2-methylbut-2-ene

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

No additional data

Link to relevant study records

Reference

Endpoint:

fertility, other

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other: GLP compliant, guideline study, available as unpublished report, no restrictions, fully adequate for assessment

Qualifier:

according to guideline

Guideline:

OECD Guideline 422 (Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Species:

rat

Strain:

other: Crl:CD®(SD)IGS BR

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River (UK) Ltd., Margate, Kent, UK
- Age at study initiation: Approximately 8-9 weeks
- Weight at study initiation: 252-314 g (males), 175-240 g (females)
- Housing: 1 male:1 female during pairing; individually (females, reproductive phase)
- Diet: Pelleted UAR VRF1 certified diet ad libitum except during exposure
- Water: ad libitum
- Acclimation period: 16 days

ENVIRONMENTAL CONDITIONS
- Temperature: 19-25°C
- Humidity: 40-70%
- Air changes (per hr): Each animal room was kept at positive pressure with respect to the outside by its own supply of filtered fresh air, which was passed to atmosphere and not re-circulated.
- Photoperiod: 12 hrs dark / 12 hrs light

IN-LIFE DATES: From: 28 September 2001 To: 18 April 2002 (pathology completed)

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

other: air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: stainless steel and glass construction and consisted of a cuboidal body fitted with a pyramidal base and top. The internal volume of each chamber was approximately 0.75 m. At the apex of the upper pyramidal figure was the tangentially mounted air duct. Immediately below this was a perforated canister, which ensured equal distribution of the test atmosphere within the chamber.
- Method of holding animals in test chamber: Exposure cages constructed of stainless steel mesh were suspended on a framework arranged on 4 levels. Each level was able to hold four cages, with each cage capable of housing 4 rats individually.
- Source and rate of air: For all groups exposed to 2-methyl-2-butene, the vapour/air mixture produced in the vapour generators was passed into the base of the secondary dilution vessel. A further supply of clean and dry air was supplied to Groups 2 and 3 to ensure a total chamber airflow of approximately 150 L/minute. The air supply for Group 4 was provided solely by the vapour generation system. The control group was exposed using a similar system to that used for the test groups, but received compressed air only at a rate of approximately 150 L/minute.
- System of generating particulates/aerosols: The vapour generation system for each of the test groups was supplied from individual reservoirs of liquid 2-methyl-2-butene maintained at pressure. The top of each reservoir was fitted with a central, "0" - ring sealed filler cap, a system to allow pressurisation and release of the helium head pressure and a safety pressure release valve set to operate at above the study operating pressure. Except during the filling procedure, 2-methyl-2-butene in the reservoirs was maintained under a helium pressure of 10 psi.
- Temperature, humidity, pressure in air chamber: Wet and dry bulb temperatures and relative humidity were recorded at approximately 30-minute intervals throughout each exposure.
- Air flow rate: The volume flow of air to the exposure chambers was measured using calibrated flow meters and also checked approximately every 30 minutes
- Treatment of exhaust air: The chamber air extract was vented to atmosphere via an exhaust stack.

TEST ATMOSPHERE
- Brief description of analytical method used: Gas chromatography
- Chamber atmosphere was sampled in sequence from each of the four exposure chambers (Chambers 4 - 1 sampled sequentially) and from one point within each chamber. Air from each chamber was continually drawn through a transfer line, which was therefore equilibrated with the mean concentration from each chamber. When not being sampled, these transfer lines were pumped to waste.
Every six minutes, air from the transfer lines was switched to the injection loop of the gas chromatograph for automated analysis and data processing.

Details on mating procedure:

- M/F ratio per cage: 1:1
- Proof of pregnancy: sperm in vaginal smear, referred to as day 0 of pregnancy
- After successful mating each pregnant female was caged individually in solid polypropylene cage with bedding material

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The study mean analysed concentrations of 2-methyl-2-butene over the duration of the study were 584, 2026 and 7097 ppm. These levels were in good agreement with the target exposure levels.

