Methylhydrazine

Endpoint summary

Description of key information

Inhalation:

Intermittent chronic exposure (6h/day 5day/week 6 months): LOAEC (dog and monkey - regenerative hemolytic anemia) = 0.2 ppm

Intermittent subchronic exposure (6h/day 5d/week 3 months because of invalid controls thereafter): NOEC rats = 0.2 ppm (poorly reliable: no hematological data

Continuous subchronic exposure (24h/day 7d/week 3 months): LOAEC (rat and dog - regenerative hemolytic anemia, increase in phosphorus) = 0.0462 ppm

Continuous subchronic exposure (24h/day 7d/week 3 months): NOEC (monkey) = 0.1 ppm (medium reliability: several repeated-dose endpoints not investigated)

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Reference 1

Endpoint:

chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Ancient study prior to GLP, non-guideline and non-specific analytical follow-up. 6-month exposure of rats should not be interpreted after 3rd month because controls were invalidated by heating equipment malfunction leading to control rat weight loss after 13th week. Reported data are reliable but a large amount of required data are missing or not reported.

Qualifier:

no guideline available

Principles of method if other than guideline:

A series of 6-month MMH chronic exposures to four animal species was undertaken to evaluate the safety factor and appropriateness of the current TLV for health of workmen.

GLP compliance:

no

Remarks:

prior to GLP

Limit test:

no

Species:

other: see below

Strain:

other: see below

Details on test animals or test system and environmental conditions:

Each of the experimental animal groups, as well as their controls, consisted of 8 beagle dogs, 4 rhesus monkeys, 50 Wistar strain rats, and 40 ICR mice. All animals were female except for rats.

Route of administration:

inhalation: vapour

Type of inhalation exposure:

not specified

Vehicle:

not specified

Remarks on MMAD:

MMAD / GSD: not applicable (vapour)

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The chamber MMH concentrations were continuously monitored and controlled using a colorimetric method with an AutoAnalyzer. This method is not specific.

Duration of treatment / exposure:

6 months in all animals except half of the dogs
At the end of the first series of experiments, half of the dogs were held for 30 days postexposure observation to determine
reversibility.
+ 4 additional weeks (7 months exposure without reversibility period) in the other half of the dogs

In this summary, the rat data are ignored after week 13 due to invalidation of controls (heating problem - weight loss).

Frequency of treatment:

Exposures were conducted on a 6-hour/day 5-day/week basis at 0, 0.2, 1, 2 and 5 ppm MMH in four experiments.
Another experiment was conducted by continuous exposure at 0.2 ppm

No. of animals per sex per dose:

see above

Control animals:

yes

Observations and examinations performed and frequency:

- weighed biweekly during the studies
- series of 15 clinical chemistry and 8 hematology tests (not conducted on rodents) biweekly during the studies

Sacrifice and pathology:

All exposed and control animals were sacrificed at the conclusion of the study and submitted for gross necropsy. Major organs from all dogs, monkeys, 10 rats, and 10 mice from each group were saved for histopathologic examination. Bone marrow studies on dogs were also performed at this time for their myeloid and erythroid elements (M/E ratio).

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Clinical biochemistry findings:

effects observed, treatment-related

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

not specified

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

not specified

Details on results:

Survival (no data on clinical signs):
- 15% and 27% deaths in mice at 2 and 5 ppm

Body weight:
- decreased in rats, except at 0.2 ppm intermittent exposure

Hematology: not investigated in rodents
- increase in methemoglobin, RBC fragility and/or Heinz bodies: at all dose-levels in dogs and monkeys
- decrease in RBC count, hematocrit and/or hemoglobin: at all dose-levels in dogs and monkeys
overall: clear dose-relationship and no apparent threshold for these effects; poorly time-dependent (maximal effect appears already during first month; the effect amplitude tends to decrease along prolonged exposure)

Clinical chemistry:
- mean bilirubin, alkaline phosphatase, and total inorganic phosphorus values for all exposed dog groups were increased: intrahepatic choleostasis

Pathology: done in dogs only:
- decrease in M/E ratio at all doses

Dose descriptor:

LOAEC

Remarks:

dog and monkey - hemolytic anemia

Effect level:

0.2 ppm

Based on:

test mat.

