxicity have to be followed.

Justification for classification or non-classification

Based on read across results from the supporting substance n-butyl acetate, butyric acid has not to be classified for reproductive toxicity. The supporting substance n-butyl acetate did not show effects on fertility, and developmental toxicity only occurred at concentrations which were already toxic to maternal animals.