3-methoxybutan-1-ol

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

300 mg/kg bw/day

Species:

rabbit

Effect on fertility: via inhalation route

Species:

rabbit

Additional information

In the absence of significant direct information on 3-methoxybutyan-1-ol for this endpoint a weight of evidence approach is proposed for reproductive toxicity. After careful consideration of structural analogues of 3-methoxybutan-1-ol, putative metabolism and kinetics, the case for which is presented in more detail in CSR Section 5.1, this summary discusses the candidate data individually for the purpose of read across. For 3-methoxybutan-1-ol, the candidate (Target substance) read-across substances (Source substances) with information reported are 3-methyl-3-methoxy-1-butanol,  butane-1,3-diol and 3-methoxy acetate (metabolic precursor). These candidate substances are related to 3-methoxybutan-1-ol in that they are a structural analogue and a putative metabolite respectively.

Two new toxicokinetics studies were conducted to strengthen this read across assessment and, as expected, the rapid metabolism of 3 methoxybutyl acetate to 3 methoxybutan 1 ol was experimentally demonstrated. The second study was performed to better characterize the rapid rate of conversion of 3 methoxybutyl acetate (Source Substance) to 3 methoxybutan 1 ol (Target Substance) and to better characterize the metabolism of 3 methoxybutan 1 ol to butane-1,3-diol (Source Substance, Metabolite 1). The more accurate half-lives for 3 methoxybutyl acetate (Source Substance) and 3 methoxybutan 1 ol (Target Substance) were between 0.48 and 0.63 min and 5.92 min, respectively. Since butane-1,3-diol was detectable, but its concentrations were not quantifiable, a half-life for butane-1,3-diol could not be calculated. However, since it was initially detected in blood three minutes after intravenous dosing, its formation is rapid.

3-methoxybutan-1-ol No data are available on the reproductive toxicity of 3-methoxybutan-1-ol or its metabolic precursor, 3 -methoxybutyl acetate.

3-methoxy-3-methyl-1-butanol (structural analogue of 3-methoxybutan-1-ol) Relevant data are available on 3-methoxy-3-methyl-1-butanol. This substance is a close structural analogue, with only an additional methyl group. In an OECD Guideline 421 reproduction/developmental toxicity test, rats (CrjCD(SD)IGS) were exposed to 3-methoxy-3-methy-1-butanol by oral gavage at 0, 8, 40, 200, or 1000 mg/kg bw/day. The test included a 14 day pre-mating exposure period and a total test duration of 47 days for males and 42-52 days for females. The NOAEL was 40 mg/kg bw/day for males and 200 mg/kg bw/day for females based on liver and kidney weight increases (in the absence of histopathological change). No changes in oestrous cycle, copulation index, fertility index, gestation period, number of corpora lutea, number of implantations, gestation index, delivery index, or delivery and nursing conditions were seen in the parent animals. Moreover, no changes in total number of pups born, number of live newborn pups, sex ratio, live birth index, body weight, morphology or viability index of newborns on day 4 of nursing were seen in the pups. The authors concluded the no-effect-level for reproductive capability of male and female parent animals was 1000 mg/kg/day.

