Manganese dioxide

Endpoint summary

Description of key information

Oral

In accordance with Section 1 of REACH Annex XI, testing does not appear to be scientifically necessary; manganese dioxide is included in Annex VI of Regulation (EC) No 1272/2008 (CLP Regulation) and is classified as acutely harmful by the oral route although there is no study available to justify this level of toxicity. Therefore, no further testing is proposed on animal welfare grounds and this classification is carried forward for risk assessment purposes.

 

Inhalation

In accordance with Section 1 of REACH Annex XI, testing does not appear to be scientifically necessary; manganese dioxide is included in Annex VI of Regulation (EC) No 1272/2008 (CLP Regulation) and is classified as acutely harmful by the inhalation route although there is no study available to justify this level of toxicity. Therefore, no further testing is proposed on animal welfare grounds and this classification is carried forward for risk assessment purposes.

 

Dermal

In accordance with Column 2 of REACH Annex VIII, acute toxicity testing by the dermal route is not appropriate as the physicochemical and toxicological properties do not suggest potential for a significant rate of absorption through the skin. The substance is practically insoluble in water and inorganic ions do not pass easily through the dermal barrier. In particular the high charge on the Mn⁴⁺cation would have great difficulty in penetrating the skin.

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records

Reference

Reference 1

Endpoint:

acute toxicity: oral

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

In accordance with Section 1 of REACH Annex XI, testing does not appear to be scientifically necessary; manganese dioxide is included in Annex VI of Regulation (EC) No 1272/2008 (CLP Regulation) and is classified as acutely harmful by the oral route although there is no study available to justify this level of toxicity. Therefore, no further testing is proposed on animal welfare grounds and this classification is carried forward for risk assessment purposes.

Reference 2

Endpoint:

acute toxicity: oral

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Method appears to have been conducted to good scientific standards, although not to GLP. However, in one part of the report it states oral dosing is via stomach intubation, but then the rest of the report appears to indicate ad libitum. It is difficult to know how an insoluble MnO2 would have been administered this way, so this lack of clarity makes it difficult to assign the results as reliable.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Rats were exposed to MnO2 via drinking water for an unspecified period of time. Bodyweights and food/water consumption were measured at 7 day intervals (results not reported).

GLP compliance:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

4 rats per cage, food (Purina Laboratory Chow; 56 ± 5 mg Mn/kg feed) and water available ad libitum.

Route of administration:

oral: drinking water

Vehicle:

water

Doses:

No data

No. of animals per sex per dose:

No data

Control animals:

yes

Sex:

male

Dose descriptor:

LD50

Effect level:

> 3 480 mg/kg bw

Based on:

test mat.

Interpretation of results:

practically nontoxic

Conclusions:

The result of this study indicating an LD50 >> 3480 mg/kg for MnO2 conflicts directly with the current classification of MnO2 which indicates acutely harmful by the oral route. Given the insoluble nature of MnO2 and low bioavailability due to this, it is easier to believe that MnO2 should not be classified as acutely harmful by the oral route and there is no published data which supports this classification. Although assignment of a reliability of 1 or 2 is not possible for this study, the conclusion from this study, that MnO2 is not acutely harmful by the oral route, is very believable.

Endpoint conclusion

Endpoint conclusion:

no study available

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:

supporting study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: Performed to good scientific standard, but not to GLP and conducted using non standard method.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Guinea pigs were exposed to MnO2 dust aerosols for 24 hours in order to assess the following parameters:
-Pulmonary clearance of MnO2
-Number of free lung cells present in the airways after an acute exposure to MnO2
- The phagocytic activity of the alveolar macrophages at different times after MnO2 exposure.
-The effects of an exposure to bacteria (E. cloacae) on the clearance of MnO2, the inflammatory response and the phagocytic activity of alveolar macrophages.

GLP compliance:

not specified

Species:

guinea pig

Strain:

not specified

Sex:

male/female

Details on test animals or test system and environmental conditions:

6-7 animals per cage (55 x 33 x 18 cm)
food and water available ad libitum.

