FINAL: 07/2008 ACUTE EXPOSURE GUIDELINE LEVELS (AEGLs) CARBON MONOXIDE (CAS Reg. No. 630-08-0) July 2008 ------- CARBON MONOXIDE FINAL: 07/2008 PREFACE Underthe authority of the Federal Advisory Committee Act (FACA) P. L. 92-463 of 1972, the National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances (NAC/AEGL Committee) has been established to identify, review and interpret relevant toxicologic and other scientific data and develop AEGLs for high priority, acutely toxic chemicals. AEGLs represent threshold exposure limits for the general public and are applicable to emergency exposure periods ranging from 10 minutes to 8 hours. AEGL-2 and AEGL-3 levels, and AEGL-1 levels as appropriate, will be developed for each of five exposure periods (10 and 30 minutes, 1 hour, 4 hours, and 8 hours) and will be distinguished by varying degrees of severity of toxic effects. It is believed that the recommended exposure levels are applicable to the general population including infants and children, and other individuals who may be sensitive or susceptible. The three AEGLs have been defined as follows: AEGL-1 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain asymptomatic, non-sensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure. AEGL-2 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, long-lasting adverse health effects, or an impaired ability to escape. AEGL-3 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience life-threatening health effects or death. Airborne concentrations below the AEGL-1 represent exposure levels that could produce mild and progressively increasing odor, taste, and sensory irritation, or certain asymptomatic, non-sensory effects. With increasing airborne concentrations above each AEGL level, there is a progressive increase in the likelihood of occurrence and the severity of effects described for each corresponding AEGL level. Although the AEGL values represent threshold levels for the general public, including sensitive subpopulations, it is recognized that certain individuals, subject to unique or idiosyncratic responses, could experience the effects described at concentrations below the corresponding AEGL level. ------- CARBON MONOXIDE FINAL: 07/2008 TABLE OF CONTENTS PREFACE ii EXECUTIVE SUMMARY vii 1. INTRODUCTION 1 2. HUMAN TOXICITY DATA 2 2.1. Acute Lethality 3 2.1.1 Case Studies 4 2.2. Nonlethal Toxicity 7 2.2.1 Experimental Studies 7 2.2.2 Case Studies 14 2.3. Developmental/Reproductive Toxicity 20 2.4. Genotoxicity 23 2.5. Carcinogen icity 23 2.6. Summary 23 3. ANIMAL TOXICITY DATA 24 3.1. Acute Lethality 24 3.1.1. Rats 24 3.1.2. Mice 25 3.2. Nonlethal Toxicity 28 3.2.1 Monkeys 28 3.2.2 Dogs 29 3.3. Developmental/Reproductive Toxicity 29 3.3.1 Pigs 29 3.3.2 Rabbits 30 3.3.3 Rats 30 3.3.4 Mice 30 3.4. Genotoxicity 31 3.5. Carcinogen icity 31 3.6. Summary 31 4. SPECIAL CONSIDERATIONS 32 4.1. Stability, Metabolism and Disposition 32 4.2. Mechanism of Toxicity 32 4.3 Issues related to post-mortem CO determination in humans 4.3.1. Potential factors influencing COHb levels 4.3.2. Influence on collection site on measured COHb levels 4.4. Other Relevant Information 33 4.4.1. Species Variability 33 4.4.2. Intraspecies Variability 35 ------- CARBON MONOXIDE FINAL: 07/2008 4.4.3. Time Scaling 36 4.4.4. Mathematical models of COHb formation 37 5. DATA ANALYSIS FOR AEGL-1 40 5.1. Human Data Relevant to AEGL-1 40 5.2. Animal Data Relevant to AEGL-1 40 5.3. Derivation of AEGL-1 40 6. DATA ANALYSIS FOR AEGL-2 41 6.1. Human Data Relevant to AEGL-2 41 6.2. Animal Data Relevant to AEGL-2 42 6.3. Derivation of AEGL-2 42 7. DATA ANALYSIS FOR AEGL-3 46 7.1. Human Data Relevant to AEGL-3 46 7.2. Animal Data Relevant to AEGL-3 46 7.3. Derivation of AEGL-3 47 8. SUMMARYOFAEGLs 48 8.1. AEGL Values and Toxicity Endpoints 48 8.2. Comparison with Other Standards and Criteria 52 8.3. Data Adequacy and Research Needs 54 9. REFERENCES 55 APPENDIX A Time Scaling Calculations for AEGLs 63 AEGL-2 64 AEGL-3 65 APPENDIX B Mathematical Model for Calculating COHb and Exposure Concentrations 66 APPENDIX C Derivation Summary for Carbon Monoxide AEGLs 75 AEGL-1 76 AEGL-2 77 AEGL-3 80 IV ------- CARBON MONOXIDE FINAL: 07/2008 LIST OF TABLES TABLE 1: CHEMICAL AND PHYSICAL DATA 2 TABLE 2: SYMPTOMS ASSOCIATED WITH COHb IN HEALTHY ADULT HUMANS 3 TABLE 3: INCIDENCE OF ATHEROSCLEROTIC CORONARY ARTERY DISEASE AND COHb IN FATALITIES THAT INVOLVED CO EXPOSURE 6 TABLE 4: EFFECTS OF ACUTE CO EXPOSURE IN A HUMAN SUBJECT 11 TABLE 5: SYMPTOM THRESHOLD VALUES FOR PEDIATRIC CO TOXICITY 16 TABLE 6: SEVERITY OF CO POISONING 19 TABLE 7: COHb, EXPOSURE DURATION AND LACTATE CONCENTRATIONS IN RELATION TO SEVERITY OF CO POISONING 19 TABLES: SEVERITY OF CO POISONING 20 TABLE 9: OVERVIEW OF CLINICAL SCORING, COHb AND FETAL OUTCOME 20 TABLE 10: OVERVIEW OF MATERNAL CLINICAL EFFECTS, COHb AND FETAL OUTCOME22 TABLE 11: SUMMARY OF LC50 DATA IN LABORATORY ANIMALS 26 TABLE 12: COHb AFTER 48 HOURS CONTINUOUS EXPOSURE TO CO 34 TABLE 13: AEGL-1 VALUES FOR CARBON MONOXIDE 41 TABLE 14: AEGL-2 VALUES FOR CARBON MONOXIDE 46 TABLE 15: AEGL-3 VALUES FOR CARBON MONOXIDE 48 TABLE 16: SUMMARY/RELATIONSHIP OF AEGL VALUES FOR CARBON MONOXIDE 49 TABLE 17: EXTANT STANDARDS AND GUIDELINES FOR CARBON MONOXIDE 52 TABLE 18: CONCENTRATION-TIME COMBINATIONS RESULTING IN 4 % COHb 71 TABLE_19: COHb VALUES FOR AEGL-2 CONCENTRATION-TIME COMBINATIONS IN DIFFERENT SUBPOPULATIONS 71 TABLE 20: CONCENTRATION-TIME COMBINATIONS RESULTING IN 40 % COHb 72 TABLE 21: COHb VALUES FOR AEGL-3 CONCENTRATION-TIME COMBINATIONS IN DIFFERENT SUBPOPULATIONS 72 TABLE 22: COMPARISON OF REPORTED AND CALCULATED COHb VALUES FOR THE DATA BYHALDANE(1895) 74 ------- CARBON MONOXIDE FINAL: 07/2008 LIST OF FIGURES FIGURE 1: LC50 VALUES FOR CO IN DIFFERENT SPECIES 27 FIGURE 2: COHb FOR DIFFERENT EXPOSURE CONCENTRATION-TIME COMBINATIONS38 FIGURE 3: CATEGORICAL REPRESENTATION OF ALL CO INHALATION DATA 51 FIGURE 4: COHb VS. EXPOSURE TIME PLOTS 69 FIGURE 5: CALCULATION OF 60-MINUTE AEGL-2 FOR HEALTHY ADULT 71 FIGURE 6: CALCULATION OF 60-MINUTE EXPOSURE CONCENTRATION THAT WOULD RESULT IN 40% COHb IN A HEALTHY ADULT 74 ------- CARBON MONOXIDE FINAL: 07/2008 EXECUTIVE SUM MARY Carbon monoxide (CO) is a tasteless, non-irritating, odorless and colorless gaseous substance. The main source of CO production is the combustion of fuels. Exposure at the workplace occurs in blast furnace operations in the steel industry and when gasoline- or propane- powered forklifts, chain-saws or other machines are used in confined spaces, such as companies, tunnels and mines. Environmental exposure to CO can occur while traveling in motorvehicles(9-25 and up to 35 ppm), visiting urban locations with heavily traveled roads (up to 50 ppm), or cooking and heating with domestic gas, kerosene, coal or wood (up to 30 ppm) as well as in fires and by environmental tobacco smoke. Endogenous CO formation during normal metabolism leads to a background carboxyhemoglobin concentration (COHb) of about 0.5-0.8 %. Smokers are exposed to considerable CO concentrations leading to a COHb of about 3-8 %. CO binds to hemoglobin forming COHb and thereby renders the hemoglobin molecule less able to bind oxygen. Due to this mechanism, the oxygen transport by the blood and the release of bound oxygen in the tissues are decreased. Tissue damage results from local hypoxia. Organs with a high oxygen requirement, such as the heart and the brain, are especially sensitive forthis effect. AEGL-1 values were not recommended because susceptible persons may experience more serious effects (equivalent to AEGL-2 level) at concentrations, which do not yet cause AEGL-1 effects in the general population. Patients with coronary artery disease show health effects at lower COHb levels than children, pregnant women or healthy adults and, thus, constitute the most susceptible subpopulation. For the derivation of AEGL-2 values a level of 4 % COHb was chosen. At this exposure level, patients with coronary artery disease may experience a reduced time until onset of angina (chest pain) during physical exertion (Allred etal., 1989; 1991). In the available studies, the CO exposure alone (i.e. with subjects at rest) did not cause angina, while exercise alone did so. However, since all studies used patients with stable exertional angina, who did not experience angina while at rest, it cannot be ruled out that in more susceptible individuals (a part of the patients with unstable angina pectoris might belong to this group) CO exposure alone could cause or increase angina symptoms. The changes in the electrocardiogram (ST-segment depression of 1 mm (corresponding to 0.1 mV) or greater) associated with angina symptoms were considered reversible, but is indicative of clinically relevant myocardial ischemia requiring medical treatment. An exposure level of 4 % COHb is unlikely to cause a significant increase in the frequency of exercise-induced arrhythmias. Ventricular arrhythmias have been observed at COHb of 5.3%, but not at 3.7 % (Sheps et al., 1990; 1991), while in another study no effect of CO exposure on ventricular arrhythmia was found at 3 or 5 % COHb (Dahms et al., 1993). This exposure level, which corresponds to COHb values of 5.0-5.6% in newborn and children was considered protective of acute neurotoxic effects in children, such as syncopes, headache, nausea, dizziness and dyspnea (Klasner et al., 1998; Crocker and Walker, 1985), and long-lasting neurotoxic effects (defects in the cognitive development and behavioral alterations) in children (Klees et al., 1985). A mathematical model (Coburn et al., 1965; Peterson and Stewart, 1975) was used to calculate exposure concentrations in air resulting in a COHb of 4 % in adults at the end of exposure periods of 10 and 30 minutes and 1, 4 and 8 hours. A total uncertainty factor of 1 was used. A level of 4 % COHb was the NOEL for AEGL-2 effects in patients with coronary artery disease, while the LOEL was estimated at 6-9 %. In comparison, the LOEL was about 10-15 % in children and 22-25 % in VII ------- CARBON MONOXIDE FINAL: 07/2008 pregnant women. Since AEGL-2 values were based on experimental data on the most susceptible subpopulation, they were considered protective also for other subpopulations and a total uncertainty factor of 1 was used. It is acknowledged that apart from emergency situations, certain scenarios could lead to CO concentrations which may cause serious effects in persons with cardiovascular diseases. These scenarios include e.g. extended exposure to traffic fume emissions (e.g., in tunnels or inside cars with defect car exhaust systems), charcoal or wood fire furnaces, and indoor air pollution by tobacco smoking. The derivation of AEGL-3 values was based on a weight of evidence analysis of human lethal and non-lethal observations. Analysis of lethal cases reported by Nelson (2005a) indicated that most lethal poisoning cases occurred atCOHb levels higherthan 40% and that survival of CO- exposed humans were likely to be seen at levels below 40%. Thus, 40%COHb level seems a reasonable threshold for lethality. This level is supported by experimental studies performed in healthy human subjects. Studies by Chiodi etal. (1941), Henderson etal. (1921), and Haldane (1895) suggest that a COHb of about 34-56 % does not cause lethal effects in healthy individuals. Further support come from the studies by Kizakevich et al. (1994), Stewart et al. (1970), and Nielsen (1971) that reported headache as the only symptom when subjects were exposed to 20-33 % COHb. A level of 40 % COHb was used as the basis for AEGL-3 derivation. This point of departure is supported by studies in animals reporting minimum lethal COHb levels in rats and mice of about 50-70 % (E.I. du Pont de Nemours and Co., 1981; Rose et al., 1970). A mathematical model (Coburn et al., 1965; Peterson and Stewart, 1975) was used to calculate exposure concentrations in air resulting in a COHb of 40 % at the end of exposure periods of 10 and 30 minutes and 1, 4 and 8 hours. A total uncertainty factor of 3 was used. A total uncertainty factor of 3 for intraspecies variability was considered adequate based on supporting evidence for susceptible subpopulations: 1) Exposure to the derived AEGL-3 concentrations will result in COHb values of about 14-17 % in adults, which, based on case reports, was considered to protect heart patients against CO-induced myocardial infarction. It should be noted, however, that a clear threshold for this endpoint cannot be defined because myocardial infarction might be triggered at lower COHb in hypersusceptible individuals. 2) This COHb level was considered protective of lethal effects in the unborn, because in the case studies available, stillbirths were found only after measured maternal COHb of about 22-25 % or higher (Caravati et al., 1988; Koren et al., 1991) and the level was supported by animal studies.. The AEGL values are listed in the table below. SUMMARY TABLE OF AEGL VALUES FOR CARBON MONOXIDE Classificatio n AEGL-1 (Nondisablin g) 10-Minute N.R.a 30- Minute N.R. 1-Hour N.R. 4-Hour N.R. 8-Hour N.R. Endpoint (Reference) - VIM ------- CARBON MONOXIDE FINAL: 07/2008 AEGL-2 b (Disabling) AEGL-3 c (Lethal) 420 ppm (480 mg/m3) 1700 ppm (1900 mg/m3) 150 ppm (170 mg/m3) 600 ppm (690 mg/m3) 83 ppm (95 mg/m3) 330 ppm (380 mg/m3) 33 ppm (38 mg/m3) 150 ppm (170 mg/m3) 27 ppm (31 mg/m3) 130 ppm (150 mg/m3) Cardiac effects in humans with coronary artery disease (Allred et al., 1989; 1991) Lethal poisoning was associated with a COHb >= 40 % in most lethal poisoning cases reported by Nelson (2005a); no severe or life-threatening effects in healthy humans at COHb of 34-56 % (Chiodi et al., 1941; Henderson et al., 1921; Haldane, 1895) a N.R., not recommended because susceptible persons may experience more serious effects (equivalent to AEGL-2 level) at concentrations, which do not yet cause AEGL-1 effects in the general population. b It was estimated that exposure to the AEGL-2 concentration-time combinations result in COHb levels of 5.3-5.6 % in newborns, 4.9-5.2 % in 5-year-old children, 4.0 % in adults and 6.2-11.5 % in adult smokers. c It was estimated that exposure to the AEGL-3 concentration-time combinations result in COHb levels of 19.5-20.1 % in newborns, 18.1-18-7 % in 5-year-old children, 13.8-17.2 % in adults and 16.1-23.0 % in adult smokers. References Allred, E.N., E.R. Bleecker, B.R. Chaitman, I.E. Dahms, S.O. Gottlieb, J.D. Hackney, M. Pagano, R.H. Selvester, S.M. Walden and J. Warren, 1989. Short-term effects of carbon monoxide exposure on the exercise performance of subjects with coronary artery disease. New England Journal of Medicine 321, 1426-1432. Allred, E.N., E.R. Bleecker, B.R. Chaitman, I.E. Dahms, S.O. Gottlieb, J.D. Hackney, M. Pagano, R.H. Selvester, S.M. Walden and J. Warren, 1991. Effects of carbon monoxide on myocardial ischemia. Environmental Health Perspectives 91, 89-132. Atkins, E.H. and E.L. Baker, 1985. Exacerbation of coronary artery disease by occupational carbon ------- CARBON MONOXIDE FINAL: 07/2008 monoxide exposure: A report of two fatalities and a review of the literature. American Journal of Industrial Medicine 7, 73-79. Caravati, E.M., C.J. Adams, S.M. Joyce and N.C. Schafer, 1988. Fetal toxicity associated with maternal carbon monoxide poisoning. Annals of Emergency Medicine 17, 714-717. Chiodi, H., D.B. Dill, F. Consolazio and S.M. Horvath, 1941. Respiratory and circulatory responses to acute carbon monoxide poisoning. American Journal of Physiology 134, 683-693. Coburn, R.F., R.E. Forsterand P.B. Kane, 1965. Considerations of the physiological variables that determine the blood carboxyhemoglobin concentration in man. Journal of Clinical Investigation 44, 1899-1910. Crocker, P.J. and J.S.Walker, 1985. Pediatric carbon monoxide toxicity. The Journal of Emergency Medicine 3, 443-448. Crocker, P.J. and J.S. Walker, 1985. Pediatric carbon monoxide toxicity. Journal of Emergency Medicine 3, 443-448. Dahms, I.E., L.T. Younis, R.D. Wiens, S. Zarnegar, S.L. Byers and B.R. Chaitman, 1993. Effects of carbon monoxide exposure in patients with documented cardiac arrhythmias. Journal of the American College of Cardiology 21, 442-450. Ebisuno, S., M. Yasuno, Y. Yamada, Y. Nishino, M. Hori, M. Inoue and T. Kamada, 1972. Myocardial infarction after acute carbon monoxide poisoning: case report. Angiology37, 621-624. Grace, T.W. and F.W. Platt, 1981. Subacute carbon monoxide poisoning. Journal of the American Medical Association 246, 1698-1700. Haldane, J., 1895. The action of carbonic acid on man. Journal of Physiology 18, 430-462. Klasner, A.E., S.R. Smith, M.W. Thompson and A.J. Scalzo, 1998. Carbon monoxide mass exposure in a pediatric population. Academic Emergency Medicine 5, 992-996. Henderson, Y., H.W. Haggard, M.C. Teague, A.L. Prince and R.M. Wunderlich, 1921. Physiological effects of automobile exhaust gas and standards of ventilation for brief exposures. Journal of Industrial Hygiene 3, 79-92. Kizakevich, P.M., M.L. McCartney, M.J. Hazucha, L.H. Sleet, W.J. Jochem, A.C. Hackney and K. Bolick, 2000. Noninvasive ambulatory assessment of cardiac function in healthy men exposed to carbon monoxide during upper and lower body exercise. Eurpean Journal of Applied Physiology83, 7-16. Klasner, A.E., S.R. Smith, M.W. Thompson and A.J. Scalzo, 1998. Carbon monoxide mass exposure in a pediatric population. Academic Emergency Medicine 5, 992-996. Klees, M., M. Heremans and S. Dougan, 1985. Psychological sequelae to carbon monoxide intoxication in the child. The Science of the Total Environment 44, 165-176. ------- CARBON MONOXIDE FINAL: 07/2008 Koren, G., R. Sharav, A. Pastuszak, L.K. Garrettson, K. Hill, I. Samson, M. Rorem, A. King and J.E. Dolgin, 1991. A multicenter, prospective study of fetal outcome following accidental carbon monoxide poisoning in pregnancy. Reproductive Toxicology 5, 397-403. Marius-Nunez, A.L., 1990. Myocardial infarction with normal coronary arteries after acute exposure to carbon monoxide. Chest 97, 491-494. Nelson.G. 2005a. Effects of Carbon Monoxide in Man. In: Carbon Monoxide and Human Lethality: Fire and Non-fire studies, M.M. Hirschler (Ed.). Taylor and Francis, New York, 2005, pp 3-60. Nielsen, B., 1971. Thermoregulation during work in carbon monoxide poisoning. Acta Physiologica Scandinavica 82, 98-106. Peterson, J.E. and R.D. Stewart, 1975. Predicting the carboxyhemoglobin levels resulting from carbon monoxide exposures. Journal of Applied Physiology 39, 633-638. Sheps, D.S., M.C. Herbst, A.L. Hinderliter, K.F. Adams, L.G. Ekelund, J.J. O'Neill, G.M. Goldstein, P.A. Bromberg, J.L. Dalton, M.N. Ballenger, S.M. Davis and G.G. Koch, 1990. Production of arrhythmias by elevated carboxyhemoglobin in patients with coronary artery disease. Annals of Internal Medicine 113, 343-351. Sheps, D.S., M.C. Herbst, A.L. Hinderliter, K.F. Adams, L.G. Ekelund, J.J. O'Neill, G.M. Goldstein, P.A. Bromberg, M. Ballenger, S.M. Davis and G. Koch, 1991. Effects of 4 Percent and 6 Percent Carboxyhemoglobin on Arrhythmia Production in Patients with Coronary Artery Disease. Research Report No. 41, Health Effects Institute, Cambridge, Massachusetts. Stewart, R.D., J.E. Peterson, E.D. Baretta, R.T. Bachand, M.J. Hosko and A.A. Herrmann, 1970. Experimental human exposure to carbon monoxide. Archives of Environmental /-/ea/f/?21,154-164. ------- ------- CARBON MONOXIDE FINAL: 07/2008 1. INTRODUCTION Carbon monoxide (CO) is a tasteless, odorless and colorless gaseous substance (WHO, 1999a). CO is produced by both natural and anthropogenic processes. The main source of CO production is the combustion of fuels. The burning of any carbonaceous fuel produces CO and carbon dioxide as the primary products. The production of carbon dioxide predominates when the air or oxygen supply is in excess of the stoichiometric needs for complete combustion. If burning occurs under fuel-rich conditions, with less air or oxygen than is needed, CO will be produced in abundance (WHO, 1999a). Emission sources include gasoline-and diesel-powered motor vehicles, stationary combustion equipment, such as heating and power generating plants, industrial processes, such as blast furnace operation in steel industry, indoor sources, such as gas ovens, unvented kerosene and gas space heaters and coal and wood stoves, as well as wildfires and tobacco smoking. Exposure at the workplace occurs in blast furnace operations in the steel industry and when gasoline- or propane-powered forklifts, chain-saws or other machines are used in confined spaces, such as companies, tunnels and mines. Low concentrations are produced in the atmosphere by reactions of hydroxyl radicals with methane and other hydrocarbons as well as by the reactions of alkenes with ozone. In addition to exogenous sources, humans are also exposed to small amounts of CO produced endogenously. In the process of natural degradation of hemoglobin to bile pigments, oxidation of the tetrapyrrol ring of heme leads to opening of the ring and formation of biliverdin and CO (WHO, 1999a). The endogenous CO formation leads to a background carboxyhemoglobin concentration in blood (COHb) of about 0.5 to 0.8 % (NIOSH, 1972). Increased destruction of red blood cells, e.g. caused by hematomas, blood transfusion or intravascular hemolysis, and accelerated breakdown of other heme proteins will lead to increased production of CO. In patients with hemolytic anemia, the CO production rate was 2-8 times higher and blood COHb was 2-3 times higher than in healthy individuals (Coburn et al., 1966). Smokers are exposed to considerable CO concentrations leading to an average COHb of 4 %, with a usual range of 3-8 % (Radford and Drizd, 1982). Exposure to CO can also be caused indirectly by exposure to certain halomethanes, particularly dichloromethane (synonym: methylene chloride), because these solvents are at least partly metabolized oxidativelyto CO by cytochrome P450 (Gargas et al., 1986; see ATSDR, 1998 for review). Environmental exposure to CO can occur while traveling in motorvehicles, working, visiting urban locations associated with combustion sources, or cooking and heating with domestic gas, charcoal or wood fires, as well as by environmental tobacco smoke. WHO (1999a) summarized environmental concentrations as follows: CO concentrations in ambient air monitored from fixed-site stations are generally below 9 ppm (8-hour average). However, short-term peak concentrations up to 50 ppm are reported on heavily traveled roads. The CO levels in homes are usually lowerthan 9 ppm; however, the peak value in homes could be up to 18 ppm with gas stoves, 30 ppm with wood combustion and 7 ppm with kerosene heaters. The CO concentrations inside motorvehicles are generally around 9-25 ppm and occasionally over 35 ppm. Similar exposure levels were reported by EPA (2000). 1 ------- CARBON MONOXIDE FINAL: 07/2008 TABLE 1: CHEMICAL AND PHYSICAL DATA Parameter Molecular formula Molecular weight CAS Registry Number Physical state Color Synonyms Density Melting point Boiling point Solubility Odor Explosive limits in air Conversion factors Value CO 28.01 630-08-0 gaseous colorless none 1 .250 g/l at 0 °C 1.145g/lat25°C -199°C -191.5°C 35.4 ml/l at 0 °C 21 .4 ml/l at 25 °C odorless 12.5 % (LEL) to 74.2 % (UEL) 1 ppm = 1 . 1 45 mg/m3 1 mg/m3 = 0.873 ppm Reference WHO, 1999a WHO, 1999a WHO, 1999a WHO, 1999a WHO, 1999a WHO, 1999a WHO, 1999a WHO, 1999a WHO, 1999a WHO, 1999a WHO, 1999a WHO, 1999a 2. HUMAN TOXICITY DATA | Based on older literature^ the COHb in the blood has been correlated with symptoms in healthy adults, shown in the left half of Table 2 (WHO, 1999a). Very similar tables or descriptions are found in different publications (e.g. AIHA, 1999; Winter and Miller, 1976; Holmes, 1985; Stewart, 1975; Roos 1994). However, with respect to both lethal and nonlethal effects of CO, susceptible subpopulations have been identified and effects on these are depicted in the right half of Table 2 for comparison (see subsequent sections for references). The unborn fetus and adults with coronary artery disease are considerably more susceptible for lethal effects of CO than healthy adults. For nonlethal effects of CO, subjects with coronary artery disease (increased frequency of arrhythmias and reduced time to onset of angina and to changes in the electrocardiogram and children (syncopes, long-lasting neurotoxic effects) constitute susceptible subpopulations. ------- CARBON MONOXIDE FINAL: 07/2008 TABLE 2: SYMPTOMS ASSOCIATED WITH COHb IN HEALTHY ADULT HUMANS AND SUSCEPTIBLE SUBPOPULATIONS Healthy Adults; adopted from WHO, 1999a COHb (%) ••-'I 3-8 10 20 30 40-50 60-70 80 Symptoms physiologic background concentration background concentration in smokers no appreciable effect, except shortness of breath on vigorous exertion, possible tightness across the forehead, dilation of cutaneous blood vessels shortness of breath on moderate exertion, occasional headache with throbbing in temples decided headache, irritable, easily fatigued, judgment disturbed, possible dizziness, dimness of vision headache, confusion, collapse, fainting on exertion unconsciousness, intermittent convulsion, respiratory failure, death if exposure is long continued rapidly fatal Susceptible Subpopulations COHb (%) 2 5-6 7 13 15 25 25 Symptoms during physical exertion reduced time to onset of angina and electrocardiogram signs of myocardial ischemia in subjects with coronary artery disease increase in cardiac arrhythmias in subjects with coronary artery disease headache, nausea in children cognitive development deficits in children myocardial infarction in subjects with coronary artery disease syncopes in children Stillbirths 2.1. Acute Lethality Mortality from CO poisoning is high: for England and Wales, 1365 deaths due to CO exposure were reported in 1985. In the USA, more than 3800 people annually die from accidental or intentional CO exposure (WHO, 1999a). ------- CARBON MONOXIDE FINAL: 07/2008 Immediate death from CO is most likely caused by effects on the heart, because the myocardial tissue is most sensitive to hypoxic effects of CO. Severe poisoning results in marked hypotension and lethal arrhythmias, which have been considered responsible for a large number of pre-hospital deaths. Rhythm disturbances include sinus tachycardia, atrial flutter and fibrillation, premature ventricular contractions, ventricular tachycardia and fibrillation (WHO, 1999a). The susceptible subpopulations for lethal effects are subjects with coronary artery disease and the unborn fetus (see Section 2.3). The review on death causes by Balraj (1984) shows an association between coronary artery disease and relatively lowCOHb. A number of case studies is presented in which CO exposure contributed to myocardial infarction (all cases of infarction are presented in this section irrespective of whetherthe patients were rescued from death by intensive medical care or not). The British Standards Institution (BSI, 1989) has published the following concentration-time combinations as lethal exposures to CO (used for hazard estimation in fires): 40000 ppm x 2 minutes, 16000 ppmx 5 minutes, 8000 ppmx 10 minutes, 3000 ppm x 30 minutes and 1500 ppmx 60 minutes. The International Standard Organization has published lethal exposure concentrations of 12000-16000 ppm for 5 minutes and 2500-4000 ppm for 30 minutes (for an adult engaged in light activity) (ISO, 1989). From the documents it was concluded that the published values are for normal, healthy adults and that the values were based on animal data (especially monkeys; Purser and Berrill, 1983); the documents did not discuss the issue of subpopulations at higher risk for lethal effects. 