Butane-1,3-diol (a putative metabolite of 3-methoxybutan-1-ol) Potential developmental and reproductive effects of this substance were evaluated in a complex 2-year, 5-generation study, with dietary incorporation of butane-1,3-diol at up to 24% (Hess et al, 1981). The 1,3-butanediol in this series of experiments was included in the diet at concentrations of 0, 5, 10 and 24% (prepared by substituting 1,3-butanediol for equal amounts by weight of corn starch and dextrose).  The F0 generation comprised of groups of 25 male and 25 female rats (Wistar derived). After exposure to test diets for 28 days, blood and urine samples were taken (10 males and 10 females) for clinical chemistry examination (blood; alkaline phosphatase, glucose, hematocrit, hemoglobin and total and differential leucocyte counts: urine; albumin, glucose, ketones, occult blood, pH, specific gravity and microscopic examination of the sediment). F0 generation rats were then paired (1 to 1 within each group). Mating was confirmed by a vaginal sperm plug and the day designated day 0 of pregnancy. If mating was not confirmed (7 days) the female was paired with another male animal from the same exposure group (additional 7 days). Females not confirmed pregnant within this time period were discarded. F0 generation females were fed test diets throughout the mating, gestation and lactation phase of the study and were allowed to deliver naturally. The number of pregnant females, the number of pups born live or dead, the number of pups surviving and their body weights were recorded and this first series of litters was the F1A generation. Selected pups were brought to maturity and after 11 weeks blood and urine samples were collected from 10 rats per sex per group for clinical chemistry analysis, as before. Thereafter 25 males and 25 females per group were paired to produce the F2 generation. A second series of litters (F1B) was produced by the F0 parents1-2 weeks after weaning of the first litters, with each female mated with a different male and data collected as described above. Ten males per group were reared to sexual maturity and used in a dominant lethal test. After some 77 weeks, five successive mating cycles were achieved with the F1A rats and the reproductive index was calculated for each litter. For FIA rats, which survived for at least 66 weeks, the gonads and pituitary glands were examined microscopically. Selected pups of the first litters of the F1A females became the F2A parents, and were used to produce the F3 generation. Each set of F2A parents was mated twice to yield two litters of offspring F3A and F3B. The F3A females were allowed to produce F4A and F4B litters. However, only 25% of the F2A female rats were allowed to produce the F3B litter the remaining 75% were allocated to the developmental study. In this rather unusual study, for four of five generations of rats fed extremely high concentrations of 1,3 -butanediol, 24% of diet (240,000 ppm), reproduction and lactation parameters were similar to those of controls and no adverse effects were indicated. For the F1A generation mated to produce 5 successive litters, there was an apparent dose-related decrease in fertility for the production of the last 2 litters only (F2D & F2E). This decrease was considered by the authors to be related to a physiological stress induced by the highly ketogenic, semi-synthetic diet rather than a direct effect of 1,3 -butanediol on the fertility of the males. However it can be concluded that there were no adverse effects on the fertility of at least three successive matings of rats fed extraordinary high levels (240,000 ppm) of 1,3 -butanediol. Futhermore, butane-1,3-diol is one potential metabolite of 3 -methoxybutan-1 -ol and therefore the corresponding dose level of 3 -methoxybutan-1 -ol required to deliver such high quantities of this metabolite would be so high that it would not be relevant to human health and probably unachievable in animal studies.

3-methoxybutyl acetate In a time-mated female New Zealand White rabbits were treated with 3-methoxybutyl acetate (source substance, metabolic precursor) from Day 7 to 28 post-coitum, inclusive by daily oral gavage at dose levels of 100, 300 and 1000 mg/kg/day. Four females were sacrificed for animal welfare reasons between Days 17-20 post-coitum. All these females had a severely reduced food consumption for at least 7 consecutive days and a significant body weight loss (5-13% of their initial weights) during the treatment period. Therefore, mean food consumption was significantly lower in females at 1000 mg/kg/day between Days 7-12 post-coitum compared to controls. Food consumption appeared to recover to control levels from Day 13 post-coitum onwards. Despite the apparent recovery, given the size of the observed effects on body weight gain and food consumption resulting in sacrifice of four high-dose dams, these effects were considered adverse Clinical signs of toxicity noted in a single early sacrificed animal included piloerection, lean appearance, hunched posture, moribundity, and pale appearance. Macroscopic observations at necropsy revealed many dark red foci in the forestomach or irregular surface of the forestomach for 4/22 females at 1000 mg/kg/day. This finding was most likely related to the physical-chemical properties of the test item and at the incidence observed, it was considered related to treatment with the test item. It was noted that this finding occurred in 2 females that was prematurely sacrificed due to absent food consumption and body weight loss. No test item-related effects were seen at treatment up to 300 mg/kg/day. The number of corpora lutea, implantation sites, viable or dead fetuses, early or late resorptions, and pre- and postimplantation loss were considered not affected by treatment up to 300 mg/kg/day. 