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

whole body

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE
- Method of holding animals in test chamber: Animals were put in 4 cages each holding 6-7 animals. The cages were placed in a stainless steel chamber with a volume of 0.67 m³.
- Source and rate of air: MnO2 dust was mixed with sterile filtered air and introduced into the chamber from the top and sucked through the chamber at a flow of 8m³/h.
- System of generating particulates/aerosols: Dust aerosol was generated using a Rag Pe generator
- Method of particle size determination: A ROYCO optical particle counter model 225 was used to measure the size of the particle and their distribution.
- Temperature, humidity, pressure in air chamber: A negative pressure of 5 mm of water was maintained within the chamber during the exposure.

TEST ATMOSPHERE (if not tabulated)
- Particle size distribution: 87 ±13.4% of particles were ≥ 3.0 µm

Analytical verification of test atmosphere concentrations:

yes

Duration of exposure:

24 h

Concentrations:

22 ± 9.2 mg MnO2/m³ air

No. of animals per sex per dose:

6-7

Control animals:

yes

Clearance of MnO2 from the lungs of guinea pigs was rapid; at 7 days post exposure nearly all MnO2 had been cleared. The number of macrophages was significantly decreased immediately after MnO2 exposure; following which a successive increase took place during the following 7 days. The increase in the number of leukocytes followed a wave pattern response with peaks at 1 and 3 days post exposure.

Approx. 50% of macrophages contained phagocytised particles immediately after exposure. This value decreased to 15% 7 days after exposure.

An increased clearance of viable bacteria took place 1 h after exposure to bacteria in animals already exposed to MnO2. This value decreased at 3, 5 and 24 hrs.

Conclusions:

MnO2 induces pathological reactions in the lung via cellular elements normally present in the lungs.

Executive summary:

Guinea pigs were exposed to MnO2 dust aerosols for 24 hours in order to assess the following parameters:

-Pulmonary clearance of MnO2

-Number of free lung cells present in the airways after an acute exposure to MnO2

- The phagocytic activity of the alveolar macrophages at different times after MnO2 exposure.

-The effects of an exposure to bacteria (E. cloacae) on the clearance of MnO2, the inflammatory response and the phagocytic activity of alveolar macrophages.

Under the conditions of the study clearance of MnO2 from the lungs of guinea pigs was rapid; at 7 days post exposure nearly all MnO2 had been cleared. The number of macrophages was significantly decreased immediately after MnO2 exposure; following which a successive increase took place during the following 7 days. The increase in the number of leukocytes followed a wave pattern response with peaks at 1 and 3 days post exposure. Approximately 50% of macrophages contained phagocytised particles immediately after exposure. This value decreased to 15% 7 days after exposure. An increased clearance of viable bacteria took place 1 hour after exposure to bacteria in animals already exposed to MnO2. This value decreased at 3, 5 and 24 hours.

It can therefore be concluded that MnO2 induces pathological reactions in the lung via cellular elements normally present in the lungs.

Reference 2

Endpoint:

acute toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: Conducted to basic scientific standards but no claim of GLP and conducted using non standard method.

Qualifier:

no guideline followed

Principles of method if other than guideline:

The study was designed to investigate the influence of specific surface area on the biological activity of MnO2 particles. In vitro and in vivo methods were employed to evaluate the cytotoxic potential of the particles and the lung inflammatory response respectively.