Sex:

female

Basis for effect level:

other: intermittent exposure (6h/day 5day/week 6 months)

Dose descriptor:

NOEC

Remarks:

rats - growth (no data on hemolysis)

Effect level:

0.2 ppm

Based on:

test mat.

Sex:

male

Basis for effect level:

other: intermittent exposure (6h/day 5d/week, 13 weeks because of invalid controls thereafter) NOAEC may not cover hemolytic anemia (not investigated)

Critical effects observed:

not specified

Executive summary:

Chronic MMH inhalation leads to lethality in mice and decreased body weight gain in rats. In dogs and monkeys, it produces a dose-related hemolytic anemia (not investigated in rodents) with Heinz body formation for which there appears to be no threshold effect level. The anemia is reversible with removal from further exposure at least up to a level of 5 ppm intermittent exposure.

In dogs and monkeys, the 6-month intermittent exposure (6 h/day, 5 days/week) LOAEC was 0.2 ppm (nominal) due to hemolysis. In rats, the 3-month (longer exposure was not validated by appropriate controls) apparent NOEC was 0.2 ppm (nominal) but a large variety of required investigations were not carried out or reported, notably hematological investigations.

The maximal hematological effect appeared already during the first month, plateaued, and gradually the effect amplitude tended to decrease along prolonged exposure.

It may well be asked where man fits in the spectrum of species responses seen with MMH chronic exposure. In a study of the in vitro formation of methemoglobin by MMH (Leahy, 1970), blood samples from four species were compared to determine their equilibrium conversion rates for oxyhemoglobin. In this study, man was found to rank next to the dog in susceptibility with a higher conversion equilibrium than the rat and monkey.

Reference 2

Endpoint:

sub-chronic 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 and non-specific analytical follow-up. Reported data are reliable but a large amount of required data are missing or not reported.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

no guideline followed

Principles of method if other than guideline:

A series of up to 3-month MMH chronic exposures to three animal species was undertaken to evaluate the safety factor and appropriateness of the current TLV for health of workmen.

GLP compliance:

no

Remarks:

prior to GLP

Limit test:

no

Species:

other: see below

Strain:

other: see below

Details on test animals or test system and environmental conditions:

Each dose-group included female beagle dogs, female rhesus monkeys, male albino rats (Sprague- Dawley).
food ad libitum during exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Remarks:

continuous

Vehicle:

other: nitrogen-air mixture

Remarks on MMAD:

MMAD / GSD: not applicable (vapour)

Details on inhalation exposure:

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 doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

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.
Each of the three exposure domes was sampled sequentially for 40 minutes around the clock, giving a 2-hour cycle for monitoring all three exposure domes (control, low-dose, high-dose).

Duration of treatment / exposure:

Rats: 45 days or 90 days
dog, monkey: 90 days

Frequency of treatment:

Daily

Remarks:

Doses / Concentrations:
0.100 and 0.0462 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

Rat, 45 days: 30
Rat, 90 days: 50
Dogs: 8
Monkeys: 4

Control animals:

yes

Positive control:

none

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes / No / No data
- Time schedule:
- Cage side observations checked in table [No.?] were included.

DETAILED CLINICAL OBSERVATIONS: Yes / No / No data
- Time schedule:

BODY WEIGHT: Yes in rat

HAEMATOLOGY: Yes
- Time schedule for collection of blood: 0, 2, 4, 6, 8, 10, 12 and 13 (terminal) weeks in dogs/monkeys; days 45 and 90 in rats
- Parameters checked: hematocrit, hemoglobin, RBC count, WBC count (all species), reticulocytes, Heinz bodies (dog/monkey only), RBC fragility (dog in week 13 only)

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: 0, 2, 4, 6, 8, 10, 12 and 13 (terminal) weeks in dogs/monkeys; days 45 and 90 in rats
- Parameters checked: total inorganic phosphorus, alkaline phosphatase

All other: not mentioned

Sacrifice and pathology:

20 rats per group were used for gross pathology at 90 days; weights of heart, spleen, lung, liver and kidney recorded.
dogs and monkeys at 90 days: gross and histopathology

