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11 Ethanol J. Torin McCoy Toxicology Group Habitability and Environmental Factors Division Johnson Space Center National Aeronautics and Space Administration Houston, Texas INTRODUCTION This document presents the results of an update and reassessment of the toxicity of ethanol as it relates to the establishment of appropriate spacecraft maximum allowable concentrations (SMACs). This reassessment refers to a chapter on ethanol published in Volume 3 of Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants (James 1996). Since publi- cation of Volume 3, a number of research articles on ethanol have been pub- lished in the scientific literature. However, a large quantity of them focus on the health consequences of oral consumption and abuse of ethanol and have limited relevance to inhalation exposures in a spacecraft environment. As documented in Volume 3, the overall lack of information on inhalation exposures seems to be driven by the presumption that exposures to ethanol vapors are not widely appli- cable and that ethanol vapors have low toxicity and are a minimal health risk. A fairly recent development that somewhat catalyzed a renewed interest in the health consequences of exposure to ethanol by inhalation is the emergence of ethanol as a significant additive or replacement for motor vehicle fuels. For ex- ample, ethanol is often introduced into gasoline as an oxygenate (5-10%) to help limit emissions of carbon monoxide, ozone, and various volatile organic com- pounds (Ahmed 2001). Additionally, certain vehicles are equipped to use E85 fuels (85% ethanol blended with 15% unleaded gasoline). Although exposure assumptions for these routes can differ significantly from spacecraft applica- tions, some useful data have been generated and were considered in this reas- sessment (Winebrake et al. 2001, Nadeau et al. 2003, Chu et al. 2005). This reassessment evaluates new data to determine whether the SMACs established in Volume 3 can still be supported as the most appropriate spacecraft exposure limits for ethanol. The toxicologic end points previously evaluated for which acceptable concentrations (ACs) were calculated in Volume 3 include neurotoxicity, irritation, hepatotoxicity, and flushing. New studies applicable to 190
Ethanol 191 these end points were reviewed and are incorporated in this reassessment. Any other relevant end points for which data emerged since publication of Volume 3 were addressed as they were identified. Another important aspect of this review is the need to set 1,000-d SMACs for longer-term crew exposures. Longer expo- sures would be of interest in assessing possible lengthy missions on the Interna- tional Space Station (ISS) or in future lunar or Martian exploration efforts. The intent of this reassessment is not to revisit all the studies that were considered in the original Volume 3 chapter. Much of the foundation for this review (e.g., discussion on metabolism, rationale for not addressing fetal risks) was provided in Volume 3; thus, these two write-ups should be viewed as complementary. ISS MONITORING DATA Volume 3 was written before NASAâs full involvement with ISS and thus does not contain information on the relevance of ethanol in that environment or on monitored concentrations of ethanol in the ISS atmosphere. As a compound potentially used in a variety of spacecraft applications, ethanol can be introduced to the ISS atmosphere through many sources, including cleaning products such as alcohol wipes, payloads, substances in medical kits, and crew hygiene prod- ucts. Other possible contributors to consider are the small amounts of ethanol that can be formed and released endogenously by humans. Ethanol is generally monitored (near-instantaneous readings) around 5-8 milligrams per cubic meter (mg/m3) in the ISS atmosphere, although measurements have approached 20 mg/m3 on occasion. Because of its extreme solubility in water, a main concern with ethanol in the ISS atmosphere is its potential to affect the processing of humidity conden- sate by the Russian water processing system. Recycled humidity condensate provides a significant percentage of potable water on ISS (50%+). Ethanol is a common organic component of ISS condensate, being measured at concentra- tions as high as 156 mg/liter (L), with average ethanol concentrations around 50- 55 mg/L. For reasons that are not fully understood, U.S. Laboratory condensate frequently contains higher ethanol concentrations than condensate from the Rus- sian Service Module (Figure 11-1). As these ethanol concentrations can double the system design limit for the Russian processing equipment (80 mg/L), significant efforts have been made to identify and limit releases of ethanol and other volatiles to the ISS atmosphere. The presence of excess volatiles in humidity condensate can affect the process- ing system in several ways. As the Russian system includes an oxidizing reactor and downstream multifiltration beds, system resources may be spent in oxidiz- ing and removing relatively low-toxicity liquid components (e.g., ethanol). This has operational impacts for these limited life items and can impair performance when the system is also challenged with more toxic organic compounds.
