2-methylpropan-2-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

1 000 mg/kg bw/day

Species:

rat

Additional information

The reproductive toxicity of tertiary butyl alcohol was investigated in an enhanced guideline reproductive/developmental screening study. In this study, Sprague-Dawley rats (12/dose/sex) were administered, via oral gavage, 0, 64, 160, 400 or 1000 mg/kg bw/day tertiary butyl alcohol for 4 weeks pre-mating and then until termination: week 9 (males) and PND 21 (females). Selected pups were then administered tertiary butyl alcohol directly for a period of seven days before termination on PND 27.

At 1000 mg/kg bw/day, F0 toxicity manifested itself as clinical signs (unresponsiveness/ lethargy, ataxia, increased vocalisation and rapid breathing). Body weight was mildly affected in males (non-significant decreases in male body weight from week one) and during the later stages of gestation in females. The only effect on feed consumption was a 15 % reduction in females over the first two weeks of lactation. During lactation a large increase in female body weight gain was observed. The significance of this finding is unknown. Increases in both liver and kidney weight were observed in males. At 400 mg/kg bw/day, lower incidences of clinical signs (as compared to the high dose) were observed in females, although only transiently (weeks 2-4). Kidney weight was increased in males of this dose level and was the only effect observed at 160 and 64 mg/kg bw/day. This increase was not statistically significant at the lowest dose and, therefore, is not considered adverse.

There was no effect on mating performance or number of pregnancies observed in any treatment group. A slight effect on gestation length was observed; with half the females from the top dose group and almost half the females in the mid dose with a gestation length greater than 22 (all but one was a shift to 23 days). The shift was reported to be within the normal range (21-23 days, although with a distinct node of 22) and is therefore considered a chance finding.

In the F1 generation, there was no effect on the number of implantations per pregnancy; however, significant pup mortality was observed at 1000 mg/kg bw/day. Six out of 153 pups were stillborn with a further 32 pups dying between days 1-4 (the majority were found dead on day 1). The deaths include one total litter loss. The incidence of still born deaths is likely to be within the normal variation for this type of effect and is therefore not considered treatment related. The deaths observed post-parturition were only observed in the presence of maternal toxicity (unresponsiveness/lethargy and ataxia) and are considered likely to be a secondary consequence of this toxicity and not a direct effect of tertiary butyl alcohol.

In addition to the reduction in pup survival, pup bodyweight gain was also affected in pups treated with 1000 mg/kg bw/day. Direct treatment of the pups for 7 days from PND 21 had no further effect on the pups.

No treatment related effects were noted at any other dose.

The parental NOAEL was 64 mg/kg bw/day based on increased kidney weight in males. The NOAEL for this study for reproductive toxicity is 1000 mg/kg bw/day, the highest dose tested. The NOAEL for this study for offspring effects is 400 mg/kg bw/day based on increased pup mortality (mostly post-natal) at the top dose.

Data from a two-generation reproductive toxicity study with methyl tertiary butyl ether (Bevan, et al., 1997) was also used to evaluate the potential for tertiary butyl alcohol to cause reproductive toxicity. Methyl tertiary butyl ether is rapidly and irreversibly metabolized to tertiary butyl alcohol and significant blood levels of tertiary butyl alcohol can be found following methyl tertiary butyl ether exposures. The basis for using methyl tertiary butyl ether data is further explained in the accompanying “Read-Across” document included within Section 5.1.1.

Methyl tertiary butyl ether and tertiary butyl alcohol have similar properties of toxicity including central nervous system effects and decreases in body weight or body weight gain at high exposure concentrations. In terms of reproductive toxicity, neither chemical caused any effect on an measures of fertility or reproductive success, in either male or female rats. In terms of effects on the offspring, both chemicals cause an increased incidence of postnatal death in pups born to dams receiving these chemicals. The increase in postnatal deaths was linked to maternal toxicity and reduced care of the newborn pups. The severity of the increase in postnatal deaths in more apparent in the tertiary butyl alcohol study as the dams were receiving the chemical during the days immediately post-parturition while the methyl tertiary butyl ether dams and litters were less affected as the inhalation exposures were (necessarily) discontinued during the period of parturition and the first four days of lactation. As described in the “Read-Across” document, the Cmax micromolar concentrations of tertiary butyl alcohol are similar between these two studies and the NOEC of 400 ppm methyl tertiary butyl ether is expected to be the same NOEC for tertiary butyl alcohol, with similar effects being reported in terms of effects on fertility and offspring.

Short description of key information:

No effects on fertility were noted in a screening study conducted with tertiary butyl alcohol or in a two-generation reproductive toxicity study with methyl tertiary butyl ether where significant blood levels of tertiary butyl alcohol would be expected throughout the treatment period. Use of this read-across data is further explained in the “Read-Across” document found in Section 5.1.1. In addition, no effects of concern were noted in either the tertiary butyl alcohol screening study or the methyl tertiary butyl ether toxicity study that would warrant further investigation.

Effects on developmental toxicity

Description of key information

Information on developmental toxicity for tertiary butyl alcohol is available from an oral screening study in rats; a published developmental toxicity study (similar to guideline) in the rat conducted via the inhalation route and two non-standard published dietary studies in mice. No malformations were observed in the only good quality study in rat indicating tertiary butyl alcohol is not developmentally toxic. At the top dose in the screening study, 6 pups were stillborn (compared to 2 in the control) and a further 32 pups died by day 4. At this dose level, maternal toxicity was evident (ataxia, sedation and bodyweight reduction during gestation).  It is likely that the deaths observed between days 1-4 may be due to neglect by the dams rather than a direct effect of tertiary butyl alcohol. Reduced fetal weights were also observed at all doses; the extent of the reduction was considered adverse in the top two doses. The available studies in mice and  are not considered of sufficient quality to provide any useful information on the developmental toxicity of tertiary butyl alcohol. Overall, tertiary butyl alcohol does not appear to be developmentally toxic.