2.1.1 Case Studies Nelson (2005a) reported data from unvented space heaters related to human lethality cases related to CO poisoning. Sixteen out of 22 lethal cases had COHb levels more than 40%. Six out of 22 victims had COHb < 40% and 2/6 cases had pre-existing conditions such as arteriosclerotic disease and cardiorespiratory failure. A1942 fatality study reported by Nelson (2005a) summarized COHb data for 68 victims that were found dead in a gas-filled room or in a garage containing exhaust gases at high concentrations. CO concentrations were not provided. Sixty-seven percent of the 68 cases died with 40-88% COHb levels. Three-percent of the cases died with 30-40% COHb levels. Summary of another fatality study from Poland showed a similar trend of COHb levels (Nelson, 2005a). Individual data were not provided and the CO source was not discussed. However, the Polish study considered 321 lethal CO poisonings from 1975-1976 and provided COHb levels for survivors (n=220) and fatal cases (n=101). The survivors had a mean COHb level of 28.1% (SD=14.1), whereas the lethal cases showed an average COHb level of 62.3% (SD=10.1). Over 80% of the survivors had COHb levels below 40%. In contrast, around 90% of the deceased had COHb levels above 50%. Similar percentages of survivors and deceased were observed at COHb levels between 40-50% with a slight increase in the number of survivors when compared to that of the lethal cases. These three studies showed a trend that most lethal cases occurred at COHb levels higher than 40% and that survivorship was likely to be seen at levels below 40%. Another study from the Center of Forensic Sciences in Canada evaluated 304 fatal cases from 1965-1968 (Nelson, 2005a). The mean lethal COHb level was 51 ± 12% with a majority range between 40 and 59% and the highest single frequency range at 45-59%. A report on CO exposure from exhaust fumes in the state of Maryland during 1966-1971 showed COHb levels in the 40-79% ------- CARBON MONOXIDE FINAL: 07/2008 range for 98% of lethal cases (Nelson, 2005a). The Institute of Forensic Medicine in Oslo reported a study of COHb levels in automobile exhaust victims (n=54). The mean fatal COHb level was 70 percent and 40% was the minimum COHb level exhibited by less than 2% of the cases (Nelson, 2005a). Another forensic study (Nelson et al. 2005c) examining 2241 fatalities between the years of 1976-1985 found that the mean COHb level of all the cases was 64.20% with a standard deviation of 17.47. The data showed that 34% of victims had COHb levels of less than 60%. Of those who died in fires, 41 % had COHb levels of less than 60% compared to 22% of the non-fire deaths. Pach et al. (1978; 1979) reviewed a cases of carbon monoxide in the Toxicological Clinic, Cracow, Poland in the years 1975-1976. Excluded from this study were mixed intoxications, e.g., by CO and medicaments. Group A were 101 persons (60 men and 41 women, mean age 48 +/-15 years) that had died from CO poisoning before arrival at the clinic. Measurement of COHb and autopsy was done on these subjects. Group B comprised 220 subjects (95 men and 125 women, mean age 38 +/-18 years) that were treated for CO poisoning. COHb was determined upon arrival at the clinic. Patients for which the time between the end of exposure and blood drawing at the clinic was longer than 120 minutes (N = 62) were excluded from further analysis. For the patients, the COHb at the end of exposure was recalculated. Mean COHb values for Groups A and B were 62 +/-10 % and 28 +/- 14 %, respectively. In Group A, the percentages of subjects with COHb between 30-40, 40-50, 50-60, 60-70, 70-80 and 80-90 % were 2, 6, 26, 44, 21 and 2, respectively, while 3, 25, 32, 24, 12, 3, 0.6 and 0.6 % of the patients in the corrected Group B had COHb values between 0-10,10-20, 20-30, 30-40, 40-50, 50-60, 60-70 and 70-80 %, respectively. Within each group no correlation between COHb and either sex, blood alcohol above 0.1% or poisoning circumstances (accidental or suicidal) were found. Group A showed a higher percentage (34 %) of subjects that were 60 years or older than Group B (13 %), while Group B had a higher percentage of subjects younger than 30. Grace and Platt(1981) reported two cases of myocardial infarction due to CO poisoning. In the first case, a 67-year-old man was exposed to increased CO concentrations for about a few weeks in his home due to a rusted-outflue of a gas-furnace. The man presented to the emergency room after three days of persistent light-headedness with vertigo, brief stabbing anterior chest pain that worsened with deep inspiration, a dry cough, chills and a mild headache. His wife experienced similar malaise and dizziness that had been resolving over the past week. At the hospital, his symptoms were explained with a diagnosis of viral syndrome, hypokalemia of unclear origin and diabetes mellitus with diabetic peripheral and autonomic neuropathy. Ten days after discharge he was seen in the emergency room with true vertigo, palpitations and nausea, but was sent home to be followed up as an outpatient. Four days later he returned to the emergency room after development of rectal urgency and an explosive incontinent diarrheal stool, followed by a severe crushing anterior chest pain. With the pain he collapsed on the floor. The electrocardiogram showed an acute myocardial infarction. His COHb (measured on arterial blood gases) was 15.6 %, the level of the patient's wife was 18.1 %. The patient survived and recovered completely. In the second case, a 69-year-old man came to the emergency room after awakening two days earlier with confusion, nausea and vomiting. He then passed out and awoke the next day in the bathroom. He crawled to the living room, where he again passed out for an undetermined amount of time, awoke to open his door for fresh air, and then went to bed. He later experienced auditory and visual hallucinations and phoned his neighbor for help. An acute inferior myocardial ------- CARBON MONOXIDE FINAL: 07/2008 infarction with secondary mild congestive heart failure and chronic obstructive pulmonary disease was diagnosed. During his hospitalization, his sister and daughter-in-law spent a night in his mobile home. They arrived at the emergency room early the next morning with throbbing headaches, vomiting and vertigo. Their COHb values were 28 and 32 %. A faulty gas water heater had caused CO exposure. The patient survived and recovered completely. Atkins and Baker (1985) described two fatal cases of workers with severe atherosclerotic coronary artery disease. The first worker (age not stated) was a shipping employee in a plant that reconditioned steel dyes. A gas-fired furnace was used fortempering the dyes, but also for heating the plant. One day the worker was found unconscious and resuscitation efforts at a nearby hospital were unsuccessful. Autopsy showed a severe two-vessel coronary artery disease and old scarring, and a COHb of 30 %. Four other workers of the plant complaining of nausea were seen in the emergency room, but COHb was not obtained. The second worker (age not stated) was operating a bale press in a used-clothing company. As well as gas- and oil-fired heaters, there were a number of propane-fueled forklifts used to transport bales of clothing and ventilation was poor. Resuscitation was unsuccessful after his collapse. Autopsy revealed three-vessel coronary artery disease and global subendocardial ischemia. Two blood samples showed COHb of 24.1 and 21.5 %. Five other workers from the same company were also seen, complaining of light nausea, lightheadedness and headache. One was hospitalized with a COHb of 35 %; the others had levels from 4.1 to 12.8 %. CO measurement was performed in the company the next day and revealed concentrations of 135-310 ppm. Concentrations were highest near forklifts (250-310 ppm) and near the bale press (120-230 ppm), which was where the patient had been working at the time of his death. Ebisuno et al. (1972) reported a case of myocardial infarction after acute CO poisoning in a healthy young man. A 28-year-old male ironworker was admitted to the emergency room complaining of precordial pain. Two hours before admission the patient had been exposed accidentally to CO for about one hour while working at a blast furnace. After the exposure he experienced a sense of fullness of the head and precordial pain following transient unconsciousness. Blood samples two hours after the exposure contained COHb of 21 %. The electrocardiogram was interpreted as an acute anterior myocardial infarction. The coronary arteriogram one month after onset of infarction showed no significant narrowing on both left and right coronary arteries. The left ventriculogram showed a giant aneurysm in the apical portion. At operation from the ventricular aneurysmectomy, a massive transmural myocardial necrosis was observed. After surgical treatment, the patient is free of symptoms. Marius-Nunez (1990) reported the case of a 46-year-old man, who suffered an acute myocardial infarction after CO exposure. He was found unconscious in a doorway of a burning apartment. Artificial respiration was initiated until arrival at the emergency room. The electrocardiogram showed sings of myocardial infarction, which was confirmed by high levels of cardiac enzymes in the patient's serum. Blood gas analysis revealed a COHb of 52.2 %. After 3 hours treatment with 100 % oxygen, the patient became alert and oriented, COHb was 23 %. After 7 hours, he was extubated and a COHb of 13.4 % was measured. The patient's medical profile was negative for coronary heart disease risk factors, such as smoking, hypertension, diabetes mellitus or coronary artery disease. A coronary angiogram performed one week later failed to reveal evidence of coronary obstructive lesions. ------- CARBON MONOXIDE FINAL: 07/2008 Balraj (1984) reviewed all deaths that were certified by the Cuyahoga County Coroner's Office from the years 1958-1980, wherein asphyxia by CO was the primary caused of death and a natural disease was the ,,other" diagnosis or vice versa. During the 23-year period, 38 deaths were certified. These were divided into two groups: Group 1 consisted of 28 cases where all diagnosis including the abnormal COHb was documented by complete postmortem examination. Group 2 consisted of 10 cases where the diagnosis of the "other" condition was based on review of medical records, including results of coronary angiogram, serum enzymes, and clinical history; autopsy was not performed on these 10 cases. The Group 3 served for comparison and comprised all deaths that occurred in individuals 35 to 86 years of age in whom the COHb was 60 % and more (n = 100). A complete autopsy had been performed in each of these cases. Of the 28 cases in Group 1, the primary cause of death was asphyxia by CO in 21 cases. The "other" condition in 19 of these cases was atherosclerotic coronary artery disease. Of these, 8 persons had hypertensive cardiovascular disease and 2 had pulmonary emphysema in addition. In the remaining 7 cases of this group, the primary cause of death was atherosclerotic coronary artery disease and the "other" condition was asphyxia by CO. In Group 2 atherosclerotic coronary artery disease was the primary cause of death and asphyxia by CO was the "other" condition in 3 cases. In the remaining 7 cases asphyxia by CO was the primary cause of death and in all but one of these cases, the "other" condition was atherosclerotic coronary artery disease, two of the individuals had hypertensive cardiovascular disease in addition. The results are presented in Table 3. ------- CARBON MONOXIDE FINAL: 07/2008 TABLE 3: INCIDENCE OF ATHEROSCLEROTIC CORONARY ARTERY DISEASE AND COHb IN FATALITIES THAT INVOLVED CO EXPOSURE; adopted from Balraj, 1984 Total Age (years) COHb (%) Delayed deaths Coronary atherosclerosis Myocardial infarct Heart weight (g) 30-40 41-50 51-60 61-70 71-80 81-90 10-30 40-50 60 and more mild moderate severe recent old 415 and more Number of cases Group 1 28 1 1 7 10 5 4 14 4 0 10 2 2 24 1 4 20 Group 2 10 0 0 2 4 2 2 5 3 0 2 unknown unknown 5 0 1 unknown Group 3 100 22 31 28 10 6 3 0 0 100 0 89 5 6 0 2 13 2.2. Nonlethal Toxicity Nonlethal effects of CO on humans have been reported in experimental studies in both healthy individuals and in patients with coronary artery disease (see Section 2.2.1). Case studies (see Section 2.2.2) are presented for children and adults and identify children as another susceptible subgroup for nonlethal CO effects. 2.2.1 Experimental Studies 2.2.1.1 Subjects with Coronary Disease ------- CARBON MONOXIDE FINAL: 07/2008 A large number of studies investigated the effects of low CO exposure (COHb <10 %) on healthy individuals and high-risk groups. These experiments have been reviewed extensively by WHO (1999a) and EPA (2000). In healthy individuals, symptoms, such as decreases in work capacity and decrements of neurobehavioral function, start at COHb of 5 % (WHO, 1999a; EPA, 2000; Hazucha, 2000). With respectto high-risk groups, studies evaluating ST-segment changes in the electrocardiogram and cardiac arrhythmogenic effects in patients with coronary artery disease will be presented here, because these gave the most consistent results and also were considered most relevant for AEGL derivation (for review see WHO 1999a; EPA, 2000). Caracteristic points of an electrocardiogramm are the P wave, reflecting atrial depolarization, the QRS-complex, representing the ventricular muscle depolarization, and the T- wave, reflecting ventricular muscle repolarization. In the normal electrocardiogramm, the ST- segment is isoelectric, resting at the same potential as the interval between the T-wave and the next P wave. Horizontal depression or a downsloping ST-segment merging into the T-wave occurs as a result of ischemia, ventricular strain, changes in the pattern of ventricular depolarization or drug effects. In chronic ischemic heart disease, there may be moderate degrees of horizontal ST- segment depression or a downward sloping ST-segment, flattening or inversion of T-waves and prominent U-waves. It is difficult to define an abnormal ST-segment depression in precise quantitative terms. However, a myocardia ischemia has to be considered if the beginning of the ST- segment is more than 0.5 mm (corresponding to 0.05 mV) below the isoelectric line and there is an associated T-wave abnormality (Wilson et al., 1991). Allred et al. (1989a; b; 1991) conducted a multicenter study of effects of low COHb on 63 individuals with coronary artery disease. Male subjects aged 41-75 (mean = 62.1 years) with stable exertional angina pectoris (diagnosis established for >3 months; no at rest symptoms) and a positive stress test (measured by a greater than 1-mm change in the ST-segment of the electrocardiogram and occurrence of angina symptoms), were studied in three different test centers using standardized test protocols. Only patients showing reproducible effects before and after a test stay in the exposure chamber on the qualifying visit were included. On the subsequent exposure days, the stress test was repeated before the exposure and if the result was not reproducible compared to the qualifying visit, the visit was repeated on another date and at the second failure in the pretest the subject was dropped from the study. Further evidence that these subjects had coronary artery disease was provided by the presence of at least one of the following criteria: angiographic evidence of narrowing (-70 %) of at least one coronary artery, documented prior myocardial infarction or a positive stress thallium test demonstrating an unequivocal perfusion defect. All patients were tested three times on separate days in a double-blind fashion. On each of the 3 exposure days, the subject performed a symptom-limited exercise test on a treadmill (pretest), he was then exposed for 50-70 minutes randomly to air and to CO (subjects were exposed to CO concentrations that were experimentally determined to produce end-exposure COHb of 2.2% or4.4 %; these COHb values were 10 % higher than the targeted concentrations to compensate for the CO loss during exercise) and afterwards he performed a second symptom-limited exercise test. The mean exposure levels and ranges for the test environment were clean air(0 ppm), 117 ppm (range 42-202 ppm) for COHb of 2 % and 253 ppm (range 143-357 ppm) for COHb of 4 %. Gas chromatographic measurements of COHb were performed 1 minute afterthe pretest, after 30 and 40 minutes into exposure, at the end of exposure and 1 minute after the second stress test and ------- CARBON MONOXIDE FINAL: 07/2008 revealed postexercise COHb of 2.0+/-0.1 and 3.9+/-0.1 %, respectively. The time to onset of angina and the time to 1-mm ST-segment change were determined for each test. The percent changes following exposure at both 2 % and 4 % COHb were then compared with the same subject's response to the randomized exposure to room air. When potential exacerbation of the exercise-induced ischemia by exposure to CO was tested using the objective measure of time to 1-mm ST-segment change, exposure to CO levels producing COHb of 2 % resulted in a overall statistically significant 5.1 % decrease in the time to attain this level of ischemia. For individual centers, results were significant in one, borderline significant in one and nonsignificant in one center. At 4 % COHb, the decrease in time to the ST criterion was 12.1% (statistically significant for all patients, the effect was found in 49/62 subjects) relative to the air-day results. Significant effects were found in all three test centers. The maximal amplitude of the ST-segment change was also significantly affected by the carbon monoxide exposures: at 2 % COHb the maximal increase was 11 % and at 4 % COHb the increase was 17 % relative to the air day. At 2 % COHb, the time to angina was reduced by 4.2 % in all patients (effects were significant in two test centers and nonsignificant in one center). At 4 % COHb, the time was reduced by 7.1 % in all patients (effects were significant in one, borderline significant in one and nonsignificant in one center). The two end-points (time to angina and time to ST change) were also significantly correlated. Only at 4 % COHb a significant reduction in the total exercise time and in the heart rate- blood pressure product was found (this double product provides a clinical index of the work of the heart and myocardial oxygen consumption). A number of other studies also evaluated the same endpoints. A reduced time to onset of exercise-induced chest pain was reported at COHb of 2.5-3.0 % (Aronow et al., 1972), 3 % (Kleinman et al., 1989), 2.9 % and 4.5 % (Anderson et al., 1973) and at 3.9 % (Kleinman et al., 1998). No significant depression of the ST-segment was found at COHb of 3.8 % (Sheps et al., 1987) and 3.9 % (Kleinman et al., 1998). WHO (1999a) has tried to explain the differences between these studies by differences in experimental methodology and analysis of data and by differences in subject populations and sample size. Sheps etal. (1990; 1991) assessed the effect of CO exposure on ventricular arrhythmias. 41 subjects with established coronary artery disease (36 men and 5 women) with a mean age of 62.8 +/- 1.1 years were analyzed. Patients were categorized based on arrhythmia frequency on the training day before, during and 6 hours after exercise: 10 had no arrhythmias (0-2 ventricular premature depolarizations (VPD)/h), 11 had low-level arrhythmias (3-50 VPD/h), 11 had intermediate-level arrhythmias (51-200 VPD/h) and 9 had high-level arrhythmias (>200 VPD/h). The protocol was performed over 4 consecutive days. Day 1 was the familiarization session and instructions were given how to use the 24-hour ambulatory electrocardiogram recorder; a symptom- limited maximal bicycle exercise test was done. Days 2 to 4 were exposure days with either pure room air or CO (100 or 200 ppm) administered in a randomized double-blind fashion. COHb measurements were performed before exposure, after 30 and 60 minutes into the exposure, at the end of the exposure and before and after exercise using an IL-282 CO-oximeter. Exposures were stopped when the target levels of 4 or 6 % COHb was reached. Exposure durations were 94.2 +/- 4.2 (SE) minutes (range 40 to 170 min) for the 4 % level and 82.3 +/- 2.9 (SE) minutes (range 39 to 135 min) for the 6 % level. On all three test days, the mean pre-exposure COHb was 1.8 %. The post-exposure and post-exercise COHb measured were 1.46 and 1.36 % for air exposure, 4.01 and 10 ------- CARBON MONOXIDE FINAL: 07/2008 3.93 % forthe 4-% group and 5.91 and 5.02 % forthe 6-% group. Comparisons of arrhythmia data were done at COHb of 1.41, 3.71 and 5.33 %, respectively. During the exposure period, the mean number of single VPD/h on the room air day was significantly higher than on the 4 % COHb day, while no significant difference in the mean number of VPD/h was noted between room air and 6 % COHb exposure. When the baseline level of VPD frequency was controlled for by calculating the difference between the VPD frequency during exposure and the VPD frequency before exposure, there was no significant difference between the room air and 4 % COHb exposure. During exercise period, the frequency of single VPD/h was greater in the 6-% day than on room-air day (167 +/- 38 vs. 127+/-28 VPD/h; p=0.03). This effect was still significant, when the baseline VPD level was controlled for (117+/-S4 vs. 74+/-26, p=0.04). For this analysis, data from subjects in the low, medium and high VPD frequency groups were pooled. The difference remained significant when all subjects, including those categorized in the "no arrhythmia" group were included in the analysis. The VPD frequency was not significantly increased at 4 % COHb. The initial findings (essentially negative) of this study in 10 patients with ischemic heart disease and no ectopy during baseline monitoring were also published separately (Hinderliteretal., 1989). Dahms et al. (1993) studied 28 men and 5 women with documented coronary artery disease and a minimum of 30 ventricular ectopic beats per hour over a 20-h period studied. On three testing days, the subjects were exposed in a randomized double-blind fashion to either room air or sufficient CO to elevate their COHb to 3 or 5% in 1 hour. The mean exposure concentrations during this hour were 159+/-25 ppmand 292+/-31 ppm, respectively. This was followed by a maintenance exposure to mean concentrations of 19.3 and 31 ppm, respectively, for an additional 90 minutes, which included the exercise test (after 60 minutes of equilibrium exposure) and immediate postexercise phase. The subjects then left the laboratory and resumed their normal daily activity to determine changes in ventricular ectopic beats after CO exposure. To this end, continuous 20-h ambulatory electrocardiograms were obtained with the recorder placed on the patients 2 hours before CO exposure. There was no significant change in the frequency of single ventricular ectopic beats at rest from 115+/-28 (in room air) to 121+/-31 at 3 % and 94+/-2S at 5 % COHb. Exercise itself increased the frequency of ventricular ectopic beats (from a baseline of 116 to 206 during exercise and 375 during exercise recovery forthe room air exposure), but there was no additional effect of CO exposure. Analysis of the data based on grouping of the subjects by the severity of disease (ventricular ectopic beat frequency, ejection fraction, presence of exercise-induced ischemia) indicated no proarrhythmic effect of CO. 2.2.1.2 Healthy Adults Chiodi et al. (1941) exposed each of 4 male subjects (aged 21-33 years) repeatedly to CO concentrations of 0.15-0.35 % (1500-3500 ppm) for 70 minutes or longer. During 1 hour before exposure, basal oxygen consumption, ventilation, pulse rate and blood pressure were recorded and arterial blood for pH determination was obtained. The subject, remaining in rest during exposure, then breathed CO-containing air from a 600-liter gasometer. The measurement of the above mentioned parameters was continued during exposure. In one set of experiments the test subjects reached COHb between 3.4 and 10.4 % (8 experiments in total with the following COHb at the end of exposure: 4.6, 6.3, 7.2, 9.2 and 9.8% in subject H.C. and 3.4, 9.5 and 10.4 % in subject F.C.). In 11 ------- CARBON MONOXIDE FINAL: 07/2008 another set of experiments, three subjects reached COHb of 27-52% at the end of exposure (in 11 of a total of 22 experiments COHb between 40 and 52 % were measured). The following COHb values were measured at the end of exposure: 0, 31, 32, 32, 33, 39, 41, 42, 43, 45 and 52 % in subject H.C., 0, 27, 35, 41, 43 and 48 % in subject F.C. and 0, 0, 41, 42 and 44 % in subject S.H. No statement was made on whether any symptoms were observed. The cardiac output increased 20-50 % at COHb >40 %, while the changes were negligible at COHb of <30 %. No effects on the other parameters measured were found. Henderson et al. (1921) exposed volunteers in a 6.4-m3 gas-tight, steel-walled exposure chamber. CO was generated by dripping formic acid into strong sulfuric acid. A defined volume of CO was led into the chamber and mixed with an electric fan. Analysis of the exposure concentration in the chamber was done using the iodine pentoxide method. Subjects (9 men and 1 woman; number of subjects at each concentration given in brackets) were exposed for 1 hour at 200 ppm (2), 300 ppm (3), 400 ppm (11), 500 ppm (1), 600 ppm (9), 800 ppm (4), 900 ppm (1) or 1000 ppm (1) CO. Blood samples were taken before exposure, at 30 minutes into the exposure, at the end of the exposure (60 minutes) and once ortwice during the next three hours after end ofthe exposure. The COHb was determined using the carmine method. Directly after leaving the exposure chamber, subjects breathed several times into a bladder bag and CO was determined in the exhaled air using the iodine pentoxide method. CO concentrations in alveolar air after 60 minutes was 130-136 ppm at an exposure concentration of 400 ppm, 120-230 ppm at 600 ppm and 140-230 ppm at 800 ppm. The COHb percentage ranged from 11-12 % at 200 ppm, 10-14 % at 300 ppm, 14-22 % at 400 ppm, 16-26 % at 600 ppm, 26-34 % at 800 ppm, 34 % at 900 ppm and 38 % at 1000 ppm. After exposure to up to 500 ppm for 60 minutes, no symptoms were observed. At 600 ppm, 2/9 subjects reported slight frontal headache. At 800 ppm all subjects reported decided frontal headache during 4-8 hours. At 900 ppm insomnia and irritability occurred in addition to headache. At 1000 ppm, irritability, throbbing frontal headache and at times Cheyne-Stokes breathing were observed. The Romberg test (ability to stand erect with eyes closed) showed a marked loss of equilibrium after a 60-minute exposure to 800 ppm or higher. Haldane (1895) reported on a series of 11 studies in which the author exposed himself to different CO concentrations for different exposure times. The exposure conditions and effects are summarized in the following Table 4. The subject breathed the CO atmosphere from a mouthpiece. No mentioning of an analytical measurement of the exposure concentrations used was made. At the end or one or more times during the exposure, the exposure was interrupted and the subject walked in the room or ran up a flight of stairs (once or a few times) to investigate the effect of physical exertion at different COHb levels. The COHb was determined colorimetrically by measuring the amounts of carmine solution that had to be added to the diluted blood sample or to an equal dilution of normal, oxygenated blood to adopt the color of a CO-saturated blood dilution. For COHb <70 %, the author found his COHb determinations accurate within a 5 % error. Although the exposure measurement of this study does not meet today's standards, the reported COHb values are in fairly well agreement with the values calculated from the given exposure concentration and exposure time using the mathematical model of Coburn, Forsterand Kane (see Section 4.4.4) when assuming a resting ventilation rate (see Table 21 in Appendix B). 12 ------- CARBON MONOXIDE FINAL: 07/2008 TABLE 4: EFFECTS OF ACUTE CO EXPOSURE IN A HUMAN SUBJECT; adopted from Haldane, 1895 No 1 2 3 4 5 6 Exp. cone. (vol. %) [ppm] 0.50 [5000] 0.39 [3900] 0.40 [4000] 0.36 [3600] 0.41 [4100] 0.12 [1200] Total exposure time (min) 11.5 30.5 24 29 29 120 Observations no symptoms; hyperpnea after running upstairs no symptoms slight feeling of palpitation, pulse 102 palpitation, respiration 18, pulse 120, feeling abnormal after running upstairs became giddy, much out of breath, palpitations, slightly impaired vision no symptoms except unusual hyperpnea and giddiness after running upstairs - on walking throbbing in the head and palpitations, on running giddy, short of breath - very slight hyperpnea and palpitations after running marked giddiness and impairment of vision and hearing (for 1-2 min) - slight tendency to palpitations, pulse 96 no symptoms slight palpitations, sleepy after running (no exposure) distinct dimness of vision and hearing, slight tendency to stagger, abnormal hyperpnea slight hyperpnea while sitting distinct hyperpnea, feeling uneasy, dull and abnormal; after running: weak in the legs, markedly impaired vision and hearing, confusion at time (min)/ COHb (%) 15 min 723% 22 min 29 min 30.5 min 739 % 24 min 7 27 % 18 min 7 26% 29 min 7 37 % 15 min 7 13% 28 min 29 min 7 35 % 1 5 min 7 8 % 33 min 46 min 7 18% 67 min 90 min 7 27 % 104 min 120 min 7 37% 13 ------- CARBON MONOXIDE FINAL: 07/2008 7 8 9 10 11 0.21 [2100] irregular due to disconnected tubing, 0.43 % for last 10 min 0.027 [270] 0.021 [210] 0.046 [460] 71.5 35 210 240 240 - very slight feeling of fullness, throbbing in the head - feeling decidedly abnormal, slight hyperpnea, marked throbbing breathing decidedly deeper, pulse 104 feeling decidedly abnormal, impaired vision, slight feeling of giddiness hyperpnea more distinct, beginning to look pale/yellowish - feeling worse shortly after any movement in the chair hyperpnea marked, slight confusion of mind vision dim, limbs weak, difficulty in getting up and walking without assistance; at 6 min after exposure stop very unsteady walking, nearly falling, very indistinct vision hardly able to stand, no walking alone without falling down - - - no symptoms; after running: very slight unusual shortness of breath and palpitations - - - no symptoms - 20 min 717% 34 min 40 min / 39 % 43 min 45 min 54 min 59 min 61 min 744.5 % 63 min 65 min 71 min / 49 % 35 min, 56 % 60 min / 7 % 120 min 711 % 180 min 715% 210 min 7 14% 60 min 7 8 % 120 min 7 13% 180 min 7 13% 240 min 7 13% 60 min 7 17% 14 ------- CARBON MONOXIDE FINAL: 07/2008 - - no symptoms; after running: unusual hyperpnea, slight palpitations 120min/28% 180min/28% 240 min / 23 % Stewart et al. (1970) performed 25 inhalation exposure experiments on a total of 18 healthy men (age 24-42). These were exposed sedentary in an exposure chamber at <1, 25, 50, 100, 200, 500 or 1000 ppm for periods of 30 minutes to 24 hours. The chamber atmosphere was monitored continuously by infrared spectroscopy and periodically by gas chromatography. The subjects performed the following psychoneurological tests: hand and foot reaction time in a driving simulator, Crawford collar and pin test, Crawford screwtest, hand steadiness test, Flanagan coordination test, othorator visual test, complete audiogram, resting 12-lead electrocardiogram, standard electroencephalogram, visual evoked response and time estimation-hand reaction time test. No subjective symptoms or objective signs of illness were noted during or in the 24-hour period following exposure to 25 ppm for 8 hours, 50 ppm for 1, 3 or 8 hours, or 100 ppm for 1, 3 or 8 hours. There was no detectable change from control values in the clinical tests. A significant relationship between the Crawford collar and pin test and CO concentration was considered a chance finding by the authors. Of 11 subjects exposed to 200 ppm for 4 hours, 3 subjects reported they had developed a ,,mild sinus" headache in the final hour. In the clinical tests, no detectable statistical change from control values was observed. In the first exposure to 500 ppm for 1.8 hours, one of the two subjects reported light-headedness after20 minutes of exposure, which was believed to be due to his hyperventilation. After 1 hour of exposure, both subjects were aware of a 10 % increase in heart rate with the minimal exertion of walking to the blood port. After 90 minutes of exposure the second subject noted the onset of mild frontal headache. During the second exposure to 500 ppm for 2.3 hours, the same subjects both developed mild frontal headaches after 1 hour of exposure. Minimal exertion caused a transient intensification of the pain. Both headaches remained mild during the first postexposure hour, then they intensified into excruciatingly severe occipitofrontal headaches, reaching a pain peak 3.5 hours after exposure, and persisted for 7 hours. During the third exposure to 500 ppm, the occurrence of mild frontal headaches was noted after 1 hour of exposure. Immediately after exposure, both subjects were placed in a hyperbaric chamber and administered oxygen and the mild headaches were gone within minutes. The mean COHb reached after 2.3-h exposure to 500 ppm was about 25.5%, after 4-h exposure to 200 ppm about 16.0 % and after 8-h exposure to 100 ppm about 12.5 %. In another experiment (Kizakevich et al., 1994) evaluating cardiovascular responses of exercising individuals, 16 health young men performed a sequence of brief (5 minutes) multi-level treadmill and hand-crank exercises at <2 % COHb and after attaining 5, 10, 15 or 20 % COHb on different days . Non-invasive impedance cardiography was used to estimate cardiac output, stroke volume, heart rate, cardiac contractility and time-to-peak ejection time. The electrocardiogram was used to assess myocardial irritability and ischemia and changes in cardiac rhythm. The results showed that compensatory cardiovascular responses to submaximal upper- and lower-body exercise (e.g., increased heart rate, cardiac contractility, cardiac output) occur after CO exposures. These changes were highly significant for exposures attaining 20% COHb. The authors concluded that healthy young men can perform submaximal exercise without overt impairment of cardiovascular function after CO exposures attaining 20 % COHb. 15 ------- CARBON MONOXIDE FINAL: 07/2008 Nielsen (1971) investigated the effect of CO exposure on thermoregulation. Experiments were performed repeatedly on two subjects. Subject JHB reached COHb levels of 25% (mean of 8 experiments) and 33 % (4 experiments) and subject PJC reached 30 % (4 experiments). After reaching the desired COHb level, the subjects exercised on a chair-ergometer for 1 hour at a medium to high workload (mean heart rate 120-170 beats per minute). The subjects were not exposed continuously to CO during exercise, but the COHb level was maintained by breathing a calculated volume of CO from an anesthesia bag for 1-1.5 minutes every 15 minutes during exercise. CO exposure led to an increase in the plateau level of the deep body temperature during exercise of 0.3-0.5 °C. The lactic acid concentration was not increased after exercise at air exposure (120 mg/l in JHB and 79 mg/l in PJC), but increased during CO exposures (309-660 mg/l in both subjects). The authors stated neitherthe absence northe presence of any symptoms of CO exposure. 