2-methoxy-2-methylbutane

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Link to relevant study records

Reference

Endpoint:

two-generation reproductive toxicity

Remarks:

based on test type (migrated information)

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP-compliant guideline study, no restrictions, fully adequate for assessment.

Qualifier:

according to guideline

Guideline:

other: U.S. EPA Toxic Substances Control Act (TSCA) testing guidelines (US EPA, 1985), US EPA Office of Prevention, Pesticides and Toxic Substances (OPPTS) draft guidelines (US EPA, 1996)

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories
- Age at study initiation: 7 weeks
- Weight at study initiation: 175-225 gram
- Housing: individual
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature : 65-75°F
- Humidity (%): 40-70
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation

Type of inhalation exposure (if applicable):

whole body

Vehicle:

unchanged (no vehicle)

Details on exposure:

TAME exposure concentrations were generated by metering liquid TAME from a stainless steel reservoir into a J-tube generator with an FMI pump. The FMI pump was calibrated and set to the nominal flow rate expected for the target exposure concentration. Nitrogen flowed up through the J-tube at a flow rate of approximately 20 L/min. The TAME was pumped into the upper portion of the J-tube and allowed to flow downward through glass beads, counter-current to the nitrogen flow. A heating jacket warmed the J-tube to approximately 40 to 60 oC. The heat and the increased surface area from the glass beads facilitated the vaporization of the TAME. A sight gauge at the bottom of the J-tube verified total vaporization of the TAME. The vaporized TAME was carried in the nitrogen stream from the top of the J-tube into a 'T" in the stainless steel, HEPA-filtered air inlet to the inhalation chambers. The "T" was located approximately three feet upstream of the chamber. The TAME vapor flowed into the "T" and counter-current to the HEPA-filtered chamber air flow to facilitate mixing of the TAME vapor with dilution air. The total chamber air flow through each chamber was maintained at approximately 220-250 L/min.
Four H-1000 inhalation exposure chambers (Lab Products, Maywood, NJ) were used for these exposures. One H-1000 was used for each target exposure concentration (0, 250, 1500 or 3000 ppm). Each H-1000 was located inside one eight cubic meter Hinners-style stainless steel and class inhalation exposure chamber. The H-1000 is constructed of stainless steel and glass with silicon seals on the doors.

Details on mating procedure:

Animals were mated randomly within treatment groups to produce F1-generation. F1- litters were culled to 10 pups on post-natal day (PND) 4 and weaned on PND 28. 30 animals/sex/dose were selected as parents of the F2-generation. The selected F1-weanlings were exposed 10 weeks with acquisition of vaginal patency and the assessment of preputial separation in males and vaginal cytology evaluated during the last three weeks. Results from these measurements triggered the measurement of anogenital distance in F2 offspring at birth. F1 animals were mated in a two-week mating period following the procedure used with F0 animals. At weaning 30 animals/sex/dose were selected for post-wean retention with no exposure through acquisition of vaginal patency in females and preputial separation in males.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The concentration of TAME inside the exposure chamber was confirmed using IR analysis (MIRAN 1A).

Duration of treatment / exposure:

Premating exposure period:
males: 5 days/week for 10 weeks (6 hours/day, 5 days/week)
females: 5 days/week for 10 weeks (6 hours/day, 5 d/week)

Exposure period:
males: mating, postmating (30 days)
frequency: 7 days/week during mating, then returning to a 5 days/week schedule until necropsy.

females: mating through gestational day 19, lactation (postnatal day 5 through 28)
frequency of treatment: 6 hours/day, 7 days/week throughout mating, gestation and lactation. F0 females were necropsied on post-natal day (PND) 28.

Frequency of treatment:

See section on Duration of treatment / exposure

Remarks:

Doses / Concentrations:
250, 1500 or 3000 ppm
Basis:
other: target concentrations

Remarks:

Doses / Concentrations:
245(7), 1493(13), 2992(46) ppm (SD between brackets)
Basis:
analytical conc.