Clinical signs:

no effects observed

Description (incidence and severity):

clinical signs not reported

Mortality:

no mortality observed

Description (incidence):

clinical signs not reported

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

rat 0.1 ppm, dog/monkey not reported

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

rat and dog 0.0462 and 0.1 ppm

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

rat and dog 0.0462 and 0.1 ppm

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

rat only reported

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

dog 0.1 ppm

Histopathological findings: non-neoplastic:

not examined

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
No data on clinical signs. One monkey in the 0.0462 ppm exposure group died on the 10th day of exposure; there was no evidence of any relationship of the MMH exposure to death.
Other species: no data

BODY WEIGHT AND WEIGHT GAIN
Rat, 90 days: slightly reduced growth at 0.1 ppm only
Other species: no data

HAEMATOLOGY
Rat: hematocrit, hemoglobin, RBC count were slightly, up to 9-10% lower (most sensitive: RBC count, all significant) at both test concentrations on day 45 and RBC count was 13% lower (significant) at 0.1 ppm at 90 days.
Dog: Same effects at 90 days at 0. 1 ppm; non significant but notable at 0.0462 ppm (-14% RBC count); increased reticulocytes (x3) at both doses; increased osmotic RBC fragility at 0.1 ppm.
Monkey: no noteworthy effect

CLINICAL CHEMISTRY
Rat: slight dose-related increase in phosphorus (8% and 13% at 0.0462 and 0.1 ppm) on day 90.
Dog: idem, but only significant at 0.1 ppm (because of low number of animals; +18% at 0.0462 ppm). Important increase (up to x4) in alkaline phosphatase levels at 0.1 ppm.
Monkey: no noteworthy effect

GROSS PATHOLOGY
dogs: at 0.1 ppm, livers had a nutmeg appearance consistent with passive congestion
Monkey, rat: no noteworthy effect

Dose descriptor:

LOAEC

Remarks:

Male rat, female beagle dog

Effect level:

0.046 ppm

Based on:

test mat.

Remarks:

achieved concentration; continuous exposure

Sex:

male/female

Basis for effect level:

other: minimal regenerative (investigated in dog only) hemolytic anemia and increase in phosphorus.

Dose descriptor:

NOEC

Remarks:

female monkey

Effect level:

0.1 ppm

Based on:

test mat.

Remarks:

achieved concentration; continuous exposure

Sex:

female

Basis for effect level:

other: No effect but several effects not investigated or not reported

Critical effects observed:

not specified

Executive summary:

Subchronic MMH inhalation leads to decreased body weight gain (rat), regenerative (not investigated in rats) hemolytic anemia (in rats/dogs/monkeys) with fragilisation of RBC (dogs), elevation of phosphate and/or alkaline phosphatase levels sis (rat and dog).

The 3-month continuous exposure (24 h/day, 7 days/week) LOAEC was 0.0462 ppm as achieved concentration in both rats and dogs. Monkeys did not show any noteworthy effect (NOEC = 0.1 ppm), but a large variety of required investigations were not carried out or reported.

The nature and amplitude of the effects at the investigated dose-levels does not warrant repeated-dose toxicity classification.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LOAEC

0.57 mg/m³

Study duration:

chronic

Species:

other: dog, monkey

Quality of whole database:

LOAEC value normalized to 4h/day, 5d/week

System:

cardiovascular

Organ:

blood

Repeated dose toxicity: inhalation - local effects

Link to relevant study records

Reference

Reference 1

Endpoint:

chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Ancient study prior to GLP, non-guideline and non-specific analytical follow-up. 6-month exposure of rats should not be interpreted after 3rd month because controls were invalidated by heating equipment malfunction leading to control rat weight loss after 13th week. Reported data are reliable but a large amount of required data are missing or not reported.

Qualifier:

no guideline available

Principles of method if other than guideline:

A series of 6-month MMH chronic exposures to four animal species was undertaken to evaluate the safety factor and appropriateness of the current TLV for health of workmen.

GLP compliance:

no

Remarks:

prior to GLP

Limit test:

no

Species:

other: see below

Strain:

other: see below

Details on test animals or test system and environmental conditions:

Each of the experimental animal groups, as well as their controls, consisted of 8 beagle dogs, 4 rhesus monkeys, 50 Wistar strain rats, and 40 ICR mice. All animals were female except for rats.

