Methylhydrazine

Endpoint summary

Description of key information

Oral: LD50 Rat = 33 mg/kg (reported and peer-reviewed by HSDB) or 71 mg/kg (reported by www.reptox.csst.qc.ca)

Inhalation: LC50-4h values: squirrel monkey: 20 ppm, dog: 24 ppm,rhesus monkey: 40 ppm, mouse: 65 ppm, rat: 78 ppm. This range corresponds to 0.038-0.15 mg/L at 25°C, atmospheric pressure.

Dermal: LD50 Rat = 183 mg/kg and LD50 Rabbit = 93 mg/kg (both reported and peer-reviewed by HSDB)

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records

Reference

Reference 1

Endpoint:

acute toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

secondary literature

Principles of method if other than guideline:

No data

GLP compliance:

not specified

Test type:

other: not specified

Limit test:

no

Species:

mouse

Strain:

not specified

Sex:

not specified

Route of administration:

oral: gavage

Vehicle:

not specified

Dose descriptor:

LD50

Effect level:

33 mg/kg bw

Interpretation of results:

Category 2 based on GHS criteria

Reference 2

Endpoint:

acute toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

secondary literature

Principles of method if other than guideline:

No data

GLP compliance:

not specified

Test type:

other: not specified

Limit test:

no

Species:

rat

Strain:

not specified

Sex:

not specified

Route of administration:

oral: gavage

Vehicle:

not specified

Dose descriptor:

LD50

Effect level:

33 mg/kg bw

Interpretation of results:

Category 2 based on GHS criteria

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LD50

Value:

33 mg/kg bw

Acute toxicity: via inhalation route

Link to relevant study records

Reference

Reference 1

Endpoint:

acute toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP, no guideline mentionned, but similar to the applicable guideline and adequate design and coherence. Unknown purity is the only aspect with possible impact on results.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 403 (Acute Inhalation Toxicity)

Version / remarks:

not referenced but similar

GLP compliance:

no

Remarks:

prior to GLP

Test type:

standard acute method

Limit test:

no

Species:

other: see below

Strain:

other: see below

Details on test animals or test system and environmental conditions:

- Groups of 10 male Sprague-Dawley rats (125-175 g)
- Groups of 20 male ICR (Swiss) mice (17-23 g) - x2 parallel experiments
- Groups of 1 to 5 male and/or female beagle dogs, 8 to 30 months of age (7 to 13 kg)
- Groups of 1 to 5 young female squirrel monkeys (Saimiri sciurea) (560 to 680 g)
- Groups of 1 or 2 male and/or female rhesus monkeys (Macaca mulatta).
care was taken to include as much as possible the same range of body weights in each of the exposure groups.

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

other: nitrogen-air mixture

Details on inhalation exposure:

Rodents were exposed for 30-, 60-, 120-, and 240-minute periods,
dogs and squirrel monkeys for 15, 30, and 60 minutes,
and rhesus monkeys for 60 minutes only.

exposure: filtered air in Rochester Chambers; MMH was introduced under nitrogen.

Analytical verification of test atmosphere concentrations:

yes

Remarks:

by electron capture instrument measuring a MMH / trifluoroacetic acid reaction

Duration of exposure:

>= 0.25 - <= 4 h

Remarks on duration:

see above

Concentrations:

Initial analytical and toxicity experiments evidenced oxidative degradation of MMH. Therefore corrective changes were made to equipment
and methods to provide the air flow capacity, temperature, and relative humidity control necessary for conducting animal exposures to unreacted MMH.

No. of animals per sex per dose:

see above

Control animals:

yes

Details on study design:

All rodents were weighed on the day of exposure, at least 3-, 7-, and 14-day postexposure, and observed for toxic signs during exposure and for 14 days.
All dogs/monkeys were weighed on the day of the exposure; symptoms of toxic stress observed during exposure and postexposure until the animals died or were killed for pathologic examination were recorded.

Hematology and blood chemistry determinations were made before and after exposure at several intervals, on blood samples collected from the femoral vein of the rhesus monkeys and from the jugular or cephalic vein of the beagles.