2.2.2 Case Studies 2.2.2.1 Children Klasner et al. (1998) published a retrospective chart review on a mass poisoning at an elementary school. The CO leak was discovered at noon, about 4 hours after school started. Of the 564 people at school, 504 were children. Any child who showed evidence or complained of symptoms was sent to a hospital by ambulance or school bus. 177 children (mean age 8.7+/-1.8 years, range 4-12 years) were taken to one of three hospitals. All children were given 100 % oxygen by face mask in the hospital (the authors stated that only few of these received simple face mask oxygen en route to the hospital). The level of poisoning was assessed according to standardized poison center data sheets (TESS, toxic exposure surveillance sheets) and was recorded as unknown (n=6), no effect (n=16), minor effect (n=124) or moderate effect (n=30). One child, for whom the data sheet classification was that of a major effect, was considered miscoded by the authors because the medical record showed that this child was sent home from the hospital without further treatment. Symptoms were present in 155 children and a mean COHb of 7.0 % (95 %-C.I. 6.6-7.5 %) was measured in a total of 147 children (blood was drawn at the same time oxygen therapy began). The authors estimated that the children were exposed at least 60 minutes (in some cases 90 to 120 minutes) to fresh air prior to obtaining their initial COHb. In the 177 children the following symptoms (number of mentionings) were observed (some children reported more than one symptom): headache (139), nausea (69), dizziness (30), dyspnea (19), vomiting (13), abdominal pain (11), drowsiness (9), other symptoms (0). The authors found a correlation between the total number of symptoms reported and the COHb, such that children with higher COHb were slightly more likely to report more symptoms. The authors did not mention how many of the 60 adults experienced symptoms, but stated that symptomatic adults were taken adult hospital facilities. 16 ------- CARBON MONOXIDE FINAL: 07/2008 Crocker and Walker (1985) analyzed 28 patients with CO poisoning that were 14 years old or younger. 25/28 CO exposures were secondary to faulty venting or faulty combustion of gas furnaces, 2/28 were secondary to faulty combustion of a gas stove and 1/28 to motor vehicle exhaust. 12 patients had COHb of less than 15 % and were completely asymptomatic. These patients were considered to have nontoxic exposures, and they were not studied further. Of the 16 patients (mean age 7.0+/-3.8 years, 3 children were younger than 5 years) with COHb of 15 % or higher, 16/16 experienced nausea, 12/16 experienced associated vomiting, 13/14 (no information on 2) complained of headache and 11/16 patients were reported to be lethargic.3/14 patients reported visual problems, such as blurred or double vision. 9/16 reported at least one syncopal episode with an average COHb of 31.6 % and a threshold level of 24.3 %. Every patient with a COHb of 24.5% or higher experienced syncope. Lethargy was reported in 11/16 patients at a mean COHb of 25.9 % and a threshold of 18.6 %. Symptoms and COHb are presented in Table 5. All patients were successfully treated with hyperbaric oxygen. The authors provided the COHb measured after hospital admission, but did not give any information on the delay between the end of exposure and measurement and on (probable) oxygen administration before hospital admission, e.g. oxygen by face mask during ambulance transport. Patient follow-up utilizing parental telephone interview and medical record review 3-12 months after the poisoning was used to screen for neurologic sequelae. Three patients had developed problems: a 12-year-old boy with 36.1 %COHb had developed chronic headaches, a 6- year-old girl with 36.9 % COHb had developed memory difficulties after suffering a major motor seizure during the poisoning episode and an 8-year-old girl with 24.5 % COHb developed poor school performance, which were attributed to her long-standing poor reading ability; psychological evaluation revealed no cognitive deficits. The former two children reported complete resolution of their symptoms by 9 months post exposure. TABLE 5: SYMPTOM THRESHOLD VALUES FOR PEDIATRIC CO TOXICITY; adopted from Crocker and Walker, 1985 Symptom none Nausea Vomiting Headache Lethargy Visual symptoms Syncope Seizures Threshold COHb (%) <15 16.7 19.8 16.7 18.6 24.5 24.5 36.9 Average COHb (%) <15 27.1 29.4 28.3 25.9 32.5 31.6 36.9 Percentage of patients * (%) 100 100 78.6 91.6 78.6 25.0 64.3 6.3 * The percentage of patients showing the respective symptom refers to the 16 patients with COHb >15 ' except for asymptomatic patients ("none"), which refers to the 12 patients with COHb <15 %. 17 ------- CARBON MONOXIDE FINAL: 07/2008 Kleesetal. (1985) investigated the neurotoxic sequelae of CO poisoning in children that had been brought to the emergency department of St. Pierre Hospital, Brussels following CO poisoning (irrespective of whetherthey were subsequently hospitalized or not). Cases were only studied when follow-up was possible: in a short-term follow-up of 20 children that were submitted to psychological tests at the time of the intoxication and who were re-examined again about 3 months later, and in a long-term follow-up of 14 children that were re-examined between 2-11 years after the intoxication. The authors listed the COHb measured after hospital admission, but did not give any information on the delay between the end of exposure and measurement neither did they indicate a (probable) oxygen administration before hospital admission, e.g. oxygen by face mask during ambulance transport. In the long-term follow-up, 6 of the 14 children (age 2.8-12.1 years at the time of intoxication; mean age 7.8 years) exhibited serious disorders (spatial organization problems, constructive apraxia, deterioration of lexical activity, as well as spelling and arithmetic); two of them had a previous history of psychological difficulties, but displayed additional difficulties afterthe poisoning. COHb between 13 and 32 % (mean 21 %) have been reported for 4/6 children (no data on the other 2 children were available). Seven of the 14 children (age >6 years, except for one 3.5-year old child; mean age 9.8 years) exhibited slight impairment of visual memory and concentration; these children had COHb between 16 and 26 % (mean 22 %). One child of this group did not display any sequelae. In the short-term follow-up, the authors grouped the 20 children according to age. In children below 3 years of age (n=6, 2.0-2.9 years), medium intoxications (n=5, symptoms included loss of consciousness, but no coma; reported COHb 16-27 %)did not produce manifest sequelae except fora momentary standstill in the child's progress of about 2 months, but their negative behavior was found to be amplified (children were more nervous, more irritable, more anxious); however it was not possible to determine if these behavioral disturbances were a direct effect of the CO intoxication ofwhetherthey were due to neurophysiological causes ortothe stressful psychological conditions surrounding the intoxication. In one case of severe intoxication (symptoms included coma; COHb 37 %) developmental level regression (motricity and language), violent anger and nervosity were observed. In children from 4 to 9 years old (n=8), the intoxication did not alter the intellectual capacities, but in 6 cases (reported COHb of 4, 6, 25 and 27 %; missing data for two children) the mnesticand instrumental aspects of the cognitive development were modified (the othertwo were difficult to evaluate due to intellectual retardation and language retardation). Visuo-spatial perceptions and topographical memory were particularly perturbed, as was auditory memory. In children over 10 years of age (n=10), difficulty in perceiving and organizing the material to be memorized either auditory or visually was found in the three children less than 12 years (COHb of 26, 27 and 36 %). With the three children over 14 years, one case (30 % COHb) of serious balance impairment was observed and only some slowness and instability with the othertwo (COHb of 26 and 30%). Meert et al. (1998) evaluated clinical characteristics and neurologic outcome of all children with CO poisoning admitted to the Children's Hospital of Michigan, Detroit between January 1987 and December 1996. Exposures were categorized as 1) severely toxic when COHb was >25 %, 2) toxic when COHb was between 10.1 and 25 %, 3) suspected toxic when COHb was <=10 % with acute neurologic manifestations, or 4) nontoxic when COHb was <=10 % without acute neurologic manifestations. Of 106 cases (median age 3.5 years, range 0.1 to 14.9 years) were investigated, 37 18 ------- CARBON MONOXIDE FINAL: 07/2008 with severe toxic, 37 with toxic, 13 with suspected toxic and 19 with nontoxic exposures. The most common presenting symptoms included altered level of consciousness (lethargy, unresponsiveness), metabolic acidosis, tachycardia and hypertension. All exposures were accidental, occurring as a result of smoke inhalation during house fires in 95, motor vehicle exhaust in 6 and defective heating system in 5 cases. Forty-three children had an associated cutaneous burn injury. All patients received normobaric oxygen fora median period of 5.5 hours (range 0.6 to 44 hours). Fifteen patients died, 8 from hypoxic-ischemic encephalopathy after cardiopulmonary arrest at presentation, 3 from massive burn injury and 4 from late complications of burn injury. Nine survivors suffered neurologic sequelae: 1) 6 had persistent deficits, such as cognitive and motor deficits or developmental delay (of these 4 had presented with respiratory or cardiorespiratory arrest with COHb between 31.5 and 45 % and the other two; COHb 14.8 and 5.9 %; had severe burns with 40 and 75 %, respectively, of the body surface area affected) and 2) 3 patients developed delayed neurologic syndromes (2 children; COHb 33.3 and 34.8 %; with transient tremors, cognitive deficits and hallucinations starting after 4 and 14 days, that resolved spontaneously after about 2 months, and 1 child; COHb 3.1 %; that developed deficits in cognitive and interpersonal skills after 51 days and in whom brain imaging revealed bilateral occipital lobe infarcts). Further information on pediatric CO poisoning can be found in the review of White (2000). 2.2.2.2 Adults Burney et al. (1982) reported an epidemiologic and clinical investigation of 184 persons exposed to CO in a public school. CO release was from a furnace and was caused because of a door to the exhaust chamber had been inadvertently left ajar. The CO was distributed throughout the school building by a forced air heating system. Exposure began at 7.30 a.m. and ended at 10.00 a.m. Of the 184 exposed persons (146 students and 38 teachers, mean age for all exposed was 20 years) 160 became ill and 96 were transported to four hospitals fortreatment. COHb levels were measured on 66 persons and showed a mean of 18.2+7-6.4 %, with almost half falling between 21 and 25 %. Persons in whom COHb levels were drawn had a mean exposure time of 107+/-33 minutes. Of the 160 persons who became ill, the following symptoms were reported for 159 persons: headache (90 %), dizziness (82 %), weakness (53 %), nausea (46 %), trouble thinking (46 %), shortness of breath (40%), trouble with vision (26%), and loss of consciousness (6 %). For headache, dizziness, muscle weakness, trouble with vision and trouble with thinking, a strong correlation between symptom and duration of exposure was found, while nausea, shortness of breath and loss of consciousness did not show this correlation. The authors corrected the measured COHb level for the delay between exposure and the drawing of blood samples and reported a corrected mean COHb of 20.7+/-7.0 %. Ely etal. (1995) reported a poisoning incident in a warehouse of a small sewing company. A propane-fueled forklift was in use in the warehouse, in which a total of 30 people worked. The forklift was parked in a position where its exhaust focused directly into an air intake duct, that communicated with a vent opening above a table in the inspection and packing area, where 5 people worked. On the day of the incident, one man reported pronounced nausea, vomiting, dizziness and had a tonic-clonic seizure. Simultaneous, other coworkers developed chest pain and dyspnea. The warehouse was evacuated immediately. Air CO measurements were 386 ppm in the sewing area and 370 ppm in an unrelated work area. Thirty persons with complaints of severe 19 ------- CARBON MONOXIDE FINAL: 07/2008 headaches (93 %), dizziness (63 %), weakness (63 %), nausea (60 %), chest pain ortightness (57 %), shortness of breath (50 %), vomiting (37 %), abdominal pains (33 %), muscle cramping (30 %), difficulty concentrating (23 %), visual changes (20 %) and confusion (17 %) were treated for CO exposure. Twenty-six patients had expiratory CO analyses after being treated with 100 % oxygen for over 2 hours. Expiratory CO was higher in those from the inspection and packing area (21.1+/- 0.7 % versus 8.4+7-4.8 %). These persons were among the most severely ill. The authors extrapolated the mean expiratory CO concentration of 21.1 % back to a COHbof about 35 % at the end of exposure. Two years after the incident, follow-up was obtained for25 (83%) of the patients: 11 (44 % of those reached) reported seeing physicians for persisting symptoms (numbness in arms or legs, 36 %; restlessness, 36 %; persistent headaches, 32 %; irritable or violent behavior, 16 %; confusion, 16%; incontinence, 16%; difficulty walking or moving arms/legs, 16%; memory loss, 16 %; difficulty speaking, 4 %). Sokal and Kralkowska (1985) analyzed 39 patients (18 men, 21 women) that were hospitalized foracute CO poisoning. 25 patients were intoxicated by household gas and 14 patients by coal-stove gas. The patient's ages ranged from 13 to 78 years. The duration of the poisoning varied between 1 and 14 hours and was established on the basis of an epidemiological review of the circumstances of poisoning. The severity of poisoning evaluated on admission to hospital according to the clinical criteria presented in Table 6. On basis of the clinical criteria, 16 cases were classified as degree I, 12 as degree II, 8 as degree III and 4 as degree IV. For statistical analysis the mild and moderate cases (I and II) were pooled into one group and the severe and very severe cases (III and IV) into another. Results presented in Table 7 show that mean COHb in severe and very severe poisonings were only slightly higher (not statistically significant) than those in the mild and moderate group. On the other hand, the average duration of exposure which induced severe or very severe poisonings was about twice as long as that associated with mild and moderate poisonings. In the severe and very severe poisonings, the lactic acid concentration in blood, as an indicator of metabolic acidosis, was significantly higher. For pyruvate and glucose concentrations no significant differences were found (not shown). TABLE 6: SEVERITY OF CO POISONING; from Sokal and Kralkowska, 1985 Grade I (mild) Grade II (moderate) Grade III (severe) Grade IV (very severe) headache, vomiting, tachycardia, no disturbances of consciousness disturbances or loss of consciousness without other neurological symptoms, tachycardia, pain-induced reflexes still intact loss of consciousness, intense muscular tonus, neurological symptoms, tachycardia and tachypnea, circulatory and respiratory disturbances not observed loss of consciousness, clinical signs of central nervous system damage, circulatory and respiratory disturbances 20 ------- CARBON MONOXIDE FINAL: 07/2008 TABLE 7: COHb, EXPOSURE DURATION AND LACTATE CONCENTRATIONS IN RELATION TO SEVERITY OF CO POISONING; from Sokal and Kralkowska, 1985 COHb (%) Exposure duration (h) Blood lactate concentration (nmol/ml)a Mild and moderate poisonings (I and II) (n) 27+7- 12 (27) 4.6 +/- 3.3 (27) 4.1 +1-3.6 (27) Severe and very severe poisonings (III and IV) (n) 34+7- 13 (11) 9.1 +1-3.5 (12) 8.8+7- 3.1 (11) Very severe poisonings (IV) (n) 31 +7-14 (3) 10.3+7-1.3 (4) 1 1 .0 +7- 2.2 (3) a Blood lactate concentrations in 12 control individuals was 1.4 +7- 0.3 ^mol/ml. Deschamps et al. (2003), in a prospective study, measured effects on memory one month after an acute CO intoxication. Of all patients examined in the hospital for suspicion of acute CO intoxication over 4 years (N=944), 230 patients fulfilled the inclusion criterion of a COHb level of 11 % or higher in the first blood sample measured at the hospital. After applying further inclusion criteria, i.e., age between 18 and 60, fluent in French language, no disease or risk factor which might impair memory, e.g., excessive alcohol consumption, treatment with psychotropic drugs, drug abuse, neurological or psychiatric diseases and exposure to solvents or heavy metals, 38 patients were suitable for inclusion, of which 32 were examined. The median COHb in the first blood sample was 23 %. Median blood CO at the end of exposure was calculated as 30 %. The median number of days between intoxication and psychometric testing was 31. Each patient was paired with a control with respect to gender, age and educational level. Tests were selected to study several types of memory, i.e., long term and working memory (verbal Buschke's test) and short term memory (digit span (verbal) and Corsi's test (visual)). Other tests addressed disturbances of attention (simple reaction time test, verbal fluence test) and divided attention (reaction time test with double task and color/word decoding test). The only tests indicating a lower performance of patients were for number recall and fatagability (mean reaction time was higher for the second part of the trial than for the first part. The results did not correlate with the end-of-exposure COHb. In several other tests, patients showed a better performance than controls, some of these tests showed a positive correlation between result and the end-of-exposure COHb. The authors concluded that one month afterthe incident, the memory of the patients was not lowerthan in paired controls, and was even higher for learning and word recall. 2.3. Developmental/Reproductive Toxicity Koren et al. (1991) described a prospective, multicenter study of acute CO poisoning during pregnancy. Between December 1985 and March 1989, a total of 40 cases of CO poisoning during pregnancy were collected. All pregnant women were in good health prior to the CO poisoning and had not suffered from a known chronic illness. The 40 pregnancies included 3 twin births, 1 termination of pregnancy at 16 weeks of gestation, and 4 births that were pending. The CO 21 ------- CARBON MONOXIDE FINAL: 07/2008 poisoning was caused by malfunctioning furnaces (n = 23), malfunctioning water heaters (n = 7), car fumes (n = 6), methylene chloride exposure (n = 3) and yacht engine fumes (n = 1). The exposure occurred during the first trimester (n = 12), second trimester (n = 14) or third trimester (n = 14). The clinical grade of poisoning was based on clinical signs and symptoms as shown in Table 8. Cases in which COHb values were available or could be estimated from the known ambient CO concentrations are presented in Table 9. Adverse fetal outcome occurred only after Grade 4 or 5 poisoning. TABLE 8: SEVERITY OF CO POISONING; adopted from Keren et al., 1991 Grade 1 Grade 1 + Grade 2 Grade 3 Grade 4 Grade 5 Alert, oriented, headache, dizziness, nausea As Grade 1 , but another person exposed in the same incidence was unconscious Alert, alterations of mental state, more pronounced headache, dizziness, nausea Not alert, disorientation, loss of recent memory, muscle weakness, incoordination Disoriented, depressed sensorium, limited and inappropriate response to simple commands Comatose, responding only to pain or not responding to any stimulus TABLE 9: OVERVIEW OF CLINICAL SCORING, COHb AND FETAL OUTCOME; adopted from Koren etal., 1991 Grade 5 5 4 4 4 2 1 1 1 COHb (%) 40-50 26 39 25 21 13.8 18 14 6.2 Time of exam after exposure (h) 2 1 2 2 2 1 unknown unknown 1.5 Treatment a HfO, 2 h HfO, 3 h HybO, 2 h HfO, 2 h HybO, 2 h HfO, 7 h and HybO, 2 h HfO, 12 h none none Outcome Elective termination (in the text the authors state: fetal death at term followed by maternal demise) Stillborn Normal Cerebral palsy compatible with postanoxic encephalopathy Normal Normal Normal Normal Normal 22 ------- CARBON MONOXIDE FINAL: 07/2008 1 1 1 2.4 0.8 2 unknown 1 unknown none none none Normal Normal Normal Cases with indirect measures of exposure 1 + 1 + 1 1 1 1 32, measured in affected son 32 32 14 14 5 2 - - - - - HfO, 12 h none none none none none Normal Fetal bradycardia Normal Normal 36-week gestation Normal ' HfO = high-flow oxygen; HybO = hyperbaric oxygen Caravati et al. (1988) reported on six cases of acute CO poisoning during pregnancy (all cases of patients with CO poisoning during pregnancy admitted to two teaching hospitals in Salt Lake City during a two-year period). Results of COHb measurements and outcomes are given in Table 10. Cases 5 and 6 were treated with 100 % oxygen for 5 hours before the COHb measurement, which is between 3 and 4 half-lifetimes of CO under this condition, using a half-life time of 80 minutes for treatment with 100 % oxygen (Peterson and Stewart, 1970). It can be concluded that the end-of-exposure COHb values were about 8-16 fold higher and thus were about 40-80 % in Case 5 and 22-44 % in Case 6. In conclusion, the three cases of stillbirths were associated with maternal COHb concentrations of 22 % or higher. 23 ------- CARBON MONOXIDE FINAL: 07/2008 TABLE 10: OVERVIEW OF MATERNAL CLINICAL EFFECTS, COHb AND FETAL OUTCOME; adopted from Caravati et al., 1988 Case 1 28-year- old, pregnancy week 20 2 32-year- old, pregnancy week 16 3 1 9-year- old, pregnancy week 30 4 1 8-year- old, pregnancy week 41 5 20-year- old, pregnancy COHb (%) 9.6 23 39 32 5 Time between end of exposure and blood sampling (h) 8 not stated not stated not stated 5 hours with oxygen treatment Treatment 1 00 % oxygen by face mask for 10 h; then COHb had reduced to 1 .7 % 1 00 % oxygen by face mask for 10 h; after 2.5 and 9.5 h COHb was 8.9 and 1 .8 %, respectively. 1 00 % oxygen by face mask for 8 h; after 5 h COHb had reduced to 4 % oxygen treatment using iron lung 1 00 % oxygen by face mask during ambulance and helicopter transport Maternal Effects and Fetal Outcome Poisoning was caused by a gas-leak in the restaurant where the woman worked; during a 6-hour working period, she developed severe headache, nausea and dizziness; she visited hospital 6 hours later with persisting headache, lethargy and dizziness; she was discharged in good health and delivered a normal female infant weighing 2900 g four months later. Poisoning was caused by clogged furnace; she complained of headache, nausea and dizziness of 48 hours duration; she was discharged 36 hours later in good health and delivered a term healthy male infant weighing 2920 g. Poisoning was caused by a malfunctioning heater; after 18 hours exposure she complained of severe headache and nausea; she was discharged after 8 hours of oxygen therapy and delivered a healthy 3940- g male infant. The woman was found unconscious and was combative on arrival in the emergency department; her mental status rapidly improved an she recalled having nausea, vomiting and headache earlier that day; fetal heart tones were absent and the woman delivered a stillborn female infant the next day. The woman was found awake outside her home together with case 6; they had occluded the furnace the evening before to improve heating; she 24 ------- CARBON MONOXIDE FINAL: 07/2008 week 38 6 1 8-year- old, pregnancy week 13 2.8 5 hours with oxygen treatment to the hospital 1 00 % oxygen by face mask during ambulance and helicopter transport to the hospital delivered a stillborn 3380-g male fetus 36 hours later. The woman was found unconscious together with case 5; fetal heart rate was 1 36 per min at the scene and 1 90-200 per min 5 hours after the exposure; after 5 hours, she was somnolent but oriented and regained full mental alertness during the next 2 hours; fetal heart rate decreased to 1 50-1 60 per min the next day and the woman was discharged; she delivered a nonviable 1210-g fetus at 33 weeks of gestation; autopsy revealed brachycephaly, craniosynostosis, multiple organ cavity anomalies, multiple contractures of extremities, hypoplastic lungs and a small brain with hydrocephalus. Farrow et al. (1990) reported a case of fetal death in a 20-year-old woman, who was exposed to CO due to use of a portable propane heater in her unventilated mobile home. She arrived by ambulance at the hospital approximately 60 minutes after being found unconscious at her mobile home. En route to hospital she had been intubated and had received 100 % supplemental oxygen. Her measured COHb at the time of admission was 7 %. On the second day in hospital, the patient delivered a 1050-g stillborn female fetus. On gross autopsy, bright red discoloration of the skin and visceral organs was noted. A fetal COHb of 61 % was measured. The authors assumed that the mother had reached a minimal COHb of 40 to 50 % since she was found unconscious. 2.4. Genotoxicity No studies documenting genotoxic effects of CO in humans were located in the available literature. 2.5. Carcinogenicity No studies documenting carcinogenic effects of CO in humans were located in the available literature. 2.6. Summary In healthy adults, death from CO poisoning occurs at COHb larger than 50 % (AIHA, 1999; WHO, 1999a; Steward, 1971; Steward etal, 1970; Pachetal., 1978; 1979). At COHb of about 16% headaches can develop (Steward etal., 1970). Subtle (non-adverse) effects, such as decrements in neurobehavioral function start at about 5 % COHb (WHO, 1999a; EPA, 2000). 25 ------- CARBON MONOXIDE FINAL: 07/2008 Analysis of lethal cases reported by Nelson (2005a) indicated that most lethal poisoning cases occurred at COHb levels higher than 40% and that survival of CO-exposed humans were likely to be seen at levels below 40%. Persons with coronary artery disease constitute a subpopulation that is much more susceptible to the effects of CO. Case reports indicate that death through myocardial infarction can occur at COHb around 20-30 % and as low as about 15 % in this group (Balraj, 1984; Atkins and Baker, 1985; Ebisuno et al., 1986; Grace and Platt, 1981). In individuals with coronary artery disease, a COHb of 2.0 or 4.0 % can significantly reduce the time to onset of angina and the time to 1 -mm ST-segment change in the electrocardiogram during physical exercise (Allred etal., 1989a; b; 1991). At 5.3 %, but not at 3.7 % COHb an increased arrhythmia frequency was observed in subjects with coronary artery disease (Sheps et al., 1990; 1991). Children and the unborn also constitute susceptible subpopulations: Measured COHb of higher than 22-25% in the mothers' blood may lead to stillbirths (Koren etal., 1991; Caravatietal., 1988). After CO poisonings associated with mean COHb of 21 % (range 13-32%) irreversible neurotoxic effects resulting in defects in the cognitive development and in behavioral alterations were observed in a long-term follow-up study, especially in young children (mean COHb 21 %) (Klees et al., 1985). Acute symptoms of CO poisoning in children include effects, such as nausea, vomiting, headache and lethargy. These symptoms were reported to occur already at a COHb of 7 % in one study (Klasner et al., 1998), while in another study a threshold of 16.7-19.8 % COHb was found (Crocker and Walker, 1985). Visual symptoms and syncopes occurred at a threshold of 24.5 % COHb, at higher COHb every child experienced at least one syncope (Crocker and Walker, 1985). 3. AN IM AL TOXICITY DATA 3.1. Acute Lethality Lethality data for acute inhalation exposure have been reported for rats, mice and guinea pigs. The lethality data are summarized in Table 12 and graphically presented in Figure 1. 3.1.1. Rats E.I. du Pont de Nemours and Co. (1981) determined LC50 values for male Crl:CD rats (weight 250+/-25 g) at exposure times of 5,15, 30, and 60 minutes. The experiment was performed in duplicate with one set of animals exposed head only to the test gas while the other set was unrestrained inside a 175-liter rectangular exposure chamber. In restrained rats, respiration rate was monitored by recording pressure fluctuations due to breathing in a body plethysmograph. During CO exposures the chamber atmosphere was monitored continuously for oxygen (BioMarine Industries model 225 oxygen meter), carbon dioxide and CO (InfraRed Industries model 702-D non- dispersive analyzer) using infrared analyzers. Blood from CO exposed rats that died during or within 30 minutes post-exposure was collected by cardiac puncture. The blood was measured for hemoglobin, COHb and oxyhemoglobin by an Instrumentation Laboratories model 282 CO- Oximeter. The post-exposure observation period was 14 days during which time body weights were monitored. 26 ------- CARBON MONOXIDE FINAL: 07/2008 Nearly all of the deaths occurred during the exposure period; of all animals that died only 2 of 216 restrained and 3 of 148 unrestrained rats died after the end of the exposure period. The authors reported LC50 values for the 5-, 15-, 30-, and 60-minute exposure periods for the unrestrained rats of 10151 ppm (95% C.I., 9580-10953 ppm), 5664 ppm (95% C.I., 5218-6078 ppm), 4710 ppm (95% C.I., 4278-5254 ppm), and 3954 ppm (95% C.I., 3736-4233 ppm), respectively. The LC50 values were lower (higher toxicity) for restrained rats. For the respective exposure durations values of 10754, 4318, 2890 and 1888 ppm were obtained. The RD50 for rats exposed to CO was 15000 ppm. The COHb values were 60 % or higher in rats that had died after unrestrained exposure and 50 % or higher in rats that had died after restrained exposure. Darmer et al. (1972) reported a LC50 of 14200 ppm for 5 minutes exposure. Haskell Laboratory (1978) obtained a LC50 of 4070 ppm for 30 minutes exposure. Hartzell et al. (1985) reported a LC50 of 8636 ppm for 15 minutes exposure and 5207 ppm for 30 minutes exposure. Kimmerle (1974) reported a LC50 of 5500 ppm for 30 minutes and 4670 ppm for 60 minutes exposure. Rose et al. (1970) reported a LC50 of 2070 mg/m3 (95 % C.I. 1831-2241 mg/m3) (1807, 1598-1956 ppm) for 4 hours exposure in male Sprague-Dawley rats. The COHb in animals that had died was between 50 and 80 %. 