No. of animals per sex per dose:

Each exposure group had 30 animals/sex

Control animals:

yes

Details on study design:

The target exposure concentrations were 250, 1500, and 3000 ppm. The rationale for choosing these exposure concentrations was as follows. A previous developmental toxicity study in pregnant rats based on a range-finding study in pregnant rats which employed exposure concentrations of 0, 250, 1500 and 3500 ppm resulted in demonstrable maternal toxicity and developmental toxicity at 1500 and 3500 ppm, and no maternal toxicity or developmental toxicity at 250 ppm. In addition, a preliminary study on weanling rats (to model the beginning of the F1 exposure period) exposed to 3500 ppm for four days six hours per day, resulted in severe and persistent toxicity. The highest exposure concentration level, 3000 ppm, was therefore chosen to induce overt maternal and offspring toxicity, but not excessive mortality.

Parental animals: Observations and examinations:

Body weights, feed consumption and clinical signs were recorded daily.

Oestrous cyclicity (parental animals):

An andrological assessment was conducted to all parental males.
Vaginal cytology was evaluated for F0 females daily during the last three weeks of the 10-week prebreed exposure period.
Vaginal cytology was also performed in F1 females.

Sperm parameters (parental animals):

An andrological assessment was conducted to all parental males.
Testis weight, epididymis weight, daily sperm production, sperm count in testes, sperm count in epididymides, enumeration of cauda epididymal sperm reserve, sperm motility, sperm morphology

Litter observations:

Up to three F1 weanlings/sex/litter were chosen for necropsy.
Up to three F2 weanlings/sex/litter were selected for necropsy with selected organ weights.

Postmortem examinations (parental animals):

F0 males were submitted to necropsy and evaluation of reproductive and other selected organs (high and control animals) after the delivery period.
F0 females were submitted to necropsy and histopathology of reproductive and other selected organs of high and control dose animals.

Postmortem examinations (offspring):

Up to three F1 weanlings/sex/litter were chosen for necropsy.
Up to three F2 weanlings/sex/litter were selected for necropsy with selected organ weights.

Statistics:

Statistical analysis used either the male, the female, the pregnant female or the litter as the unit of comparison. Appropriate parametric- or non-parametric tests were applied to the data after initial analysis using Bartlett's test for homogeneity of variances.

Clinical signs:

effects observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

no effects observed

Other effects:

no effects observed

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

effects observed, treatment-related

Reproductive performance:

no effects observed

Systemic toxicity in adult F0 and F1
Adult systemic toxicity was present in F0 and F1 animals at 1500 and 3000 ppm. Both sexes and generations displayed ataxia and persistently reduced body weights at 3000 ppm. Body weights were reduced during gestation in F0 (GD 0-7, ~6%) and F1 (GD 0-20, ~9%) and during lactation in F0 (PND 0 – 4, 5-9%) and F1 (PND 0-14, 7-10%) at 3000 ppm. Ataxia was present in the 1500 ppm F0 animals but there were no effects on body weights or food efficiency. F1-dams had a reduction in lactation period weight gain. In necropsy, the liver weights (absolute and relative) were increased in the F0 and F1 males and less in females. In F0 males, the relative to body weight increase was at 1500 ppm 29% and 3000 ppm 33% and F0 females at 3000 ppm 24%. In F1 males, the relative liver weight increase was 22% in the 1500 ppm and 3000 ppm dose group. In F1 females, the relative liver weight increase at 3,000 ppm was 14%. The relative kidney were significantly increased in the 1500 F0 males (21%) and 3000 ppm F0 males (26%) and females (9%), while male absolute kidney weight was significantly increased at all levels (8-19%) and in females only 9% at 3000 ppm. F1 males, but not females, had increased kidney weight at 1500 ppm (18%) and 3000 ppm (22%). Relative but not absolute spleen weights were significantly increased in F1 males at 1,500 and 3000 ppm. Relative and absolute adrenal weights were significantly increased at the 3000 ppm group in males and females.