Route of administration:

inhalation: vapour

Type of inhalation exposure:

not specified

Vehicle:

not specified

Remarks on MMAD:

MMAD / GSD: not applicable (vapour)

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The chamber MMH concentrations were continuously monitored and controlled using a colorimetric method with an AutoAnalyzer. This method is not specific.

Duration of treatment / exposure:

6 months in all animals except half of the dogs
At the end of the first series of experiments, half of the dogs were held for 30 days postexposure observation to determine
reversibility.
+ 4 additional weeks (7 months exposure without reversibility period) in the other half of the dogs

In this summary, the rat data are ignored after week 13 due to invalidation of controls (heating problem - weight loss).

Frequency of treatment:

Exposures were conducted on a 6-hour/day 5-day/week basis at 0, 0.2, 1, 2 and 5 ppm MMH in four experiments.
Another experiment was conducted by continuous exposure at 0.2 ppm

No. of animals per sex per dose:

see above

Control animals:

yes

Observations and examinations performed and frequency:

- weighed biweekly during the studies
- series of 15 clinical chemistry and 8 hematology tests (not conducted on rodents) biweekly during the studies

Sacrifice and pathology:

All exposed and control animals were sacrificed at the conclusion of the study and submitted for gross necropsy. Major organs from all dogs, monkeys, 10 rats, and 10 mice from each group were saved for histopathologic examination. Bone marrow studies on dogs were also performed at this time for their myeloid and erythroid elements (M/E ratio).

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Clinical biochemistry findings:

effects observed, treatment-related

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

not specified

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

not specified

Details on results:

Survival (no data on clinical signs):
- 15% and 27% deaths in mice at 2 and 5 ppm

Body weight:
- decreased in rats, except at 0.2 ppm intermittent exposure

Hematology: not investigated in rodents
- increase in methemoglobin, RBC fragility and/or Heinz bodies: at all dose-levels in dogs and monkeys
- decrease in RBC count, hematocrit and/or hemoglobin: at all dose-levels in dogs and monkeys
overall: clear dose-relationship and no apparent threshold for these effects; poorly time-dependent (maximal effect appears already during first month; the effect amplitude tends to decrease along prolonged exposure)

Clinical chemistry:
- mean bilirubin, alkaline phosphatase, and total inorganic phosphorus values for all exposed dog groups were increased: intrahepatic choleostasis

Pathology: done in dogs only:
- decrease in M/E ratio at all doses

Dose descriptor:

LOAEC

Remarks:

dog and monkey - hemolytic anemia

Effect level:

0.2 ppm

Based on:

test mat.

Sex:

female

Basis for effect level:

other: intermittent exposure (6h/day 5day/week 6 months)

Dose descriptor:

NOEC

Remarks:

rats - growth (no data on hemolysis)

Effect level:

0.2 ppm

Based on:

test mat.

Sex:

male

Basis for effect level:

other: intermittent exposure (6h/day 5d/week, 13 weeks because of invalid controls thereafter) NOAEC may not cover hemolytic anemia (not investigated)

Critical effects observed:

not specified

Executive summary:

Chronic MMH inhalation leads to lethality in mice and decreased body weight gain in rats. In dogs and monkeys, it produces a dose-related hemolytic anemia (not investigated in rodents) with Heinz body formation for which there appears to be no threshold effect level. The anemia is reversible with removal from further exposure at least up to a level of 5 ppm intermittent exposure.

In dogs and monkeys, the 6-month intermittent exposure (6 h/day, 5 days/week) LOAEC was 0.2 ppm (nominal) due to hemolysis. In rats, the 3-month (longer exposure was not validated by appropriate controls) apparent NOEC was 0.2 ppm (nominal) but a large variety of required investigations were not carried out or reported, notably hematological investigations.

The maximal hematological effect appeared already during the first month, plateaued, and gradually the effect amplitude tended to decrease along prolonged exposure.

It may well be asked where man fits in the spectrum of species responses seen with MMH chronic exposure. In a study of the in vitro formation of methemoglobin by MMH (Leahy, 1970), blood samples from four species were compared to determine their equilibrium conversion rates for oxyhemoglobin. In this study, man was found to rank next to the dog in susceptibility with a higher conversion equilibrium than the rat and monkey.