3.1.2. Mice Pesce et al. (1987) exposed groups of about 100 OFrstrain mice/age group/sexto S.STorr (about 7200 ppm; final analytical concentration) for 76 minutes or to 4.4 Torr (about 5800 ppm) for 146 minutes. For the 76-minute exposure, survival rates for males were 36 % for 31-day-old males and 22 % for 184-day-old males. Of the exposed females, 57 % of 31-day-old females and 63 % of 184-day-old females survived. After exposure for 146 minutes, survival rates were 40 %for34-day- old males, 27 % for 85-day-old males, 24 % for 230-day-old males and 27 % for 387-day-old males and 48 % for 34-day-old females, 67 % for 85-day-old females and 56 % for 387-day-old females. Except for the about 1-month-old mice, male mice showed a significantly lower survival than females. Survival was not significantly influenced by age. Winston and Roberts (1978) investigated the influence of age on lethal effects of CO on mice (strain not stated; male mice were used in all groups, except for the two youngest groups that comprised both males and females). Animals of different age were exposed to 2000 ppm CO for up to 6 hours in stainless steel exposure chambers. The analytical concentration was determined by an automated gas chromatograph. Mortality occurred in 3/37 two-day old mice, 21/32 17-day-old mice, 16/20 30-day-old mice, 11/1754-day-old mice, 10/20 108-day-old mice and 6/18 150-day-old mice. The animals of the youngest and that of the oldest age group were found to be more resistant to CO. These two groups were also found less susceptible to lethal effects from hypoxic hypoxia when mice were exposed to a reduced oxygen concentration of 7.5 %. Hilado et al. (1978) reported 30-minutes LC50 values of 3570 ppm for Swiss-Webster mice and 8000 ppm for ICR mice. Respiratory distress was the only sign observed during the exposures. Rose et al. (1970) reported a LC50 of 2800 mg/m3 (95 % C.I. 2679-2926 mg/m3) (2444, 2339-2554 ppm) for 4 hours exposure in male Swiss albino mice. COHb was not determined. 27 ------- CARBON MONOXIDE FINAL: 07/2008 3.1.3. Guinea Pigs Rose et al. (1970) reported a LC50 of 6550 mg/m3 (95 % C.I. 5509-7788 mg/m3) (5718, 4809-6799 ppm) for 4 hours exposure in Hartley guinea pigs. The COHb in animals that had died was between 57 and 90 %. TABLE 11: SUMMARY OF LC50 DATA IN LABORATORY ANIMALS Specie s Rat Rat Rat Rat Rat Rat Rat Rat Rat Rat Rat Rat Mouse Mouse Mouse Mouse Guinea pig Concentration (ppm) 14200 10151 8636 5664 5607 5500 5207 4710 4070 4670 3954 1807 10127 3570 8000 2444 5718 Exposure time (min) 5 5 15 15 30 30 30 30 30 60 60 240 15 30 30 240 240 Remark Crl:Cd strain, male Crl:Cd strain, male Crl:Cd strain, male Crl:Cd strain, male Sprague-Dawley strain, male Swiss-Webster strain ICR strain Swiss albino strain, male Hartley strain, male Reference Darmeretal., 1972 E.I. du Pontde Nemours and Co., 1981 Hartzelletal., 1985 E.I. du Pontde Nemours and Co., 1981 Herpoletal., 1976 Kimerle, 1974 Hartzelletal., 1985 E.I. du Pontde Nemours and Co., 1981 Haskell Laboratories, 1978 Kimerle, 1974 E.I. du Pontde Nemours and Co., 1981 Rose etal., 1970 Kishitani etal., 1979 Hiladoetal., 1978 Hiladoetal., 1978 Rose etal., 1970 Rose etal., 1970 28 ------- CARBON MONOXIDE FINAL: 07/2008 LC50 values in different species log concentration (ppm) 4 0 3 3 3.4 3 9 ° ^-\,^ CJ """"--—-_, ™"^\li • c: K~-\_ '— ' ^----^ A --.^ ""^•\^_ 0,5 1.0 1.5 2,0 log tim^min) • rat (DuPont) l~l rat (other) O mouse A guinea pig 2,5 FIGURE 1: LC50 VALUES FOR CO IN DIFFERENT SPECIES The solid line was calculated by Probit analysis from the data in E.I. du Pont de Nemours and Co. (1981). The slope of this line indicates a time scaling exponent of n=2.6. Analysis of all data yielded a value of n=2.8. The LC50 values are taken from Table 11. 3.2. Nonlethal Toxicity A large number of studies investigated nonlethal effects of single and repeated CO exposures in animals (see WHO, 1999a for review). Reported here are only studies that support or add information to the effects seen in humans, because these studies were considered most relevant. These include syncope-like observations and behavioral effects in monkeys, effects on heart function in dogs as well as developmental/reproductive toxic effects in different species. 3.2.1 Monkeys Purser and Berrill (1983) studied the behavioral effects of CO exposure on cynomolgus monkeys (3 male animals, 4-5 years old). The basic behavioral model consisted of an individual monkey placed in a chamber with a lever press at one end a reward (chocolate candy) dispenser at the other. At 5-minute intervals throughout the test session a buzzer was sounded and a light flashed over the lever. If the monkey pressed the lever within a 1-minute period, a candy was 29 ------- CARBON MONOXIDE FINAL: 07/2008 presented in the dispenser. The monkey then moved the length of the chamber to pick up the candy. The major performance parameter measured was the time from the animal releasing the leverto its first touch of the dispenser, i.e., the time taken to traverse the chamber. Each session consisted of the following stages: 1) a 25-minute preexposure period during which baseline carbon dioxide production and behavioral task performance times were established, 2) 2.5 % CO was introduced into the chamber at a sufficiently high flow rate to increase the concentration to 900 ppm within 1 minute, 3) 900 ppm CO were maintained for 30 minutes, during which the effects on clinical condition, carbon dioxide production and behavioral task performance were examined, 4) the chamber was flushed of CO, decreasing the concentration to less than 100 ppm within 4 minutes, 5) animals were maintained for anther 45 minutes in the chamber while their clinical condition, carbon dioxide production and behavioral task performance were monitored. Carbon dioxide and CO concentrations were monitored continuously using infrared analyzers. Five preliminary experiments were conducted at a 1000 ppm CO, followed by the main experimental series that consisted of 10 exposures at 900 ppm, 3 for each animal, and 1 preliminary run. For 3 exposures (one for each animal) the animals were removed from the chambers minutes after the end of the | exposure period so that venous blood samples could be taken for COHb analysis. During the 4 preliminary exposures to 1000 ppm CO, there was generally no visible effect of the animals until 18-20 minutes of exposure had elapsed, at which time they generally became less active, occasionally sitting down for short periods. At approximately 25 minutes a dramatic change occurred over a period of 1-2 minutes and the animals went from an apparently normal state to one of severe intoxication. This change was preceded by one or more warning signs at approximately 23 minutes, which consisted of momentary closure of eyes, yawning and shaking of the head. Immediately priorto collapse the animals sometimes paced around in a mechanical fashion, often swaying as they walked. As few as 20 seconds later the animals were lying or rolling on the floor, sometimes attempting to rise before sitting on the floor or lying down again. During recovery, the animals remained in a state of severe intoxication for approximately 30 minutes, lying down with their eyes closed. On three occasions animals vomited during this period. After 25-30 minutes the animals were usually sufficiently recovered to get up and move around the chamber, in response to the buzzer they would sometimes move towards or even press the lever although they made no attempt to fetch the candy. The performance of the behavioral task was unaffected during the first 15 minutes of exposure, but before the first minor clinical signs there was generally a slowing of response. During exposures to 900 ppm, the first signs generally occurred after 20-25 minutes when the animals became less active, followed by the minor warning signs at approximately 26 minutes. Although in most cases the animals were lying down at the end of the exposure period, they did not appear to be severely intoxicated and in 6 of 9 exposures the signs were mild and the animals did not reach a state of collapse. During the recovery period the animals remained in a state of intoxication for approximately 16 minutes. Recovery was more rapid than that following exposure to 1000 ppm, as all animals performed the behavioral task within 25 minutes of the end of exposure. The first effects upon the chamber traverse time occurred at 15 minutes into the exposure as a slight, statistically significant decrement in performance. The decrement at 20 minutes was not statistically significant while at 25 minutes it was highly significant, as the mean response time was twice the preexposure response time (1.10 sec vs. 0.62 sec). The first time that the test was conducted successfully on all occasions was after 25 minutes of recovery when the mean chamber traverse time was 3 times as long as the mean preexposure time. From 30 to 45 minutes the 30 ------- CARBON MONOXIDE FINAL: 07/2008 animals were more active and response times gradually improved but did not reach the preexposure level. The mean COHb measured at the end of the exposure was 32.9 % (range 31.7-34.8 %). Carbon dioxide production, indicating the metabolism in the animals, decreased gradually throughout the exposure (statistically significant at 25 and 30 minutes of exposure) and then increased gradually towards preexposure levels during the recovery period (significantly lower until 15 minutes into the recovery period). From earlier experiments, the authors estimated COHb of 16-21 % for the period of 15-20 minutes when deficits in behavioral task performance were started during the exposure period. In the state of severe intoxication, the animals were capable of performing some coordinated behavioral actions when they were sufficiently stimulated, e.g. by loud noise or removing them from the chamber. The authors report that in unpublished experiments using higher CO concentrations the animals passed rapidly from this stage to one of deep coma. DeBias et al. (1979) reported that CO exposure (100 ppm for 16 h; resulting in a COHb of 9.3 %) reduced the threshold for ventricular fibrillation induced by an electrical shock applied to the myocardium of monkeys during the final stage of ventricular repolarization. The voltage required to induce fibrillation was highest in normal animals breathing air and lowest in infarcted animals breathing CO. Additivity was found for the effects of infarction alone and CO exposure alone each of which required significantly less voltage for fibrillation. 3.2.2 Dogs Aronow et al. (1979) reported that CO exposure increased the vulnerability of the heart to induced ventricular fibrillation in normal dogs breathing 100 ppm CO for 2 hours (resulting COHb was 6.3-6.5 %). The ventricular fibrillation was induced by an electrical stimulus applied to the myocardium. Sekiya et al. (1983) reported that exposure to CO concentrations of 3000 ppm for 15 minutes followed by 130 ppm for 1 hour (resulting COHb was 13-15 %) increased the severity and extent of ischemic injury and the magnitude of ST-segment elevation which was induced in anaesthetized dogs by coronary artery ligation more than did ligation alone. 3.3. Developmental/Reproductive Toxicity 3.3.1 Pigs Dominick and Carson (1983) exposed pregnant sows to CO concentrations between 150 and 400 ppm for 48-96 hours between gestational days 108-110 (average gestation was 114 days). They showed a significant linear increase in the number of stillbirths as a function of increasing CO concentration. Stillbirths were significantly elevated above control levels when the maternal COHb exceeded 23 % saturation. These saturation levels were obtained at approximately 250 ppm. Morris et al. (1985) exposed 16 pigs to 0, 200 or 250 ppm from gestational day 109 until birth (maternal COHb at 24 hours into the exposure was 0,13.6 and 17.1 %, respectively). Stillbirth rate for the 3 groups (total of 123 piglets) were2.3, 2.4 and 4.8 %, respectively. The study authors stated that the stillbirth rate was not affected because the observed rates were lower than the 31 ------- CARBON MONOXIDE FINAL: 07/2008 industrial norm of 5-10 %. The COHb in neonatal piglets at birth were 0, 19.8 and 22.4 %, respectively. The authors found impairment of negative geotaxis behavior and open field activity 24 hours after birth in the 250-ppm group. Activity in open field was significantly reduced at 48 hours after birth in piglets from both exposure groups. 3.3.2 Rabbits Astrup et al. (1972) reported an increase in fetal mortality and malformations in rabbits exposed to 180 ppm CO continuously throughout gestation. Maternal COHb was 16-18 %. Rosenkrantz et al. (1986) exposed rabbits to high concentrations of CO-containing cigarette smoke (12 puffs of 2700-5400 ppm CO; exposure to puffs of cigarette smoke by face mask; each puff sequence consisted of 30 seconds cigarette smoke and 30 seconds fresh air) for 12 minutes daily from gestational days 6-18. The COHb level reached at the end of each exposure was 16 %. A large number of fetal deaths, but no malformations were observed in exposed animals. 3.3.3 Rats Choi and Oh (1975) exposed rats to 750 ppm CO for 3 h/d on gestational days 7, 8 or 9. An excess of fetal absorptions and stillbirths as well as a decrease in body length and an increase in skeletal anomalies were observed. COHb was not determined. Penney et al. (1980) exposed pregnant COBS rats for the last 18 days of gestation to 200 ppm CO. The mean maternal COHb was about 27.8 % and the mean fetal level was 27.0 %. The body weight of the pups was significantly lower than that of controls. The heart weight of both exposed females and pups was significantly increased. Mactutus and Fechter (1985) exposed Long-Evans rats continuously throughout gestation to 0 or 150 ppm CO. Mean COHb was 15.6 % vs. 1 % in control subjects. At 120 days of age, CO- exposed rats acquired a conditioned avoidance response equally well as control animals. However, following a 24-h interval the CO-exposed rats failed to demonstrate significant retention. In a second experiment, in which animals received 50 training trials per day until a criterion of ten consecutive avoidance responses was met, the prenatal CO-exposed rats again acquired the task as well as control animals. When tested for retention 28 days later, a significant memory impairment was again observed in terms of trials required to retain the avoidance criterion as well as in total percent avoidance. At one year of age, the CO-exposed rats showed impairment relative to air- exposed controls in both the original learning and retention of the two-way avoidance response. 3.3.4 Mice Singh and Scott (1984) exposed groups of 17 pregnant CD-1 mice to CO concentrations of 0, 65, 125, 250 or 500 ppm for 24 h/d on gestational days 6 to 17. Mice were sacrificed and examined on day 18. No signs of maternal toxicity were observed at any dose. The mean percent fetal mortality per litter was 4.52, 5.89, 12.50, 15.50 and 55.30 %, respectively. Besides a dose- dependent increase in embryolethality, fetus weights were significantly reduced at exposure levels of 125 ppm or higher. No fetal malformations were detected. COHb was not determined. 32 ------- CARBON MONOXIDE FINAL: 07/2008 Singh (1986) exposed CD-1 mice to 0, 65 or 125 ppm CO continuously during gestational days 7 to 18(COHb not determined). No signs of maternal toxicity were observed. Exposure did not affect the number of live pups born per litter or their birth weight. Prenatal exposure to 125 ppm significantly increased the time required by pups for righting reflex on day 1 of birth and negative geotaxis on day 10. Prenatal exposure at both concentrations significantly decreased the mean aerial righting score of pups on day 14. 3.4. Genotoxicity No information regarding the carcinogenicity of CO in animals was located in the available literature. 3.5. Carcinogenicity No information regarding the carcinogenicity of CO in animals was located in the available literature. 3.6. Summary Several studies reported LC50 values in rats, mice and guinea pigs. In the study of E.I. du Pont de Nemours and Co. (1981), the following LC50 values were calculated by Probit analysis: 10151 ppm for 5 minutes, 5664 ppm for 15 minutes, 4710 ppm for 30 minutes and 3954 ppm for 60 minutes. In a study in cynomolgus monkeys, at exposure to 900 ppm no signs of intoxication occurred during the first 20-25 minutes (corresponding to COHb of about 16-21 %), at 25 minutes the animals' performance in a behavioral test significantly decreased and at the end of the exposure period (30 min) animals became less active and were lying down. After about 25 minutes at a 1000 ppm, within 1- 2 minutes the animals went into a state of severe intoxication, virtually unable to perform coordinated movements (Purser and Berrill, 1983). In developmental toxicity tests, CO caused an increase in the rate of stillbirths or fetal mortality in pigs after a 2-3 day-exposure to COHb above 23 % (Dominick and Carson, 1983), in rabbits after continuous exposure to 16-18 % COHb throughout gestation (Astrup et al., 1972) as well as after daily exposure to high CO concentrations in cigarette smoke (exposure for 12 minutes/day on gestational days 6-18, resulting in COHb of 16%)(Rosenkrantzetal., 1986), in rats after 3 exposures to 750 ppm for 3 h/d (Choi and Oh, 1975) and in mice after exposure to 125 ppm for 11 d (Singh and Scott, 1984). Significant memory impairment in behavioral tests were found in young rats after continuous CO exposure throughout gestation (mean maternal COHb was 15.6%) (Mactutus and Fechter, 1985). In monkeys, a COHb of 9.3 % resulted in reduced threshold for electric shock-induced ventricular fibrillation (DeBias et al., 1979). A similar effect was found in dogs at 6.3-6.5 % COHb (Aronowet al., 1979). A COHb of 13-15 % increased the severity and extent of ischemic injury and the magnitude of ST-segment elevation in a myocardial infarction model in dogs (Sekiya et al., 1983). 33 ------- CARBON MONOXIDE FINAL: 07/2008 4. SPECIAL CONSIDERATIONS 4.1. Stability, Metabolism and Disposition CO is produced endogenously in normal metabolism: when an a-methylene bridge in the heme group of hemoglobin is broken during the catabolic process, one molecule of CO is released. It has been estimated that this production amounts to approximately 0.3 to 1.0 ml/h with an additional 0.1 ml/h resulting from a similar catabolic process involving other heme-containing compounds (e.g., myoglobin as well as cytochrome and catalase enzymes). This endogenous production of CO gives rise to an baseline or back ground level approximately of 0.5-0.8 % COHb (NIOSH, 1972). Almost all of the CO that has been inhaled is eliminated through the lungs when the previously exposed person enters an atmosphere free of CO. Carbon monoxide not only binds to hemoglobin forming COHb, but 10-50 % of the total body store of CO is also distributed to extravascular sites such as skeletal muscle, where it can bind to myoglobin. Extravascular CO can be slowly metabolized to carbon dioxide (Fenn, 1970). Inside the cells, CO can bind to all heme proteins capable of binding oxygen, such as myoglobin, cytochrome c oxidase, cytochrome P450 enzymes and tryptophan oxygenase (WHO, 1999a). However, the exact extent of this binding in vivo as well as the physiological consequences in terms of inhibition of protein and enzyme function and the existence and relevance of possible toxic effects has not been clearly shown up until now (cf. extensive discussion in WHO, 1999a). The time required to eliminate half of the gas is 3 to 5 hours (Landaw, 1973), depending on the amount of respiration, which acts to wash it out of the body. Peterson and Stewart (1970) reported a range for the elimination half-time from 128 to 409 minutes from 39 experiments, with an average of 320 minutes in human subjects that breathed normal air after CO exposure. Increased oxygen pressure helps to dislodge it from the hemoglobin. One hundred percent oxygen given at atmospheric pressure reduces the half-elimination rate to about 80 minutes (Peterson and Stewart, 1970). Weaver et al. (2000) reported a half-life of 74+7-25 minutes for COHb in CO-poisoned patients receiving 100 % oxygen. Klasner et al. (1998) reported a half-time of 44 minutes for children (n=26, 4-12 years old) when given 100 % oxygen via face mask. Hyperbaric oxygen at 3 | bar pressure reduces the half time to about 20-25 minutes (Beard, 1982; Landaw, 1973). 4.2. Mechanism of Toxicity If not stated otherwise, the information on the mechanism of toxicity is taken from the extensive recent reviews of WHO (1999a) and EPA (2000). The best understood biologic effect of CO is its combination with hemoglobin (Hb) to form COHb, thereby rendering the hemoglobin molecule less able to bind with oxygen. Although the rate of CO binding with hemoglobin is about one-fifth slower and the rate of dissociation from hemoglobin is an order of magnitude slower than the respective rates for oxygen, the CO chemical affinity for hemoglobin (represented by the Haldane coefficient M) is about 245 times greater than that for oxygen. One part of CO and 245 parts of oxygen would form equal parts of oxyhemoglobin and COHb (50 % each), which would be achieved by breathing air containing 21 % oxygen and 570 ppm CO. The steady-state ratio of COHb/oxyhemoglobin is proportional to the ratio of their respective partial pressures: COHb/O2Hb = M (Pco / P02) 34 ------- CARBON MONOXIDE FINAL: 07/2008 Under dynamic conditions, competitive binding of oxygen andCOto hemoglobin is complex: the greater the number of heme groups bound to CO, the greater the affinity of free heme groups for oxygen. CO not only occupies oxygen binding sites, molecule for molecule, thus reducing the amount of available oxygen, but also alters the characteristic relationship between oxyhemoglobin and the partial pressure of oxygen, which in normal blood is S-shaped. The difference in the partial pressure of oxygen between freshly oxygenated arterial blood (P(O2) = 100 mm Hg) and mixed venous blood (P(O2) = 40 mm Hg) represents a release to the tissues of approximately 5 ml O2/100 ml blood (NIOSH, 1972). With increasing COHb in blood, the dissociation curve is shifted gradually to the left, and its shape is transformed into that of a rectangular hyperbola. This changes the release of oxygen to the tissues appreciably: the oxygen content of the blood is not only lowered during exposure to CO, but the shift of the oxyhemoglobin dissociation curve to the left decreases the amount of remaining oxygen that is made available to the tissues. Both mechanisms serve to effectively lower the tissue partial pressure of oxygen and hence can create a generalized tissue hypoxia. Because the shift occurs over a critical saturation range for release of oxygen to tissues, a reduction in oxyhemoglobin by CO poisoning will have more severe effects on the release of oxygen than the equivalent reduction of hemoglobin due to anemia. While the brain has a higher requirement for oxygen than the heart, in contrast to the cerebral circulation the coronary circulation must supply an even increased amount of oxygen during periods of generalized tissue hypoxia; since underthese circumstances the heart is forced to increase both its rate and its output in orderto meetthe normal oxygen demands of the body. This increase in myocardial activity demands an increased oxygen supply to the myocardium, which must be met by the coronary circulation. Under hypoxic conditions increased oxygen supply to the peripheral tissues can be accommodated by increased blood flow (via vascular dilatation) and/or increased oxygen extraction by the tissues. The myocardium underthese circumstances appears only to increase the flow of blood rather than to extract an additional amount of oxygen from the coronary circulation. While the peripheral tissues normally extract only 25 percent of the oxygen content of the perfusing arterial blood during resting conditions, the myocardium extracts 75 percent, thus leaving the mixed venous blood only 25 percent saturated. This mechanism has the overall effect of maintaining the myocardial oxygen tension at a higher level than would be present in other muscle tissue and thus insures a continual aerobic metabolism, even under hypoxic duress. In terms of oxygen partial pressure, the mixed venous blood of the peripheral tissues is approximately 40 mm Hg while the mixed venous blood of the coronary circulation is only 20 mm Hg. In the presence of COHb (and the shift to the left of the oxyhemoglobin dissociation curve), however, the arterio-venous difference can only be maintained by an increased flow in the coronary circulation. In an individual with diminished coronary circulation because of coronary heart disease, however, this situation may result in a decrease in the venous oxygen partial pressure of the myocardium precipitated by an inability to maintain the normal arterio-venous gradient. Studies in dogs suggest that exercise plus an increased COHb, in addition to the global myocardial hypoxia, leads especiallyto areas of relative hypoxia in the leftventricle secondaryto redistributive changes in subendocardial blood flow(Einzig, 1980). This hypoxic effect is further enhanced, as mentioned above, by an increase in cardiac rate and output as a general response to peripheral tissue hypoxemia. A person with diminished coronary circulation caused by coronary heart disease, consequently, may be constantly near the point of myocardial tissue hypoxia, which can ultimately lead to myocardial infarction. 35 ------- CARBON MONOXIDE FINAL: 07/2008 4.3 Issues related to post-mortem CO determination in humans 4.3.1. Potential factors influencing COHb levels Data on the post-mortem decay of carboxyhemoglobin is limited. Rodat et al. (1987) reported about the stability of carbon monoxide after death. A CO poisoining due to a running truck engine in a non-ventilated area was discussed. The autopsy was performed 10 months after the death due to insurance claims. The body was decomposed but some muscle tissue was recovered and tested for carboxyhemoglobin levels, which were 26%. Muscle tissue as well as other human tissues, such as brain, lung, and kidney may be used for diagnosing death due to lethal exposure to CO (Vreman et al., 2006). The report did not discuss measurements from blood samples, presumably due to the decomposition of blood. Following death, the report indicated that carboxyhemoglobin levels disintegrate overtime releasing reduced hemoglobin. In addition, the report indicated that the formation of sulfur compounds in a putrefied cadaver makes it difficult to interpret the absorption spectra of the carboxyhemoglobin measurements, a phenomenon that has been acknowledged by others (Kojima et al., 1986; Winek and Prex 1981). Rodat et al. (1987) and Kojima et al. (1986) also suggested that the endogenous formation of CO after death is very low, People who die of CO poisoning often show sub-lethal COHb levels in their blood (Ronald Coburn, personal communication). The lungs rapidly absorb carbon monoxide, which avidly combines with hemoglobin at 230 to 270 times greater than oxygen (Ellenhorn, 1997; Larsen 2005). Oxygen therapy increases oxygen delivery and pulmonary excretion of carbon monoxide by displacing carbon monoxide from the hemoglobin and decreasing the half-life time of COHb (Ellenhorn, 1997; Roos 1994), in turn explaining the sub-lethal COHb levels in blood samples from deceased people exposed to CO. Carbon monoxide shifts from the blood into the muscle tissue have been reported in the literature (Bruce and Bruce 2006; Luomanmaki and Coburn, 1969). In order for shifts to occur, blood must be flowing in capillaries. Presumably during the moving of corpses after death, blood could be pushed through capillaries to a small extent (Ronald Coburn, personal communication) leading to carbon monoxide shifts, but no studies were found reporting this phenomenon in dead people. Oxidation of CO to CO2 has been reported in living animals and humans. The rate of oxidation in skeletal and cardiac muscle was found to be small but still measurable (Fenn and Cobb, 1932; Clark 1950; Luomanmaki and Coburn, 1969). It is unknown whether this oxidation occurs in cadavers and its effects on the CO decay rates after death. Once blood is collected from a cadaver, the postmortem samples may be measured more than once and results would depend on storage and treatment of samples. Levin et al. (1990) found a 19% decrease in measured COHb levels when blood was refrigerated for three months and then frozen for three months. The refrigerated blood samples were first tested by microdiffusion techniques (sensitivity of -5%) within one month of being obtained from victims of a hotel fire on December 31, 1986. The samples remained refrigerated until being mailed frozen to a second laboratory for testing (received March 26, 1987). The samples were frozen upon arrival and were thawed and refrozen several times during the next three months for 36 ------- CARBON MONOXIDE FINAL: 07/2008 experimental purposes. After sonication and filtration, the samples were analyzed on a CO- oximeter IL-282 (sensitivity not given). The authors concluded that aging of blood samples and methods of storage could affect accuracy of analytical results. This result was supported by another study which determined that the contact of the sample with air could decrease the %COHb saturation (Chace et al. 1986). This is in contrast to reports that CO would be stable for months to years in stored samples (vacutainer tubes, especially heparin-anticoagulated tubes) (Hampson 2008, Kunsman et al. 2000). Proper storage of samples would prevent loss of CO (Nelson 2005b). 