Duration of treatment / exposure:

Over a 2-week pre-mating period, throughout mating and through to Day 19 of gestation. The females were allowed to litter and rear their offspring to Day 4 of lactation.

Frequency of treatment:

6 hours/day , daily

Remarks:

Doses / Concentrations:
0, 580, 2000 or 7000 ppm
Basis:
nominal conc.

Remarks:

Doses / Concentrations:
0, 1665, 5740 or 20090 mg/m3
Basis:
nominal conc.

Remarks:

Doses / Concentrations:
0, 584, 2026 or 7097 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

12

Control animals:

yes, concurrent no treatment

Parental animals: Observations and examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: At least twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Detailed observations were made daily, on the days of exposure, as follows:
Pre exposure observations; Observations during exposure; Observations within ½ to 1 hour of return to home cage.
During the daily exposure, obvious signs were recorded as a group response. Due to the type of exposure system used, the ability to observe individual animals during the exposures was severely restricted.
A more detailed weekly physical examination was performed on each animal to monitor general health.

BODY WEIGHT: Yes
- Time schedule for examinations: The weight of each rat was recorded on the day that treatment commenced (Week 0), then weekly to Week 2, and then on Days 0, 7, 14 and 20 after mating, and Days 1 and 4 of lactation.
During the exposure period, bodyweights were recorded before the daily exposure.

FOOD CONSUMPTION:
- Food consumption was recorded weekly to Week 2, then between Days 0-6, 7-13, and 14-19 of gestation, and Days 1 and 4 of lactation.

Oestrous cyclicity (parental animals):

Dry vaginal smears were taken from all reproductive females for 10 days before pairing in order to assess the regularity and duration of oestrous cycles.
Wet vaginal smears were taken from all females following pairing until evidence of mating was confirmed

Sperm parameters (parental animals):

Histopathological examinations of testes was sufficient to enable any changes with regard to the stage in the spermatogenic cycle and cell integrity to be evaluated.

Litter observations:

- Litter observations: All offspring were examined approximately 24 hours after birth (Day 1) and the number of offspring born (live and dead) were recorded. Live offspring were individually identified within each litter by toe tattoo and individual bodyweight, sex and any clinical observations were recorded.
- Litters were subsequently observed daily for evidence of abnormal appearance or behaviour of the offspring. Daily records were maintained of mortality and consequent changes in litter size. Wherever possible, any offspring found dead were preserved in industrial methylated spirit prior to an external examination.
- The offspring were sexed at Days 1 and 4 of lactation.
- The offspring were weighed individually on Days 1 and 4 of age.
- Sacrifice and pathology

Postmortem examinations (parental animals):

GROSS PATHOLOGY: Yes
- Reproductive females and their litters were killed on Day 4 of lactation. Any reproductive females failing to mate were killed approximately 14 days after the last day of pairing or day of mating.
All animals were killed by intraperitoneal injection of sodium pentobarbitone, followed by exsanguination for adults.

ORGAN WEIGHTS
- The following organs, taken from each reproductive phase female, were dissected free of adjacent fat and other contiguous tissue and the weights recorded: brain, kidneys, liver, lungs and bronchi.
- Bilateral organs were weighed together.

HISTOPATHOLOGY: Yes
- No microscopic examinations were performed on tissues from reproductive phase animals.

Postmortem examinations (offspring):

Offspring, both scheduled and unscheduled, were subjected to a macroscopic external examination then discarded.

Statistics:

All statistical analyses were carried out separately for males and females.
Data relating to food consumption was analysed on a cage basis. For all other parameters, the analyses were carried out using the individual animal as the basic experimental unit. Significant differences between control and treated groups were expressed at the 5% (p<0.05) or 1% (p<0.01) level.

Reproductive indices:

Percentage mating, conception rate; and fertility index were calculated separately for males and females.

Offspring viability indices:

Mean survival indices for each group were calculated based on individual litter values.

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:

no effects observed

Other effects:

no effects observed

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

no effects observed

Reproductive performance:

no effects observed

CLINICAL SIGNS AND MORTALITY (PARENTAL ANIMALS)
- There were no unscheduled deaths. Half closed eyes was seen on Day 1 of exposure in Inter dose and High dose animals. High dose animals were seen to be less responsive to outside stimuli on Days 1 and 14 of exposure.