Reproductive toxicity in F0 animals
In F0 and F1 males, minimal effect on gonads were noted at 3000 ppm, which was expressed as increased relative but not absolute testes weight, probably due to reduced terminal body weights in this group. The absolute prostate weight was significantly reduced at 3000 ppm for F1 males but not for F0 males. At 3000 ppm, F1, but not F0 males had reduced sperm concentrations of the epididymis. Both the 1500 ppm (3.13%) and 3000 ppm (5.49%) F0 males had an increase of abnormal sperm counts compared to the concurrent control group (0 ppm (2.26%, 250 ppm (2.40%)), but not when compared to the historical values (range: 2.0 ± 0.3% to 6.1 ± 3.3%). The F1 males also had an increasing trend of abnormal sperm counts, although none of the figures was statistically significantly over the concurrent control group (0 ppm: 2.5%, 250 ppm: 2.7%, 1500 ppm: 3.9%, 3000 ppm: 3.5%). The treatment had no effect on mating or survival indices, on absolute testes weight, on absolute or relative epididymides or seminal vesicles with coagulating gland, on relative prostate weight, sperm motility, or sperm production. There were no treatment-related findings in the histopathology.

In females, no treatment-related change was noted in the vaginal cyclicity, or oestrous cycle length. Gestational length was significantly longer in the F1 1500 ppm females but this was probably of no toxicological significance, because the effect was not seen in the F1-3000 ppm group or the F0 females. No significant changes were seen on the number implantation sites per litter, on prenatal mortality index or the number of live or dead pups on PND 0.

Dose descriptor:

NOAEC

Remarks:

parental toxicity

Effect level:

250 ppm

Basis for effect level:

other: Changes in liver adrenal and kidney weights and reduction in body weight, general signs of toxicity to central nervous system, such as ataxia

Dose descriptor:

NOAEC

Remarks:

effects on reproductive toxicity

Effect level:

3 000 ppm

Basis for effect level:

other: no toxicological relevant effects were observed

Remarks on result:

other: Generation not specified (migrated information)

Clinical signs:

no effects observed

Mortality / viability:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Sexual maturation:

effects observed, treatment-related

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

no effects observed

Histopathological findings:

no effects observed

Reproductive toxicity in F0 and F1
In the offspring, the acquisition of preputial separation was significantly delayed in the 1500 and 3000 ppm F1 males and F2 males at 3000 ppm. Acquisition of vaginal patency was significantly delayed at 3000 ppm in F1 females and at 250 and 3000 ppm in F2 females. These effects were considered as the landmarks, which triggered the measurement of anogenital distance (AGD) in the F2 animals. The AGD was significantly decreased in both sexes of the F2 3000 ppm rats. This was accompanied and probably caused by a significant reduction (~ 8%) in body weights/litter in the F2 pups on PND 0. Although the 3000 ppm F1 body weights per litter were significantly lowered on the post-natal days 4, 7, 14, 21 and 28, the survival indices were not affected in the F1 offspring throughout lactation. The F1 1500 ppm animals had reduced litter body weights on PND 4 and 7 (females) and 14, 12 and 28. The 250 ppm F1 pup body weights per litter were reduced on PND 14, 21 and 28 (28 days, males only). At 3000 ppm, F2 offspring had reduced survival indices on PND 4 and 21 and the pup body weights were significantly reduced during lactation on PND 0, 4, 7, 14, 21 and 28. In the 1500 ppm group significantly reduced pup weights were observed on PND 14 and 21. There were no effects on F2 pups at 250 ppm. The increased offspring mortalities at 1500 and 3000 ppm were thought to have been due to the “overt toxicity and the compromised status” of the dams. The observations included lethargic or hypothermic pups with little or no milk in stomach, tail chewed off, thin fur and haematomas at various locations.

Dose descriptor:

NOAEC

Remarks:

toxicity to offspring

Generation:

F1

Effect level:

250 ppm

Basis for effect level:

other: see 'Remark'

Dose descriptor:

NOAEC

Remarks:

toxicity to offspring

Generation:

F2

Effect level:

250 ppm

Basis for effect level:

other: see effects on F1 generation

Reproductive effects observed:

not specified

Endocrine disruption potential

The authors state that TAME changes seen in the reproductive landmarks, the acquisition of preputial separation and vaginal patency cannot be interpreted as endocrine disruption activity. This is because if TAME would have androgenic or anti-androgenic or estrogenic or anti-estrogenic activity, depending on the activity and sex in question one of the landmarks would have been delayed while the other one was accelerated or not affected. For example, if TAME was an estrogenic antagonist, vaginal patency would be delayed and preputial separation unchanged. The same is true for the reductions seen in the anogenital distance. If TAME was, e.g., an anti-androgen, males only would be expected to exhibit shorter AGD, whereas females would be unaffected or have a longer AGD. Neither was true in this case. On the other hand, if the preputial separation and AGD were earlier dismissed as evidence for reproductive toxicity by the authors because the differences were said to have been caused by significantly different pup weights on PND 0, then their use as negative evidence for endocrine disruption is questionable.