 Regarding developmental toxicity, at 300 mg/kg/day test item-related skeletal variations were noted: The litter incidence of an ossification site near the 7th cervical vertebra was statistically significantly increased compared with the control group, although this specific finding was within the historical control range and the percent per litter with total variations was almost identical to controls. In addition, three cases of 7th cervical full ribs were observed in this study that occurred in three 300 mg/kg/day litters that had fetuses with 7th cervical ossification sites. As these skeletal findings only consisted of variations, they were considered not adverse. No test item-related toxicologically significant changes were noted in any of the remaining developmental parameters investigated in this study, up to the highest dose level evaluated (300 mg/kg/day) (i.e. litter size, sex ratio, fetal body weights, external, visceral and skeletal malformations, and external and visceral developmental variations).

Based on the results in this prenatal developmental toxicity study (i.e. adverse effects on body weight and food consumption and unscheduled deaths in dams treated at 1000 mg/kg/day) the maternal No Observed Adverse Effect Level (NOAEL) for 3‑methoxybutyl acetate (Source Substance) was established as being 300 mg/kg/day. Due to the absence of any 3‑methoxybutyl acetate related effects on development and fetal morphology, the developmental No Observed Adverse Effect Level (NOAEL) for 3‑methoxybutyl acetate was established as being at least 300 mg/kg/day.

 Discussion

For 3-methoxybutan-1-ol and the read-across candidates discussed above a range of fertility/developmental test protocols have been reported. No significant reproductive potential has been highlighted in these studies. The evidence supports the conclusions that there is sufficient evidence to assess the reproductive potential of 3-methoxybutan-1-ol and that there are no fertility effects associated with 3-methoxybutan-1-ol exposure.

 

Short description of key information:
The read across assessment (see Section 13) indicates that there are no fertility effects associated with 3-methoxybutan-1-ol exposure.

 

Effects on developmental toxicity

Description of key information

The weight of evidence indicates that there are no developmental toxicity effects associated with 3-methoxybutan-1-ol exposure.

Additional information

In the absence of significant direct information on 3-methoxybutan-1-ol for this endpoint a weight of evidence approach is proposed for developmental toxicity. After careful consideration of structural analogues of 3-methoxybutan-1-ol putative metabolism and kinetics, the case for which is presented in more detail in CSR Section 5.1, this summary discusses the candidate data individually followed by an overall weight of evidence discussion. For 3-methoxybutan-1-ol, the candidate read-across substances are 3-methoxybutyl acetate, 3-methyl-3-methoxy-1-butanol, butane-1,3-diol, and n-butanol.  The first substance, 3-methoxybutyl acetate is predicted to rapidly and extensively metabolise to 3-methoxybutan-1-ol. The other candidate substances are related to 3-methoxybutan-1-ol in that they are either structural analogues or putative metabolites, .

3-methoxybutan-1-ol

No data are available on the developmental toxicity of 3-methoxybutan-1-ol

3 -Methoxybutyl acetate (putative metabolic precursor of 3 -methoxybutan-1 -ol)

An oral gavage OECD 414 prenatal developmental toxicity study in which 20 female Wistar rats received daily doses of 1000 mg/kg/day from day 7 to day 16 of pregnancy has been reported (Hoechst, 1997). There was no evidence of either maternal or developmental toxicity at this limit dose.

3-methoxy-3-methyl-1-butanol (structural analogue of 3-methoxybutan-1-ol)

Relevant data are available on 3-methoxy-3-methyl-1-butanol. This substance is a close structural analogue, with only an additional methyl group, of putative metabolite 3-methoxybutan-1-ol.

In an OECD Guideline 421 reproduction/developmental toxicity test, rats (CrjCD(SD)IGS) were exposed to 3-methoxy-3-methy-1-butanol by oral gavage at 0, 8, 40, 200, or 1000 mg/kg bw/day. The test included a 14 day pre-mating exposure period and a total test duration of 47 days for males and 42-52 days for females. The NOAEL was 40 mg/kg bw/day for males and 200 mg/kg bw/day for females based on liver and kidney weight increases (in the absence of histopathological change). No changes in total number of pups born, number of live newborn pups, sex ratio, live birth index, body weight, morphology or viability index of newborns on day 4 of nursing were seen in the pups (RIAS, 2003b).