Some rodents that died during or were killed following exposure were submitted for histopathologic studies of the lung, liver, kidney, heart,
and spleen after routine gross examination. All dogs/monkeys that died during or following exposure were submitted for postmortem gross and histopathologic examination.

Statistics:

The respective LC50 values and their 95% confidence limits were calculated by
- rodents: the probit method utilizing the BMD03S Computer Program
- dogs/monkeys: Thompson method of moving averages

Preliminary study:

The initial animal exposure attempts showed that MMH was a highly toxic substance that required the use of relatively low concentrations.

Sex:

male

Dose descriptor:

LC50

Effect level:

65 ppm

Based on:

test mat.

95% CL:

63 - 66

Exp. duration:

4 h

Remarks on result:

other: mouse

Sex:

male

Dose descriptor:

LC50

Effect level:

78 ppm

Based on:

test mat.

95% CL:

71 - 86

Exp. duration:

4 h

Remarks on result:

other: rat

Sex:

female

Dose descriptor:

LC50

Effect level:

82 ppm

Based on:

test mat.

95% CL:

67 - 101

Exp. duration:

1 h

Remarks on result:

other: squirrel monkey

Sex:

male/female

Dose descriptor:

LC50

Effect level:

96 ppm

Based on:

test mat.

Exp. duration:

1 h

Remarks on result:

other: dog

Sex:

male/female

Dose descriptor:

LC50

Effect level:

162 ppm

Based on:

test mat.

95% CL:

118 - 222

Exp. duration:

1 h

Remarks on result:

other: rhesus monkey

Sex:

male/female

Dose descriptor:

other: LOAEC for hemolysis

Effect level:

<= 92 ppm

Based on:

test mat.

Exp. duration:

1 h

Remarks on result:

other: dog

Mortality:

extremely steep dose-lethality curves in all species. no measurable difference due to sex.

rodents, dogs and squirrel monkeys: LC50 x Exposure Time was a constant, with:
- dog: LC50 x T = 5860 ppm.min
- squirrel monkey: LC50 x T = 4840 ppm.min
- these data enable extrapolation of LC50 for the required 4h duration for classification.

Clinical signs:

other: dose and concentration-dependent lists: Rodents: - irritation of nose and eyes - diarrhea, abnormally frequent urination and more rapid labored breathing - Increased alertness; piloerection; hyperactivity, interrupted by periods of inactivity with rigid

Body weight:

loss or reduced gain

Gross pathology:

all species:
pulmonary congestion with some hemorrhage, hepatic congestion of varying degree, and swelling of the renal tubular epithelium which was frequently glassine and eosinophilic in appearance.

In large animals whose brain tissues were examined, subarachnoid hemorrhage was frequently observed (probably related to the severe convulsions); in dogs remarkably bloodless spleens in which the sinusoids were virtually empty. In some cases, the splenic smooth muscle bundles appeared thickened and contracted.
The amount of visceral congestion / hemorrhage observed was not sufficient to produce death: death was due to CNS damage only.

At 2 months post-exposure, renal damage from mild swelling of the tubular epithelium to vacuolization and coagulative necrosis of those epithelial cells, was noted.

Other findings:

blood in urine/feces, frequent, in dogs (all doses)

Hematocrit, hemoglobin, red blood cell and reticulocyte values obtained from blood samples taken before, immediately after, and twice weekly postexposure from surviving dogs and rhesus monkeys clearly indicated red blood cell hemolysis. Anemia occured in all exposed dogs and rhesus monkeys (all doses). Recovery took around one month.

Interpretation of results:

very toxic

Remarks:

Migrated information also Acute Tox 1 Criteria used for interpretation of results: EU

Executive summary:

Key data after acute inhalation of MMH:

• Lethality: LC50-4h values:

- squirrel monkey: 20 ppm*

- dog: 24 ppm*

- rhesus monkey: 40 ppm**

- mouse: 65 ppm

- rat: 78 ppm

The lowest of above values corresponds to 38 µg/L at 25°C, atmospheric pressure.

• Intense hemolytic anemia with halving of all RBC parameters, taking up to 2 months to recover, occured at or extremely close to the LC50, notably at 0.047 mg/L** in dogs (23 ppm**).