192 SMACs for Selected Airborne Contaminants 180 160 Ethanol in USL Condensate 140 Ethanol in SM Condensate 120 Concentration (mg/L) 100 80 60 40 20 0 00 01 02 03 04 05 06 1 2 3 4 5 6 00 00 00 00 00 00 20 20 20 20 20 20 20 /2 /2 /2 /2 /2 /2 3/ 3/ 3/ 3/ 3/ 3/ 3/ 13 13 13 13 13 13 /1 /1 /1 /1 /1 /1 /1 6/ 6/ 6/ 6/ 6/ 6/ 12 12 12 12 12 12 12 Sample Date FIGURE 11-1 Ethanol concentrations (mg/L) measured in U.S. Lab Condensate (USL) and Russian Service Module (SM) condensate on ISS. Source: Data generated by NASA Johnson Space Center, Water and Food Analytical Laboratory. REVIEW OF ACS FOR ETHANOL IN VOLUME 3 (James 1996) In Volume 3, available toxicologic data on ethanol were presented and discussed in terms of specific end points. The review did not discuss the full range of toxicologic data on ethanol, as much of the data were not relevant to spacecraft applications or were deemed to be an issue only in association with chronic abuse (e.g., effects on skeletal or vascular smooth muscle). The docu- ment discussed adverse reproductive and developmental effects resulting from ethanol intake in some detail, but developing an AC was not deemed necessary given the lack of evidence that non-narcotic exposures could cause these effects (James 1996). Ultimately, ACs were developed for neurotoxicity, irritation, âflush responseâ (elevated skin temperature, pulse rate, and observable facial responses), and hepatotoxicity (Table 11-1). Most ACs were consistent across exposure time frames, as peak blood ethanol concentrations (BECs) are gener- ally achieved in the first few hours of exposure (Pastino et al. 1997), and effects were not expected to be time dependent. For the irritation and flush response ACs, the 7- to 180-d ACs were set lower than the 1- and 24-h ACs not because of exposure time considerations but because a small margin of discomfort is allowable for the shorter-term ACs. CONSIDERATION OF NEW DATA The subsequent sections discuss new data available on the potential effects of inhalation exposure to ethanol. This includes studies not reviewed in Volume 3, and new studies published since 1996, as summarized in Table 11-2.
TABLE 11-1 Acceptable Concentrations for Ethanol End Points in Volume 3 Acceptable Concentration (mg/m3) End Point 1h 24 h 7d 30 d 180 d Neurotoxicity 7,000 7,000 7,000 7,000 7,000 Mucosal irritation 10,000 10,000 2,000 2,000 2,000 (eye, nose) Flush response 4,000 4,000 2,000 2,000 2,000 a a Hepatotoxicity N/A N/A 2,000 2,000 2,000 a For hepatotoxicity, it was determined that non-narcotic exposures could not cause the relevant effects during these exposure time frames. Source: James 1996. 193
TABLE 11-2 Toxicity Summary (For New Studies or Those Not Reviewed in Volume 3 SMAC Document) 194 Concentration (mg/m3) Exposure Duration Species Results Referencea Inhalation 0, 500, 6h Human No observable adverse neuromotor effects. BEC reached only Nadeau et al. 1,000, 2,000 (NOAEL) (n=5) 0.44 mg/dL (0.0004%). 2003 Inhalation 12,000 4 wk (6 h/d, 5 d/wk) SD rats Measured levels of certain neurochemicals (mediodorsal Chu et al. 2005 (15 male, 15 thalamus 5-hydroxyindoleacetic acid and hippocampal 5- female) hydroxytryptamine) were significantly reduced relative to controls in female but not in male rats. Inhalation 2,500 Nasal lateralization Human None of the 6 volunteers could reliably lateralize ethanol at Wise et al. 2006 (NOAEL), 3,100, evaluated with 1- to (n=6) 2,500 mg/m3, but 4/6 (66%) could lateralize 3,100 mg/m3. 