4.3.2 Influence on collection site on measured COHb levels Reductions in the %COHb saturation are also associated with differences between carboxyhemoglobin measurements derived from heart blood and peripheral blood specimens. Levine et al. (2002) studied data from 42 CO poisoning cases. The Office of the Chief Medical Examiner in the state of Maryland provided the data. Blood samples from the heart and the subclavian veins were analyzed in a CO-oximeter. The specific heart site for blood collection was not reported. Also, the report did not indicate whether the deceased individuals with decreased carboxyhemoglobin were given oxygen therapy. Blood samples with COHb saturation levels greater than 12% were confirmed and quantitated by gas chromatography. The latter analysis measured both CO content and CO capacity, and not hemoglobin concentration, which tends to vary in postmortem specimens (Levine et al. 2002). Samples were normalized for hemoglobin ensuring that differences between the heart blood and peripheral blood were not caused by significant differences in hemoglobin between the two blood samples. The average heart blood COHb level was 42 (range= 11-79; standard deviation=19.95, median=38) and the average peripheral blood COHb level was 39 (range= 4.2- 71; standard deviation =17.07, median=37). The average heart blood to peripheral blood (H/P) ratio was 1.09. Sixty-two percent (26 of 42) of the cases had an H/P ratio between 0.9 and 1.1, whereas 74% (31 of 42) of the cases had an H/P ratio between 0.8 and 1.2. Statistical analysis showed no statistically significant differences in COHb levels between heart and peripheral blood samples (Levine et al. 2002). The report acknowledged that there might be instances (e.g. cardiopulmonary resuscitation) where differences between heart blood and peripheral blood COHb levels might occur in isolated cases, but in general, there were no significant differences between the two blood sources. Dalpe-Scott et al. (1995) calculated the H/P ratio of drug concentrations in postmortem blood samples for 113 drugs representing 320 cases. Thirty-five carbon monoxide poisoning cases were examined. The average H/P ratio was 1.0, range 0.9-1.5. The specific COHb levels were not provided. Data from Dalpe-Scott et al. (1995) confirmed those findings presented by Levine et al. (2002). Differences between COHb levels in the heart blood when compared to those found in the periphery (e.g. femoral vein) have been reported in cases that received cardiopulmonary resuscitation. Rice (1976) found wide variation in carboxyhemoglobin levels in 300 consecutive fatal cases of CO poisoning. Source of CO poisoning (fire, gas heaters, etc.) was not identified in most of the 300 cases with the exception of 4 case studies discussed in the paper. The author hypothesized that levels below 50% COHb were probably low due to the dissociation of carboxyhemoglobin after death when oxygen therapy was given as an attempt to resuscitate the 37 ------- CARBON MONOXIDE FINAL: 07/2008 person. A summary of the case findings is given below. • Casel: a child (14 months) was found apparently dead in a smoldering room fire. Artificial respiration was given on the way to the hospital and continued for about an hour before death was pronounced. Subclavian blood showed carboxyhemoglobin levels of 15%. The report did not indicate if it was collected from the subclavian artery or vein. Blood from the femoral vein reported a 31% carboxyhemoglobin level, or a 2-fold difference between sites. Subclavian blood to femoral blood ratio: 0.48 • Case 2: a man of 57 yrs died of CO poisoning. The CO source was a disconnected coal gas supply pipe. The emergency personnel found him cold but gave him artificial respiration on the way to the hospital where he was pronounced dead. Subclavian blood showed carboxyhemoglobin levels of 32%. The report did not indicate if it was collected from the subclavian artery or vein. Blood from the femoral vein reported a 52% carboxyhemoglobin level, or a 1.6-fold difference between sites. Subclavian blood to femoral blood ratio: 0.62 • Case 3: a woman of 43 yrs was exposed to CO during a fire. Fire personnel recovered her and attempted resuscitation using artificial respiration and pure oxygen. Subclavian blood showed carboxyhemoglobin levels of 42%. The report did not indicate if it was collected from the subclavian artery or vein. The common iliac vein showed 45% carboxyhemoglobin level. Blood from the femoral vein reported a 59% carboxyhemoglobin level, or a 1.2-fold difference when compared to the subclavian vein. Subclavian blood to femoral blood ratio: 0.71 Subclavian blood to iliac blood ratio: 0.93 • Case 4: an infant of 5 months old died in a room fire. Artificial respiration was performed with the infant. Femoral samples were not provided. Blood draining the blood cavity was taken and reported a 48% level of carboxyhemoglobin, whereas the subclavian blood reported a 34% level of carboxyhemoglobin. The report did not indicate if it was collected from the subclavian artery or vein. Subclavian blood to peripheral blood ratio: 0.71 Rice (1976) explained the results by pointing out that blood with high concentration of carboxyhemoglobin does not coagulate and artificial respiration would have pushed blood to move into and out of the lungs. Thus, oxygen therapy would have increased the dissociation of carboxyhemoglobin in the blood, and the amount of the dissociation would have depended on the vigor and the duration of the artificial respiration. The disassociation would be higher in the blood from the lungs, the heart, and the blood vessels in close proximity to the lungs and heart. Currently, the standard forensic practice is to collect blood from suitably isolated peripheral sites (e.g. femoral vein) which are less likely to be subject to postmortem chemical redistribution (Flanagan et al. 2005; Drummer 2007). The common practice of procuring blood samples from live persons has been venipuncture of the antecubital area of the arm (Ernst 2005). Gas chromatography is considered the most precise and accurate technique to measure COHb levels, but other techniques such as spectrophotometric analyses worked well (Lee et al. 38 ------- CARBON MONOXIDE FINAL: 07/2008 1975; Mahonoey et al. 1993; Ronald Coburn personal communication). 4.4. Other Relevant Information 4.4.1. Species Variability With regard to lethal effects, COHb of 50-80 % have been reported as lethal level in rats and guinea pigs (Rose et al., 1970; E.I. du Pont de Nemours and Co., 1981). In apparently healthy people that died from CO poisoning, usually COHb of 60 % or higher are found (Balraj, 1984; AIHA, 1999; Winter and Miller, 1976, Holmes, 1985, Stewart, 1975). Syncopes have been reported to occur in children at a threshold of 24.5 % COHb (Crocker and Walker, 1985). In monkeys, at COHb little higher than 16-21 % syncope-like effects occurred (Purser and Berrill, 1983). The lowest COHb that resulted in cognitive development defects in children in a long-term follow-up study was 13 % (Klees et al., 1985). In mice, memory impairment was found in the offspring of rats exposed continuously at 15.6 % COHb during gestation (Mactutus and Fechter, 1985). Taken together, these studies imply a limited species variability for different effects with regard to the COHb at which these effects occur. However, the exposure conditions necessary to reach a certain COHb differ between species due to different affinities of their hemoglobin for CO. The equilibrium COHb of different species is determined by the species-specific Haldane (affinity) constant M. Reported values are 228 for dogs (Sendroy and O'Neal, 1955), 195 for monkeys (Sendroy and O'Neal, 1955), 170 for rats (Rodkey and O'Neal, 1970) and 117 for guinea pigs (Rodkey and O'Neal, 1970). Jones etal. (1971) reported equilibrium COHb in different species after 48-hour continuous exposure as shown in Table 12. Using the mathematical model described in Appendix B, corresponding COHb values for a 70-kg man can be calculated as 7.9, 13.8 and 25.0 % for 51, 96 and 200 ppm, respectively^ TABLE 12: COHb AFTER 48 HOURS CONTINUOUS CO; adopted from Jones et al., 1971 CO concentration (ppm) 51 51 51 51 96 96 96 species dog monkey rat guinea pig dog monkey rat EXPOSURE TO COHb in blood (%) (n) 5.7 5.3 5.1 3.2 12.5 10.3 7.5 (2) (3) (15) (15) (2) (3) (15) 39 ------- CARBON MONOXIDE FINAL: 07/2008 96 200 200 200 200 guinea pig dog monkey rat guinea pig 4.9 20.8 20.0 16.4 9.4 (15) (2) (3) (15) (15) 4.2.2. Intraspecies Variability Experiments in mice did not indicate that very young or very old animals were more susceptible to lethal effects of CO exposure (Pesce et al., 1987; Winston and Roberts, 1978). However, there is considerable variability within human subpopulations: aCOHb of about 15% only leads to very slight symptoms, such as headache, in healthy adults (Stewart et al., 1970; WHO, 1999a). In contrast, the same COHb was reported to cause long-lasting defects in the cognitive development and behavioral alterations in children (Klees et al., 1985) or even to contribute to death from myocardial infarction in individuals with coronary artery disease (Grace and Platt, 1981; Balraj, 1984). In case reports of myocardial infarction, other subjects that were exposed underthe same conditions (and sometimes had higher COHb) did not experience effects above the AEGL-2 level (Atkins and Baker, 1985; Grace and Platt, 1981). Subpopulations at higher risk for toxic effects of CO include the following groups: a) fetuses because of higher CO affinity and slower CO elimination (see Sections 2.3 and 4.4.4). The severity of exposure and maternal clinical signs appear to be associated with fetal mortality (Koren et al. 1991). A review by Greingor et al. (2001) noted that carbon monoxide crosses the placenta through passive diffusion or facilitated by a carrier. As the fetus increases in age and weight, placental carbon monoxide diffusion increases. When the mother is exposed to carbon monoxide, the amount of oxygen in her blood decreases, and oxygen transported across the placenta decreases and puts the fetus in a hypoxic state. Carbon monoxide crosses the placenta as it dissociates from maternal hemoglobin and binds to fetal hemoglobin. The only source of fetal oxygen is the mother, and maternal treatment for carbon monoxide poisoning reduces fetal COHb levels (Greingor etal. 2001). Clearance of carbon monoxide in the fetus would be dependent on the mother's oxygen intake. Children have the same type of hemoglobin as adults, but are more susceptible than adults because they breathe a greater amount of air per body weight than adults. The binding affinities of embryonic hemoglobins suggest fetuses are more susceptible to CO intoxication when compared to that of the adult hemoglobin. Embryonic hemoglobins (Gower I, Gower II, Portland) are present until about 8-12 weeks of gestation. Fetal hemoglobin is expressed from about 5 weeks of gestation until 9 months after birth. Adult hemoglobin starts being produced between 3-6 months after birth (Orville, 2008). Under physiological conditions, the binding constants of fetal and adult hemoglobin to carbon monoxide are 0.09 uM and 0.13 uM, respectively, meaning that the binding affinity for carbon monoxide is higher for fetal hemoglobin than adult 40 ------- CARBON MONOXIDE FINAL: 07/2008 hemoglobin (Di Cera et al. 1989). The rate constants for the binding of carbon monoxide to the three embryonic hemoglobins are 3.Ox 10~6 M/s (Gower I), 2.0 x10~6 M/s (Gower II), and 3.5x 10~6 M/s (Portland) compared to 4.0 x 10~6 M/s for adult hemoglobin at pH 6.5 (Hofmann and Brittain, 1996). No data were located reporting if embryos are more susceptible than fetuses. Data regarding susceptibility of embryos to carbon monoxide is mostly qualitative. b) children because they develop acute neurotoxic effects (e.g. headaches, nausea), long-lasting neurotoxic effects (e.g. memory deficits) and impaired ability to escape (i.e. syncopes) at lower COHbthan adults (see Section 2.2.2.1). Children also have developing organs (brain, lungs)which may be affected differently than the developed organs of adults (ATSDR 2002). Children tend to be more susceptible than adults because they breathe a greater amount of air per body weight than adults. c) people with pre-existing diseases, either known or unknown, that already decrease the availability of oxygen to critical tissues, including subjects with coronary artery disease (see Sections 2.2.1 and 2.2.1.1), chronic obstructive lung disease, chronic anemia and hemoglobinopathies, such as sickle cell anemia._For example, in sickle-cell disease, the average lifespan of red blood cells with abnormal hemoglobin is 12 days compared to an average of 120 days in healthy individuals with normal hemoglobin. "As a result, baseline COHb levels can be as high as 4%. Presumably, exogenous exposure to CO, in conjunction with higher endogenous CO levels, could result in critical levels of COHb. However, it is not known how ambient or near-ambient levels of CO would affect individuals with these disorders" (EPA, 2000; see also WHO, 1999a). Due to the physiologic adaptation in these subpopulations, they are not considered more susceptible than patients with coronary artery disease. d) people at high altitude, especially those not living there long enough for physiological adaptation. "It is important to distinguish between the long-term resident of high altitude and the newly arrived visitor from low altitude. Specifically, the visitor will be more hypoxemic than the fully adapted resident. One would postulate that the combination of high altitude with carbon monoxide would pose the greatest risk to persons newly arrived at high altitude who have underlying cardiopulmonary disease, particularly because they are usually older individuals. Surprisingly, this hypothesis has never been tested adequately" (WHO, 1999a). Due to physiologic adaptation, people living at high altitude are not considered generally more susceptible than patients with coronary artery disease. Since it is generally not advisable for patients with severe coronary artery disease to travel to places at high altitude, it is not considered necessary to especially take that part of the identified susceptible subpopulation (i.e. patients with coronary artery disease; see below) into account when deriving AEGL values. An estimated 62 million people in the United States (about 20% of the population) have one or more types of cardiovascular disease (American Heart Association, 2003). For the major diseases within the category of total cardiovascular disease, about 50 million Americans have high blood pressure, 13 million have coronary heart disease, 4.9 million have heart failure, 4.7 million have cerebrovascular disease (stroke), and 1 million have congenital cardiovascular defects. The prevalence of cardiovascular diseases increases with age. It is 10% for males and 4% for females at age 25-34, 51 % for males and 48 % for females at age 55-64 and 71 % for males and 79 % for females at age 75 or older (American Heart Association, 2003). 41 ------- CARBON MONOXIDE FINAL: 07/2008 Coronary heart disease caused more than 1 of every 5 deaths in the USA in 2000. Coronary heart disease was mentioned as cause of death in 681,000 cases and myocardial infarction in 239,000 deaths. Fifty percent of men and 63 % of women who died suddenly of coronary heart disease had no previous symptoms of this disease (American Heart Association, 2003). Within the group of people with coronary heart disease, 7.6 million had myocardial infarction (heart attack) and 6.6 million of angina pectoris (chest pain) (American Heart Association, 2003). The prevalence of angina pectoris in the British adult population is about 4 % (Williams and Stevens, 2002). Angina pectoris is a symptom of coronary heart disease. Common features of an attack are central chest pain, pain radiating to the lower jaw, or arms, and shortness of breath. The pain occurs when there is insufficient oxygen delivery to the heart, leading to ischemia. This is usually, although not exclusively, a result of an atheromatous narrowing (stenosis) in one or more of the coronary arteries. Angina can classified broadly as stable or unstable, depending on its severity and pattern of occurrence. Stable angina is typically provoked by exercise (e.g., hurrying across a street or climbing a long flight of stairs), stress or extremes of temperature and is relieved by either rest or sublingual nitrates or both. Unstable angina is understood as anginal pain that occurs with lesser degrees of exertion, with increasing frequency, or at rest (i.e., without exertion). The pain may be more severe, last longer, and requires more intensive intervention (usually hospitalization for initiation of medication under cardiac monitoring). If left untreated, unstable angina may result in a heart attack and irreversible damage to the heart. The diagnosis of angina is generally based on clinical history, electrocardiograph stress testing (where patients are exercised on a treadmill to look at the effect on their electrocardiogram), and coronary angiography (looking for narrowings in the | coronary arteries) (Williams and Stevens, 2002). 4.4.3. Time Scaling The L.C50 values for different exposure periods are shown in Figure 1. Overall the distribution does not seem to argue against a linear relationship between log(concentration) and log(time) and from the data from E.I. du Pontde Nemours and Co. (1981) a value of 2.6 can be calculated for the exponent n from the slope. Regression analysis of all data yielded a value of n=2.8. However, taking a closer look at the data from this study suggests that the data might be distributed non- linearly and that the slope decreases with increasing exposure time. The AEGL-2 and AEGL-3 exposure concentrations were derived from a mathematical model based on the same COHb at the end of the respective exposure periods. These values are also distributed non-linearly in a log-log plot: the slope between the two shortest exposure periods (10 and 30 min) is equivalent to n=1.0-1.1 and the slope between the two longest exposure periods (4 and 8 h) is equivalent to n=2.9-3.4. This non-linearity is probably caused by the fact that the COHb depends strongly on the ventilation rate and lung blood flow for short exposure rates, while for long exposure rates the COHb becomes independent of these parameters and exclusively depends on the affinity of hemoglobin for CO (represented by the Haldane constant M). Since rats have a higher ventilation rate per kg body weight than humans, their COHb reaches the steady state faster and therefore forthe same exposure time the slope for rats is smallerthan the corresponding slope for humans, i.e., COHb depends stronger on the ventilation rate in humans compared to rats. 42 ------- CARBON MONOXIDE FINAL: 07/2008 4.4.4. Mathematical models of COHb formation In 1965, Coburn, Forster and Kane developed a differential equation (CFK model) to describe the major physiological variables that determine the COHb in blood using data from patients with increased endogenous production of CO due to anemia (Coburn etal., 1965). The CFK model is represented by the following equation: d(COHb\ Vco COHb,*P02 Pco dt Vb M*B*Vb*OHb B*Vb where: B = 1 / DL + PL/ VA M = Ratio of affinity of blood for CO to that for O2; M = 21 8 OHb = ml of O2 per ml blood; OHb = 0,2 COHbt = ml of CO per ml blood at time P02 = average partial pressure of oxygen in the lung capillaries; P02 = 100 mm Hg Vco = rate of endogenous CO production; Vco = 0.007 ml/min DL = diffusivity of the lung for CO; DL == 30 ml / min mm Hg PL = barometric pressure minus the vapor pressure of water at body temperature, PL = 713 mm Hg Vb = blood volume; Vb = 5500 ml PCO = partial pressure of CO in the air inhaled (mm Hg) VA = alveolar ventilation rate; VA = 6000 ml/min (awake), 4000 ml (sleeping) t = exposure duration (min) Peterson and Stewart (1970) reported that the CFK model well predicted COHb measured in 18 healthy male students, aged between 24 and 42 years, that were exposed to the following combinations of CO concentrations and exposure times: about 50 ppmforSO minutes to 24 hours, about 1 00 ppm for 1 5-480 minutes, about 200 ppm for 1 5-1 20 minutes and about 500 ppm for 1 5- 114 minutes. They used the following integrated form of the CFK equation and parameters: A*COHb,-B*l''co-P,0 where A=P02/MOHb B = 1 / DL + PL / VA M = Ratio of affinity of blood for CO to that for O2; M = 21 8 OHb = ml of O2 per ml blood; OHb = 0,2 COHbt = ml of CO per ml blood at time COHbo = ml of CO per ml blood at beginning of the exposure P02 = average partial pressure of oxygen in the lung capillaries; P02 = 100 mm Hg Vco = rate of endogenous CO production; Vco = 0.007 ml/min DL = diffusivity of the lung for CO; DL == 30 ml / min mm Hg PL = the vapor pressure of water at body temperature, PL = 71 3 mm Hg Vb = blood volume; Vb = 5500 ml PCO = partial pressure of CO in the air inhaled (mm Hg) 43 ------- CARBON MONOXIDE FINAL: 07/2008 VA = alveolar ventilation rate; VA = 6000 ml/min (awake), 4000 ml (sleeping) t = exposure duration (min) PB = 750mmHg p 'QO-, IOOO pp/r. 3456 789100 345 67891000 2 34 5000 Exposure duration, minutes FIGURE 2: COHb FOR DIFFERENT EXPOSURE CONCENTRATION-TIME COMBINATIONS (from Peterson and Stewart, 1975) In another study by Peterson and Stewart (1975), data from a series of human exposures to CO were analyzed to determine the fit to the theoretical CFK equation. 19 men and 3 women were exposed to concentrations of 50, 100 or 200 ppm for 0.33-5.25 hours. Three exercise levels from sedentary to 0, 150 or 300 kpm/min on an ergometer were used (15 subjects in total). These resulted in mean ventilation rates of 10.1 (9.1 for women), 14.0, 24.0 (19.7 forwomen) and 29.7 l/min, respectively. The CFK model predicted COHb for both men and women as well as for resting and exercising subjects within a standard error of about 2 %. In contrast to the original model, which assumes all variables to be constant except t, PL, COHbt and Pco, the following parameter alterations were introduced: P02: When the partial pressure of oxygen in inspired air (Pi02) is less than the 149 mm Hg found under normal conditions, the partial pressure of oxygen in the lung capillaries will be less than the value of 100 mm Hg assumed by Coburn and coworkers. From measurements of oxygen partial pressure in arterial blood, which is assumed to be the same as the oxygen partial pressure in lung capillaries, the following equation was derived: P02 = 1 / (0.072-0.00079 Pi02 + 0.000002515 (Pi02)2) and Pio2 = Fi02 (PB - 47 - Pico) with Fi02 = fraction of oxygen in inspired air, PB = barometric pressure (mm Hg), Pico = partial pressure of CO in inspired air DL: Body size effects on diffusivity at rest were was calculated from published data as- DL = 1 / (-0.0287 + 0.1188/A) with A = body surface in m2 Vb: the published blood volume relationship of 74 mg/kg of body weight for men and 73 44 ------- CARBON MONOXIDE FINAL: 07/2008 ml/kg for women was used. VA: The alveolar ventilation rate was expressed as: VA = VE - f VD; with VE = total rate of ventilation (ml/min), f = respiration rate (min~1) and VD = dead space (ml) OHbt: At standard concentrations, 1 g of hemoglobin will hold 1.38 ml of oxygen and thus OHbmax = 1.38 [Hb]/100, with [Hb] being the hemoglobin concentration in blood (g/100 ml). During and after CO exposure, the value of OHbt that must be used is actually OHbt = OHbmax - COHbt. In this case, the CFK equation can only be solved by iterative procedures. COHb: This value can be converted to the more conventional ..percentage saturation" by: % carboxyhemoglobin = COHb 100/OHbmax Tikuisis et al. (1992) studied the rate of formation of COHb in healthy young males at a low (45 W) and moderate (90 W) exercise load. Ten nonsmoking subjects were exposed to CO on two separate occasions distinguished by the activity level. Each experiment began with an exposure to 3000 ppm for 3 minutes during a rest period followed by 3 intermittent exposures ranging from 3000 ppm for 1 minute at low exercise to 667 ppm for 3 minutes at moderate exercise. The net increase in COHb after all exposures (about 10 %) deviated by <1 % between the measured and values predicted from the CFK model. Within this deviation, there was a general tendency of the CFK equation to underpredict the increase in COHb for the exposures at rest and the first exercise exposure and to overpredict levels for the latter two exposures at exercise. Benignusetal. (1994) exposed 15 men to 7652 mg/m3(6683 ppm) CO for 3.1-6.7 minutes at rest. Except for the Haldane constant M, which was assumed to be 245, all other physiological parameters of the CFK equation were measured for each individual from the very beginning of exposure. Arterial COHb was considerably higher than the venous COHb. The rate of increase in blood COHb and the arterial-venous COHb differences varied widely among individuals. The peak arterial COHb at the end of exposure ranged from 13.9 to 20.9 %. The peak venous levels reached during the recovery period ranged from 12.4 to 18.1 %. The arterial-venous difference ranged from 2.3 to 12.1 % COHb. The CFK equation overestimated venous blood COHb, whereas arterial blood levels were significantly and consistently underestimated. Hilletal. (1977) developed a mathematical model to predict values of blood COHb in mother and fetus for prolonged exposures to 30-300 ppm CO. During CO exposure, fetal COHb lag behind maternal COHb by several hours. During prolonged uptake, fetal levels eventually overtake maternal levels and approach equilibrium values as much as 10% higher than the mother's, due to the higher affinity of CO for fetal hemoglobin compared to adult hemoglobin. During CO washout the fetal levels again lag behind the mothers. 5. DATA ANALYSIS FOR AEGL-1 5.1. Human Data Relevant to AEGL-1 CO has no odor and does not cause irritative effects. A large number of studies investigated the effects of low CO exposure (COHb <10 %)on healthy individuals and high-risk groups. In these, effects on healthy persons, such as decreases in work capacity and decrements of neurobehavioral function, start at COHb of 5% (WHO, 1999a; EPA, 2000). In patients with coronary artery disease, which constitute the most susceptible 45 ------- CARBON MONOXIDE FINAL: 07/2008 subpopulation, the time to onset of angina and the time to 1-mm ST-segment change in the electrocardiogram during physical exercise were significantly reduced at COHb of 2.0 or 4.0 % (Allredetal. 1989a; b; 1991). 5.2. Animal Data Relevant to AEGL-1 No studies in experimental animals were located that were considered relevant for the derivation of AEGL-1 values. The studies describing effects of CO on cardiac function, such as Sekiya et al. (1983), DeBias et al. (1979) and Aronow et al. (1979), normally employ models in which the heart was damaged additionally by an electric stimulus or by coronary artery ligation. Effects of CO exposure found in these systems can hardly be extrapolated quantitatively to humans. 5.3. Derivation of AEGL-1 CO is an imperceptible toxic gas. Until very severe symptoms occur (inability to walk) none or only nonspecific symptoms were noted in healthy humans and monkeys (Haldane, 1895; Purser and Berrill, 1983). In patients with coronary artery disease, which constitute the most susceptible subpopulation, effects, such as significant electrocardiogram changes, reduced time to the onset of angina and increased cardiac arrhythmia, start occurring at exposure concentrations little higher than current ambient air quality guidelines, e.g. the U.S. National Air Quality Guideline of 9 ppmfor 8 hours (National Air Pollution Control Administration, 1970; FR , 2000; EPA, 2000; Raub, 2000), the WHO Air Quality Guideline of 10 mg/m3 (9 ppm) for 8 hours (based on 2.5 % COHb) (WHO, 1999a) and the designated European Union Limit Value of 10 mg/m3 (9 ppm) for 8 hours (EC, 1999). These cardiac effects were considered above the AEGL-1 level and thus would not constitute a suitable basis for the derivation of AEGL-1 values. AEGL-1 values are not recommended because susceptible persons may experience more serious effects (equivalent to AEGL-2 level) at concentrations, which do not yet cause AEGL-1 effects in the general population. In addition, CO exposures encountered frequently in everyday life are at or above the concentration range, in which AEGL-1 level would have to be set: smokers have COHb in the range of 3-8 % (Radford and Drizd, 1982) and CO concentrations of about 10-50 ppm, which can be found on heavily traveled roads, inside motor vehicles and in homes with gas-, coal-, wood- or kerosene-fired heaters and stoves, correspond to an equilibrium COHb of 1.8-7.5 % (see Figures 2 and 4). TABLE 13: AEGL-1 VALUES FOR CARBON MONOXIDE AEGL Level AEGL-1 10 minutes N.R.a 30 minutes N.R. 1 hour N.R. 4 hours N.R. 8 hours N.R. a N.R., not recommended because susceptible persons may experience more serious effects (equivalent to AEGL-2 level) at concentrations, which do not yet cause AEGL-1 effects in the 46 ------- CARBON MONOXIDE FINAL: 07/2008 general population 6. DATA ANALYSIS FOR AEGL-2 6.1. Human Data Relevant to AEGL-2 In patients with coronary artery disease, COHb of 2 or4 % significantly reduced the time to angina and the time to 1-mm change in the ST-segment of the electrocardiogram upon physical exercise; at 4 % the total exercise time and the heart rate-blood pressure product were also significantly reduced (Allred et al., 1989a; b; 1991). A reduced time to onset of exercise-induced chest pain at COHb between 2.5 and 4.5 % was also reported by several other studies (Aronow et al., 1972; Anderson et al., 1973; Sheps et al., 1987; Kleinman et al., 1989; 1998). Sheps et al. (1990; 1991) reported that in patients with coronary artery disease the frequency of ventricular premature depolarizations was significantly increased at an COHb of 5.3 %, but not at 3.7 %, compared to room air exposure. Dahms et al. (1993) found no increased frequency of ventricular ectopic beats at COHb of 3 or 5 %. Klasner et al. (1998) analyzed a mass poisoning of 504 school children. In 147 of 155 children that showed symptoms, the mean COHb measured about 1 hour (up to 2 hours) after removal from the CO atmosphere was 7.0 % COHb. Of all children that were examined in hospital (177) (mean age 8.7 years) the following symptoms were observed: headache (139), nausea (69), dizziness (30), dyspnea (19), vomiting (13), abdominal pain (11) and drowsiness (9). In an analysis of CO poisonings in 16 children (up to 14 years of age) with COHb of 15 % or higher, Crocker and Walker (1985) reported thresholds for effects, such as nausea, vomiting, headache and lethargy between 16.7 and 19.8 % COHb (average concentrations in children displaying these symptoms were 25.9-29.4 %). Visual symptoms and syncopes occurred at a threshold of 24.5 % COHb (average 31.6-32.5 %). All 9 children with a COHb of 24.5 % or higher experienced at least one syncope. In an investigation on long-term effects of CO poisoning in children, evaluated 2-11 years after the poisoning, Kleesetal. (1985) reported that 6 of the 14 children exhibited serious disorders (spatial organization problems, constructive apraxia, deterioration of lexical activity, as well as spelling and arithmetic). Compared to the other 7 children, that exhibited only slight impairment of visual memory and concentration, the first group of more severely affected children were younger (mean age 7.8 years; range 2.8-12.1 years) than the latter group (mean age 9.8 years; range 3.5- 14.5); there was no difference in measured COHb (mean 21 (range 13-32)% in the first vs. 22(16- 26) % in the latter group). A short-term follow-up (3 months after the poisoning) suggested that medium intoxications (reported COHb 16-27 %) did not produce manifest sequelae except for a momentary standstill in the child's progress of about 2 months. Kizakevich etal. (1994) reported that healthy young men can perform submaximal exercise without overt impairment of cardiovascular function after CO exposures attaining 20 % COHb. Stewart et al. (1970) found that a CO exposure of healthy subjects resulting in 12.5 to 25.5 % COHb did not affect the results of several neurophysiological tests. Nielsen (1971) did not report on severe effects in three subjects that were repeatedly exposed to CO resulting in concentrations of 25-33% COHb. In a poisoning incident at the workplace, severe headaches, dizziness, weakness, 47 ------- CARBON MONOXIDE FINAL: 07/2008 nausea, chest pain, shortness of breath and other symptoms were reported for a COHb of about 35 %(Elyetal., 1995). 