GLP compliance:

not specified

Species:

mouse

Strain:

NMRI

Sex:

not specified

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Weight at study initiation: 25 - 30 g

Route of administration:

other: intratracheal administration

Analytical verification of test atmosphere concentrations:

no

Remarks on duration:

single administration

Concentrations:

0.037, 0.12, 0.75 or 2.5 mg/animal

No. of animals per sex per dose:

No data

Control animals:

yes

Cytotoxicity in peritoneal macrophages

The cytotoxic activity of the different MnO₂ preparations was assessed by measuring LDH release after 6 hours of incubation with increasing amounts of particles. When the results were expressed as a function of the gravimetric dose per well, a clear dose- effect relationship was found for particles of specific surface area 17 and 62 m²/g, however the coarsest particles (0.5 m²/g) did not cause any significant damage at doses of up to 500 lg/well. For the same gravimetric dose (e.g. 200 lg/well), the cytotoxic activity of the different preparations was in the following order: 62 > 17 > 0.5 m²/g. Furthermore, the cytotoxicity induced by 5 m²/g particles, which were obtained by grinding a fraction of the 0.5 m²/g sample, was almost as high as that of 62 m²/g particles. When expressed as a function of the total surface area engaged per well (gravimetric dose multiplied by specific surface area; in m²/well), a clear dose-effect relationship was found for 0.5, 17 and 62 m²/g particles. Freshly ground 5 m²/g particles behaved differently and showed a much higher cytotoxic activity.

 

Inflammatory reaction in the mouse lung

In order to compare in vivo the degree of inflammatory reaction induced by the different particles, LDH activity, total protein concentration and number of neutrophils were measured in BAL fluid obtained 5 days after intratracheal instillation. In preliminary experiments, inflammatory reaction assessed with these markers was determined to be maximal 5 days after instillation of MnO₂. For the three parameters, when the results were expressed as a function of the gravimetric dose, a clear dose-effect relationship was found for 17 and 62 m²/g particles. Particles with the lowest specific surface area did not induce any significant inflammation up to a dose of 2.5 mg/animal. For the same gravimetric dose, the toxicity of the particles increased with the specific surface area. Again, the amplitude of the effect on LDH, total protein and PMNs was better related to the total surface area (in m²) and, importantly, toxic effects were similar for different preparations administered at almost equal surface area dose (e.g. 2.5 mg of 17 m²/g particles vs 0.75 mg of 62 m²/g).

Conclusions:

In vitro and in vivo toxicity of various types of manganese dioxide samples could be predicted according to the surface area dose of particles and may be modulated by the presence of labile reactive sites present at the surface of the particles. This study indicates that, when investigating the toxicity of insoluble particles, the surface area which enters into contact with the biological system provides a better estimate of the dose than the usual gravimetric expression.

Executive summary:

The objective of this study was to examine the influence of specific surface area on the biological activity of insoluble manganese dioxide (MnO2) particles. The biological responses to various MnO₂dusts with different specific surface area (0.16, 0.5, 17 and 62 m²/g) were compared in vitro and in vivo. A mouse peritoneal macrophage model was used to evaluate the in vitro cytotoxic potential of the particles via lactate dehydrogenase (LDH) release. In vivo, the lung inflammatory response was assessed by analysis of bronchoalveolar lavage after intratracheal instillation in mice (LDH activity, protein concentration and cellular recruitment).

In both systems, the results show that the amplitude of the response is dependent on the total surface area which is in contact with the biological system, indicating that surface chemistry phenomena are involved in the biological reactivity. Freshly ground particles with a specific surface area of 5 m²/g were also examined in vitro. These particles exhibited an enhanced cytotoxic activity, which was almost equivalent to that of 62 m²/g particles, indicating that undefined reactive sites produced at the particle surface by mechanical cleavage may also contribute to the toxicity of insoluble particles.

It is therefore concluded that, when conducting studies to elucidate the effect of particles on the lung, it is important for insoluble particles such as manganese dioxide to consider the administered dose in terms of surface area (e.g. m²/kg) rather than in gravimetric terms (e.g. mg/kg).

Reference 3

Endpoint:

acute toxicity: inhalation

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

In accordance with Section 1 of REACH Annex XI, testing does not appear to be scientifically necessary; manganese dioxide is included in Annex VI of Regulation (EC) No 1272/2008 (CLP Regulation) and is classified as acutely harmful by the inhalation route although there is no study available to justify this level of toxicity. Therefore, no further testing is proposed on animal welfare grounds and this classification is carried forward for risk assessment purposes.