3,900, 4,900, 6,100, 10-s pulses. and 7,600 Inhalation 19,000 Nasal lateralization Human Identified nasal irritation threshold. Questions exist about Cometto-MuÃ±iz (LOAEL) evaluated with 1- to anosmics exposure duration. and Cain 1990 3-s pulses. (n=3) Inhalation 90,000 Nasal lateralization Human Identified eye irritation threshold. Questions exist about Cometto-MuÃ±iz (LOAEL) evaluated with 1- to (n=10) exposure duration and test method. and Cain 1996 3-s pulses. Inhalation constant Both conditions were Human Volunteers were asked to assess irritation of the eye, nose, Seeber et al. exposure 1,500 4-h exposures, but the constant throat, or skin and to rate it on a scale of 0 (not at all) to 5 2002 (NOAEL); Variable variable exposure exposure (strong). For ethanol, the mean response at 1,500 mg/m3 exposure 3,600 regime is not clearly (n=24); remained about the same as the response for clean air. The mean (NOAEL) defined. Variable response with variable exposures up to 3,600 mg/m3 was also exposure consistent with clean air, but the authors do not adequately (n=16) describe the regime. a None of these studies were used to set ACs or SMACs. Abbreviation: SD, Sprague-Dawley, LOAEL, lowest-observed-adverse-effect level; NOAEL, no-observed-adverse-effect level.
Ethanol 195 Neurotoxicity The existing neurotoxicity AC (7,000 mg/m3 for all time frames) was based on observations (Lester and Greenberg 1951) that three individuals ex- posed to ethanol in air at 15,000 mg/m3 over 3-6 h did not report neurologic symptoms. Although lack of reported effects does not confirm the lack of per- formance detriments, it was noted that the BEC in this group reached only 10 mg/dL (0.01%), well below the level at which performance detriments have been observed in other studies reported in the scientific literature. Volume 3 noted one particularly applicable example in the work of Kennedy et al. (1993), which focused on the development of testing procedures that could be used to predict operational performance of air and space flight crew. The authors evalu- ated individual responses to a computer-based battery of performance tests (rep- resented by the Armed Services Vocational Aptitude Battery) at different oral ethanol exposures (BECs of 150, 125, 100, 75, and 50 mg/dL). At each evalu- ated BEC except for 50 mg/dL (0.05%), the mean test score was below baseline performance, indicating various degrees of performance impairment. For exam- ple, the mean score at a BEC of 150 mg/dL was 17% lower than the baseline mean score. New Data Evaluation of the scientific literature since publication of Volume 3 found relatively few studies that specifically evaluated adverse neurologic impairment associated with inhalation exposures to ethanol. Nadeau et al. (2003) evaluated neuromotor effects in association with relatively low-level exposures to ethanol vapors. They exposed five volunteers to ethanol at 0, about 500, 1,000, and 2,000 mg/m3 for 6 h. Reaction time, body sway, hand tremor, and rapid alternat- ing movements were evaluated before and after the exposures. Subjects were exposed for five consecutive days, although the exposures were separated by 24 h. The authors reported that exposures up to 2,000 mg/m3 did not result in sig- nificant neuromotor changes. Consistent with this conclusion, the BECs for test subjects exposed to ethanol at 500 and 1,000 mg/m3 were below detection limits, whereas exposure to ethanol at 2,000 mg/m3 resulted in a BEC of only 0.44 mg/dL (0.0004%). Chu et al. (2005) exposed 15 male and 15 female rats to ethanol at 12,000 mg/m3 for 4 wk (6 h/d, 5 d/wk) by inhalation. For the female rats, the authors noted that concentrations of certain neurochemicals (mediodorsal thalamus 5- hydroxyindoleacetic acid and hippocampal 5-hydroxytryptamine) were signifi- cantly reduced relative to controls. The biological significance of these results for humans in spaceflight is somewhat unclear, but it is worth noting that these compounds do relate to moods. However, the results do not outweigh the human data showing no adverse performance effects at similar ethanol concentrations.