The authors concluded that the no-effect dose levels for reproductive capability of male and female parent animals and for pup development were both 1000 mg/kg/day.

n-butanol (structural analogue of 3-methoxybutan-1-ol)

Groups of approximately 15 female rats (Sprague-Dawley) were exposed by inhalation (whole body), to n-butanol (0, 3500, 6000 or 8000 ppm; 0, 11000, 18000, or 25000 mg/m3) on gestation days 1–19 for 7 hours per day . Foetuses were examined on day 20. At 6000ppm (18 000 mg/m3) and above, maternal toxicity and slightly reduced foetal weights were reported. There were no significant treatment-related increases in the incidence of foetal malformations / variations. The NOAEC for both maternal and developmental toxicity was reported as 3500ppm (11000 mg/m3) (Nelson et al.,1989).

In a developmental neurotoxicity investigation, groups of 18 male rats (Sprague-Dawley) were exposed by inhalation, 7 hours per day for 6 weeks, to n-butanol (0, 9200, or 18 000 mg/m3) before mating with untreated females. These females were allowed to deliver pups. Separately, groups of 15 pregnant female rats were exposed from days 1 to 20 of gestation to n-butanol at 0, 9200 or 1800 mg/m3 before being allowed to deliver pups. Offspring from both groups of dams were then observed during postnatal days 10–90 for indication of developmental neurotoxicity. At 6000ppm a small number of behavioural and neurochemical measures differed from those of the control group but there was no discernable pattern of effect (Nelson et al., 1989).

Butane-1,3-diol (putative metabolite of 3-methoxybutan-1-ol, also refered to as 1,3 -butandiol)

Potential developmental and reproductive effects of this substance were evaluated in a complex 2-year, 5-generation study, with dietary incorporation of butane-1,3-diol at up to 24% (Hess et al, 1981).  A brief introduction to the experimental protocols is discussed in the fertility endpoint summary. 

Developmental study

On day 19 of pregnancy, 75% of the F2A dams in each group were given a caesarean section. The numbers of implantations, resorptions, viable and nonviable foetuses, gross abnormalities, weight and gender of foetuses were recorded. Of these F3B foetuses a third were used for soft tissue examination following Bouin’s fixation and the rest were used for skeletal examination following staining with alizarin red.

No treatment-related effects were observed in the soft tissues of the foetuses from the group exposed to 25% butane-1,3-diol. An increased incidence, of incomplete ossification of sternebrae was observed in the foetuses from the groups fed 20 or 25% butane-1,3-diol and an increased incidence of missing sternebrae was observed in foetuses from the group fed 25%. The authors suggest these findings indicate slightly delayed growth of skeletal tissue, rather than a specific developmental effect, per se, particularly as the sternebrae of one quarter of the control group were only partially ossified. In addition, clinical chemistry results revealed a significant increase in the concentration of ketone bodies in blood and urine in animals fed diets containing 20 or 25% butane-1,3-diol. Therefore, although growth rate changes were unaffected even for four consecutive generations of female animals, there is clearly significant ketosis, and hence physiological stress, associated with ingestion of synthetic diet containing very large concentrations, 20 or 25%, of test substance.

The developmental toxicity of butane-1,3-diol has been investigated to extraordinary high levels of dietary incorporation without highlighting any significant teratogenic potential for this substance.

Discussion

Although there is no developmental toxicity information on 3-methoxybutan-1-ol, there is a guideline (OECD 414) prenatal developmental toxicity study on 3 -methylbutyl acetate using the oral route and a limit dose. 3-Methoxybutan-1-ol is a putative, rapidly and extensively formed metabolite of 3 -methoxybutyl acetate. For 3 -methoxybutyl acetate 1000 mg/kg/day was established as a clear NOAEL for both maternal and developmental toxicity.