Reference 2

Endpoint:

sub-chronic 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 and non-specific analytical follow-up. Reported data are reliable but a large amount of required data are missing or not reported.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

no guideline followed

Principles of method if other than guideline:

A series of up to 3-month MMH chronic exposures to three animal species was undertaken to evaluate the safety factor and appropriateness of the current TLV for health of workmen.

GLP compliance:

no

Remarks:

prior to GLP

Limit test:

no

Species:

other: see below

Strain:

other: see below

Details on test animals or test system and environmental conditions:

Each dose-group included female beagle dogs, female rhesus monkeys, male albino rats (Sprague- Dawley).
food ad libitum during exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Remarks:

continuous

Vehicle:

other: nitrogen-air mixture

Remarks on MMAD:

MMAD / GSD: not applicable (vapour)

Details on inhalation exposure:

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 doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

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.
Each of the three exposure domes was sampled sequentially for 40 minutes around the clock, giving a 2-hour cycle for monitoring all three exposure domes (control, low-dose, high-dose).

Duration of treatment / exposure:

Rats: 45 days or 90 days
dog, monkey: 90 days

Frequency of treatment:

Daily

Remarks:

Doses / Concentrations:
0.100 and 0.0462 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

Rat, 45 days: 30
Rat, 90 days: 50
Dogs: 8
Monkeys: 4

Control animals:

yes

Positive control:

none

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes / No / No data
- Time schedule:
- Cage side observations checked in table [No.?] were included.

DETAILED CLINICAL OBSERVATIONS: Yes / No / No data
- Time schedule:

BODY WEIGHT: Yes in rat

HAEMATOLOGY: Yes
- Time schedule for collection of blood: 0, 2, 4, 6, 8, 10, 12 and 13 (terminal) weeks in dogs/monkeys; days 45 and 90 in rats
- Parameters checked: hematocrit, hemoglobin, RBC count, WBC count (all species), reticulocytes, Heinz bodies (dog/monkey only), RBC fragility (dog in week 13 only)

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: 0, 2, 4, 6, 8, 10, 12 and 13 (terminal) weeks in dogs/monkeys; days 45 and 90 in rats
- Parameters checked: total inorganic phosphorus, alkaline phosphatase

All other: not mentioned

Sacrifice and pathology:

20 rats per group were used for gross pathology at 90 days; weights of heart, spleen, lung, liver and kidney recorded.
dogs and monkeys at 90 days: gross and histopathology

Clinical signs:

no effects observed

Description (incidence and severity):

clinical signs not reported

Mortality:

no mortality observed

Description (incidence):

clinical signs not reported

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

rat 0.1 ppm, dog/monkey not reported

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

rat and dog 0.0462 and 0.1 ppm

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

rat and dog 0.0462 and 0.1 ppm

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

rat only reported

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

dog 0.1 ppm

Histopathological findings: non-neoplastic:

not examined

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
No data on clinical signs. One monkey in the 0.0462 ppm exposure group died on the 10th day of exposure; there was no evidence of any relationship of the MMH exposure to death.
Other species: no data

BODY WEIGHT AND WEIGHT GAIN
Rat, 90 days: slightly reduced growth at 0.1 ppm only
Other species: no data

HAEMATOLOGY
Rat: hematocrit, hemoglobin, RBC count were slightly, up to 9-10% lower (most sensitive: RBC count, all significant) at both test concentrations on day 45 and RBC count was 13% lower (significant) at 0.1 ppm at 90 days.
Dog: Same effects at 90 days at 0. 1 ppm; non significant but notable at 0.0462 ppm (-14% RBC count); increased reticulocytes (x3) at both doses; increased osmotic RBC fragility at 0.1 ppm.
Monkey: no noteworthy effect

CLINICAL CHEMISTRY
Rat: slight dose-related increase in phosphorus (8% and 13% at 0.0462 and 0.1 ppm) on day 90.
Dog: idem, but only significant at 0.1 ppm (because of low number of animals; +18% at 0.0462 ppm). Important increase (up to x4) in alkaline phosphatase levels at 0.1 ppm.
Monkey: no noteworthy effect

GROSS PATHOLOGY
dogs: at 0.1 ppm, livers had a nutmeg appearance consistent with passive congestion
Monkey, rat: no noteworthy effect

Dose descriptor:

LOAEC

Remarks:

Male rat, female beagle dog

Effect level:

0.046 ppm

Based on:

test mat.