BODY WEIGHT AND FOOD CONSUMPTION (PARENTAL ANIMALS)
- There was a dose-related reduction in bodyweight gain in treated reproductive females over the 2 weeks prior to pairing with significance being attained for Intermediate and High dose females. Bodyweight gain of females during gestation and lactation was unaffected by treatment.

Dose descriptor:

NOAEC

Effect level:

7 000 ppm

Sex:

male/female

Basis for effect level:

other: 20,090 mg/m3

Clinical signs:

no effects observed

Mortality / viability:

no mortality observed

Body weight and weight changes:

no effects observed

Gross pathological findings:

no effects observed

Reproductive effects observed:

not specified

There were no treatment-related effects on oestrous cycles or pre-coital interval. Mating performance and fertility were unaffected by treatment, with all but one male and female pairing resulting in a viable pregnancy. The gestation length was similar in all groups and parturition was unaffected by treatment. There were no effects on implantation counts or resultant litter size at birth and Day 4. Post implantation loss and pup survival was unaffected by treatment. Pup bodyweight was not adversely affected. There were no effects on macroscopic examination of pups at Day 4 of lactation.

Conclusions:

It was concluded that the no effect level of 2-methyl-2-butene, for reproductive/developmental toxicity in this screening study, to rats for 4 weeks by inhalation administration, was 7000 ppm.

Executive summary:

The reproduction/developmental toxic potential of the test substance, 2-methyl-2-butene (an industrial chemical) to Crl:CD®(SD)IGS BR rats by inhalation administration was assessed. Three groups of twelve female rats were exposed over a 2-week pre-mating period, throughout mating and through to Day 19 of gestation. The females were allowed to litter and rear their offspring to Day 4 of lactation. All animals received 2-methyl-2-butene by whole body inhalation exposure at concentrations of 580, 2000 or 7000 ppm. A similarly constituted control group received air alone.

During the study, clinical condition, bodyweight, food consumption, oestrus cycles, mating performance, litter data, organ weights and macroscopic pathology were undertaken.

The study mean analysed concentrations of 2-methyl-2-butene over the duration of the study were 584, 2026 and 7097 ppm. These levels were in good agreement with the target exposure levels.

It was concluded that the no effect level of 2-methyl-2-butene, for reproductive/developmental toxicity in this screening study, to rats for 4 weeks by inhalation administration, was 7000 ppm.

Effect on fertility: via oral route

Endpoint conclusion:

no study available

Effect on fertility: via inhalation route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

20 090 mg/m³

Study duration:

subacute

Species:

rat

Quality of whole database:

Adequate information is available to characterise the effects of this substance on reproduction

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

In accordance with column 2 of REACH Annex VIII the reproductive toxicity study does not need to be conducted as the substance is known to be a genotoxic carcinogen and a germ cell mutagen and appropriate risk management measures are implemented.

In the combined repeat dose/reproductive/developmental study (OECD 422; HLS, 2004), rats were exposed to 2-methylbut-2-ene at concentrations up to 7,000 ppm (20,060 mg/m3), 6 hr/day, 7 days/week for two weeks prior to breeding, during breeding and through day 19 of gestation (HLS, 2004). During the study, clinical condition, bodyweight, food consumption, oestrus cycles, mating performance, litter data, organ weights and macroscopic pathology were undertaken. No evidence of reproductive toxicity was seen. There were no significant effects on oestrus cycle, mating performance, fertility indices or gestation length.  The NOAEC for reproductive toxicity was 7,000 ppm (20,090 mg/m3).

In addition, read-across to structurally similar compounds strengthens the conclusion that 2M2B has low potential for effects on fertility.  2-Methylpropene had no effects on male and female reproductive parameters in rats and mice in 14 week inhalation exposure studies. These repeat dosing studies included parameters such as sperm analysis, oestrus cycle analysis and histopathology (although mating was not carried out). NOAECs of 8000 ppm (18,359 mg/m3) for both rat and mouse studies were established (NTP 1998).