Effect on fertility: via inhalation route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

12 720 mg/m³

Species:

rat

Additional information

A well-conducted two-generation reproductive toxicity study with rats is available (CIIT, 1998). In that study, statistically significant changes in abnormal sperm counts were reported at 1500 ppm and 3000 ppm. These changes were however within the historical controls. Moreover they did not affect the reproductive parameters. Therefore the NOAEC for effects on fertility is set to 3000 ppm (12720 mg/m³). The NOAEC for parental toxicity was 250 ppm (1060 mg/m³). Toxicity to offspring was seen at 1500 ppm leading to a NOAEC of 250 ppm (1060 mg/m³) for developmental effects.

Short description of key information:
TAME did not cause effects on fertility. The NOAEC for parental toxicity is 250 ppm (1060 mg/m3), for effects on fertility 3000 ppm (12720 mg/m3, the highest concentration tested) and for offspring toxicity 250 ppm (1060 mg/m3).

Effects on developmental toxicity

Description of key information

In the rat developmental toxicity study weight reductions were observed in litters at 3500 ppm (14840 mg/m3) (NOAEC for developmental toxicity: 1500 ppm (6360 mg/m3), maternal NOAEC: 250 ppm (1060 mg/m3)).
Toxicity to offspring in the 2-generation study with rats (NOAEC of 250 ppm (1060 mg/m3)) was also observed at concentrations at which also maternal toxicity was observed (maternal NOAEC: 250 ppm (1060 mg/m3)).
In mice, malformations (cleft palate) at 1500 ppm and 3500 ppm (NOAEC of 250 ppm (1060 mg/m3)) were observed. There was clear maternal toxicity in the high dose animals (mice: 3500 ppm; rats: 1500 and 3000 ppm), while the signs of toxicity were less obvious in the intermediate dose for mice (1500 ppm).

Link to relevant study records

Reference

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP-compliant guideline study, no restrictions, fully adequate for assessment.

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.3700 (Prenatal Developmental Toxicity Study)

Version / remarks:

Current study predates the guideline, EPA OPPTS draft testing guidelines 1995b (August 11) were used.

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles river
- Age at study initiation: 9-11 weeks
- Weight at study initiation: 200-275 gram
- Housing: males singly, non-mated females: group housed (maximum 3 per cage), mated females housed individually
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature : 65-75°F
- Humidity (%): 40-70
- Air changes (per hr): 12-15
- Photoperiod (hrs dark / hrs light):12/12

Route of administration:

inhalation

Type of inhalation exposure (if applicable):

whole body

Vehicle:

unchanged (no vehicle)

Details on exposure:

TAME exposure concentrations were generated by metering liquid TAME from a stainless steel reservoir into a J-tube generator with an FMI pump. The FMI pump was calibrated and set to the nominal flow rate expected for the target exposure concentration. Nitrogen flowed up through the J-tube at a flow rate of approximately 20 L/min. The TAME was pumped into the upper portion of the J-tube and allowed to flow downward through glass beads, counter-current to the nitrogen flow. A heating jacket warmed the J-tube to approximately 120 to 150 oC. The heat and the increased surface area from the glass beads facilitated the vaporization of the TAME. A sight gauge at the bottom of the J-tube verified total vaporization of the TAME. The vaporized TAME was carried in the nitrogen stream from the top of the J-tube into a 'T" in the 2 inch stainless steel, HEPA-filtered air inlet to the inhalation chambers. The "T" was located approximately three feet upstream of the chamber. The TAME vapor flowed into the "T" and counter-current to the HEPA-filtered chamber air flow to facilitate mixing of the TAME vapor with dilution air. The total chamber air flow through each chamber was maintained at approximately 220 L/min.
Four H-1000 inhalation exposure chambers (Lab Products, Maywood, NJ) were used for these exposures. One H-1000 was used for each target exposure concentration (0, 250, 1500 or 3500 ppm). Each H-1000 was located inside one eight cubic meter Hinners-style stainless steel and class inhalation exposure chamber. The H-1000 is constructed of stainless steel and glass with silicon seals on the doors.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

IR analysis (MIRAN 1A) was used to confirm the exposure concentration.

