Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants Volume 5 (2008) / Chapter Skim
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6 C2-C9 Alkanes
6 C2-C9 Alkanes
Pages 85-111
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From page 85... ...
Rather than address each compound individually, this document initially sought to establish a group spacecraft maximum allowable concentration (SMAC) for the C2-C9 alkanes in accordance with their similarities in toxic action and their physical and chemical properties.
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From page 86... ...
Various branched isomers exist for many of the n-alkanes, and the physical and chemical properties for these isomers may differ from those presented in Table 6-1, which are specific to the n-alkanes. OCCURRENCE AND USE The group of compounds that comprise the C2-C9 saturated aliphatic alkanes (the linear and branched alkanes from ethane through nonane)
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−88.6 −42.1 −0.5 36.1 69 98.4 125.7 150.8 Lower explosive limit 3.2% 2.3% 1.9% 1.4% 1.2% 1.2% 1.0% 0.9% Upper explosive limit 12.5% 9.5% 8.4% 7.8% 7.8% 6.7% 4.7% 2.9% Vapor pressure (mm Hg)
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. Among the C2-C9 saturated alkanes, absorption into the bloodstream after inhalation exposures will generally be greater for
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From page 89... ...
of exposure during a 14-d inhalation test with rats. Distribution Once dissolved in the bloodstream, the saturated alkanes can be distributed to various organ systems.
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and liquid (C5-C9) saturated alkanes in terms of their toxicity.
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. This conclusion does not extend to the C5-C9 saturated alkanes because a number of toxicologic effects at more realistic concentrations of exposure have been reported in the scientific literature (although there is still variability in the toxic potential among members of this group)
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Exposure Duration Species Effects Reference n-Pentane 3,000 16 wk (12 h/d) Wistar rats No neurotoxic effects.
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1974 17,400 10 min CF-1 mice 50% reduced respiratory rate Kristiansen and Nielsen (RD50 b) calculated from 1988 developed concentration response relationship.
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1988 spasms, loss of Purkinje cells. a RD10 is the concentration expected to result in a 10% decrease in respiratory rate relative to controls.
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Other authors have studied specific respiratory changes in laboratory animals in response to exposure to saturated alkanes in the context of deter
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suggested that the trigeminal nerve endings in the nasal mucosa would respond to sensory irritants (resulting in a burning sensation in the mucous membranes of the eyes, nose, and throat) and that this response could be measured by a decrease in respiratory rate.
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From page 97... ...
The authors postulated that this response may be because of stabilization of the receptor-substance complex or because the greater water solubility of the shorter chain alkanes may allow them more contact with receptors deep within the nasal mucosa. Thus, these findings suggest that exposure to n-nonane may cause sensory irritation at the lowest air concentrations (among the C5-C9 alkanes)
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From page 98... ...
They used implanted electrodes and needle electrodes to measure auditory brain stem responses elicited by an instrument that emitted sounds at frequencies of 3, 8, 16, and 32 kilohertz (kHz) and eight levels of sound intensity ranging from 25 to 95 decibels (dB)
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(1998) also conducted an in vivo bone marrow micronucleus test by examining the bone marrow from the rats exposed to n-pentane at up to 7,000 ppm for 90 d (another experiment reported in the same paper)
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RATIONALE FOR ACCEPTABLE CONCENTRATIONS Table 6-4 presents occupational exposure limits set by other organizations for the C2-C9 saturated alkanes. In general, occupational exposure limits decrease with increasing length of the carbon chain for this class of compounds.
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Although sensory irritation data on every alkane of interest were not available, the data that were available suggested that nnonane was a conservative representative for the group because it was predicted to have the lowest threshold for sensory irritant effects. TABLE 6-4 Exposure Limits Set by Other Organizations ACGIH-TLVa,d OSHA PELb,d NIOSH RELb, d Russian PDKc ppm ppm ppm (360 d)
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1988 h) n-Nonane; 590 ppm Wistar rats 1 1 10 1 -- -- 60 60 60 (NOAEL)
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Predicted concentration-response relationships were calculated for n-heptane, noctane, and n-nonane and were expressed in regression equations developed for each alkane. To use these study results in SMAC development, it was necessary to identify a specific degree of sensory irritation that is consistent with the level of irritation allowable for varying exposure durations.
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Thus, we used n-nonane as a conservative representative compound in setting ACs for sensory irritation for the alkanes. To better reflect sampling variability inherent in the RD10 estimate, we used a bootstrap analysis to generate a distribution of possible RD10 values for n-nonane, with 5th, 50th, and 95th percentile estimates of the RD10 of 440 ppm, 1,095 ppm, and 1,700 ppm, respectively (90% confidence interval of 440-1,700 ppm)
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Time adjustments were not considered to be necessary for these longer term ACs because CNS effects are generally expected to be more dependent on the attainment of critical blood concentrations. This is supported by the observations of Carpenter et al.
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However, scanty data are available on the role of exposure duration in the ototoxicity of the saturated alkanes. Also, epidemiologic data from occupational cohorts suggest that length of exposure can be a contributing factor to ototoxicity for certain solvents (Morata et al.
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/b1. The goal of the bootstrap method is to generate bootstrap sample data [x, y]
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American Council of Governmental Industrial Hygienists, Cincinnati, OH. ACGIH (American Council of Governmental Industrial Hygienists)
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2002. A study of the biological partition ing behavior of n-alkanes and n-alkanols in causing anesthetic effects.
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1993. Development of a database for sensory irritants and its use in estab lishing occupational exposure limits.
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1992. Abnormal auditory brainstem responses and cochlear pathology in rats induced by an exaggerated sty rene exposure regimen.
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