196 SMACs for Selected Airborne Contaminants Pastino et al. (1997) evaluated the pharmacokinetics of inhaled ethanol in B6C3F1 mice and F344 rats to construct a physiologically based pharma- cokinetic (PBPK) model of ethanol inhalation in humans. They exposed rats and mice to ethanol by inhalation of 100, 400, and 1,200 mg/m3 over 6 h and measured peak BECs. They developed a PBPK model to allow predictions of peak BECs in humans. The authors reported that the model accurately pre- dicted the pharmacokinetics of ethanol in their inhalation study in mice and rats and was consistent with observed peak BECs for human males reported in the literature (primarily Lester and Greenberg 1951). The PBPK model pre- dicted that the peak BEC in human males would reach a maximum of 293 ÂµM (1.4 mg/dL or 0.001%) after inhalation of 1,200 mg/m3. The authors noted that this BEC was significantly lower than concentrations at which diminished fine motor skills and impaired judgment might begin to occur and was 1-2 orders of magnitude below legal blood ethanol limits. These studies suggest that the general range of BECs associated with mild performance impairment is 50-150 mg/dL (0.05-0.15%) (Nadeau et al. 2003). Consistent with this range, many states in the United States set their legal driving limit at 100 mg/dL (0.1%) or less. AC Development Ideally, the ACs would be based on an inhalation study that specifically evaluated the neurotoxicity of ethanol, as in the Nadeau et al. (2003) study. However, as the highest concentration used in that study (2,000 mg/m3) resulted in a BEC of only 0.44 mg/dL, it would be an inappropriately low no-observed- adverse-effect level (NOAEL) to use. Accordingly, the approach taken in this reassessment was to use the same Kennedy et al. (1993) and Lester and Green- berg (1951) data that served as the basis for neurotoxicity ACs in Volume 3 but to evaluate them in a slightly different manner. Kennedy et al. (1993) reported a neurotoxicity NOAEL of 50 mg/dL. Applying an adjustment from this target BEC to account for the sample size (â27/10) provides a target BEC of 26 mg/dL. Lester and Greenberg (1951) demonstrated (n = 3) that inhalation of ethanol at 15,000 mg/m3 resulted in a BEC of only 10 mg/dL, less than half the target BEC cited above. Given this margin, further adjustments to account for the small sample size in the Lester and Greenberg (1951) study were not deemed to be necessary. Further, as recent data from the Nadeau et al. (2003) study (n = 5) observed a BEC of only 0.44 mg/dL after inhalation of ethanol at about 2,000 mg/m3, it appears that the Lester and Greenberg (1951) results provide a rea- sonably conservative BEC estimate. Accordingly, an AC of 15,000 mg/m3 was established for all time frames as peak BECs are expected to occur within the first few hours of exposure, and because adverse neurologic health effects are not acceptable for any exposure period. Although benchmark dose modeling was initially considered for this end point, the small difference between the
Ethanol 197 NOAEL (50 mg/dL) and the lowest-observed-adverse-effect level (LOAEL) (75 mg/dl) suggests that it would not significantly improve the risk estimate. Target BEC = 50 mg/dL (from Kennedy et al. 1993) Ã (â27/10) (small n factor) = 26 mg/dL Lester and Greenberg (1951) BEC after ethanol exposure at 15,000 mg/m3 = 10 mg/dL (2.6 times lower than target BEC) 1- and 24-h, 7-, 30-, 180-, and 1,000-d AC = 15,000 mg/m3 Hepatotoxicity The Volume 3 SMACs were based on the work of Di Luzio and Stege (1979). The authors evaluated hepatotoxicity in Sprague-Dawley rats after 26 d of continuous exposure to ethanol at 20,000 mg/m3. The study observed tran- sient changes in liver triglyceride concentrations and glutamic-pyruvic transa- minase activity on days 3, 6, and 9 of testing. However, these changes were con- sidered adaptive, and the same parameters did not differ from controls by the end of the 26-d study. With 20,000 mg/m3 used as a NOAEL for hepatotoxicity, ACs were set for the 7-, 30-, and 180-d time frames (2,000 mg/m3 after applica- tion of an uncertainty factor of 10 for animal-to-human extrapolation). No expo- sure time adjustments were considered to be necessary given that