Details on mating procedure:

For breeding, individual females were placed in the home cage of singly-housed males (i.e., one male and one female). On the following morning and each morning thereafter, the females were examined for the presence of vaginal sperm and/or vaginal or dropped copulation plug. The days on which sperm were found were designated as gestational day (GD) 0. Sperm-positive females were individually housed until scheduled sacrifice on GD 20. Sperm negative females were retained in the same male's cage and checked for sperm on successive mornings until insemination occurred or the treatment groups were filled, whichever came first. When all treatment groups were filled, remaining sperm-negative females were euthanized by carbon dioxide asphyxiation and discarded, or transferred to other projects, according to CllT Standard Operating Procedures, with documentation of the fate of all animals in the study records.

Duration of treatment / exposure:

The female animals were exposed through the gestation days (GD) 6 to 19, resulting in 14 days of exposure.

Frequency of treatment:

daily, 6 hours/day

Remarks:

Doses / Concentrations:
250, 1500, 3500 ppm
Basis:
other: target concentrations

Remarks:

Doses / Concentrations:
246(5), 1532(45) and 3500(42) ppm (mean, SD in brackets) 
Basis:
analytical conc.

No. of animals per sex per dose:

Twenty-five sperm-positive female rats per group were exposed for 6 hours/day.

Control animals:

yes

Details on study design:

The target exposure concentrations were 250, 1500, and 3500 ppm. The rationale for choosing these exposure concentrations was based on a range-finding study in pregnant rats which employed exposure concentrations of O, 1000, 4000 and 7000 ppm. With a small number of dams per group, 7000 ppm resulted in excessive maternal mortality, 4000 ppm resulted in demonstrable maternal toxicity and developmental toxicity, and 1000 pprn resulted in minimal maternal toxicity and no developmental toxicity. The highest exposure concentration level, 3500 ppm, was therefore chosen to induce overt maternal toxicity, but not excessive mortality.

Maternal examinations:

Clinical observations were made once daily before exposure (GD 0-5) and on the exposure days before and after the daily exposure. Maternal feed consumption was evaluated on gestation days 0-6, 6-9, 9-12, 12-15, and 18-20.

Ovaries and uterine content:

Animals were killed 1-1½ days before parturition and uteri were examined for implantation sites. The body, liver, and uterus of each sperm-positive female were weighed, ovarian corpora lutea and uterine contents (implantation sites, resorptions, dead and live foetuses) were recorded.

Fetal examinations:

Live foetuses were sexed and weighed and examined for external abnormalities, including cleft palate. Approximately half of the live foetuses per litter were examined for visceral malformations and had their sex confirmed. All foetal carcasses were eviscerated, with sex determined internally in those foetuses that did not go though visceral examination, macerated and stained for examination of skeletal malformations and variations.

Statistics:

Statistical analysis used either the pregnant female or the litter as the unit of comparison. Appropriate parametric- or non parametric tests were applied to the data after initial analysis using 's test for homogeneity of variances.

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
Maternal toxicity
No dams died aborted or delivered early. The numbers of litters (and foetuses) evaluated were 23 (330) at 0 ppm, 24 (354) at 250 ppm, 24 (349) at 1,500 ppm and 21 (298) at 3500 ppm. Maternal body weight was significantly reduced only at 3500 ppm on GD 12, 15, 18 and 20. Maternal weight gain was significantly reduced at 1500 and 3500 ppm for GD 6-9 and at 3500 ppm for GD 6-20. Maternal absolute liver weights were equivalent across the groups, but liver weight relative to sacrificed body weight was increased in the 3500 ppm group. At 3500 ppm clinical signs included those typical to TAME from other experiments such as ataxia, lethargy, slow respiration and gasping and clinical weight loss (≥ 5 g within a weigh period). Most of these signs were noted during the first ten days starting exposure. The dams of the 1500 ppm group exhibited also lethargy (one each on GD 6 and 7) and piloerection (GD 15). Maternal feed consumption for GD 0-6 prior to the exposure period was equivalent
across all groups (as g/day or g/kg/day). Maternal feed consumption in g/day was significantly reduced at 3500 ppm for GD 6-9, 9-12, 12-15, 15-18, 18-20, 6-20 (exposure period) and GD 0-20 (gestation period). At 1500 ppm, feed consumption was significantly reduced only for GD 9-12. When the data were expressed as g/kg/day, maternal feed consumption at 3500 ppm was reduced for GD 6-9, 9-12, and 6-20. At 1500 ppm, feed consumption as g/kg/day was significantly reduced only for GD 6-9. There were no effects of treatment on maternal feed consumption at 250 ppm.