There are several studies, of varying design, available for structural analogues of 3-methoxybutan-1-ol and a putative metabolite, butan-1,3 -diol.  Data exists for 3-methyl-3-methoxy-1-butanol, a close structural analogue of 3-methoxybutan-1-ol. 3-methoxy-3-methyl-1-butanol differs only in that it has an additional methyl group. A reproduction/developmental toxicity study (OECD 421) is available for this substance using the oral route of exposure. The NOAEL was 1000 mg/kg bw/day for parents and offspring with NOAEL of 40 mg/kg bw/day males and 200 mg/kg bw/day for females based on liver and kidney weight increases (in the absence of histopathological change). 

Another structural analogue is n-butanol and a study by inhalation exposure has been considered as a read-across candidate for the developmental toxicity of 3-methoxybutan-1-ol. At 18000 mg/m³ and above maternal toxicity and slightly reduced foetal weights were reported for n-butanol but there was no effect on the incidence of foetal malformations or variations. Therefore the NOAEC for both maternal and developmental toxicity of n-butanol was considered to be 11 000 mg/m³ (Nelson et al.,1989).

3 -methoxybutan-1-ol may be eliminated from the body as a sulphate or glucuronide conjugate, or via metabolism. Metabolism of 3 -methoxybutan-1 -ol is via oxidation to 3 -methoxybutanoic acid (for which no data have been identified) or by O-demethylation to butane-1,3-diol; both pathways may be active (CSR section 5.1 for further detail).

For butane-1,3-diol there is a significant database available. This substance is incorporated at low levels into human foodstuffs and cosmetic products and a considerable reproductive and developmental database has been published. As part of a 2-year investigation of several endpoints including developmental and reproductive toxicity, a well-conducted teratology study was incorporated. As the substance was then being considered for use as a high-level dietary component, the amounts of butane-1,3-diol incorporated into rat feed were extremely large. Indeed at the highest levels of incorporation (20 and 25% in diet), when presumably the normal elimination routes for the proximal metabolite of butane-1,3-diol (3-hydroxybutanoic acid, a natural product) were exhausted, ketosis resulted. Despite this maternal ketosis (blood, urine and liver) induced by exposure to extraordinary high levels of dietary incorporation of butane-1,3-diol, no teratogenic potential was indicated for this substance.

For the potential metabolite 3-methoxybutanoic acid no data have been identified. Read-across to alkoxy derivatives of C2 carboxylic acids has been considered but it is known that for these substances small changes in chemical structure produce significant change in both the intrinsic biological activity and metabolic fate. Therefore direct read-across from these C2 acid substances to the C4 acid, 3-methoxybutan-1-ol and 3 -methoxybutyl acetate, has been considered unreliable. However experimental research has indicated that the potency of developmental effects attributed to alkoxy acids falls off sharply with increasing number of carbon atoms within the acid moiety. For example, Rawlings et al. (1985) compared the in vitro embryotoxicity of several alkoxy acids; they found that whereas 2-methoxyacetic acid (C2) was highly potent, 3-methoxypropionic acid (C3) and 4-methoxybutanoic acid (C4) were significantly less active. Additionally, in vivo studies, Carney et al.(2003) concluded that there were no developmental effects in the absence of maternal toxicity with the C3 acid, 2-methoxypropionic acid. Therefore it seems likely that as the carbon backbone of the acid is further increased from C3 to C4, (3-methoxybutanoic acid) the likelihood of developmental effects will diminish even further.

For 3-methoxybutan-1-ol and the read-across candidates discussed above a range of developmental test protocols have been reported. Without exception, no developmental toxicity or teratogenic potential has been highlighted in these studies. The evidence supports the conclusions that there is sufficient evidence to assess the developmental potential of 3-methoxybutan-1-ol and that there are no developmental effects associated with 3-methoxybutan-1-ol exposure.

Citations

Rawlings, SJ et al. (1985) The teratogenic potential of alkoxy acids in post-implantation rat embryo culture: structure-activity relationships. Toxicol. Lett., 28, 49-58.

Justification for classification or non-classification

According to criteria in Regulation (EC) No.1272/2008, the substance is not classified for reproductive or developmental effects.The weight of evidence assessment indicates there are no developmental or reproductive effects associated with 3 -methoxybutan-1-ol exposure.