Further weight of evidence comes from OECD 422 studies on but-1-ene and but-2-ene. Based on these data, the NOAECs for reproductive toxicity were 8000 ppm (18,359 mg/m3) for but-1-ene and 5000 ppm (11,474 mg/m3) for 2-butene, the highest concentrations tested (HLS, 2003;TNO, 1992).

There are no studies on the effects of the 2 -methylbut-2-ene on fertility in humans.

In conclusion, the weight of evidence from 2M2B and structural analogues indicates that it is not toxic to reproduction, including fertility. The NOAEC of 7,000 ppm (20,090 mg/m3) for fertility is based on the NOAEC for 2-methylbut-2-ene in the reproductive study (HLS, 2004).

Short description of key information:
An OECD 422 combined repeated dose and reproduction/developmental toxicity study was conducted in Sprague Dawley rats. The NOAEC for reproductive toxicity was 7,000 ppm (20,090 mg/m3), the highest dose tested.

Justification for selection of Effect on fertility via inhalation route:
Available information for 2M2B and for other C4-C5 mono-olefins (butenes and 2-methylpropene) indicates a low potential to adversely affect reproduction

Effects on developmental toxicity

Description of key information

An OECD 422 combined repeated dose and reproduction/developmental toxicity study was conducted in Sprague Dawley rats. The NOAEC for developmental toxicity was 7,000 ppm (20,090 mg/m3), the highest dose tested. 

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, available as unpublished report, no restrictions, fully adequate for assessment

Qualifier:

according to guideline

Guideline:

other: OECD 422

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Species:

rat

Strain:

other: Crl:CD®(SD)IGS BR

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River (UK) Ltd., Margate, Kent, UK
- Age at study initiation: Approximately 8-9 weeks
- Weight at study initiation: 252-314 g (males), 175-240 g (females)
- Housing: 1 male:1 female during pairing; individually (females, reproductive phase)
- Diet: Pelleted UAR VRF1 certified diet ad libitum except during exposure
- Water: ad libitum
- Acclimation period: 16 days

ENVIRONMENTAL CONDITIONS
- Temperature: 19-25°C
- Humidity: 40-70%
- Air changes (per hr): Each animal room was kept at positive pressure with respect to the outside by its own supply of filtered fresh air, which was passed to atmosphere and not re-circulated
- Photoperiod: 12 hrs dark / 12 hrs light

IN-LIFE DATES: From: 28 September 2001 To: 18 April 2002 (pathology completed)

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

other: air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: stainless steel and glass construction and consisted of a cuboidal body fitted with a pyramidal base and top. The internal volume of each chamber was approximately 0.75 m. At the apex of the upper pyramidal figure was the tangentially mounted air duct. Immediately below this was a perforated canister, which ensured equal distribution of the test atmosphere within the chamber.
- Method of holding animals in test chamber: Exposure cages constructed of stainless steel mesh were suspended on a framework arranged on 4 levels. Each level was able to hold four cages, with each cage capable of housing 4 rats individually.
- Source and rate of air: For all groups exposed to 2-methyl-2-butene, the vapour/air mixture produced in the vapour generators was passed into the base of the secondary dilution vessel. A further supply of clean and dry air was supplied to Groups 2 and 3 to ensure a total chamber airflow of approximately 150 L/minute. The air supply for Group 4 was provided solely by the vapour generation system. The control group was exposed using a similar system to that used for the test groups, but received compressed air only at a rate of approximately 150 L/minute.
- System of generating particulates/aerosols: The vapour generation system for each of the test groups was supplied from individual reservoirs of liquid 2-methyl-2-butene maintained at pressure. The top of each reservoir was fitted with a central, "0" - ring sealed filler cap, a system to allow pressurisation and release of the helium head pressure and a safety pressure release valve set to operate at above the study operating pressure. Except during the filling procedure, 2-methyl-2-butene in the reservoirs was maintained under a helium pressure of 10 psi.
- Temperature, humidity, pressure in air chamber: Wet and dry bulb temperatures and relative humidity were recorded at approximately 30-minute intervals throughout each exposure.
- Air flow rate: The volume flow of air to the exposure chambers was measured using calibrated flow meters and also checked approximately every 30 minutes
- Treatment of exhaust air: The chamber air extract was vented to atmosphere via an exhaust stack.