*: extrapolated for higher duration based on demonstration LC50 x Time = constant

**: same approach assumed as for *, extended to another species and/or sublethal effects

Reference 2

Endpoint:

acute toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Ancient study prior to GLP, non-guideline, excessive duration (24h), preliminary data (extremely limited reporting). However the results are relevant for STOT classification.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

no guideline followed

Principles of method if other than guideline:

Hemolytic effects of sublethal doses (for 24h) were investigated.

GLP compliance:

no

Remarks:

prior to GLP

Test type:

other: sublethal effects

Limit test:

no

Species:

other: see below

Strain:

other: see below

Sex:

not specified

Details on test animals or test system and environmental conditions:

beagle dogs, rhesus monkeys, and albino rats (Sprague-Dawley)

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Remarks:

continuous

Vehicle:

other: nitrogen-air mixture

Details on inhalation exposure:

exposure for 24h in Thomas Dome chambers.
Liquid MMH was expressed from a 20 ml glass syringe into a flow of 1 liter/minute dry nitrogen. Exposure was to a MMH-nitrogen vapour mixture.

Analytical verification of test atmosphere concentrations:

yes

Remarks:

except preliminary study

Duration of exposure:

24 h

Remarks on duration:

continuous

Concentrations:

preliminary study in dogs: 1, 2, 5 and 10 ppm
definitive study: 0 and 1 ppm in all three species

No. of animals per sex per dose:

preliminary study in dogs: 2 (combined sexes) per dose
definitive study: 8 dogs, 8 monkeys, 50 rats, per group

Control animals:

yes

Details on study design:

preliminary study in dogs: animals were thereafter maintained for 30 days postexposure

analytics:
MMH dissolved in the absorber liquid reacted with iodine in a colorimetric reaction.
No real validation was reported, but the standard curve was always a straight line through the origin for concentration versus absorbance.

animals were followed up 30 days after exposure:
- blood sampling several times per week: hematology, serum alkaline phosphatase, total phosphorus and red blood cell fragility.
- all animals were weighed each week
- pathology at 30 days

Sex:

not specified

Dose descriptor:

other: LOAEC for hemolysis

Effect level:

2 ppm

Based on:

test mat.

Exp. duration:

24 h

Remarks on result:

other: dog

Sex:

not specified

Dose descriptor:

other: NOEC

Effect level:

1 ppm

Based on:

test mat.

Exp. duration:

24 h

Remarks on result:

other: rat, dog, rhesus monkey

Mortality:

no data but most probably no deaths

Clinical signs:

other: no data

Body weight:

no data for preliminary study in dogs
no effect in definitive study

Gross pathology:

no data for preliminary study in dogs
no effect in definitive study

Other findings:

Preliminary study: Exposure at 2 ppm MMH produced a 5-7% hemolysis of red blood cells through the methemoglobin-Heinz body transformation mechanism. This effect was followed by recovery which brought hemoglobin, RBC and hematocrit values back to preexposure levels within three weeks.
Higher effects were seen at 5 and 10 ppm MMH.

No hematological/biochemical effect in definitive study (1 ppm).

Interpretation of results:

other: not applicable - test at sublethal doses

Remarks:

Criteria used for interpretation of results: EU

Executive summary:

In beagle dogs, moderate hemolysis occurred at a LOAEC of 2 ppm MMH /24h. Effects were dose-related in dogs exposed to higher concentrations. At 2 ppm, hemolysis was minimal and reversible. In rats, rhesus monkeys and beagle dogs, no hematological, biochemical or body weight effect occured at 1 ppm /24h over 1 month post-exposure (NOEC).

As it was demonstrated that, for lethality, LC50 x Duration = Constant, the LOAEC may be converted to 12 ppm /4h (recommended duration).

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LC50

Value:

150 mg/m³ air

Acute toxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LD50

Value:

93 mg/kg bw

Additional information

ORAL:

- Registered substance: LD50 Rat = 33 mg/kg (reported and peer-reviewed by HSDB) or 71 mg/kg (reported by www.reptox.csst.qc.ca)

- Hydrazine (CAS: 302-01-2), 1,1-dimethylhydrazine (CAS: 57-14-7) and 1,2-dimethylhydrazine (CAS: 540-73-8) are all subject of a harmonized classification as Acute tox 3 (H301).