BECs and liver triglyceride levels were reached quickly in the testing and declined sharply by the end of the exposure period. Additionally, no short-term ACs were estab- lished, as hepatotoxicity over these time frames was not deemed to be credible without narcotic exposures. New Data No new studies were identified that specifically evaluated the hepatotoxic- ity of ethanol after inhalation exposures. AC Development Given that no new studies were identified, the Volume 3 ACs based on the Di Luzio and Stege (1979) findings were retained. Consistent with the rationale in Volume 3 for the lack of necessity for exposure time adjustments, a 1,000-d AC for hepatotoxicity was also established (2,000 mg/m3). Di Luzio and Stege (1979) noted that inhalation exposure concentrations would have to be increas- ing on a stepwise basis for BECs to be sustained to a point where sustained he- patic effects might be observed. The authors concluded that âthe ethanol vapor inhalation technique does not induce the classical hepatic alterations associated with ethanol liquid formula diets or following the acute oral administration of
198 SMACs for Selected Airborne Contaminants ethanol.â Given that only one dose was used in the critical study, benchmark dose modeling was not pursued for this end point as part of this reevaluation. Mucosal Irritation The Volume 3 ACs for mucosal irritation were based on the findings of Lester and Greenberg (1951). In their study, the five volunteers reported only mild irritation (coughing and smarting of the eyes and nose) when exposed to ethanol at 10,000 mg/m3, and the effects dissipated so that no irritation was noted after 5-10 min of exposure. In contrast, there was continuous lacrimation at 30,000 mg/m3, and 40,000 mg/m3 was reported as intolerable. On the basis of these results, short-term ACs were set at 10,000 mg/m3, with long-term ACs set at 2,000 mg/m3 based on incorporation of an adjustment factor to account for the small sample size. New Data Several studies evaluated the nasal pungency associated with ethanol through nasal lateralization techniques (Wise et al. 2006, Cometto-MuÃ±iz and Cain 1990). In these studies, both ethanol and clean air were introduced into a subjectâs nostrils, and the concentration at which the subject could consistently identify which nostril received the ethanol exposure (through interaction with nerve endings and reports of burning, stinging, or other signs of irritation) was recorded. A limitation of these studies for SMAC purposes is that the developed detection thresholds may correspond to a relatively minor degree of irritation, and it is difficult to evaluate the impact of exposure duration. The exposure du- ration may have not been long enough to elicit a maximum response; con- versely, any observed nasal sensation may dissipate with time. Using these tech- niques, Wise et al. (2006) found that none of the six volunteers could reliably lateralize ethanol at concentrations of 2,500 mg/m3, whereas four of six (66%) could lateralize about 3,000 mg/m3. These results support the long-term AC of 2,000 mg/m3 for ethanol set in Volume 3. Using similar lateralization tech- niques, Cometto-MuÃ±iz and Cain (1990) reported that the threshold for nasal pungency (irritation) was about 19,000 mg/m3 in a group of three anosmics. These results are consistent with the upper end of the 10,000-20,000 mg/m3 pro- posed as an irritation threshold range by Lester and Greenberg (1951). With regard to eye irritation, Cometto-MuÃ±iz and Cain (1996) observed that irritation did not occur until about 90,000 mg/m3, although the degree to which the test method (a specialized bottle cap) influenced the study findings is not clear. Seeber et al. (2002) also evaluated sensory irritation associated with inhalation exposures to ethanol. They exposed volunteers to ethanol under two test conditions: (1) 4 h of constant exposure to 0, 150, 760, and 1,500 mg/m3, and (2) 4 h of variable concentration exposure at 0, 200, 2,000, and 3,600 mg/m3. The volunteers (n = 24 for the constant exposure group, n = 16 for the