TEST ATMOSPHERE
- Brief description of analytical method used: Gas chromatography
- Chamber atmosphere was sampled in sequence from each of the four exposure chambers (Chambers 4 - 1 sampled sequentially) and from one point within each chamber. Air from each chamber was continually drawn through a transfer line, which was therefore equilibrated with the mean concentration from each chamber. When not being sampled, these transfer lines were pumped to waste.
Every six minutes, air from the transfer lines was switched to the injection loop of the gas chromatograph for automated analysis and data processing.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The study mean analysed concentrations of 2-methyl-2-butene over the duration of the study were 584, 2026 and 7097 ppm. These levels were in good agreement with the target exposure levels.

Details on mating procedure:

- M/F ratio per cage: 1:1
- Proof of pregnancy: sperm in vaginal smear, referred to as day 0 of pregnancy
- After successful mating each pregnant female was caged individually in solid polypropylene cage with bedding material

Duration of treatment / exposure:

6 hours/day , daily

Frequency of treatment:

Over a 2-week pre-mating period, throughout mating and through to Day 19 of gestation.

Duration of test:

The females were allowed to litter and rear their offspring to Day 4 of lactation.

Remarks:

Doses / Concentrations:
0, 580, 2000 or 7000 ppm
Basis:
nominal conc.

Remarks:

Doses / Concentrations:
0, 1665, 5740 or 20090 mg/m3
Basis:
nominal conc.

Remarks:

Doses / Concentrations:
0, 584, 2026 or 7097 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

12 females

Control animals:

yes, concurrent no treatment

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: At least twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Detailed observations were made daily, on the days of exposure, as follows:
Pre exposure observations; Observations during exposure; Observations within ½ to 1 hour of return to home cage.
During the daily exposure, obvious signs were recorded as a group response. Due to the type of exposure system used, the ability to observe individual animals during the exposures was severely restricted.
A more detailed weekly physical examination was performed on each animal to monitor general health.

BODY WEIGHT: Yes
- Time schedule for examinations: The weight of each rat was recorded on the day that treatment commenced (Week 0), then weekly to Week 2, and then on Days 0, 7, 14 and 20 after mating, and Days 1 and 4 of lactation.
During the exposure period, bodyweights were recorded before the daily exposure.

FOOD CONSUMPTION:
- Food consumption was recorded weekly to Week 2, then between Days 0-6, 7-13, and 14-19 of gestation, and Days 1 and 4 of lactation.

Ovaries and uterine content:

Not applicable

Fetal examinations:

Not applicable

Statistics:

All statistical analyses were carried out separately for males and females.
Data relating to food consumption was analysed on a cage basis. For all other parameters, the analyses were carried out using the individual animal as the basic experimental unit. Significant differences between control and treated groups were expressed at the 5% (p<0.05) or 1% (p<0.01) level.

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
- There were no unscheduled deaths. Half closed eyes were seen on Day 1 of exposure in Inter dose and High dose animals. High dose animals were seen to be less responsive to outside stimuli on Days 1 and 14 of exposure.
- There was a dose-related reduction in bodyweight gain in treated females over the 2 weeks prior to pairing with significance being attained for Intermediate and High dose females. Bodyweight gain of females during gestation and lactation was unaffected by treatment.

Dose descriptor:

NOAEC

Effect level:

7 000 ppm

Basis for effect level:

other: developmental toxicity

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:no data

Abnormalities:

not specified

Developmental effects observed:

not specified

Conclusions:

It was concluded that the no effect level of 2-methyl-2-butene, for reproductive/developmental toxicity in this screening study, to rats for 4 weeks by inhalation administration, was 7000 ppm.