6.2. Animal Data Relevant to AEGL-2 In a study in cynomolgus monkeys, Purser and Berrill (1983) reported that during exposure to 900 ppm CO for a total of 30 minutes, no signs of intoxication occurred until 20-25 minutes (corresponding to COHb of about 16-21 %). At 25 minutes into the exposure, the animals' performance in a behavioral test significantly decreased. At the end of the exposure period, the animals became less active, most of them were lying down, but animals did not collapse. At a 1000 ppm, no effects were observed during the first 16-20 minutes. At this time the animals became less active and sat down for short periods. At about 25 minutes, the animals went into a state of severe intoxication within 1-2 minutes, in which animals were lying down with eyes closed, they sometimes vomited and were virtually unable to perform coordinated movements. Significant memory impairment in behavioral tests were found in young rats after continuous CO exposure throughout gestation (mean maternal COHb was 15.6 %) (Mactutus and Fechter, 1985). In monkeys, a COHb of 9.3 % resulted in reduced threshold for electric shock-induced ventricular fibrillation (DeBias et al., 1979). Aronow et al. (1979) reported that CO exposure increased the vulnerability of the heart to induced ventricular fibrillation in normal dogs breathing 100 ppm CO for 2 hours (resulting COHb was 6.3-6.5 %). The ventricular fibrillation was induced by an electrical stimulus applied to the myocardium. A COHb of 13-15 % increased the severity and extent of ischemic injury and the magnitude of ST-segment elevation in a myocardial infarction model in dogs (Sekiya et al., 1983). 6.3. Derivation of AEGL-2 The derivation of AEGL-2 values was based on effects in patients with coronary artery disease. An estimated 62 million people in the United States (about 20 % of the population) have one or more types of cardiovascular disease (American Heart Association, 2003). For the major diseases within the category of total cardiovascular disease, about 50 million Americans have high blood pressure, 13 million have ischemic (coronary) heart disease, 5 million have heart failure, 4 million have cerebrovascular disease (stroke), and 2 million have rheumatic fever or heart disease. For the derivation of AEGL-2 values a level of 4 % COHb was chosen. At this exposure level, patients with coronary artery disease may experience a reduced time until onset of angina (chest pain) during physical exertion (Allred et al., 1989a; b; 1991). Caracteristic points of an electrocardiogramm are the P wave, reflecting atrial depolarization, the QRS complex, representing the ventricular muscle depolarization, and the T wave, reflecting ventricular muscle repolarization. In the normal electrocardiogramm, the ST segment is isoelectric, resting at the same potential as the interval between the T wave and the next P wave. Horizontal depression or a downsloping ST segment merging into the T wave occurs as a result of ischemia, ventricular strain, changes in the pattern of ventricular depolarization or drug effects. In chronic ischemic heart disease, there may be moderate degrees of horizontal ST 48 ------- CARBON MONOXIDE FINAL: 07/2008 segment depression or a downward sloping ST segment, flattening or inversion of T waves and prominent U waves. It is difficult to define an abnormal ST segment depression in precise quantitative terms. However, a myocardia ischemia has to be considered if the beginning of the ST segment is more than 0.5 mm (corresponding to 0.05 mV) below the isoelectric line and there is an associated T wave abnormality (Wilson et al., 1991). According to the practice guidelines for chronic stable angina (Gibbons et al., 1999), a ST-segment depression at rest is a marker for adverse cardiac events in patients with and without known coronary artery disease. Additional exercise-induced ST-segment depression in the patient with >=1 mm rest ST-segment depression is a reasonably sensitive indicator of coronary artery disease. The ST-segment depression is indicative of clinically relevant myocardial ischemia requiring medical treatment. From the ST-segment depression, the Duke treadmill score can be calculated. It equals the exercise time in minutes minus (5x the ST-segment deviation, during or after exercise, in millimeters) minus (4x the angina index, which has a value of "0" if there is no angina, "1" if angina occurs, and "2" if angina is the reason for stopping the test). Among outpatients with suspected coronary artery disease, the two thirds of patients with scores indicating low risk (score >=5) had a four-year survival rate of 99% (average annual mortality rate 0.25%), and the 4% who had scores indicating high risk (score <-10) had a four-year survival rate of 79% (average annual mortality rate 5%) (Gibbons et al., 1999). In the available experimental studies, the CO exposure alone (i.e. with subjects at rest) did not cause angina, while exercise alone did so. Moreover, the changes in the electrocardiogram (ST- segment depression of 1 mm or greater) as well as the angina symptoms can be considered fully reversible after a single incident. This effect level was considered to be below that defined for AEGL-2. It should be noted that all experimental studies used patients with stable exertional angina, who did not experience angina while at rest. Thus, it is considered likely that in more susceptible individuals (a part of the patients with unstable angina pectoris might belong to this group) CO exposure alone could increase angina symptoms. In hypersusceptible patients more severe effects, even including myocardial infarction cannot be ruled out. It should be noted that in contrast to the anecdotal case reports on myocardial infarction discussed in the derivation of AEGL-3, the studies investigating electrocardiogram changes and angina symptoms in patients with coronary artery disease, used here for the derivation of AEGL-2 values, are high-quality, well-conducted experimental studies with well-characterized exposure conditions and information on interindividual variability. An exposure level of 4 % COHb is unlikely to cause a significant increase in the frequency of exercise-induced arrhythmias. This effect has been observed at COHb of 5.3 %, but not at 3.7 % (Sheps et al., 1990; 1991), while in another study no effect of CO exposure on ventricular arrhythmia was found at 3 or 5 % COHb (Dahms et al., 1993). No experimental studies in heart patients are available that used significantly higher levels of COHb. Use of a level of 4 % COHb as a point of departure for the derivation of AEGL-2 values is supported by the studies in animals: a COHb of 9.3 % resulted in a reduced threshold for electric shock-induced ventricular fibrillation in monkeys (DeBias et al., 1979) and a COHb of 6.3-6.5 % increased the vulnerability of the heart to electrically induced ventricular fibrillation in healthy dogs (Aronow et al., 1979). These animal studies suggest that a level below 6-9 % COHb should be 49 ------- CARBON MONOXIDE FINAL: 07/2008 selected for AEGL-2 derivation in order to protect individuals with compromised cardiac function. A total uncertainty factor of 1 forintraspecies variability was considered adequate based on supporting evidence in other susceptible subpopulations (children, pregnant women, elderly people and smokers): 1) The derived AEGL-2 values would result in a COHb of 4.9-5.2 % in 5-year-old children (see Table 19 in Appendix B). This level is considered protective of neurotoxic effects in children: 1) in the study by Klasneret al. (1998) acute neurotoxic effects, such as headache, nausea, dizziness, dyspnea and vomiting were found at a mean COHb of 7.0% (measured after a mean time of 1 hour (up to 2 hours) after removal of the children from the CO atmosphere). This suggests that the end of exposure COHb had been between 10 and 14 % (these values were estimated using the mathematical model of Coburn et al. (1965) and Peterson and Stewart (1975). 2) In the study by Crocker and Walker (1985) a threshold of 24.5 % COHb for syncopes in children, an effect that was considered to impair the ability to escape, was reported. 3) In the study by Klees et al. (1985), that investigated long-lasting neurotoxic effects (defects in the cognitive development and behavioral alterations) in children, the lowest concentration resulting in cognitive development defects was 13 % COHb in the long-term follow-up study. The COHb reported in the Crocker and Walker (1985) as well as in the Klees et al. (1985) studies were measured after hospital admission and may have been considerably lower than levels at the time of the end of the CO exposure, as has also been described in the Klasneret al. (1998) study. Also the percentage of children that received oxygen before hospital admission was probably considerably higher in these two studies since after acute exposure to high CO concentrations (e.g. by fires in homes) severe poisoning symptoms occurred. Oxygen administration reduces the elimination half time in children to about 44 minutes (Klasner et al., 1998). The observations in children are supported by observations in experimental animals. In the study by Purser and Berrill (1983) at COHb little higherthan 16-21 % syncope-like effects occurred in monkeys and in mice memory impairment was found in the offspring of rats exposed continuously at COHb of 15.6 % during gestation (Mactutus and Fechter, 1985). 2) Caravati etal. (1988) and Koren et al. (1991) described cases of stillbirth after CO exposure of pregnant women. In these cases, the COHb measured in the maternal blood were higherthan 22- 25 %. There are no studies reporting effects on the unborn after a single acute exposure resulting in lower COHb levels (EPA, 2000). Cigarette smoking of pregnant women is associated with a lower birth weight, however, these effects cannot be clearly attributed to CO only because cigarette smoke is a complex mixture of chemicals (EPA, 2000). There is no evidence that a single elevation of COHb has any negative effects on pregnancy. 3) There is no evidence that elderly people without cardiovascular disease are more susceptible to an acute CO exposure than younger adults (EPA, 2000; WHO, 1999a). Therefore, AEGL-2 values derived on effects in coronary artery disease patients are likely to protect other elderly people. 4) In smokers with a background COHb of 3-8 % from smoking, exposure to the AEGL-3 concentration-time combinations will result in 6.2. and 11.5 % COHb (see Table 19 in Appendix B). Smokers may show an adaptive response to their chronically elevated COHb levels, as evidenced by increased red blood cell volumes or reduced plasma volumes (EPA, 2000). This adaptive 50 ------- CARBON MONOXIDE FINAL: 07/2008 response is likely to reduce the effect level in smokers compared to non-smokers exposed to the same total COHb level. The estimated COHb exposure level in smokers who are healthy adults is unlikely to lead to significant health effects (Kizakevich et al., 1994; Stewart et al., 1970; Nielsen, 1971). For pregnant women, cigarette smoking alone may cause effects on the unborn (EPA, 2000). A single additional exposure to COHb levels of 6.2-11.5% overthe "smoking background" of 3-8 % COHb is considered unlikely to significantly contribute to the effects of smoking during pregnancy. No study is available that compared the effects on the cardiovascular system of a 4 % elevation of the background COHb level in non-smoking and smoking patients with coronary artery disease. However, a single exposure to COHb levels of 6.2-11.5% overthe "smoking background" of 3-8 % COHb is considered unlikely to significantly contribute to the effects of smoking on the cardiovascular system. In conclusion, patients with coronary artery disease must be considered more susceptible to the effects of CO than other subpopulations that may be more susceptible than healthy adults, i.e., children, elderly people and pregnant women. A level of 4 % COHb was the NOEL for AEGL-2 effects in patients with coronary artery disease, while the LOEL was estimated at 6-9 %. In comparison, the LOEL was about 10-15 % in children and 22-25 % in pregnant women. Since AEGL-2 values were based on experimental data on the most susceptible subpopulation, they were considered protective also for other subpopulations and a total uncertainty factor of 1 was used. Using the CFK model (Coburn et al., 1965; Peterson and Stewart, 1975), exposure concentrations were calculated for 10 minutes, 30 minutes, 1 hour, 4 hours and 8 hours, that would result in a end-of-exposure COHb of 4 % in adults (see Appendix B). It should be noted that calculations were performed for a 70-kg man with a starting COHb of 0.75 % due to endogenous CO production and using a ventilation rate of 23 m3/day. Somewhat higher end-of-exposure COHb would result for children. For a 5-kg child with an alveolar ventilation rate of 3580 mg/min, COHb values between 4.9 to 5.2 % were calculated for the different AEGL time points. For a 3.5-kg newborn with an alveolarventilation rate of 1250 ml/min, COHb values between 5.3 and 5.6% were calculated. Higher COHb value will also be obtained in people having a higher starting COHb as a result from other exposures. For smokers having typical starting COHb levels between 3 and 8 %, COHb values between 6.2 and 11.5 % will result from exposure to AEGL-2 concentration-time combinations. A total uncertainty factor of 1 was used. An intraspecies uncertainty factor of 1 was considered adequate because the values are based on observations in the most susceptible human subpopulation (patients with coronary artery disease). It is acknowledged that apart from emergency situations, certain scenarios could lead to CO concentrations which may cause serious effects in persons with cardiovascular diseases. These scenarios include e.g. extended exposure to traffic fume emissions (e.g., in tunnels or inside cars with defect car exhaust systems), charcoal or wood fire furnaces, and indoor air pollution by tobacco smoking. The values are listed in Table 14 below. TABLE 14: AEGL-2 VALUES FOR CARBON MONOXIDE i i i i i 51 ------- CARBON MONOXIDE FINAL: 07/2008 AEGL Level AEGL-2 10 minutes 420 ppm (480 mg/m3) 30 minutes 150 ppm (170 mg/m3) 1 hour 83 ppm (95 mg/m3) 4 hours 33 ppm (38 mg/m3) 8 hours 27 ppm (31 mg/m3) 7. DATA ANALYSIS FOR AEGL-3 7.1. Human Data Relevant to AEGL-3 A large number of deaths occur annually due to acute poisonings in fires and in closed locations (e.g. in private homes and workplaces). In the latter instance, poisoning usually occurs because gas-, oil- or coal-fired furnaces or stoves are operated without sufficient ventilation. In apparently healthy people that died from CO poisoning, usually COHb of 60 % or higher are found (Balraj, 1984; AIHA, 1999; AIHA, 1999; Winter and Miller, 1976, Holmes, 1985, Stewart, 1975). In early experimental studies, healthy subjects were exposed to sufficient concentration-time combinations to reach levels of about 40 to 55 % COHb (Haldane, 1895; Chiodi et al., 1941). Effects described at this level of CO exposure included hyperpnea, confusion of mind, dim vision and unsteady/inability to walk (Haldane, 1895). Henderson etal. (1921) exposed subjects for 1 hour to 34-38 % COHb. Subjects showed a marked loss of equilibrium in the Romberg test, irritability, throbbing frontal headache and at times Cheyne-Stokes breathing was observed. Nelson (2005a) reported data from unvented space heaters related to human lethality cases related to CO poisoning. Sixteen out of 22 lethal cases had COHb levels more than 40%. Six out of 22 victims had COHb < 40% and 2/6 cases had pre-existing conditions such as arteriosclerotic | disease and cardiorespiratory failure._A 1942 fatality study reported by Nelson (2005a) summarized COHb data for 68 victims that were found dead in a gas-filled room or in a garage containing exhaust gases at high concentrations. CO concentrations were not provided. Sixty-seven percent of the 68 cases died with 40-88% COHb levels. Three-percent of the cases died with 30-40% COHb levels. Summary of another fatality study from Poland showed a similar trend of COHb levels (Nelson, 2005a). Individual data were not provided and the CO source was not discussed. However, the Polish study considered 321 lethal CO poisonings from 1975-1976 and provided COHb levels for survivors (n=220) and fatal cases (n=101). The survivors had a mean COHb level of 28.1% (SD=14.1), whereas the lethal cases showed an average COHb level of 62.3% (SD=10.1). Over 80% of the survivors had COHb levels below 40%. In contrast, around 90% of the deceased had COHb levels above 50%. Similar percentages of survivors and deceased were observed at COHb levels between 40-50% with a slight increase in the number of survivors when compared to that of the lethal cases. These three studies showed a trend that most lethal cases occurred at COHb levels higher than 40% and that survivorship was likely to be seen at levels below 40%. Another study from the Center of Forensic Sciences in Canada evaluated 304 fatal cases from 1965-1968 (Nelson, 2005a). The mean lethal COHb level was 51 ± 12% with a majority range between 40 and 59% and the highest single frequency range at 45-59%. A report on CO exposure from exhaust fumes in the state of Maryland during 1966-1971 showed COHb levels in the 40-79% range for 98% of lethal cases (Nelson, 2005a). The Institute of Forensic Medicine in Oslo reported a study of COHb levels in automobile exhaust victims (n=54). The mean fatal COHb level was 70 percent and 40% was the minimum COHb level exhibited by less than 2% of the cases (Nelson, 2005a). Another forensic study (Nelson et al. 2005c) examining 2241 fatalities between the years of 1976-1985 found that the mean COHb level of all the cases was 64.20% with a standard 52 ------- CARBON MONOXIDE FINAL: 07/2008 deviation of 17.47. The data showed that 34% of victims had COHb levels of less than 60%. Of those who died in fires, 41 % had COHb levels of less than 60% compared to 22% of the non-fire deaths. Kizakevich etal. (1994) reported that healthy young men can perform submaximal exercise without overt impairment of cardiovascular function after CO exposures attaining 20 % COHb. Stewart et al. (1970) found that a CO exposure of healthy subjects resulting in 12.5 to 25.5 % COHb did not affect the results of several neurophysiological tests. Nielsen (1971) did not report on severe effects in three subjects that were repeatedly exposed to CO resulting in concentrations of 25-33% COHb. In susceptible groups of the population, deaths may be caused by considerable lower exposure to CO: Caravati etal. (1988) and Koren etal. (1991) described cases of stillbirth after CO exposure of pregnant women. In these cases, the COHb measured in the maternal blood were higher than 22-25%. Persons with coronary artery disease constitute another susceptible subpopulation (Balraj, 1984). Several case reports indicate that death through myocardial infarction can occur after repeated or prolonged exposure, the corresponding COHb levels measured after transport to the hospital (and thus not representing the end-of-exposure concentrations) were around 20-30 % and as low as about 15 % (Atkins and Baker, 1985; Ebisuno etal., 1986; Grace and Platt, 1981). 7.2. Animal Data Relevant to AEGL-3 Several studies reported LC50 values for rats, mice and guinea pigs for exposure durations between 5 minutes and 4 hours. The values are given in Table 11 and are shown in Figure 1. Similarto humans, the minimum lethal COHb in rats and mice were about 50-70 % (E.I. du Pont de Nemours and Co., 1981; Rose et al., 1970). An increase in the rate of stillbirths was reported in pigs after a 2-3 day-exposure to CO resulting in maternal COHb above 23 % (Dominick and Carson, 1983). Increased rates in fetal mortality were also observed in rabbits after continuous exposure maternal COHb of 16-18 % throughout gestation (Astrup et al., 1972) as well as after daily exposure to high CO concentrations in cigarette smoke (exposure for 12 minutes/day on gestationaldays6-18, resulting in COHb of 16 %) (Rosenkrantz et al., 1986). 7.3. Derivation of AEGL-3 Most of the human reports did not document for how long the victims were acutely exposed to CO. Despite this uncertainty in the exposure duration, it was possible to set AEGL-3 values by using the CFK model, which calculated the exposure concentrations at the various AEGL time durations (i.e. 10 min, 30 min, 1 hr, 4 hr, 8 hr) that would produce a certain COHb% in the blood associated with a lethality threshold. Although victims of CO poisoning exhibit a wide range of COHb levels, a weight-of-evidence analysis of numerous lethal human cases and their COHb levels at their time of death helped setting the lethality threshold to a 40% COHb level. Note that the 53 ------- CARBON MONOXIDE FINAL: 07/2008 database included reports of COHb levels in individual cases or summaries where COHb data were averaged or reported by COHb ranges. The approach of using all available data was preferred over the selection of an individual key study for AEGL-3 derivations because it was the only way the evaluation could have a broad picture of COHb levels reported in humans with different demographics (e.g. sex, age, disease status), type of CO exposure source, possible variation in sample collection, and absence or presence of oxygen therapy to humans priorto death. Also, the weight-of-evidence approach would average out the studies' uncertainties. Nelson (2005a) reported data from unvented space heaters related to deaths due to CO poisoning. Twenty-two lethal cases were reported and 16/22 (73%) had COHb levels more than 40%. Six out of 22 victims (27%) had COHb < 40% and 2/6 cases had pre-existing conditions such as arteriosclerotic disease and cardiorespiratory failure. A 1942 fatality study reported by Nelson (2005a) summarized COHb data for 68 victims that were found dead in a gas-filled room or in a garage containing exhaust gases at high concentrations. CO concentrations were not provided. Sixty-seven percent of the 68 cases died with 40-88% COHb levels. Three-percent of the cases died with 30-40% COHb levels. Summary of another fatality study from Poland showed a similar trend of COHb levels (Nelson, 2005a). Individual data were not provided and the CO source was not discussed. However, the Polish study considered 321 lethal CO poisonings from 1975-1976 and provided COHb levels for survivors (n=220) and fatal cases (n=101). The survivors had a mean COHb level of 28.1%(SD=14.1), whereas the lethal cases showed an average COHb level of 62.3% (SD=10.1). Over 80% of the survivors had COHb levels below 40%. In contrast, around 90% of the deceased had COHb levels above 50%. Similar percentages of survivors and deceased were observed at COHb levels between 40-50% with a slight increase in the number of survivors when compared to that of the lethal cases. These three studies showed a trend that most lethal cases occurred at COHb levels higher than 40% and that survivorship was likely to be seen at levels below 40%. Thus, 40%COHb level seems a reasonable threshold for lethality. Additional support comes from a study conducted by the Center of Forensic Sciences in Canada evaluated 304 fatal cases from 1965-1968 (Nelson, 2005a). The mean lethal COHb level was 51 ± 12% with a majority range between 40 and 59% and the highest single frequency range at 45-59%. A report on CO exposure from exhaust fumes in the state of Maryland during 1966-1971 showed COHb levels in the 40-79% range for 98% of lethal cases (Nelson, 2005a). The Institute of Forensic Medicine in Oslo reported a study of COHb levels in automobile exhaust victims (n=54). The mean fatal COHb level was 70 percent and 40% was the minimum COHb level exhibited by less than 2% of the cases (Nelson, 2005a). Another forensic study (Nelson etal. 2005c) examining 2241 fatalities between the years of 1976-1985 found that the mean COHb level of all the cases was 64.20% with a standard deviation of 17.47. The data showed that 34% of victims had COHb levels of less than 60%. Of those who died in fires, 41% had COHb levels of less than 60% compared to 22% of the non-fire deaths. The 40% COHb level is also supported by experimental studies performed in healthy human subjects. Studies by Chiodi etal. (1941), Henderson etal. (1921), and Haldane (1895) suggest that a COHb of about 34-56 % does not cause lethal effects in healthy individuals. Further support comes from the studies by Kizakevich etal. (1994), Stewart et al. (1970), and Nielsen (1971) that reported headache as the only symptom when subjects were exposed to 20-33 % COHb. Several case reports indicate that in patients with coronary artery disease, CO exposure can contribute to myocardial infarction. In the published cases of myocardial infarction, the following COHb values were measured after transport to the hospital: 52.2 % (Marius-Nunez, 1990), 30 %, 22.8 % (Atkins 54 ------- CARBON MONOXIDE FINAL: 07/2008 and Baker, 1985), 21 % (Ebisuno et al., 1986), 15.6 % (Grace and Platt, 1981). A level of 40 % COHb was used as the basis for AEGL-3 derivation. This point of departure is further supported by studies in animals reporting minimum lethal COHb levels in rats and mice of about 50-70% (E.I. du Pont de Nemours and Co., 1981; Rose et al., 1970). Another uncertainty of the human reports used to support a lethality threshold level of 40% COHb was that they did not address whether the carboxyhemoglobin measurement was derived from a peripheral site (e.g. femoral vein) or from central blood. This type of information is missing in many of the carbon monoxide poisoning reports. Although it remains uncertain where the blood samples were taken from, data from Levine et al. (2002) and Dalpe-Scott et al. (1995) ruled out significant postmortem changes in COHb levels demonstrated by similar heart blood to peripheral blood (H/P) ratios between central and peripheral blood. Using the CFK model (Coburn et al., 1965; Peterson and Stewart, 1975), exposure concentrations were calculated that would result in a COHb of 40% at the end of exposure periods for 10 and 30 minutes as well as for 1, 4 and 8 hours (see Appendix B). AEGL-3 values calculated with an intraspecies uncertainty factor of 10 would lead to an approximately 4% COHb level in exposed healthy adults. The values would be conservative and more protective of susceptible populations including the developing fetus, children, and those with compromised circulatory systems, especially at longer exposure durations. However, this is the approximate background level in smokers (WHO 1999a). At that level, healthy individuals have decreases in work capacity and decrements of neurobehavioral functions (WHO 1999a; EPA 2000; Hazucha2000). Furthermore, workers complained of light nausea, lightheadedness, and headache at COHb levels of 4.1-12.8% (Atkins and Platt 1985). These effects are below the lethality threshold. At slightly higher COHb level (5-6%), there may be an increase in cardiac activity in subjects with coronary artery disease (WHO 1999a). Therefore, a total uncertainty factor of 3 for intraspecies variability was considered adequate based on the following supporting evidence in susceptible subpopulations: 1) Exposure to the derived AEGL-3 concentrations will result in COHb values of about 14-17 % in adults (see Table 21 in Appendix B). In the reported cases of myocardial infarction, the measured COHb was normally above 20 %, except in one case in which the measured COHb was about 15 %. In this case (Grace and Platt, 1981), the man was exposed during several weeks to (presumably) the same high CO concentration in his home and presented two times to the emergency room with signs of CO intoxication (which were misdiagnosed) until the infarction occurred. Therefore, the derived AEGL-3 values are considered to protect heart patients against CO-induced myocardial infarction. It should be noted, however, that a clear threshold for this endpoint cannot be defined because myocardial infarction might be triggered at lower COHb in hypersusceptible individuals and myocardial infarction can also occur spontaneously or by trigger effects (e.g. psychological stress, physical exertion) which have no relevant effects on the health of normal subjects. 2) With regard to stillbirths, a COHb of 14-17 % was considered protective of lethal effects on the unborn, because in the case studies available, stillbirths were found only after measured maternal COHb of about 22-25 % or higher (Caravati et al., 1988; Koren et al., 1991). In the clinic, a measured COHb of about 15-20 % in pregnantwomen (implicating a higher end-of-exposure level) 55 ------- CARBON MONOXIDE FINAL: 07/2008 is considered a severe CO intoxication that could require hyperbaric oxygen treatment (Ellenhorn, 1997; Tomaszewski, 1998). Available animal studies reported increased rates of stillbirths after a 2- 3 day exposure at maternal COHb above 23 % (Dominick and Carson, 1983), after continuous exposure at maternal COHb of 16-18 %(Astrupetal., 1972), and repeated short-term exposures at 16 % maternal COHb (Rosenkrantz et al., 1986). Taken together, the animal data support the conclusion that pregnant women should not be exposed to COHb levels higherthan about 14-17% in order to prevent lethal effects on the unborn. 