INHALATION:

- Registered substance:

Lethality: LC50-4h values: squirrel monkey: 20 ppm, dog: 24 ppm, rhesus monkey: 40 ppm, mouse: 65 ppm, rat: 78 ppm. Does not relate clearly to species size so this may not be related to corrosion/irritation; convulsions highly related to lethality. This range corresponds to 0.038-0.15 mg/L at 25°C, atmospheric pressure.

Convulsions favorising/causing death; permanent renal damage; hemolytic anemia occured with the most sensitive being hemolysis: LOAEC values-4h of squirrel monkey: <19 ppm, dog: 12 ppm (a twice lower concentration was an overall NOEC in rat, dog and monkey), rhesus monkey: <40 ppm, mouse: 55 ppm, rat: 75 ppm. Same remark about species size. The lowest value, 12 ppm, corresponds to 0.023 mg/L at 25°C, atmospheric pressure.

- Hydrazine (CAS: 302-01-2), 1,1-dimethylhydrazine (CAS: 57-14-7) and 1,2-dimethylhydrazine (CAS: 540-73-8) are all subject of a harmonized classification as Acute tox 3 (H331).

DERMAL:

- Registered substance: LD50 Rat = 183 mg/kg and LD50 Rabbit = 93 mg/kg (both reported and peer-reviewed by HSDB)

- Hydrazine (CAS: 302-01-2) and 1,2-dimethylhydrazine (CAS: 540-73-8) are both subject of a harmonized classification as Acute tox 3 (H311).

ALL ROUTES:

- Furthermore, hydrazine and 1,1-dimethylhydrazine are also classified as C (corrosive) and R34. This local effect, also applicable for the registered substance methylhydrazine, could possibly be more important than true systemic toxicity and explain why lower LD50 or LC50 are often obtained in larger species (see inhalation and dermal data). It is also an exemption from acute toxicity testing by any route.

- The registered susbtance only differs from one methyl group (additional or less) when compared with the reference substances cited above.

- Testing is unnecessary for risk assessment because the substance is used in Strictly Controlled Conditions along whole lifecycle, and never used by consumers/general population, so that acute oral, inhalative or dermal exposure is impossible.

Justification for classification or non-classification

ORAL:

The registered substance is proposed to be classified as Acute Tox 2, H300 (as a worst-case) based on:

- Harmonized classification Acute tox 3, H301 of three closely related substances, only differing by one additional or absent methyl.

- Secondary literature data on the registered substance, reporting rat (recommended species) oral LD50s of 33-71 mg/kg. As a worst-case the lowest LD50, cited by a peer-reviewed source (HSDB), is retained.

INHALATION:

The registered substance is proposed to be classified as Acute Tox 1, H330 (as a worst-case) based on:

- Harmonized classification Acute tox 3 (H331) of three closely related substances, only differing by one additional or absent methyl, this category encompassing the registered substance.

- A report with rat (recommended species for classification) LC50-4h of 0.15 mg/L vapor. This is a worst-case when compared with harmonized classifications, and will be retained.

The convulsions very frequently led to death and hemolysis was only observed, with severe intensity, at or extremely close to the LC50 or lethal doses:

- at 0.047 mg/L (23 ppm): intense, with halving of all RBC parameters, taking up to 2 months to recover,

- at 0.023 mg/L (12 ppm): minimal, taking 3 weeks to recover.

Therefore, STOT SE classification is not required since the hazard is already evidenced by standard classification for acute toxicity. Furthermore, irreversibility criterium was not met for convulsions and hemolysis. Induction of nephotoxicity (likely irreversible) was not taken into account for classification as the corresponding doses were unclear.

DERMAL:

The registered substance is proposed to be classified as Acute Tox 2, H310 (as a worst-case) based on:

- Harmonized classification Acute tox 3, H311 of two closely related substances, only differing by one additional or absent methyl.

- Secondary literature data on the registered substance, reporting rat and rabbit (recommended species) dermal LD50s of 93-183 mg/kg. As a worst-case the lowest LD50, cited by a peer-reviewed source (HSDB), is retained.