Executive summary:

The reproduction/developmental toxic potential of the test substance, 2-methyl-2-butene (an industrial chemical) to Crl:CD®(SD)IGS BR rats by inhalation administration was assessed. Three groups of twelve female rats were exposed over a 2-week pre-mating period, throughout mating and through to Day 19 of gestation. The females were allowed to litter and rear their offspring to Day 4 of lactation. All animals received 2-methyl-2-butene by whole body inhalation exposure at concentrations of 580, 2000 or 7000 ppm. A similarly constituted control group received air alone.

During the study, clinical condition, bodyweight, food consumption, oestrus cycles, mating performance, litter data, organ weights and macroscopic pathology were undertaken.

The study mean analysed concentrations of 2-methyl-2-butene over the duration of the study were 584, 2026 and 7097 ppm. These levels were in good agreement with the target exposure levels.

It was concluded that the no effect level of 2-methyl-2-butene, for reproductive/developmental toxicity in this screening study, to rats for 4 weeks by inhalation administration, was 7000 ppm.

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

20 090 mg/m³

Quality of whole database:

Adequate information is available to characterise the effects of this substance on foetal development

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

There are no developmental studies available for 2 -methylbut-2-ene (2M2B) that fulfil Annex IX requirements, but 2M2B is considered not toxic to development by consideration of data for 2M2B and read across to other C4 -C5 mono-olefins (butenes and 2 -methylpropene). There is sufficient weight of evidence to preclude the need for further testing (i.e. scientifically unjustified; Annex XI adaptation).

In the combined repeat dose/reproductive/developmental study (OECD 422; HLS, 2004), rats were exposed to 2-methylbut-2-ene at concentrations of up to 7,000 ppm (20,090 mg/m3), 6 hr/day, 7 days/week for two weeks prior to breeding, during breeding and through day 19 of gestation (HLS, 2004). Dams were allowed to deliver their litters, which were retained until lactation Day 4. No evidence of developmental toxicity was seen. There were no adverse effects upon survival or growth of the offspring in utero or up to day 4 of lactation.  Thus, the NOAEC for developmental toxicity is 7,000 ppm (20,090 mg/m3).

Read-across to the structurally similar compound 2-methylpropene, strengthens the conclusion that 2-methyl-2-butene has low potential for developmental toxicity. 2-Methylpropene has been tested in a rat developmental toxicity study (OECD Guideline 414) by inhalational exposure at concentrations of 500, 2000 and 8000 ppm (1147, 4589, 18,359 mg/m3). 2-Methylpropene had no effect on the females during gestation. There were also no effects on the number, growth or survival of the foetuses in utero and no effects on foetal development (determined by visceral and skeletal analysis). A NOAEC of 8000 ppm (18,359 mg/m3) (the highest concentration tested) was established for maternal toxicity and foetal toxicity (CTL, 2002).

The low developmental toxicity of 2-methylpropene is consistent with that of other members of the butene category. 2-Butene and but-1-ene also had no effect on developmental toxicity when tested in OECD Guideline 422 studies by inhalation exposure. None of these isomers produced treatment-related effects on the development of pups during the reproductive toxicity element of the studies. There were no effects on pup body weight gain or observed during macroscopic examination of pups at post mortem (HLS, 2003;TNO, 1992). The NOAECs for developmental toxicity were 8000 ppm (18,359 mg/m3) for but-1-ene and 5000ppm (11,474 mg/m3) for 2-butene (the highest concentrations tested).

There are no data on the developmental toxicity of 2M2B in humans

In conclusion, the weight of evidence from 2M2B and structural analogues indicates that it is not a developmental toxin. The NOAEC of 7000 ppm (20,090 mg/m3) for developmental toxicity is based on the NOAEC for 2M2B in the OECD 422 study (HLS, 2004).

Justification for selection of Effect on developmental toxicity: via inhalation route:
Available information for 2M2B and for other C4-C5 mono-olefins (butenes and 2-methylpropene) indicates a low potential to adversely affect foetal development

Justification for classification or non-classification

No classification of 2 -methylbut-2 -ene (2M2B) is warranted under CLP.