3) In smokers with a background COHb of 3-8 % from smoking, exposure to the AEGL-3 concentration-time combinations will result in COHb levels between 16.1 and 23.0% (see Table 21 in Appendix B). Smokers may show an adaptive response to their chronically elevated COHb levels, as evidenced by increased red blood cell volumes or reduced plasma volumes (EPA, 2000). This adaptive response is likely to reduce the effect level in smokers compared to non-smokers exposed to the same total COHb level. The estimated COHb exposure level in smokers is considered protective of lethal effects if they are healthy adults. Also, from the discussion above, it is considered unlikely that smoking pregnant women will have an increase risk of stillbirths at the AEGL-3 exposure level. As discussed above, a threshold forthe induction of myocardial infarction by CO exposure cannot be defined. Therefore, heavy smokers with coronary artery disease, which have a higher risk for myocardial infarction already from smoking (American Heart Association, 2003), may be at somewhat higher risk compared to non-smoking patients. The values are listed in Table 15 below. TABLE 15: AEGL-3 VALUES FOR CARBON MONOXIDE AEGL Level AEGL-3 10 minutes 1700 ppm (1900 mg/m3) 30 minutes 600 ppm (690 mg/m3) 1 hour 330 ppm (380 mg/m3) 4 hours 150 ppm (170 mg/m3) 8 hours 130 ppm (150 mg/m3) 8. SUMMARYOFAEGLs 8.1. AEGL Values and Toxicity Endpoints The AEGL values for various levels of effects and various time periods are summarized in Table 16. They were derived using the following key studies and methods. AEGL-1 values are not recommended because susceptible persons may experience more serious effects (equivalent to AEGL-2 level) at concentrations, which do not yet cause AEGL-1 effects in the general population. The AEGL-2 was based on cardiovascular effects in patients with coronary artery disease, which constitute the most susceptible subpopulation. Forthe derivation of AEGL-2 values a level of 4 % COHb was chosen. At this exposure level, patients with coronary artery disease may experience a reduced time until onset of angina (chest pain) during physical exertion. The changes in the electrocardiogram (ST-segment depression of 1 mm or greater) associated with angina symptoms were fully reversible. An exposure level of 4 % COHb is unlikely to cause a significant 56 ------- CARBON MONOXIDE FINAL: 07/2008 increase in the frequency of exercise-induced arrhythmias. A mathematical model (Coburn et al., 1965; Peterson and Stewart, 1975) was used to calculate exposure concentrations resulting in a COHb of 4 % at the end of exposure periods of 10 and 30 minutes and 1, 4 and 8 hours. An intraspecies uncertainty factor of 1 was used. A total uncertainty factor of 1 was used. An intraspecies uncertainty factor of 1 was considered adequate because the values are based on observations in the most susceptible human subpopulation (patients with coronary artery disease). The AEGL-3 values were based on the study on COHb levels of 40% in human blood derived from a weight-of-evidence analysis of lethal and non-lethal poisoning cases (Nelson, 2005a). A threshold for lethality of 40 % is also supported by experimental studies by Chiodi et al. (1941), Henderson et al. (1921), and Haldane (1895), in which exposures resulting in COHb of 34-56 % did not cause lethal effects in healthy individuals. Further support comes from the studies of Kizakevich et al. (1994), Stewart et al. (1970), and Nielsen (1971) that reported headache as the only symptom when health adults were exposed to 20-33 % COHb. A level of 40 % COHb was used as the basis for AEGL-3 derivation. A mathematical model (Coburn et al., 1965; Peterson and Stewart, 1975) was used to calculate exposure concentrations resulting in a COHb of 40 % at the end of exposure periods of 10 and 30 minutes and 1, 4 and 8 hours. An intraspecies uncertainty factor of 3 was used. The derived values (corresponding to a COHb value of about 15%) are supported by information on effects, such as myocardial infarction and stillbirths, reported in more susceptible subpopulations. TABLE 16: SUMMARY/RELATIONSHIP OF AEGL VALUES FOR CARBON MONOXIDE Classification AEGL-1 (Non^disabling) AEGL-2 (Disabling) AEGL-3 (Lethal) 10-Minute N.R. a 420 ppm (480 mg/m3) 1700 ppm (1900 mg/m3) 30-Minute N.R. 150 ppm (170 mg/m3) 600 ppm (690 mg/m3) 1-Hour N.R. 83 ppm (95 mg/m3) 330 ppm (380 mg/m3) 4-Hour N.R. 33 ppm (38 mg/m3) 150 ppm (170 mg/m3) 8-Hour N.R. 27 ppm (31 mg/m3) 130 ppm (150 mg/m3) a N.R., not recommended because susceptible persons may experience more serious effects (equivalent to AEGL-2 level) at concentrations, which do not yet cause AEGL-1 effects in the general population All inhalation data are summarized in Figure 3 below. The data were classified into severity categories chosen to fit into definitions of the AEGL level health effects. The category severity definitions are "No effect"; "Discomfort"; "Disabling"; "Some Lethality"; "Lethal" and "AEGL". In the figure depicting the COHb levels, the AEGL lines are drawn at the COHb levels for adults. The grey boxes above the lines indicate the range of COHb levels in neonates, children and smokers (with 8 % COHb from smoking). The single exposure animal data point in the AEGL-2 COHb box represents the study by Aronowetal. (1979) using dogs with electrically damaged hearts. The two single exposure human data points in the bos represent the study by Sheps et al. (1990; 1991) reporting increase arrhythmiajn heart patients and the study by Klasner et al. (1998) reporting moderate neurotoxic | 57 ------- CARBON MONOXIDE effects in children. FINAL: 07/2008 Consistency of Data for Carbon Monoxide with Derived AEGL Values o 0 180 240 300 Time (minutes) Consistency of Data for Carbon Monoxide with Derived AEGL Values ° c o Single exposure I Repeated or continuous exposure FIGURE 3: CATEGORICAL REPRESENTATION OF ALL CO INHALATION DATA 58 ------- CARBON MONOXIDE FINAL: 07/2008 8.2. Comparison with Other Standards and Criteria Other standards and guidance levels for workplace and community exposures are listed in Table 17. The German BAT(BiologischerArbeitsstoff-Toleranz-Wert; biological exposure index) is 5 % COHb, equivalent to a concentration of 30 ppm CO (Greim und Lehnert, 1994). The ACGIH BEI (biological exposure index) is 3.5 % COHb at the end of shift, equivalent to a CO concentration in end exhaled air of 20 ppm (ACGIH, 1999). TABLE 17: EXTANT STANDARDS AND GUIDELINES FOR CARBON MONOXIDE Guideline AEGL-1 AEGL-2 AEGL-3 ERPG-1 (AIHA)a ERPG-2 (AIHA) ERPG-3 (AIHA) EEGL(NRC)b PEL-TWA (OSHA) c IDLH(NIOSH)d REL-TWA(NIOSH)6 TLV-TWA (ACGIH)' MAK (Germany) 9 MAK Spitzenbegrenzung (Germany) h MAC (The Netherlands) ' Einsatztoleranzwert J WHO Air Quality Guideline k U.S. National Ambient Air Quality Standard ' EU Ambient Air Limit Value m Exposure Duration 10 minutes N.R. 420 ppm 1700 ppm 1500 ppm 87 ppm for 15 min 30 minutes N.R. 150 ppm 600 ppm 800 ppm 1200 ppm 60 ppm 52 ppm 1 hour N.R. 83 ppm 330 ppm 200 ppm 350 ppm 500 ppm 400 ppm 26 ppm 35 ppm 4 hours N.R. 33 ppm 150 ppm 100 ppm 8 hours N.R. 27 ppm 130 ppm 50 ppm [24 hours] 50 ppm 35 ppm [200 ppm ceiling] 25 ppm 30 ppm 25 ppm 9 ppm 9 ppm 9 ppm N.R., not recommended because susceptible persons may experience more serious effects (equivalent to AEGL-2 level) at concentrations, which do not yet cause AEGL-1 effects in the general population. 59 ------- CARBON MONOXIDE FINAL: 07/2008 a ERPG (Emergency Response Planning Guidelines, American Industrial Hygiene Association) (AIHA, 1999) The ERPG-1 is the maximum airborne concentration below which it is believed nearly all individuals could be exposed for up to one hour without experiencing other than mild, transient adverse health effects or without perceiving a clearly defined objectionable odor. The ERPG-1 value is based on a COHbof 5-6%, which, based on the original CFK model using a ventilation rate at rest, is considered to be produced by 1-hour CO exposure to 200 ppm.. This exposure level is not expected to produce any effects during a 1 -hour exposure period. While delayed transient effects, such as headache, are possible, no permanent effects in more susceptible individuals are expected. The ERPG-2 is the maximum airborne concentration below which it is believed nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms that could impair an individual's ability to take protective action. The ERPG-2 value is based on a COHb of 10-12 %, which, based on the original CFK model using a ventilation rate at rest, is considered to be produced by 1 -hour CO exposure to 350 to 500 ppm.. This exposure level is expected to cause slight neurological symptoms (increased threshold of visual light) in healthy individuals and chest pain at less exertion in heart patients. (Comment: The ERPG derivation does not discuss the CO effects on children. Moreover, model calculation for deriving ERPG values assumed a resting ventilation rate, while for derivation of AEGL values a ventilation rate corresponding to light to moderate activity was assumed). The ERPG-3 is the maximum airborne concentration below which it is believed nearly all individuals could be exposed for up to one hour without experiencing or developing life-threatening health effects. The ERPG-3 is based on the believe that humans can generally tolerate COHb of 20 % for brief periods without substantial toxicity. Based on the original CFK model using a ventilation rate at rest, it was considered that exposure to 500 ppm for 1 hour will lead to a COHb of about 15 %. (Comment: The ERPG derivation does not discuss the CO effects on children. Moreover, model calculation for deriving ERPG values assumed a resting ventilation rate, while for derivation of AEGL values a ventilation rate corresponding to light to moderate activity was assumed). b EEGL (Emergency Exposure Guidance Levels, National Research Council) (NRC, 1987) is the concentration of contaminants that can cause discomfort or other evidence of irritation or intoxication in or around the workplace, but avoids death, other severe acute effects and long-term or chronic injury. The NRC document states that 400 ppm (460 mg/m3) was determined as the concentration of CO to which a 1 -hour exposure would result in a carboxyhemoglobin (COHb) level of less than 10% in resting individuals. The committee cautions that sensitive individuals, such as persons with angina or heart disease, should not be exposed to concentrations approaching the EEGL as they may incur serious adverse health effects (Comment: The EEGL derivation excludes patients with coronary artery disease. Moreover, model calculation for deriving EEGL values assumed a resting ventilation rate, while for derivation of AEGL values a ventilation rate corresponding to light to moderate activity was assumed). c OSHA PEL-TWA (Occupational Health and Safety Administration, Permissible Exposure Limits -Time Weighted Average) (OSHA, website) is defined analogous to the ACGIH-TLV-TWA, but is for exposures of no more than 10 hours/day, 40 hours/week. 60 ------- CARBON MONOXIDE FINAL: 07/2008 d IDLH (Immediately Dangerous to Life and Health, National Institute of Occupational Safety and Health) (NIOSH, 1996) represents the maximum concentration from which one could escape within 30 minutes without any escape-impairing symptoms, or any irreversible health effects. The IDLH value is based on the observation by Henderson etal., 1921, that exposure of a healthy man at 1000 ppmfor 1 hour caused unpleasant but no dangerous symptoms, and that more severe symptoms develop at 40 % COHb (Steward, 1975). According to the CFK model, a 30-minute exposure at 1200 ppm will produce a COHb of 10-13 %. (Comment: The IDLH derivation does not discuss patients with coronary artery disease. In the Henderson et al. (1921) study, the subject was sitting still during exposure and developed Cheyne-Stokes breathing at the end of exposure, which is considered a serious effect. Moreover, model calculation in the IDLH derivation assumed a resting ventilation rate, while for derivation of AEGL values a ventilation rate corresponding to light to moderate activity was assumed). e NIOSH REL-TWA (National Institute of Occupational Safety and Health, Recommended Exposure Limits - Time Weighted Average) (NIOSH, 1996) is defined analogous to the ACGIH-TLV-TWA. f ACGIH TLV-TWA (American Conference of Governmental Industrial Hygienists, Threshold LimitValue - Time Weighted Average) (ACGIH, 2001) is the time-weighted average concentration fora normal 8-hourworkday and a 40-hour workweek, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect. "This value is intended to maintain blood COHb levels below 3.5 %, to minimize the potential for adverse neurobehavioral changes, and to maintain cardiovascular work and exercise capacities". 9 MAK (Maximale Arbeitsplatzkonzentration [Maximum Workplace Concentration], Deutsche Forschungsgemeinschaft [German Research Association], Germany) (Henschler, 1981; DFG, 1999) is defined analogous to the ACGIH-TLV-TWA. h MAK Spitzenbegrenzung (Kategorie II,2) [Peak Limit Category 11,1] (DFG, 1999) constitutes the maximum average concentration to which workers can be exposed for a period up to 30 minutes, with no more than 4 exposure periods per workshift; total exposure may not exceed 8- hour TWA MAK. 1 MAC ([Maximum Workplace Concentration], Dutch Expert Committee for Occupational Standards, The Netherlands) (MSZW, 1999) is defined analogous to the ACGIH-TLV-TWA. 1 Einsatztoleranzwert [Action Tolerance Levels] (Vereinigung zur Forderung des deutschen Brandschutzes e.V. [Federation for the Advancement of German Fire Prevention]) (Greim, 1996) constitutes a concentration to which unprotected firemen and the general population can be exposed to for up to 4 hours without any health risks. "Air Quality Guideline (WHO, 1999a) is based on a COHb of 2.5 %, which should not be exceeded even when a normal subject engages in light or moderate exercise. 'U.S. National Ambient Air Quality Standard (National Air Pollution Control Administration, 1970; FR.2000; EPA, 2000) m EU Limit Value for Ambient Air (EC, 1999) 61 ------- CARBON MONOXIDE FINAL: 07/2008 8.3. Data Adequacy and Research Needs A sufficient number of experimental and case studies in humans is available for the derivation of AEGL values. CO is the classical example of an imperceptible toxic gas. Until very severe symptoms occur (inability to walk) none or only nonspecific symptoms were noted in monkeys and healthy humans. For this reason no AEGL-1 values for CO are recommended. AEGL-2 values were based on cardiac effects in subjects with coronary artery disease. Several high quality studies are available addressing endpoints such as time to the onset of exercise-induced angina, time to the onset of exercise-induced 1-mm ST-segment changes in the electrocardiogram and frequency of exercise-induced arrhythmias. However, no experimental studies in heart patients are available that used significantly higher levels of COHbthan about 5 % COHb. AEGL-3 values were based analysis of clinical cases of lethal and non-lethal poisoning supporting 40% COHb as the lethality threshold. The AEGL-3 values derived using an intraspecies uncertainty factor of 3 (corresponding to an COHb of about 15 %) are supported by the available case reports of lethal effects (myocardial infarction, stillbirths) in more susceptible subpopulations. Lethal effects from myocardial infarction in hypersusceptible patients with coronary artery disease at even lower CO concentrations, which could be at the upper end of the range of CO concentrations found inside buildings and in ambient air outside, cannot be excluded. Most studies relating COHb on health effects do not investigate whether the frequency or severity of the effects increase with exposure time (at a constant COHb). There is thus an uncertainty concerning the increase of effects with time at a constant COHb. This is true for all AEGL levels. Studies elucidating this exposure-effect-time relationship could support the derived AEGL-2 and AEGL-3 values. 9. REFERENCES ACGIH, American Conference of Governmental Industrial Hygienists, 2001. Carbon monoxide. Documentation of the Threshold Limit Values and Biological Exposure Indices. ACGIH, Cincinnati, OH, USA, Suppl. pp.1-4. ACGIH, American Conference of Governmental Industrial Hygienists, 1999. 1999 TLVs and BEIs. ACGIH, Cincinnati, OH, USA. AIHA, American Industrial Hygiene Association, 1999. Carbon Monoxide. Emergency Response Planning Guidelines. AIHA Press, Fairfax, VA, USA. Allred, E.N., E.R. Bleecker, B.R. Chaitman, T.E. Dahms, S.O. Gottlieb, J.D. Hackney, D. Hayes, M. Pagano, R.H. Selvester, S.M. Walden and J. Warren, 1989a. Acute Effects of Carbon Monoxide Exposure on Individuals with Coronary Artery Disease. Research Report No. 25, Health Effects Institute, Cambridge, Massachusetts, USA, 1989, cited in WHO, 1999a. Allred, E.N., E.R. Bleecker, B.R. Chaitman, T.E. Dahms, S.O. Gottlieb, J.D. Hackney, M. Pagano, R.H. 62 ------- CARBON MONOXIDE FINAL: 07/2008 Selvester, S.M. Walden and J. Warren, 1989b. Short-term effects of carbon monoxide exposure on the exercise performance of subjects with coronary artery disease. New Engl. J. Med. 321, 1426-1432. Allred, E.N., E.R. Bleecker, B.R. Chaitman, I.E. Dahms, S.O. Gottlieb, J.D. Hackney, M. Pagano, R.H. Selvester, S.M. Walden and J. Warren, 1991. Effects of carbon monoxide on myocardial ischemia. Environ. Health Perspect. 91, 89-132. American Heart Association, 2003. Heart Disease and Stroke Statistics — 2003 Update. American Heart Association, Dallas, Texas; available on the internet at http://www.americanheart.org. Anderson, E.W., R.J. Andelman, J.M. Strauch, N.J. Fortuinand J.H. Knelson, 1973. Effect of low-level carbon monoxide exposure on onset and duration of angina pectoris: a study in ten patients with ischemic heart disease. Ann. Intern. Med. 79, 46-50, cited in EPA, 2000. Aronow, W.S., R. Charter and G. Seacat, 1979. Effect of 4% carboxyhemoglobin on human performance in cardiac patients. Preventive Med. 8, 562-566. Aronow, W.S., C.N. Harris, M.W. Isbell, S.N. Rokawand B. Imparato, 1972. Effect of freeway travel on angina pectoris. Ann. Intern. Med. 77, 669-676, cited in WHO, 1999a. Astrup, P., H.M. Olsen, D. Trolle and K. Kjeldsen, 1972. Effect of moderate carbon monoxide exposure on fetal development. Lancet 7789, 1220-1222. ATSDR, Agency for Toxic Substances and Disease Registry, 1998. Methylene Chloride. Update. U.S.Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry, Atlanta, Georgia, USA. Atkins, E.H. and E.L. Baker, 1985. Exacerbation of coronary artery disease by occupational carbon monoxide exposure: A report of two fatalities and a review of the literature. Am. J. Ind. Med. 7, 73-79. Balraj, EX., 1984. Atherosclerotic coronary artery disease and "low" levels of carboxyhemoglobin: Report of fatalities and discussion of pathophysiologic mechanisms of death. J. Foren. Sci. 29, 1150-1159. Beard, R.R., 1982. Inorganic compounds of oxygen, nitrogen, and carbon. In: Patty's Industrial Hygiene and Toxicology. Vol. 2C, G.D. Clayton and F.E. Clayton (Eds.), John Wley & Sons, New York, 1982, pp. 4114-4124. Benignus, V.A., M.J. Hazucha, M.V. Smith and P.A. Bromberg, 1994. Prediction of carboxyhemoglobin formation due to transient exposure to carbon monoxide. J. Appl. Physiol. 76, 1739-1745, cited in WHO, 1999a. Bruce, M. C., Bruce, E. N., 2006. Analysis of factors that influence rates of carbon monoxide uptake, distribution, and washout from blood and extravascular tissues using a multicompartment model. J Appl Physiol. 100, 1171-80. BSI, British Standards Institution, 1989. Guide for the assessment of toxic hazards in fire in buildings and transport. Draft for Development. British Standards Institution, Milton Keynes, UK, 1989. Caravati, E.M., C.J. Adams, S.M. Joyce and N.C. Schafer, 1988. Fetal toxicity associated with maternal carbon monoxide poisoning. Ann. Emerg. Med. 17, 714-717. Chase, D.H., L.R. Goldbaum and NT. Lappas. 1986. Factors affecting the loss of carbon monoxide from 63 ------- CARBON MONOXIDE FINAL: 07/2008 stored blood samples. J. Anal. Toxicol. 10: 181-189. Chiodi, H., D.B. Dill, F. Consolazio and S.M. Horvath, 1941. Respiratory and circulatory responses to acute carbon monoxide poisoning. Am. J. Physiol. 134, 683-693. Choi, K.D. and Y.K. Oh, 1975. [A teratological study on the effects of carbon monoxide exposure upon the | fetal development of albino rats] (in Korean). Chungang Uihak 29, 209-213, cited in WHO, 1999a. Clark, R. T., Jr., 1950. Evidence for conversion of carbon monoxide to carbon dioxide by the intact animal. Am J Physiol. 162,560-4. Coburn, R.F. (personal communication dated April 08, 2008) Coburn, R.F., R.E. Forsterand P.B. Kane, 1965. Considerations of the physiological variables that determine the blood carboxyhemoglobin concentration in man. J. Clin. Invest. 44, 1899-1910. Coburn, R.F., W.J. Williams, and S.B. Kahn, 1966. Endogenous carbon monoxide production in patients with hemolytic anemia. J. Clin. Invest. 45, 460-468, cited in WHO, 1999a. Crocker, P.J. and J.S. Walker, 1985. Pediatric carbon monoxide toxicity. J. Emerg. Med. 3, 443-448. Dahms, I.E., L.T. Younis, R.D. Wens, S. Zarnegar, S.L. Byersand B.R. Chaitman, 1993. Effects of carbon monoxide exposure in patients with documented cardiac arrhythmias. J. Am. Coll. Cardiol. 21, 442-450. Dalpe-Scott, M., M. Degouffe, D. Garbutt and M. Drost, 1995. A comparison of drug concentrations in postmortem cardiac and peripheral blood in 320 cases. Can. Soc. Forens. Sci. J. 28, 113-121. Darmer, MacEwen and Smith, 1972. AMRL-TR-72-130. Paper No. 22, cited in E.I. du Pontde Nemoursand Co., 1981. DeBias, D.A., C.M. Banerjee, N.C. Birkhead, C.H. Greene, S.D. Scott, and W.V. Harrer, 1976. Effects of carbon monoxide inhalation on ventricular fibrillation. Arch. Environ. Health 31, 42-46, cited in WHO, 1999a. Deschamps, D., C. Geraud, H. Julien, F.J. Baud and S. Dally, 2003. Memory one month after acute carbon monoxide intoxication: a prospective study. Occup. Environ. Med. 60, 212-216. DFG, Deutsche Forschungsgemeinschaft, 1999. MAK- und BAT-Werte-Liste 1999. Senatskommission zur Prufung gesundheitsschadlicher Arbeitsstoffe, Deutsche Forschungsgemeinschaft, Wley-VCH Verlag GmbH, Weinheim, Germany, 1999. Dominick, M.A. and T.L. Carson, 1983. Effects of carbon monoxide exposure on pregnant sows and their fetuses. Am. J. Vet. Res. 44, 35-40, cited in WHO, 1999a. Drummer, O.H. 2007. Requirements for bioanalytical procedures in postmortem toxicology. Anal. Bioanal. Chem. 388: 1495-1503. Ebisuno, S., M. Yasuno, Y. Yamada, Y. Nishino, M. Hori, M. InoueandT. Kamada, 1972. Myocardial infarction after acute carbon monoxide poisoning: case report. Angiology 37, 621-624. E.I. du Pont de Nemours and Co., 1981. Inhalation Toxicity of Common Combustion Gases. Haskell Laboratory Report No. 238-81. Haskell Laboratory, Newark, DE, USA, 1981. Einzig, S., D.M. Nicoloff and R.V. Lucas Jr., 1980. Myocardial perfusion abnormalities in carbon monoxide 64 ------- CARBON MONOXIDE FINAL: 07/2008 poisoned dogs. Can. J. Physiol. Pharmacol. 58, 396-405, cited in Penney etal., 1980. EC, European Commission, 1999. Vorschlag fur eine Richtlinie des Rates uber Grenzwerte fur Benzol und Kohlenmonoxid in der Luft (1999/C 53/07), issued by the European Commission on 20.01.1999. Ellenhorn, M.J., 1997. "Carbon Monoxide" in: Ellenhorn's Medical Toxicology. 2nd ed. Lippincott, Williams & Wilkins, Baltimore, pp.1465-1476. Ely, E.W., B. Moorehead and E.F. Haponik, 1995. Warehouse workers' headache: emergency evaluation and management of 30 patients with carbon monoxide poisoning. Am. J. Med. 98, 145-155. EPA, U. S. Environmental Protection Agency, 2000. Air quality criteria for carbon monoxide. EPA 600/P- 99/001F, U. S. Environmental Protection Agency, Office of Research and Development, Washington, D.C. Ernst, D.J. 2005. Performing the Venipuncture. Chapter 3 in: Applied Phlebotomy. Lippincott Wlliams & Wilkins, Baltimore, Maryland, pp. 59-97. Farrow, J.R., G.J. Davis, T.M. Roy, L.C. McCloud and G.R. Nichols II, 1990. Fetal death due to nonlethal maternal carbon monoxide poisoning. J. Foren. Sci. 35, 1448-1452. Fenn,W.O., 1970. The burning of CO in tissues. In: Biological effects of carbon monoxide, R.F. Coburn (Ed.). Ann. N. Y. Acad. Sci. 174, 64-71, cited in WHO, 1999a. Fenn, W.O. and D. M. Cobb, 1970. The burning of carbon monoxide by heart and skeletal muscle. Am. J. Physiol. 102:393-401. Flanagan, R. J., G. Connally, and J. M. Evans. 2005. Analytical toxicology: guidelines for sample collection postmortem. Toxicol. Rev. 24, 63-71. Fowles, J.R., G.V. Alexeeff and D. Dodge, 1999. The use of benchmark dose methodology with acute inhalation lethality data. Reg. Toxicol. Pharmacol. 29, 262-278. FR, Federal Register, 2000. Air Quality Criteria for Carbon Monoxide (Final). Federal Register Volume 65, Number 160, August 17, 2000. Gargas, M.L., H.J. Clewell and M.E. Andersen, 1986. Metabolism of inhaled dihalomethanes in vivo: differentiation of kinetic constants for two independent pathways. Toxicol. Appl. Pharmacol. 82, 211 -223. Gibbons R.J.,, K. Chatterjee, J. Daley, J.S. Douglas, S.D. Fihn, J.M. Gardin, M.A. Grunwald, D. Levy, B.W. Lytle, R.A. O'Rourke, W.P. Schafer, S.V. Wlliams, 1999. ACC/AHA/ACP-ASIM guidelinesforthe management of patients with chronic stable angina: a report of the American College of Cardiology/American Heart Association Task Force on Practice_Guidelines (Committee on the Management of Patients Wth Chronic | Stable Angina). J. Am. Coll. Cardiol. 33, 2092-2197. Grace, T.W. and F.W. Platt, 1981. Subacute carbon monoxide poisoning. J. Am. Med. Assoc. 246,1698-1700. Greim, H., 1996. Entwicklung von Verfahren zurAbschatzung dergesundheitlichen Folgen von GroUbranden. Bericht zum Forschungsvorhaben 4b/92 des Bundesamtes fur Zivilschutz, Germany. Greim, H. and G. Lehnert, 1994. Kohlenmonoxid. Biologische Arbeitsstoff-Toleranz-Werte (BAT-Werte) und Expositionsaquivalente fur krebserzeugende Arbeitsstoffe (EKA), Arbeitsmedizinisch-toxikologische Begrundungen, Band 1. 7. Lieferung. DFG, Deutsche Forschungsgemeinschaft, VCH Verlag Weinheim, 65 ------- CARBON MONOXIDE FINAL: 07/2008 Germany, 1994, pp.1-2. Haldane, J., 1895. The action of carbonic acid on man. J. Physiol. 18, 430-462. Hampson, N.B. 2008. Stability of carboxyhemoglobin in stored and mailed blood samples. Am. J. Emerg. Med.26: 191-195. Hartzell, G.E., D.N. Priest and W.G. Switzer, 1985. Modeling of toxicological effects of fire gases. II. Mathematical modeling of intoxication of rats by combined carbon monoxide and hydrogen cyanide. J. Fire Sci. 3, 115-128, cited in NIOSH, 1996. Haskell Laboratories, 1978. No further information, cited in E.I. du Pontde Nemours and Co., 1981. Hazucha, M.J., 2000. Effect of Carbon Monoxide on Work and Exercise Capacity in Humans. Chapters in: Carbon Monoxide Toxicity. D.G. Penney (Ed.). CRC Press, Boca Raton, London, New York, Washington D.C., 2000, pp. 101-134. Henderson, Y., H.W. Haggard, M.C. league, A.L. Prince and R.M. Wunderlich, 1921. Physiological effects of automobile exhaust gas and standards of ventilation for brief exposures. J. Ind. Hyg. 3, 79-92. Henschler, D., 1981. Monochloressigsaure. In: Gesundheitsschadliche Arbeitsstoffe, Toxikologisch- arbeitsmedizinische Begrundungen von MAK-Werten, Loseblattsammlung, 8. Lfg., DFG, Deutsche Forschungsgemeinschaft, VCH Verlag Weinheim, Germany. Herpol, C., R. Minne and E. VanOutryve, 1976. Biological evaluation of the toxicity of gases produced under fire conditions by synthetic materials. Parti. Methods and preliminary experiments concerning the reaction of animals. Combust. Sci. Technol. 12, 217-228, cited in Fowlesetal., 1999. Hilado, C.J., H.J. Cumming, A.M. Machado, C.J. Casey and A. Furst, 1978. Effect of individual gaseous toxicants on mice. Proc. West. Pharmacol. Soc. 21, 159-160, cited in AIHA, 1999. Hill, E.P., J.R. Hill, G.G. Power and L.D. Longo, 1977. Carbon monoxide exchanges between the human fetus and mother: a mathematical model. Am. J. Physiol. 232, H311-H323. Hinderliter, A.L., K.F. Adams, C.J. Price, M.C. Herbst, G. Koch and D.S. Sheps. Effects of low-level carbon monoxide exposure on resting and exercise-induced ventricular arrhythmias in patients with coronary artery disease and no baseline ectopy. Arch. Environ. Health 44, 89-93. Holmes, R.S., 1985. Genetic variants of enzymes of alcohol and aldehyde metabolism. Alcoholism: Clinical and Experimental Research 9, 535-538. ISO, International Standard Organization, 1989. Toxicity testing of fire effluents- Parti. ISO/TR 9122-1. Jones, R.A., J.A. Strickland, J.A. Stunkard and J. Siegel, 1971. Effects on experimental animals of long-term inhalation exposure to carbon monoxide. Toxicol. Appl. Pharmacol. 19, 46-53. Kimmerle, 1974. Combustion Toxicol. 1, 4-51, cited in E.I. du Pontde Nemours and Co., 1981. Kishitani, K., K. Nakamura, 1979. Research on evaluation of toxicities of combustion gases generated during fires. In Proceedings of the Third Joint Panel Conderence of the U.S.-Japan Cooperative Program in Natural Resources held March 13-17, 1978, at the National Bureau of Standards, Gaithersburg, MD, M.D. Sherald (Ed.). U.S. Department of Commerce, Washington, D.C., cited in Fowlesetal., 1999. 66 ------- CARBON MONOXIDE FINAL: 07/2008 Kizakevich, P.M., M.L. McCartney, M.J. Hazucha, L.H. Sleet, W.J. Jochem, A.C. Hackney and K. Bolick, 2000. Noninvasive ambulatory assessment of cardiac function in healthy men exposed to carbon monoxide during upper and lower body exercise. Eur. J. Appl. Physiol. 83, 7-16. Klasner, A.E., S.R. Smith, M.W. Thompson and A.J. Scalzo, 1998. Carbon monoxide mass exposure in a pediatric population. Academic Emerg. Med. 5, 992-996. Klees, M., M. Heremansand S. Dougan, 1985. Psychological sequelae to carbon monoxide intoxication in the child. Sci. Total Environm. 44, 165-176. Kleinman, M.T., D.M. Davidson, R.B. Vandagriff, V.J. Caiozzo and J.L. Whittenberger, 1989. Effects of short- term exposure to carbon monoxide in subjects with coronary artery disease. Arch. Env. Health 44, 361 -369. Kleinman, M.T., D.A. Leaf, E. Kelly, V. Caiozzo, K. Osann and T. O'Niell, 1998. Urban angina in the mountains: effects of carbon monoxide and mild hypoxemia on subjects with chronic stable angina. Arch. Environ. Health 53, 388-397. | Kojima, T., I. Okamoto, M. Yashiki, T. Miyazaki, F. Chikasue, K. Degawa, S. Oshida, and K. Sagisaka. 1986. Production of carbon monoxide in cadavers. Forensic Sci. Int. 32, 67-77. Koren, G., R. Sharav, A. Pastuszak, L.K. Garrettson, K. Hill, I. Samson, M. Rorem, A. King and J.E. Dolgin, 1991. A multicenter, prospective study of fetal outcome following accidental carbon monoxide poisoning in pregnancy. Reprod. Toxicol. 5, 397-403. Kunsman, G.W., C.L. Presses and P. Rodriguez. 2000. Carbon monoxide stability in stored postmortem blood samples. J. Anal. Toxicol. 24: 572-578. Landaw, S.A., 1973. The effects of cigarette smoking on total body burden and excretion rates of carbon monoxide. J. Occup. Med. 15, 231-235, cited in WHO, 1999a. Larsen, J.B. 2005. Physiological Effects of Carbon Monoxide. In: Carbon Monoxide and Human Lethality: Fire and Non-fire studies, M.M. Hirschler (Ed.). Taylor and Francis, New York, 2005, pp 111-172. Lee, K.T., O.A. Kit and E. Jacob. 1975. Determination of carboxyhaemoglobin in blood. Mikrochimica Acta. II: 657-663. Levine, B.C., P.R. Rechani, J.L. Gurman, F. Landron, H.M. Clark, M.F. Yoklavich, J.R. Rodriguez, L. Droz, F.M., de Cabrera and S. Kaye. 1990. Analysis of carboxyhemoglobin and cyanide in blood from victims of the Dupont Plaza Hotel fire in Puerto Rico. J. Forensic Sci. 35: 151-168. Levine, B., K.A. Moore, J.M. Titus and D. Fowler. 2002. A comparison of carboxyhemoglobin saturation values in postmortem heart blood and peripheral blood specimens. J. Forensic Sci. 47: 1388- 1390. Luomanmaki, K., Coburn, R. F., 1969. Effects of metabolism and distribution of carbon monoxide on blood and body stores. Am. J. Physiol. 217, 354-63. Mactutus, C.F. and L.D. Fechter, 1985. Moderate prenatal carbon monoxide exposure produces persistent and apparently permanent memory deficits in rats. Teratol. 31, 9-12. Mohoney, J. H.J. Vreman, O.K. Stevenson and A.L. Van Kessel. 1993. Measurement of carboxyhemoglobin and total hemoglobin by five specialized spectrophotometers (CO-oximeters) in 67 ------- CARBON MONOXIDE FINAL: 07/2008 comparison with reference methods. Clin. Chem. 39: 1693-1700. Marius-Nunez, A.L., 1990. Myocardial infarction with normal coronary arteries after acute exposure to carbon monoxide. Chest 97, 491-494. Meert, K.L., S.M. Heidemann and A. P. Sarnaik, 1998. Outcome of children with carbon monoxide poisoning treated with normobaric oxygen. J. Trauma Injury Infect. Crit. Care 44, 149-154. Morris, G.L., S.E. Curtis and J. Simon, 1985. Perinatal piglets under sublethal concentrations of atmospheric carbon monoxide. J. Anim. Sci, 61, 1080-1087, cited in WHO, 1999a. MSZW, Ministerie van Sociale Zaken en Werkgelegenheid, 1999. Nationale MAC-lijst2000. Sdu Vitgeers, Den Haag, 1999. National Air Pollution Control Administration, 1970. Air quality criteria for carbon monoxide. US Department of Health, Education, and Welfare, Public Health Service, Environmental Health Service, Washington, DC, publication no. AP-62. Nelson.G. 2005a. Effects of Carbon Monoxide in Man. In: Carbon Monoxide and Human Lethality: Fire and Non-fire studies, M.M. Hirschler (Ed.). Taylor and Francis, New York, 2005, pp 3-60. Nelson.G. 2005b. Carbon monoxide determination in human blood. In: Carbon Monoxide and Human Lethality: Fire and Non-fire studies, M.M. Hirschler (Ed.). Taylor and Francis, New York, 2005, pp 173-177. Nelson.G., D.V. Canfield and J.B. Larsen. 