Remarks:

achieved concentration; continuous exposure

Sex:

male/female

Basis for effect level:

other: minimal regenerative (investigated in dog only) hemolytic anemia and increase in phosphorus.

Dose descriptor:

NOEC

Remarks:

female monkey

Effect level:

0.1 ppm

Based on:

test mat.

Remarks:

achieved concentration; continuous exposure

Sex:

female

Basis for effect level:

other: No effect but several effects not investigated or not reported

Critical effects observed:

not specified

Executive summary:

Subchronic MMH inhalation leads to decreased body weight gain (rat), regenerative (not investigated in rats) hemolytic anemia (in rats/dogs/monkeys) with fragilisation of RBC (dogs), elevation of phosphate and/or alkaline phosphatase levels sis (rat and dog).

The 3-month continuous exposure (24 h/day, 7 days/week) LOAEC was 0.0462 ppm as achieved concentration in both rats and dogs. Monkeys did not show any noteworthy effect (NOEC = 0.1 ppm), but a large variety of required investigations were not carried out or reported.

The nature and amplitude of the effects at the investigated dose-levels does not warrant repeated-dose toxicity classification.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Overall, a tendency to anemia was the critical repeated-dose toxicity effect of MMH although some less specific effects were noted (reduced body weight gain, increased phosphate and alkaline phosphatase levels). This anemia was regenerative (activated bone marrow as evidenced by increased reticulocytes and/or decreased M/E ratios) and due to hemolysis (Heinz body formation, methemoglobin formation, fragilization of RBC).

Acute toxicity studies in dogs and monkeys showed that LC50 x Duration of exposure = Constant, which is in accordance with Haber's law. Therefore, the various experimental conditions and NOECs/LOAECs may be normalized as follows, to an exposure pattern of workers (their potential exposure being only 4h/day):

Animal exposure					Resulting toxic endpoint		Value (ppm) of same endpoint, normalized to 4h/day, 5d/week, same duration in months**
Type	A) Frequency (h/day)	B) Frequency (d/week)	Duration (months)	Species	Type/effect	C) Value (ppm)
Intermittent chronic	6	5	6	dog, monkey*	LOAEC	0.2	0.30 - 6 months
Continuous subchronic	24	7	3	rat, dog	LOAEC	0.0462	0.39 - 3 months
Continuous subchronic	24	7	3	monkey	NOEC***	0.1	0.84 - 3 months

* rat ignored (no hemataological investigations)

** calculated as: D) x A)/4 x B)/5

*** poorly reliable (several lacking repeated-dose investigations)

The similar resulting normalized NOECs/LOAECs evidence:

- coherence with Haber's law except possibly in monkeys (where data from the longest study should be kept: 6-month study, first line)

- that an overall LOAEC of 0.30 ppm /(4h/day, 5 days/week) covers three species (rat, dog, monkey) and durations of 3 or 6 months

A notable exception to Haber's rule was apparent in experimental data: there was no evidence of any cumulation of effects along dosing after the first month or so. Oppositely, the amplitude of the hematological effects tended to decrease along this prolonged exposure.

Justification for classification or non-classification

INHALATION:

Hemolytic anemia was reversible due to medullar activation (regenerative anemia). Its effect amplitude peaked at around one month and decreased thereafter along prolonged exposure, with similar LOAECs after 3 or 6 months exposures (once normalized for h/day and days/week).

Based on:

- the tendency of decreasing effects upon prolonged exposure, due to efficient erythropoietic compensation by the bone marrow,

- the reversibility of the hematological effects,

- the absence of bioaccumulation potential (see relevant section),

- the fact that other classification for MMH and the use in SCC both prevent risk of significant repeated-dose effects,

it seems irrelevant to classify for repeated-dose toxicity: STOT RE is not proposed.