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Basic toxicokinetics

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basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: A non-GLP study conducted to sound scientific principles with a sufficient level of detail to assess the quality of the relevant results.

Data source

Reference Type:
Pulmonary clearance of manganese phosphate, manganese sulfate, and manganese tetraoxide by CD rats following intratracheal instillation.
Vitarella D, Moss O and Dorman DC
Bibliographic source:
Inhal Toxicol 12:941-957.

Materials and methods

Objective of study:
other: Pulmonary clearance rates in respect to particle dissolution
Test guideline
no guideline followed
Principles of method if other than guideline:
Determination of the contribution of particle dissolution on pulmonary clearance rates of Mn sulphate (MnSO4, Mn phosphate, and Mn3O4) in CD rats following an intratracheal instillation exposure. In addition, brain (striatal) Mn concentrations were evaluated following exposure.
GLP compliance:
not specified

Test material

Constituent 1
Reference substance name:
Manganese (II) sulphate
Manganese (II) sulphate
Constituent 2
Reference substance name:
Manganese (II) phosphate
Manganese (II) phosphate
Constituent 3
Reference substance name:
Manganese tetroxide
Manganese tetroxide
Details on test material:
- Name of test materials (as cited in study report): Manganese(II) sulphate [MnSO4 .H2O], Manganese(II) phosphate [Mn5(PO4)2(PO3(OH)2.4H2O] Manganese tetroxide Mn3O4

Test animals

other: CD
Details on test animals or test system and environmental conditions:
- Source: Charles River Laboratories, Inc. (Raleigh, NC)
- Weight at study initiation: Average weight 300 g
- Housing: Animals were individually housed in humidityand temperature-controlled, HEPA-filtered, mass air-displacement rooms in an animal facility accredited by the American Association for the Accreditation of Laboratory Animal Care (AAALAC).
- Diet: NIH-07 rodent feed containing approximately 100 ppm Mn.
- Water: Deionized, filtered tap water ad libitum.

- Temperature (°C): Maintained at approximately 18.5–21.5°C
- Humidity (%): Relative humidity of approximately 40–60%.
- Photoperiod (hrs dark / hrs light): Fluorescent lighting was kept on a 12-h light–dark cycle.

Administration / exposure

Route of administration:
other: 300 μl sterile Dulbecco’s phosphate-buffered saline solution at room temperature.
Details on exposure:
- MMAD (Mass median aerodynamic diameter) / GSD (Geometric st. dev.): The mass median diameter and geometric standard deviation (MMD, GSD) were estimated to be 4.9 μm and 2.0 for MnSO4, 66% at 1.67 μm and 2.3 and 34% at 15.5 μm and 2.1 for Mn phosphate, and 0.73 μm and 1.75 for Mn3O4 based on densities of 2.9, 2.8, and 4.85 g/ml, respectively. The Mn phosphate was a mixture of two different size distributions. Specific surface area by nitrogen absorption measurement was 0.29, 2.76, and 9.91 m2/g, respectively.
Duration and frequency of treatment / exposure:
A single exposure
Doses / concentrationsopen allclose all
Dose / conc.:
40 other: μg Mn/kg
Dose / conc.:
80 other: μg Mn/kg
Dose / conc.:
160 other: μg Mn/kg
No. of animals per sex per dose / concentration:
6 animals per dose
Control animals:
Details on dosing and sampling:
PHARMACOKINETIC STUDY (Pulmonary clearance, dissolution)
- Tissues and body fluids sampled: Lungs and brain
- Time and frequency of sampling: Tissues taken at 0, 1, 3 or 14 days post instillation.
To use data from the in vitro dissolution to interpret in vivo Mn clearance from the lungs, the following approach was taken. The time course of current (m, particle mass at time t) to initial (Mo, initial particle mass) particle-associated Mn (m/Mo) in the lung fluid simulant was fit with a simple exponential in order to approximate the dissolution rate under conditions of concentration dependent readsorption. Equations for the dissolution of a polydisperse distribution of particles were applied to the size distribution associated with each compound and fit to the initial slope of the in vitro dissolution curve for concentrations less than 20% of the equilibrium concentration. The curve fit was accomplished by iteratively estimating values for the dissolution rate constant (g/cm2/day) in Mercer’s (1967) equations. The highest estimated value of the dissolution rate constant for each compound was used to compare absorptive clearance to the observed (in vivo) lung clearance. The curve predicting Mn clearance due to the dissolution of particles was adjusted to fit the lung clearance data by including a single exponential function representing clearance due to mechanical transport mechanisms.

Results and discussion

Any other information on results incl. tables

All pulmonary clearance half-times were less than 0.5 day. At the concentrations used, striatal Mn levels were unaffected, and lung pathology was unremarkable. The dissolution rate constant of the Mn particles was determined in vitro using lung simulant fluids. The solubility of the Mn compounds was in general 20 to 40 times greater in Hatch artificial lung lining fluid than in Gamble lung simulant fluid. The dissolution rate constant of the water-soluble MnSO(4) particles in Hatch artificial lung fluid containing protein was 7.5 x 10(-4) g (Mn)/cm(2)/day, which was 54 times that of relatively water-insoluble Mn phosphate and 3600 times that of Mn(3)O(4). The dissolution rate constants for these compounds were sevenfold slower in Gamble lung fluid simulant. For both solutions, the time for half the material to go into solution differed only by factors of 1/83 to 1/17 to 1 for MnSO(4), Mn phosphate, and Mn(3)O(4), respectively, consistent with measured differences in size distribution, specific surface, and dissolution rate constant. These data suggest that dissolution mechanisms only played a role in the pulmonary clearance of MnSO(4), while nonabsorptive (e.g., mechanical transport) mechanisms predominate for the less soluble phosphate and oxide forms of Mn.

Applicant's summary and conclusion

Interpretation of results: bioaccumulation potential cannot be judged based on study results
In conclusion, the data suggest that absorptive (e.g., dissolution) mechanisms are likely to predominate in the pulmonary clearance of MnSO4, given the rapid rate of dissolution of this compound in lung simulant fluids. Non-absorptive (e.g., mechanical transport) mechanisms are likely to be the dominant mechanisms for the pulmonary clearance of both the tetraoxide and phosphate forms of Mn, given the slow rate of dissolution. In all cases mechanical clearance appears to have a half-life of approximately 0.5 days. Brain levels of Mn were not increased following instillation of either the MnSO4, phosphate, or Mn3O4, and significant pulmonary pathology did not occur post-instillation.