Ethanol 199 variable exposure group) were asked to assess irritation of the eye, nose, throat, or skin and to rate it on a scale between 0 (not at all) and 5 (strong). With con- stant exposures, the mean evaluated response to ethanol at 1,500 mg/m3 re- mained approximately the same as the response reported for clean air. For vari- able exposures, the mean response at 3,600 mg/m3 was also consistent with the clean air response, although the authors did not adequately describe how the variable exposure regime was implemented. AC Development Available study results support the existing Volume 3 short- and long-term ACs for ethanol, which are based on the Lester and Greenberg (1951) observa- tions. Benchmark dose analysis was not pursued for this end point because of the qualitative nature of the response measurement with irritation (presence or absence of irritant effect). With regard to setting a 1,000-d AC for irritation, the same long-term AC (2,000 mg/m3) can be applied, as solvent irritation is ex- pected to peak within an hour or less (Hempel-Jorgensen et al. 1999) and not to demonstrate time dependency beyond that point. 1- and 24-h ACs (mucosal irritation) = 10,000 mg/m3 7-, 30-, 180-, and 1,000-d ACs (mucosal irritation) = 10,000 mg/m3 (1- and 24-h ACs) Ã (â5/10) (small n factor) = 2,000 mg/m3 Flush Response In Volume 3, ACs were developed that were protective against the flush response that is frequently observed in alcohol-sensitive subpopulations. This flush response is evidenced by visible facial flushing, an increase in pulse rate, blood pressure changes, elevated skin temperature, and other physical symptoms (Shibuya et al. 1989). These effects are believed to be related to a buildup of acetaldehyde, a main metabolic product of ethanol (Chan et al. 1986), as peak BECs do not differ among flushing and nonflushing subjects (Mizoi et al. 1979). Due to genetic differences related to differences in aldehyde dehydrogenase ac- tivity, 50-80% of Asians are susceptible to this adverse response to ethanol, compared with only 5-10% of Caucasians (Wolff 1972, Zeiner et al. 1979). Given these statistics, a fair percentage of crew members may exhibit this sensi- tivity, and final ACs should ensure that the potential for these adverse effects is minimized. Volume 3 set the flush response ACs by using breath acetaldehyde con- centrations observed in a study by Zeiner et al. (1979) in which Caucasian and Asian volunteers were exposed to ethanol at 0.7 mL/kg of body weight (about 40 g of ethanol for a 70-kg individual). As Shibuya et al. (1989) reported that ethanol exposures from 0.3 to 0.5 mL/kg were sufficient to induce the flush re-
200 SMACs for Selected Airborne Contaminants sponse in flush-sensitive individuals, flushing was expected in the Zeiner et al. (1979) subjects. Among Asian volunteers, 6 of 7 experienced flushing symp- toms, whereas only 1 of 10 Caucasians reported these effects. In Volume 3, a NOAEL was estimated from this study by observing that peak breath acetalde- hyde concentrations below 10 ng/mL (Figure 11-2) did not correspond with flushing in either exposure group. As the peak individual breath acetaldehyde concentration for any test subject was 60 ng/mL, the ethanol dose was down- wardly adjusted by a factor of 6 to estimate an oral NOAEL. With standard ex- posure assumptions, this dose was extrapolated to an inhalation exposure that resulted in an AC of 2,000 mg/m3 for the 7-, 30-, and 180-d time frames. A dou- bling of the exposure concentration was deemed acceptable for short-term expo- sures (1- and 24-h ACs of 4,000 mg/m3). As part of this reevaluation it was determined that there was an error in the calculation for flush response ACs in Volume 3 (p. 196). In determining the ACs, the assumed inhalation absorption percentage (62%) was applied in the numerator rather than in the denominator of the AC equation, which resulted in an underestimation of the allowable air concentration by a factor of 2.5. Recal- culating the ACs based on the correct application of the absorption fraction yields long-term ACs of 5,000 mg/m3 and corrected 1- and 24-h ACs of 10,000 mg/m3. FIGURE 11-2 Breath acetaldehyde concentrations (ng/mL) in Asian (left) and Caucasian (right) volunteers. Source: Zeiner et al. 1979. Reprinted with permission; copyright 1979, Alcoholism: Clinical and Experimental Research.