Effect on developmental toxicity: via oral route

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

400 mg/kg bw/day

Species:

rat

Additional information

Rats

Oral

No standard guideline oral developmental studies are available for tertiary butyl alcohol. Information on developmental toxicity is available from an oral reproductive/developmental toxicity screening study conducted on tertiary butyl alcohol. Moderate to severe maternal toxicity was noted at the 1000 mg/kg bw/day dose level with mild toxicity (CNS signs) noted in the dams from the 400 mg/kg bw/day group. No effects were noted in the dams from the 160 mg/kg bw/day group. Evidence of developmental toxicity was restricted to the 1000 mg/kg bw/day group and included increased number of dead pups at birth and decreased litter size. The NOAEL for maternal toxicity was 160 mg/kg bw/day and the NOAEL for developmental toxicity was 400 mg/kg bw/day.

Inhalation

The developmental toxicity of tertiary butyl alcohol was investigated via the inhalation route (whole body) in a study considered to be similar to guideline (Nelson et al, 1989). Sprague-Dawley rats (15 control and 18 treated/group) were exposed 7 hours/day between days 1-19 to 5000, 3500 or 2200 ppm tertiary butyl alcohol. The equivalent mg/kg bw/day values have been estimated using the conversion equation in Appendix 1 of OECD guidance document 39 (temp was 24 ºC); a value of 0.34 m3/kg bw calculated for 7 hour exposure based on the information in table 8.2 of Chapter 8 of ECHA’s guidance; and an absorption value of 60 % for tertiary butyl alcohol. The resulting values were 1239, 2169 and 3098 mg/kg bw/day for the 2000, 3500 and 5000 ppm groups, respectively. These exposures were therefore higher than the maximum dose recommended by current OECD guidelines (1000 mg/kg bw/day).

At the top exposure concentration, in dams, body weight gain and feed consumption was lower compared to the controls. Clinical signs included unsteady gait and impaired locomotor activity in the top two tertiary butyl alcohol concentrations, whereas unsteady gait was observed at the lowest dose level. In fetuses, body weight gain was reduced in all tertiary butyl alcohol concentrations (≥ 9 %) compared to controls. According to the publication there was a slight increase in the number of “skeletal malformations” at the top exposure concentration. The vast majority of these “malformations” were rudimentary cervical ribs, a finding commonly considered a skeletal variation. There were also an increased number of skeletal variations (top two concentrations) and visceral variations (top concentration only) reported. Due to clinical signs in dams and reduced fetal weight at all tertiary butyl alcohol concentrations, a LOAEC of 2000 ppm (1239 mg/kg bw/day) is derived for both maternal and developmental toxicity.

Mice

Information is available on the developmental toxicity of tertiary butyl alcohol from two non-standard studies.

Oral

The effect of tertiary butyl alcohol on development and post-natal behaviour was investigated in a non-standard study in Swiss Webster mice (Daniel and Evans, 1982). These mice were administered with 0.5, 0.75 or 1 % tertiary butyl alcohol via a Modified Lieber and DiCarli liquid diet, that replaced both water and feed sources between days 6 to day 20. Typical use of these diets in the field of ethanol research required an acclimation period of two weeks, where the concentration of the alcohol was slowly increased. However, in this study, the feed and water were simply replaced with the liquid diets on GD6 without any acclimation period. Only 4 litters/treatment groups were used in the behavioral investigations.

Equivalent mg/kg bw/day values were estimated using the body weights of the mice provided in the paper on day 15 of gestation and default values for feed and water consumption for pregnant dams (table R.8-17 of ECHA’s guidance on the Characterisation of dose [concentration]-response for human health (http://echa.europa.eu/documents/10162/13632/information_ requirements r8_en.pdf)). The resulting dose levels were approximately 0, 2375, 3535 or 4714 mg/kg bw/day.

Maternal weight gain was adversely affected at 1 % (10 % lower than controls), the top dose. A lesser reduction in body weight was observed in the 0.75 % dose group (5 % lower than controls). A dose related reduction in litter size, number, weight and viability was observed. This is consistent with the effects observed in the rat reproductive/developmental toxicity screening study. At the top two doses (0.75 % and 1.0%) there were also behavioral effects observed in offspring (delayed righting reflex, open field performance differences, reduced roto-rod performance) suggesting that pups at these doses may be developmentally delayed, possibly as a result of the maternal toxicity observed. Given the non-standard nature of the study design, particularly the small group sizes employed, little confidence can be attributed to the findings of the study. No NOAEL has been derived for this study.

The pre-natal toxicity of tertiary butyl alcohol was investigated in a limited reported, non-guideline study in two strains of mice (CBA/J or C57BL/6J) (Faulkner et al, 1989). The study reported that oral gavage administration of 10.5 mmoles/kg bw (780 mg/kg bw), twice daily between gestation days 6 to 18, led to an increased number of resorptions and a decrease in fetal viability. No information on the dams was provided so it is not possible to assess maternal toxicity. Although developmental effects are reported, the small group sizes, the very high dose levels (1560 mg/kg bw administered in total each day), the limited scope of the study and limited reporting indicate little confidence can be attributed to the results. No NOAEL/LOAEL was derived

Justification for classification or non-classification

No adverse effects on fertility were observed in an rat reproductive screening study conducted up to doses of 1000 mg/kg bw/day tertiary butyl alcohol. With regards to developmental effects, information from a good quality study for tertiary butyl alcohol did not show any developmental toxicity. No classification for reproductive toxicity is warranted.