Dose descriptor:

NOAEC

Effect level:

250 ppm

Basis for effect level:

other: maternal toxicity

Dose descriptor:

NOAEC

Effect level:

1 500 ppm

Basis for effect level:

other: developmental toxicity

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:yes

Details on embryotoxic / teratogenic effects:
Developmental toxicity
There were no significant changes in the gestational parameters including number of ovarian corpora lutea, total number of uterine implantation sites, pre- or post-implantation loss, number of live foetuses per litter and sex ratio per litter (% male foetuses). Pregnancy rates were high and approximately equivalent across all groups (87.5-96.0%). Foetal body weight was significantly reduced (approximately 10%) in the 3500 ppm dose group, when calculated for all foetuses or males and females separated. There was no treatment-related increase of visceral, skeletal or total malformations or variations by litter or by foetus per litter.

Abnormalities:

not specified

Developmental effects observed:

not specified

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

6 360 mg/m³

Species:

rat

Additional information

In the developmental toxicity study with rats (CIIT, 1997a), maternal toxicity was present at 1500 and 3500 ppm and it was manifested as reduction of body weight, reduction of weight gain and various clinical signs, especially at the top dose group. The NOAEC for maternal toxicity is therefore set at 250 ppm (1060 mg/m³). Based on the weight reductions seen in the litters at 3500 ppm and the absence of embryo-foetal effects at 250 or 1500 ppm doses, 1500 ppm (6360 mg/m³) is chosen as the NOAEC for developmental toxicity in Sprague-Dawley rats.

Regarding the two-generation reproductive toxicity study with rats, toxicity to offspring was seen at 1500 ppm leading to a NOAEC of 250 ppm (1060 mg/m³) for developmental effects. The NOAEC for parental toxicity was 250 ppm (1060 mg/m³) in this study.

 

In the developmental toxicity study with mice (CIIT, 1997b), malformations (cleft palate) were observed at 1500 and 3500 ppm. Regarding maternal toxicity, four dams died during the first four days of exposure in the 3500 ppm dose group. At 1500 and 3500 ppm, maternal absolute and relative liver weights were significantly increased. The toxicity noted at 1500 ppm (11% relative liver weight increase) is likely to represent a slight adaptation of the liver rather than representing significant maternal toxicity, which would account for the foetal malformations. Based on the 90 day study, it is likely that the animals were lethargic and prostrate during exposure at 1500 ppm, which could have contributed to maternal stress. However, no clear mechanism could be attributed to cleft palate seen in mice. Nevertheless, the available data are not considered sufficient for classification of TAME for developmental toxicity. The NOAEC for developmental effects is set to 250 ppm (1060 mg/m³) based on the malformations (cleft palate) seen at 1500 (6360) and at a higher incidence at 3500 ppm (14840 mg/m³) in mice.

There is no developmental toxicity study available for TAME in non-rodent species. However, in the read across substance methyl tertiary butyl ether (see separate read across justification attached to chapter 13 of IUCLID dossier) no developmental toxicity was demonstrated in rabbits up to a concentration of 8000 ppm (28560 mg/m3). At this concentration maternal toxicity was observed (Bevan et al., 1997).

Overall, the lowest NOAECs for developmental toxicity are comparable with the NOAEC for repeated dose toxicity (250 ppm (1060 mg/m3)) which is taken as starting point for the DNEL derivation.

Justification for classification or non-classification

In accordance with the EU Classification Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008, classification is not necessary for reproductive and developmental toxicity.