Reference 4

Endpoint:

acute toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

disregarded due to major methodological deficiencies

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

other: Study not conducted to GLP. Focus of study is on combined effects of MnO2 and bacterial and viral infections.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Mice were exposed to single and multiple 3-hour exposures to aerosols of respirable MnO2 and the level of manganese in the lungs assessed. In addition, the effects of MnO2 inhalation on the susceptibility of mice to bacterial and viral pneumonias was investigated.

GLP compliance:

not specified

Species:

mouse

Strain:

CD-1

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Wilmington, MA, USA
- Age at study initiation: 4 weeks old
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 2 weeks

Animals were pathogen-free at study initiation.

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

whole body

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE
- System of generating particulates/aerosols: Wright dust feed mechanism
- Method of particle size determination: Electrostatic aerosol sampler was used to collect samples for particle size analysis. Air samples were collected at 15 minute intervals, for a total of 3 hours and collected on microscopic slides for counting under a light microscope at 800X.

TEST ATMOSPHERE (if not tabulated)
- Particle size distribution: 97% particles ≤ 5µm and 50-70% of particles ≤ 0.7µm
- Mean Particle Diameter: 0.70µm

Analytical verification of test atmosphere concentrations:

yes

Remarks on duration:

1, 2, or 3 hours

Concentrations:

Average mass concentration of MnO2 = 109 mg/m³ air

No. of animals per sex per dose:

5

Control animals:

yes

Mortality:

No mortalities were observed in mice exposed to MnO2 alone.

Gross pathology:

Microscopic examinations showed that the number of particles of MnO2 in the lung increased with the number of repeat exposures.

Concentration of manganese in lungs of mice exposed to MnO2 aerosols.

Duration of MnO2 exposure (hr)	Mn µg/g dry weight of lung
	10 min post-exposure	5hr post-exposure	14 day post-exposure
0	2.1	2.1	2.1
1	55.0	48.6	2.5
2	50.7	52.4	4.6
3	95.6	67.4	4.3

Conclusions:

The study concludes that bacterial infection may occur after acute exposure to MnO2, although this is not a toxicological effect.

Executive summary:

Single and multiple 3 -hour long exposures to manganese dioxide aerosol in respirable particle size, altered the resistance to bacterial and viral pneumonias. Increased mortality rates and reduced survival times were observed in mice exposed daily for 3 or 4 days to MnO2 aerosol and challenged with airborne K. pneumoniae within 1 hour of termination of the last aerosol exposure. When the interval between the exposure and challenge was extended to 5 hours, the altered resistance to infection was seen already after a single 3 -hour long exposure to MnO2 aerosol. Mice infected with airborne influenza virus 24 or 48 hours before initiation of the MnO2 exposures also showed increased mortality rates, reduced survival times, and increased pulmonary lesions. The effect was more pronounced in mice exposed to MnO2 at 48 hours after the infectious challenge.

Endpoint conclusion

Endpoint conclusion:

no study available

Acute toxicity: via dermal route

Link to relevant study records

Reference

Endpoint:

acute toxicity: dermal

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

In accordance with Column 2 of REACH Annex VIII, acute toxicity testing by the dermal route is not appropriate as the physicochemical and toxicological properties do not suggest potential for a significant rate of absorption through the skin. The substance is practically insoluble in water and inorganic ions do not pass easily through the dermal barrier. In particular the high charge on the Mn4+ cation would have great difficulty in penetrating the skin.

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

In accordance with the criteria for classification as defined in Annex I, Regulation (EC) No. 1272/2008, the substance is classified as acutely harmful by the oral and inhalation routes and has the following hazard phrases: H302 - Harmful if swallowed, and H332 - Harmful if inhaled.

No classification for the dermal route is required based on the very low dermal absorption expected for MnO2.