Assessment of Exposure-Response Functions for Rocket-Emission Toxicants (1998) / Chapter Skim
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Appendix F: Acute Toxicity of Nitric Acid
Appendix F: Acute Toxicity of Nitric Acid
Pages 197-208
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From page 197... ...
However, aerosols of aqueous HNO3 are readily formed by passing clean air over reagent-grade aqueous HNO3 (Koenig et al.
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From page 198... ...
. HNO3 is produced at very low concentrations in rocket emissions from the combustion of hydrazine and N2O4 under normal launch conditions but at significant concentrations when a launch is aborted after ignition for rockets using liquid propellants.
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From page 199... ...
In a study with humans, exposure of 12 nonsmoking subjects with mild asthma for 3 men to an "acid fog" that was 30 miDiosmolar (mOsm) at pH 2 significantly increased specific airway resistance (Balmes et al.
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The investigators observed a surprising increase in the phagocytic activity of alveolar macrophages from exposed individuals, but that was not believed to be an adverse effect. Therefore, no toxic effects occurred in humans exposed to HNO3 for 2 hr at 0.08 ppm.
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From page 201... ...
The subcommittee concludes that, although the results of the two human studies appear to be contradictory, exposure to HNO3 at 0.05 ppm for 40 to 45 min might cause respiratory problems In certain sensitive subgroups such as in asthmatic individuals. That low exposure concentration and duration can be used to establish a NOEL for the subgroup of asthmatic individuals In the general population.
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From page 203... ...
The reduction in respiratory burst of macrophages in rats is probably not an appropriate end point for setting a no-effect human exposure level, especially if uncertainty factors are applied to that level (see "Evaluation of Toxicity Information") , because reduction in macrophage function is not necessarily predictive of an adverse response in animals or humans.
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From page 204... ...
ACGIH 1994; NIOSH 1994a NIOSH IDLH 25 ppm NIOSH 1994b Level 1 0.033 ppm (0.086 mg/m3) Cal EPA 1995 Abbreviations: ACGIH, American Conference of Governmental Industrial Hygienists; TLV, Threshold Limit Value; TWA, time-weighted average; OSHA, Occupational Safety and Health Administration; PEL, permissible exposure level; NIOSH, National Institute for Occupational Safety and Health; REL, recommended exposure limit; STEL, short-term exposure limit; IDLH, immediately dangerous to life and health.
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From page 205... ...
Haber's rule states that the biological effects of some types of inhalation toxicants are related to the total cumulative exposure, that is the time-weighted-average concentration multiplied by the duration of exposure. Given that acute HNO3-induced inhalation toxicity results from the corrosive or acidic nature of the compound in the respiratory tract, Haber's rule is expected to apply to this compound over relatively short exposure durations.
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From page 206... ...
1994. 199~1995 Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices.
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U.S. Environmental Protection Agency, Office of Health and Environmental Assessment, Environmental Criteria and Assessment Office, Research Triangle Park, N.C.
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From page 208... ...
NIOSH (National Institute for Occupational Safety and Health)
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