Ethanol 201 New Data As stressed in Volume 3, it would be preferable to have a study that dem- onstrates that flushing is relevant to inhalation exposures to ethanol. Unfortu- nately, an inhalation study that evaluated the induction of the flush response in sensitive and nonsensitive populations was not located in the scientific literature as part of this reevaluation. Tardif et al. (2004) evaluated breath acetaldehyde concentrations (although the flush response was not specifically evaluated) in five nonsmoking Caucasian volunteers exposed to ethanol at 50, 200, and 2,000 mg/m3. In evaluating inhalation exposures (2-6 h) to ethanol at 2,000 mg/m3, the authors observed a maximum breath acetaldehyde concentration of 2.6 ng/mL among the five volunteers (Robert Tardif, University of Montreal, personal communication, October 11, 2006). Although this level is well below the NOAEL of 10 ng/mL of Zeiner et al. (1979), the Tardif et al. (2004) group did not appear to include any flush-sensitive individuals, and it is not unusual for flush-sensitive populations to exhibit breath acetaldehyde concentrations 3-5 times higher than nonflushers (Zeiner et al. 1979, Jones 1995). Thus, it is rea- sonable to conclude that flush-sensitive individuals may approach the 10-ng/mL NOAEL in association with inhalation exposure to ethanol at 2,000 mg/m3. AC Development With joint consideration of the Tardif et al. (2004) breath acetaldehyde measurements and the NOAEL estimated from Zeiner et al. (1979), an AC of 2,000 mg/m3 is established. Given that data for multiple doses are not available for the critical study, benchmark dose analysis was not pursued for this end point. 7-, 30-, 180-, and 1,000-d ACs = 2,000 mg/m3 With regard to the short-term ACs (1 and 24 h), mild flushing should be tolerable during temporary off-nominal situations. Where flushing is induced in the scientific literature (ethanol dose of 0.3-0.5 mL/kg per Shibuya et al. (1989)), the level of discomfort most test subjects experienced appears to be consistent with the degree of impairment allowable for short-term SMACs. Thus, the short-term ACs were set at the lower end of the ethanol dose used to elicit the flushing effect in sensitive individuals (0.3 mL/kg or 17 g for a 70-kg person). A short-term AC is calculated by making the same route-to-route ex- trapolation assumptions as in Volume 3. 1- and 24-h AC = 17 g (ethanol)/0.62(absorption by inhalation)/(0.015 m3/min Ã 120 min) (inhaled air volume) = 15 g/m3 1- and 24-h AC = 15 g/m3= 15 mg/L= 15,000 mg/m3
202 SMACs for Selected Airborne Contaminants UPDATED RECOMMENDATIONS Literature not reviewed in Volume 3, in addition to new literature pub- lished since 1996, was considered in the preceding sections. This was done in an effort to update, if necessary, the recommendations for acceptable concentra- tions for ethanol inhalation exposure. These updated recommendations are summarized in Table 11-3. Also included in Table 11-3 are NASAâs proposed SMACs. These values were determined based on the lowest AC for the end- points in consideration: neurotoxicity, sensory irritation, flush response, and hepatotoxicity.
TABLE 11-3 Updated Acceptable Concentrations for Ethanol Uncertainty Factor Acceptable Concentration (mg/m3) Space- End Point, Data Species Species Time Small n flight 1h 24 h 7d 30 d 180 d 1,000 d Neurotoxicity Estimated NOAEL of 15,000 Human 1 1 â27/10 1 15,000 15,000 15,000 15,000 15,000 15,000 mg/m3 (Lester and Greenberg (applied 1951); based on target BEC of 26 to target mg/dL (Kennedy et al.1993) BEC) Sensory Irritation NOAEL of 10,000 mg/m3 Human 1 1 â3/10 1 10,000 10,000 2,000 2,000 2,000 2,000 (Lester and Greenberg 1951) Flush Response LOAEL of 0.3 mL/kg Human 1 1 1 1 15,000 15,000 - - - - (Shibuya et al. 1989) NOAEL of 2,000 mg/m3 Human 1 1 1 1 - - 2,000 2,000 2,000 2,000 (Tardif et al. 2004) based on 10 ng/dL target breath acetaldehyde level (Zeiner et al. 1979) Hepatotoxicity NOAEL, 20,000 mg/m3, Rat 10 1 1 1 - - 2,000 2,000 2,000 2,000 (Di Luzio and Stege 1979) SMACs 10,000 10,000 2,000 2,000 2,000 2,000 -, Flush Response: Mild flushing should be tolerable during temporary off-nominal situations, so short-term ACs were set at the lower end of the ethanol dose used to elicit the flushing effect in sensitive individuals. -, Hepatotoxicty: Non-narcotic exposures could not cause the relevant effects during these exposure timeframes. 203
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