2005. Carbon monoxide and fatalities. In: Carbon Monoxide and Human Lethality: Fire and Non-fire studies, M.M. Hirschler (Ed.). Taylor and Francis, New York, 2005, pp 179-196. Nielsen, B., 1971. Thermoregulation during work in carbon monoxide poisoning. Acta Physiol. Scand. 82, 98- 106. NIOSH, National Institute for Occupational Safety and Health, 1972 . Occupational Exposure to Carbon Monoxide. U.S. Department of Health, Education and Welfare. NIOSH, National Institute of Occupational Safety and Health, 1996. Carbon Monoxide. Documentation for Immediately Dangerous to Life and Health Concentrations. Http://www.cdc.gov/niosh/idlh/630080.html. Download date 15.03.2000. NRC, National Research Council, 1987. Emergency and continuous exposure guidance levels for selected airborne contaminants. Vol. 7. National Research Council, Commission of Life Sciences, Board on Toxicology and Environmental Health Hazards, Committee on Toxicology, National Academy Press, Washington, DC, USA, pp. 1738, cited in NIOSH, 1996. Numa, A.H. and C.J. Newth, 1996. Anatomic dead space in infants and children. J. Appl. Physiol. 80, 1485- 1489. OSHA, Occupational Health and Safety Administration. Code of Federal Regulations 29, Part 1910, 1910.1000. http://www.osha-slc.gov/OshStd_data/1910_1000_TABLE_Z-1 .html. Download date 04.05.2000. Pach, J., L. Cholewa, Z. Marek, M. Bogusz and B. Groszek, 1978. Analysis of predictive factors in acute carbon monoxide poisoning. Vet. Hum. Toxicol. 21 Suppl, 158-159. 68 ------- CARBON MONOXIDE FINAL: 07/2008 Pach, J., L. Cholewa, Z. Marek, M. Bogusz and B. Groszek, 1978. Various factors influencing the clinical picture and mortality in acute carbon monoxide poisoning [in Polish]. Folia Medica Cracoviensia, 20,159-168. Penney, D.G., M.S. Baylerian and K.E. Fanning, 1980. Temporary and lasting cardiac effects of pre- and postnatal exposure to carbon monoxide. Toxicol. Appl. Pharmacol. 53, 271-278. Pesce, V.H.D., M. Stupfel, V. Gourletand C. Lemercerre, 1987. Age and survival of an acute carbon monoxide intoxication: an animal model. Sci. Total Environ. 65, 41-51. Peterson, J.E. and R.D. Stewart, 1970. Absorption and elimination of carbon monoxide by inactive young men. Arch. Environ. Health 21, 165-171. Peterson, J.E. and R.D. Stewart, 1975. Predicting the carboxyhemoglobin levels resulting from carbon monoxide exposures. J. Appl. Physiol. 39, 633-638. Purser, D.A. and K.R. Berrill, 1983. Effects of carbon monoxide on behavior in monkeys in relation to human fire hazard. Arch. Environ. Health 38, 308-315. I Radford, E.P. and T.A. Drizd, 1982. Blood carbon monoxide levels in persons 3-74 years of age: United States, 1976-80. Hyattsville, Maryland, US Department of Health and Humans Services, National Center for Health Statistics (DHHS Publication No. (PHS) 82-1250), cited in WHO, 1999a. Raub, J.A., 2000. The Setting of Health-Based Standards for Ambient Carbon Monoxide and Their Impact on Atmospheric Levels. Chapter 4 in: Carbon Monoxide Toxicity. D.G. Penney (Ed.). CRC Press, Boca Raton, London, New York, Washington D.C., 2000, pp. 83-99. | Rice, H. M., 1976. Carboxyhaemoglobin dissociation in the cadaver following attempted resuscitation. J. Clin. Pathol. 29, 27-9. Rodat, O., G. Nicolas, A. Lugnierand P. Mangin, 1987. Stabilite tissulaire du monoxyde de carbone apres la mort. La Presse Medicale 16, 826-827. Roos, R.A.C., 1994. Neurological complications of carbon monoxide intoxication. Chapters in: Handbookof Clinical Neurology, Vol. 20 (64): Intoxications of the nervous system, Part I. P.J. Vinken and G.W. Bruyn (Editors). Elsevier Science, Amsterdam, pp. 31-38. Rose, C.S., R.A. Jones, L.J. Jenkins and J. Siegel, 1970. The acute hyperbarictoxicity of carbon monoxide. Toxicol. Appl. Pharmacol. 17, 752-760. Rosenkrantz, H., R.J. Grant, R.W. Fleischman and R.J. Baker, 1986. Marihuana-induced embryotoxicity inthe rabbit. Fundam. Appl. Toxicol. 7, 236-243. Sekiya, S., S. Sato, H. Yamaguchi and K. Harumi, 1983. Effects of carbon monoxide inhalation on myocardial infarct size following experimental coronary artery ligation. Jpn. Heart J. 24, 407-416, cited in WHO, 1999a. Sheps, D.S., K.F. Adams Jr., P.A. Bromberg, G.M. Goldstein, J.J. O'Neil, D. Horstman and G. Koch, 1987. Lack of effect of low levels of carboxyhemoglobin on cardiovascular function in patients with ischemic heart disease. Arch. Environ. Health 42, 108-116. Sheps, D.S., M.C. Herbst, A.L. Hinderliter, K.F. Adams, L.G. Ekelund, J.J. O'Neill, G.M. Goldstein, P.A. Bromberg, J.L. Dalton, M.N. Ballenger, S.M. Davis and G.G. Koch, 1990. Production of arrhythmias by 69 ------- CARBON MONOXIDE FINAL: 07/2008 elevated carboxyhemoglobin in patients with coronary artery disease. Ann. Intern. Med. 113, 343-351. Sheps, D.S., M.C. Herbst, A.L. Hinderliter, K.F. Adams, L.G. Ekelund, J.J. O'Neill, G.M. Goldstein, P.A. Bromberg, M. Ballenger, S.M. Davis and G. Koch, 1991. Effects of 4 Percent and 6 Percent Carboxyhemoglobin on Arrhythmia Production in Patients with Coronary Artery Disease. Research Report No. 41, Health Effects Institute, Cambridge, Massachusetts. Singh, J., 1986. Early behavioral alterations in mice following prenatal carbon monoxide exposure. Neurotoxicol. 7, 475-482. Singh, J. and L.H. Scott, 1984. Threshold for carbon monoxide induced fetotoxicity. Teratol. 30, 253-257. Sokal, J.A. and E. Kralkowska, 1985. The relationship between exposure duration, carboxyhemoglobin, blood glucose, pyruvate and lactate and the severity of intoxication in 39 cases of acute carbon monoxide poisoning in man. Arch. Toxicol. 57, 196-199. Stewart, R.D., 1975. The effect of carbon monoxide on humans. Annual Review of Pharmacology 15, 409-423. Stewart, R.D., J.E. Peterson, E.D. Baretta, R.T. Bachand, M.J. HoskoandA.A. Herrmann, 1970. Experimental human exposure to carbon monoxide. Arch. Environ. Health 21, 154-164. Tikuisis, P., D.M. Kane, T.M. McLellan, F. Buick and S.M. Fairburn, 1992. Rate of formation of cyrboxyhemoglobin in exercising humans exposed to carbon monoxide. J. Appl. Physiol. 72, 1311-1319. Tomaszewski, C., 1998. Carbon Monoxide. Chapter 96 in: GoldfranksToxicologic Emergencies, 6th Ed., L.R. Goldfrank, N.E. Flomenbaum, N.A. Lewin, R.S. Weisman, M.A. Howland and R.S. Hoffman (Eds.). Appleton | and Lange, Stamford, CT, 1998, p. 1551-1563. Vreman, H. J., R. J. Wong, D. K. Stevenson, J. E. Smialek, D. R. Fowler, L. Li, R. D. Vigorito, and H. R. Zielke. 2006. Concentration of carbon monoxide (CO) in postmortem human tissues: effect of environmental CO exposure. J. Forensic Sci. 51, 1182-90. Weaver, L.K., S. Howe, R. Hopkins and K.J. Chan, 2000. Carboxyhemoglobin half-life in carbon monoxide- poisoned patients treated with 100% oxygen at atmospheric pressure. Chest 107, 801 -808. White, S.R., 2000. Pediatric Carbon Monoxide Poisoning. Chapter 21 in: Carbon Monoxide Toxicity. D.G. | Penney (Ed.). CRC Press, Boca Raton, London, New York, Washington D.C., 2000, pp. 463-491. WHO, World Health Organization, 1999a. Environmental Health Criteria 213, Carbon Monoxide (Second Edition), IPCS, International Programme on Chemical Safety; World Health Organization, Geneva, Switzerland, 1999. WHO (World Health Organization), 1999b. Principles for the Assessment of Risks to Human Health from Exposure to Chemicals. Environmental Health Criteria 210. IPCS, International Programme on Chemical Safety; World Health Organization, Geneva, 110 pp. Wlson, J.D., E.Braunwald, K.J. Isselbacher, R.G. Petersdorf, J.B. Martin, A.S. Fauci and R.K. Root (Eds.) 1991. Harrison's Principles of Internal Medicine. 12th Ed. McGraw-Hill, Inc., New York. Wnek, C. L., Prex, D. M., 1981. A comparative study of analytical methods to determine postmortem changes in carbon monoxide concentration. Forensic Sci. Int. 18, 181-7. 70 ------- CARBON MONOXIDE FINAL: 07/2008 Winston, J.M. and R.J. Roberts, 1978. Influence of increasing age on lethality induced by carbon monoxide or hypoxic hypoxia. Biol. Neonate 34, 199-202. Winter, P.M. and J.N. Miller, 1976. Carbon monoxide poisoning. J. Am. Med. Assoc. 236, 1503. 71 ------- CARBON MONOXIDE FINAL: 07/2008 APPENDIX A Time Scaling Calculations for AEGLs 72 ------- CARBON MONOXIDE Key study: Toxicity endpoint: FINAL: 07/2008 Time Scaling Calculations for AEGL-2 Allred et al. (1989a; b; 1991); Sheps et al. (1990; 1991) In an experimental study in 63 subjects with coronary artery disease, a significantly reduced time to ST-segment depression in the electrocardiogram and a significantly reduced time to onset of angina pectoris during physical exercise were found at 2 or 4 % COHb (Allred et al., 1989a; b; 1991). At higher COHb of 5.3, but not at 3.7 %, a significantly increased frequency of exercise-induced arrhythmias was found (Sheps et al., 1990; 1991). AEGL-2 values were derived on a COHb of 4 %. Mathematical model: The CFK model (Coburn et al., 1965; Peterson and Stewart, 1975) was used to calculate exposure concentrations resulting in a COHb of 4 % at the end of the exposure periods. Concentrations were calculated for 10 and 30 minutes, 1, 4 and 8 hours (see Appendix B). Scaling: Uncertainty factors: Calculations: 10-minute AEGL-2 30-minute AEGL-2 1-hour AEGL-2 4-hour AEGL-2 8-hour AEGL-2 Instead of a time scaling according to C"xT = const., a mathematical model was used to calculated exposure concentrations for the relevant time periods (see Appendix B). Uncertainty factor of 1 1 for intraspecies variability 10-min AEGL-2 = 424 ppm/1 = 420 ppm (480 mg/m3) 30-min AEGL-2 = 150 ppm/1 = 150 ppm (170 mg/m3) 1-hour AEGL-2 = 83 ppm/1 = 83 ppm (95 mg/m3) 4-hour AEGL-2 = 33 ppm/1 = 33 ppm (38 mg/m3) 8-hour AEGL-2 = 27 ppm/1 = 27 ppm (31 mg/m3) 73 ------- CARBON MONOXIDE FINAL: 07/2008 Key study: Toxicity endpoint: Time Scaling Calculations for AEGL-3 Nelson (2005a) ;Chiodi et al. (1941); Henderson et al. (1921); Haldane 1895) Exposure of healthy subjects to sufficient concentration-time combinations to reach levels of about 34 to 56 % COHb did not result in severe or life- threatening effects. At this level of CO exposure, Haldane described symptoms including hyperpnea, confusion of mind, dim vision and unsteady/inability to walk. Also, analysis of lethal cases reported by Nelson (2005a) indicated that most lethal poisoning cases occurred at COHb levels higher than 40% and that survival of CO-exposed humans were likely to be seen at levels below 40%. Thus, 40%COHb level seems a reasonable threshold for lethality. Mathematical model: The CFK model (Coburn et al., 1965; Peterson and Stewart, 1975) was used to calculate exposure concentrations resulting in a COHb of 40 % at the end of the exposure periods. Concentrations were calculated for 10 and 30 minutes and 1, 4 and 8 hours (see Appendix B). Scaling: Instead of a time scaling according to C"xT = const., a mathematical model was used to calculated exposure concentrations for the relevant time periods (see Appendix B). Uncertainty factors: Total uncertainty factor of 3 3 for intraspecies variability Calculations: 10-minute AEGL-3 10-min AEGL-3 = 5120 ppm/3 = 1700 ppm (1900 mg/m3) 30-minute AEGL-3 30-min AEGL-3 = 1810 ppm/3 = 600 ppm (690 mg/m3) 1-hour AEGL-3 1-hour AEGL-3 = 998 ppm/3 = 330 ppm (380 mg/m3) 4-hour AEGL-3 4-hour AEGL-3 = 439 ppm/3 = 150 ppm (170 mg/m3) 8-hour AEGL-3 8-hour AEGL-3 = 403 ppm/3 = 130 ppm (150 mg/m3) The COHb levels corresponding to the AEGL-3 values are given in Table 21 in Appendix B. 74 ------- CARBON MONOXIDE FINAL: 07/2008 APPENDIX B Mathematical Model for Calculating COHb and Exposure Concentrations 75 ------- CARBON MONOXIDE FINAL: 07/2008 Mathematical Model for Calculating COHb and Exposure Concentrations Study describing model: Coburn et al. (1965); Peterson and Stewart (1975) Model: Forthe calculation of concentration-time combinations that result in a certain COHb, the model of Coburn, Forsterand Kane (CFK model) (see Section 4.4.4) was used. Since this model in the formulation of Peterson and Stewart (1975) calculates COHb larger than 100 % at high exposure concentrations, the following correction proposed by Peterson and Stewart (1975) was used: the amount of bound oxygen is actually not constant, but is dependent on the COHb, therefore: OHbt=OHbmax-COHbt. Since in this case, the CFK equation can only be solved iteratively, calculations were done using time steps (At) of 1 minute for the period of 0-10 minutes, steps of 5 minutes between 10 and 60 minutes, steps of 15 minutes between 60 and 240 minutes, and steps of 20 minutes between 240 and 480 minutes. In each step, the COHb of the step before was used to calculate OHbt. For the first step, a background COHb of 0.75 % was assumed. The alveolar ventilation rate was calculated as: VA = VE - f VD (Peterson and Stewart, 1975); with VE = total rate of ventilation (ml/min), f = respiration rate (min~1) and VD = dead space (ml). Derivations were done for a 70-kg man, assuming a blood volume of 5500 ml (Coburn et al., 1965) and a daily inhalation volume (VE) of 23 m3 (8 hours resting and 16 hours light/non-occupational activity; WHO, 1999b), a respiration rate (f) of 18 min"1 and a dead space (VD) of 2.2 ml/kg (Numa and Newth, 1996). 76 ------- CARBON MONOXIDE FINAL: 07/2008 Calculations using the following equation were carried out in a spreadsheet computer program: A (COHb)t = V, CO COHbt_, * P02 P, Vb M*B*Vb(OHbm^-COHbt_l} B* where: temperature, COHbt = ml of CO per ml blood at time t (min) Conversion: % carboxyhemoglobin = COHb 100 /OHbmax Vco = rate of endogenous CO production; Vco = 0.007 ml/min Vb = blood volume; Vb (70-kg man) = 5500 ml; Vb (5-yr child, 20 kg) = 1500 ml; Vb (newborn, 3.5 kg) = 400 ml M = Ratio of affinity of blood for CO to that for O2; M = 218 (newborn: M = 240) B = 1 / DL + PL / VA with: DL = diffusivity of the lung for CO; DL = 30 ml / min mm Hg PL = barometric pressure minus the vapor pressure of water at body PL = 713 mm Hg VA = alveolar ventilation rate; VA (70-kg man) = 23 m3/d * 1 • 106 ml/m3 * 1/1440 min/d -18 /min * 2,2 ml/kg * 70 kg VA (70-kg man) = 13200 ml/min VA (5-yr child) = 3580 ml/min VA (newborn) = 1250 ml/min OHbmax = ml of O2 per ml blood under normal conditions; OHb = 0,2 P02 = average partial pressure of oxygen in the lung capillaries; P02 = 100 mm Hg PCO = partial pressure of CO in the air inhaled (mm Hg); Conversion: PCo (mm Hg) = PCo (ppm) /1316 t = exposure duration (min) 77 ------- CARBON MONOXIDE FINAL: 07/2008 100 .0 I o o 10 10 100 Exposure time (min) 1.000 FIGURE 4: COHb VS. EXPOSURE TIME PLOTS Data are shown for CO exposure concentrations indicated (70-kg man). 78 ------- CARBON MONOXIDE FINAL: 07/2008 CFK Modell for Calculation of COHb Dr. Peter Gr em Physiologic parameters. Mtxielby Cotium, Former anc Kane (1965) w!t?i ccfrecGore Introduced By Petersor ana 70-kg 20-kg crrld 3.5-kg sie*ar: n&75) ad:ult newborn Model parameters (see TSD): PL M OHb PO2 Vb Voo D Va DL COHbt COHbo ExpT.ro Dtp. Cone. CO 713 mm Hg 218 0.2 ml/nil blood 100 mmHg 5500 ml 0.007 ml/irtn 0.0015 ml CO/rrJ blood 13200 ml/nln 30 ml.'min mm Hg 0.02 ml CO/if. blood 00015 nil CC.'rr MOOT 60 min Auxiliary expressions: A B COHbt COHbo a calculates COHb a'ter exps&jre to COHb: ^J^^^^_^^^^_ 2.293578 0.0373485 0.02 0.0015 0.7509257 >?:c:rc ic to orlg ns CFK node : in %: 0.75 in %: 10 in %: 0.75 Results for exposure to time(rrin) COHb (%) 10 1.3631498 30 2.5132273 60 4.0330397 240 9.4791254 4&0 11.619731 83 ppm for 60 min: 4 07OQ77 200 0.27 SE:O 1500 400 13200 3580 1250 83 ppm: Cacu:31ec COHb according la n*sdel by CBbum. Footer and Kane F=:=-sor and ste time (min) 1 2 3 4 5 6 7 8 9 10 15 20 25 30 35 40 45 50 55 60 15?5| '.vtn ccr-ectoria hfodLt=d by t3rt :19T5; dt 1 1 5 5 5 5 5 5 5 5 5 5 dHbCO HbCO 0.0015 0.0001253 0.0016253 0.0001247 0.0017501 0.0001241 0.0018742 0.0001235 0.0019977 0.0001229 0.0021206 0.0001223 0.002243 0.0001217 0.0023647 0.0001211 0.0024358 0.0001235 0.0026064 0.0001199 0.0027263 0.0005968 0.0033231 0.0005821 0.0039052 0.0005677 0.0044729 0.0005536 0.0050265 0.0005397 0.0055661 0.0005261 0.0060922 0.0005128 0.006505 0.0004997 0.0071047 0.0004369 0.0075917 0.0004744 0.0080661 % 0.75 0.81267 C. 875:35 0.937098 0.998659 i.:6-:3i9 1.12148 1.182343 1.2425:6 1.303176 1.36315 1.661547 1 .9526 2.236448 2.513227 2.753274 3.2^E124 3.302513 3.552373 3.795838 FIGURE 5: CALCULATION OF 60-MINUTE AEGL-2 FOR HEALTHY ADULT Calculations: For the derivation of AEGL-2 values, exposure concentrations were calculated that would result in a COHb of 4 %. A representation of the spreadsheet for the 60- minute AEGL-2 is shown in Figure 5. Results are shown in the following Table 18. ------- CARBON MONOXIDE FINAL: 07/2008 TABLE 18: CONCENTRATION-TIME COMBINATIONS RESULTING IN Exposure time (min) 10 30 60 240 480 4%COHb for a 70-kg adult man exposure concentration (ppm) 424 150 83 33 27 exposure concentration (ppm), rounded 420 150 83 33 27 For children, newborns and adult smokers, the end-of-exposure COHb values for exposure to the concentrations calculated in Table 18 were computed using the CFK model: TABLE 19: COHb VALUES FOR AEGL-2 CONCENTRATION-TIME COMBINATIONS IN DIFFERENT SUBPOPULATIONS Exposure Exposure 5-yr Newborn time concentration Child (min) (ppm) 10 420 5.2 5.5 30 150 5.2 5.6 60 83 5.2 5.6 240 33 5.0 5.4 480 27 4.9 5.3 Healthy adult 4.0 4.0 4.0 4.0 4.0 Smoker (3% COHb) 6.2 6.3 6.4 6.6 6.7 Smoker (8% COHb) 11.2 11.3 11.4 11.5 11.5 For the derivation of AEGL-3 values, exposure concentrations were calculated that would result in a COHb of 40 %. A representation of the spreadsheet for the 60- minute value is shown in Figure 6. Results are shown in the following Table 20. 80 ------- CARBON MONOXIDE FINAL: 07/2008 TABLE 20: CONCENTRATION-TIME COMBINATIONS RESULTING IN Exposure time (min) 10 30 60 240 480 40%COHb for a 70-kg adult man exposure concentration (ppm) 5120 1810 998 439 403 exposure concentration (ppm), rounded 5100 1800 1000 440 400 For children, newborns, healthy non-smoking adults and smokers, the end-of-exposure COHb values for exposure to the AEGL-3 exposure concentration-time combinations were computed using the CFK model. For all subpopulations, the endogenous CO production rate was adjusted so that the starting level of 0.75 % for children and newborn and 3 and 8 % for smokers were constant without additional CO exposure. TABLE 21 : COHb VALUES FOR AEGL-3 CONCENTRATION-TIME COMBINATIONS IN DIFFERENT SUBPOPULATIONS Exposure Exposure 5-yr Newbor time concentration Child n (min) (ppm) 10 1700 18.7 19.9 30 600 18.5 19.8 60 330 18.3 19.6 240 150 18.6 20.1 480 130 18.1 19.5 Healthy adult 13.8 14.0 14.1 16.4 17.2 Smoker (3 % COHb) 16.1 16.2 16.4 18.6 19.2 Smoker (8% COHb) 21.1 21.1 21.2 22.7 23.0 81 ------- CARBON MONOXIDE FINAL: 07/2008 CFK Model! for Calculation of COHb Dr. Peter Griem Physiologic parameters: MotSil by Cabjrr ForsteranQ Kans I19C-5I witncorrac-:tons IntroDucea by Ps:efsor ard JQ^Q 20-kg child 3 5-kg adult newborn 5le*ai:i1J75) Model oa'amelers (see TSD',: PL 713mmHg M 218 OHb 0.2 ml/ml blood PO2 1DD mm Hg Vb 55DD ml Vco 0.007 rnlj'min D 0.0015 mICO/ml biood Va 13200 ml/min DL 3D ml/min mm Hg COKbt C.D2 ml CO.'ml blood COhco C.CC15 ml CO'm b coo Exp. Time £3 mm Exp. Cone- CO 868 ppm Aux.liary expressions: A 2-29357B B 0.0373485 COHbt 0.02 COHbo D.B015 a 0.7508257 caiDi atea CCHS :aco:rc 13 :o o-gns CFK nocsn arer exposure to COHb: 0-083547B ml;'ml blood CalsialeJ CC-lc aeCD-dhg to -ncOeiBj CoCun. For&ter ans Kaie i;J9€Ei WEI correcusns irfocjc^c ty Peterson anfl Ste*art (1975}: time (min) dt t 1 2 1 3 1 4 1 5 1 6 1 7 1 e 1 8 1 10 1 15 5 20 5 25 5 3D 5 35 5 4C E 4£ 5 SO 5 55 5 6D 5 in %: in %: in%: 0.76 10 D.7S Results for e>:posjre tc lime (mm) 10 3D SB 240 48D 3S3 po-71 dHbCO 0.0015726 0.0015648 0.0015572 0.0015493 0.0015414 0.0015333 0.0015252 D. DO" 5'7 0.0015087 0.0015003 0,0074583 0.0072378 0.0070043 0.0067554 O.OQ64998 0.0062291 3. D 359462 0.0056522 0.0053477 0.0050342 COHb (%) 8.434959S 22.884894 40.019622 62.314719 62.3289 for 80 r-in: HbCO 0.0015 0.0030726 0.0046375 O.OQ61S47 D. 007744 0.0092553 0.01081S7 0.012343S 0.0138608 0.0153696 0.0168695 0.0243292 0.0315671 0.0385714 0.0453298 0.0518297 Q.058058S 0.0640051 0.0696572 D.D75005 O.OB00392 5500 1500 1 3200 3580 398 ppm: ^H % n.75 1.536301 2.31878 3.D87335 3.871833 4.642682 5.^09326 6.171832 6.&3D437 7.684784 8.43496 12.1646 15.79355 18.28572 22.884.B9 25.81485 2S.D2839 32.D0254 34.S28S2 37.50243 4Q.D18S2 200 0.27 400 1250 FIGURE 6: CALCULATION OF 60-MINUTE EXPOSURE CONCENTRATION THAT WOULD. RESULT IN 40 % COHb IN A HEALTHY ADULT ------- CARBON MONOXIDE FINAL: 07/2008 The following end-of-exposure COHb values were calculated for the series of experiments reported by Haldane (1895). Since exposure occurred while the subject was sitting on a chair, a ventilation rate of 7.5 l/min was used for the calculation (WHO, 1999b). The alveolar ventilation rate was calculated as: VA (70-kg man) = 3600 I/8 h * 1 • 103 ml/l* 1/480 min/8 h -18 /min * 2,2 ml/kg * 70 kg VA (70-kg man) = 4700 ml/min TABLE 22: Experiment No. 1 2 3 4 5 6 7 8 9 10 11 COMPARISON O VALUES FORTH Concentration (ppm) 5000 3900 4000 3600 4100 1200 2100 irregular 270 210 460 F REPOR1 E DATA B Time (min) 11.5 30.5 24 29 29 120 71 35 210 240 240 FEDANDCALCUL Y HALDANE (189S COHb measured (%) not done 39 27 37 35 37 49 56 14 13 23 ATEDCOHb ) COHb calculated (%) 22 43 35 38 43 46 50 - 17 15 30 83 ------- CARBON MONOXIDE FINAL: 07/2008 APPENDIX C Derivation Summary for Carbon Monoxide AEGLs 84 ------- CARBON MONOXIDE FINAL: 07/2008 ACUTE EXPOSURE GUIDELINES FOR CARBON MONOXIDE (CAS NO. 630-08-0) 10 minutes N.R. 30 minutes N.R. 1 hour N.R. 4 hours N.R. 8 hours N.R. AEGL-1 VALUES a N.R., not recommended because susceptible persons may experience more serious effects (equivalent to AEGL-2 level) at concentrations, which do not yet cause AEGL-1 effects in the general population Reference: Not applicable Test Species/Strain/Number: Not applicable / not applicable / not applicable Exposure Route/Concentrations/Durations: Not applicable / not applicable / not applicable Effects: Not applicable Endpoint/Concentration/Rationale: CO is the classical example of a tasteless, non-irritating, odorless and colorless toxic gas. Until very severe symptoms occur (inability to walk) none or only nonspecific symptoms were noted in monkeys and healthy humans (Haldane, 1895; Purser and Berrill, 1983). In patients with coronary artery disease, which constitutes the most susceptible subpopulation, effects, such as significant electrocardiogram changes, reduced time to the onset and increased cardiac arrhythmia, start occurring at exposure concentrations little higher than current ambient air quality guidelines, e.g. the U.S. National Air Quality Guideline of 9 ppm for 8 hours (National Air Pollution Control Administration, 1970; FR , 2000; EPA, 2000), the WHO Air Quality Guideline of 10 mg/m3 (9 ppm) for 8 hours (based on 2.5 % COHb) (WHO, 1999a) and the designated European Union Limit Value of 10 mg/m3 (9 ppm) for 8 hours (EC, 1999). These effects were considered above the AEGL-1 effect level and thus would not constitute a suitable basis for the derivation of AEGL-1 values. AEGL-1 values were not recommended because susceptible persons may experience more serious effects (equivalent to AEGL-2 level) at concentrations, which do not yet cause AEGL-1 effects in the general population._ln addition, CO exposures encountered | frequently in everyday life are at or above the concentration range, in which AEGL-1 level would have to be set: smokers have COHb in the range of 3-8 % (Radford and Drizd, 1982) and CO concentrations between about 10 and 50 ppm, which can be found on heavily traveled roads, inside motor vehicles and in homes with gas-, coal-, wood- or kerosene-fired heaters and stoves, correspond to an equilibrium COHb of 1.8-7.5 % (see Figures 2 and 4). Uncertainty Factors/Rationale: Not applicable Modifying Factor: Not applicable Animal to Human Dosimetric Adjustment: Not applicable Time Scaling: Not applicable Data Adequacy: Not applicable 85 ------- CARBON MONOXIDE FINAL: 07/2008 ACUTE EXPOSURE GUIDELINES FOR CARBON MONOXIDE (CAS NO. 630-08-0) 10 minutes 420 ppm 30 minutes 150 ppm 1 hour 83 ppm 4 hours 33 ppm 8 hours 27 ppm AEGL-2 VALUES Reference: Allred, E.N., E.R. Bleecker, B.R. Chaitman, I.E. Dahms, S.O. Gottlieb, J.D. Hackney, D. Hayes, M. Pagano, R.H. Selvester, S.M. Walden and J. Warren, 1989a. Acute Effects of Carbon Monoxide Exposure on Individuals with Coronary Artery Disease. Research Report No. 25, Health Effects Institute, Cambridge, Massachusetts, USA, 1989; Allred, E.N., E.R. Bleecker, B.R. Chaitman, I.E. Dahms, S.O. Gottlieb, J.D. Hackney, M. Pagano, R.H. Selvester, S.M. Walden and J. Warren, 1989b. Short-term effects of carbon monoxide exposure on the exercise performance of subjects with coronary artery disease. New England Journal of Medicine 321, 1426-1432; Allred, E.N., E.R. Bleecker, B.R. Chaitman, I.E. Dahms, S.O. Gottlieb, J.D. Hackney, M. Pagano, R.H. Selvester, S.M. Walden and J. Warren, 1991. Effects of carbon monoxide on myocardial ischemia. Environmental Health Perspectives 91, 89-132. Test Species/Strain/Sex/Number: Humans with coronary artery disease / not applicable / male / 63 Exposure Route/Concentrations/Durations: Inhalation / mean concentrations of 0, 117 or 253 ppm for 50-70 minutes were used, adjusted individually to reach carboxyhemoglobin concentrations of 2.2 % or 4.4 % at the end of exposure (about 2 or 4 % COHb in the subsequent exercise tests) Effects: When potential exacerbation of the exercise-induced ischemia by exposure to CO was tested using the objective measure of time to 1-mm ST-segment change in the electrocardiogram, exposure to CO levels producing COHb of 2 % resulted in a overall statistically significant 5.1 % decrease in the time to attain this level of ischemia. For individual centers (patients were tested in one of three centers), results were significant in one, borderline significant in one and nonsignificant in one center. At 4 % COHb, the decrease in time to the ST criterion was 12.1% (statistically significant for all patients, the effect was found in 49/62 subjects) relative to the air-day results. Significant effects were found in all three test centers. The maximal amplitude of the ST-segment change was also significantly affected by the carbon monoxide exposures: at 2 % COHb the maximal increase was 11 % and at 4 % COHb the increase was 17 % relative to the air day. At 2 % COHb, the time to exercise-induced angina was reduced by 4.2 % in all patients (effects were significant in two test centers and nonsignificant in one center). At 4 % COHb, the time was reduced by 7.1 % in all patients (effects were significant in one, borderline significant in one and nonsignificant in one center). The two end-points (time to angina and time to ST change) were also significantly correlated. Only at 4 % COHb a significant reduction in the total exercise time and in the heart rate- blood pressure product was found (this double product provides a clinical index of the work of the heart and myocardial oxygen consumption). Endpoint/Concentration/Rationale: Patients with coronary artery disease show health effects at lower COHb levels than children, pregnant women or healthy adults and, thus, constitute the most susceptible subpopulation. For the derivation of 86 ------- CARBON MONOXIDE FINAL: 07/2008 AEGL-2 values a level of 4 % COHb was chosen. At this exposure level, patients with coronary artery disease may experience a reduced time until onset of angina (chest pain) during physical exertion (Allred et al., 1989; 1991). In the available studies, the CO exposure alone (i.e. with subjects at rest) did not cause angina, while exercise alone did so. However, it should be noted that all studies used patients with stable exertional angina, who did not experience angina while at rest. Thus, it cannot be ruled out that in more susceptible individuals (a part of the patients with unstable angina pectoris might belong to this group) CO exposure alone could increase angina symptoms. The changes in the electrocardiogram (ST-segment depression of 1 mm or greater) associated with angina symptoms were considered reversible, but is indicative of clinically relevant myocardial ischemia requiring medical treatment. An exposure level of 4 % COHb is unlikely to cause a significant increase in the frequency of exercise-induced arrhythmias. Ventricular arrhythmias have been observed at COHb of 5.3 %, but not at 3.7 % (Sheps et al., 1990; 1991), while in another study no effect of CO exposure on ventricular arrhythmia was found at 3 or 5 % COHb (Dahms et al., 1993). An exposure level of 4 % COHb was considered protective of acute neurotoxic effects in children, such as syncopes, headache, nausea, dizziness and dyspnea (Klasner et al., 1998; Crocker and Walker, 1985), and long-lasting neurotoxic effects (defects in the cognitive development and behavioral alterations) in children (Klees et al., 1985). It is acknowledged that apart from emergency situations, certain scenarios could lead to CO concentrations which may cause serious effects in persons with cardiovascular diseases. These scenarios include e.g. extended exposure to traffic fume emissions (e.g., in tunnels or inside cars with defect car exhaust systems), charcoal or wood fire furnaces, and indoor air pollution by tobacco smoking. Uncertainty Factors/Rationale: Total uncertainty factor: 1 Interspecies: Not applicable Intraspecies: 1 - A level of 4 % COHb was the NOEL for AEGL-2 effects in patients with coronary artery disease, while the LOEL was estimated at 6-9 %. In comparison, the LOEL was about 10-15 % in children and 22-25 % in pregnant women. Since AEGL-2 values were based on experimental data on the most susceptible subpopulation, they were considered protective also for other subpopulations and a total uncertainty factor of 1 was used. Modifying Factor: Not applicable Animal to Human Dosimetric Adjustment: Not applicable Time Scaling: A mathematical model (Coburn et al., 1965; Peterson and Stewart, 1975) was used to calculate exposure concentrations in air resulting in a COHb of 4 % at the end of exposure periods of 10 and 30 minutes and 1, 4 and 8 hours. Data Adequacy: AEGL-2 values were based on cardiac effects in subjects with coronary artery disease, which constitute the most susceptible subpopulation. Several high quality studies are available addressing endpoints such as time to the onset of exercise-induced angina, time to the onset of exercise-induced 1-mm ST- segment changes in the electrocardiogram and frequency of exercise-induced arrhythmias. However, no experimental studies in heart patients are available that used significantly higher levels of COHb than about 5 % COHb. 87 ------- CARBON MONOXIDE FINAL: 07/2008 ACUTE EXPOSURE GUIDELINES FOR CARBON MONOXIDE (CAS NO. 630-08-0) 10 minutes 1700 ppm 30 minutes 600 ppm 1 hour 330 ppm 4 hours 150 ppm 8 hours 130 ppm AEGL-3 VALUES Reference: Nelson.G. 2005a. Effects of Carbon Monoxide in Man. In: Carbon Monoxide and Human Lethality: Fire and Non-fire studies, M.M. Hirschler (Ed.). Taylor and Francis, New York, 2005, pp 3-60; Chiodi, H., D.B. Dill, F. Consolazio and S.M. Horvath, 1941. Respiratory and circulatory responses to acute carbon monoxide poisoning. American Journal of Physiology 134, 683-693; Haldane, J., 1895. The action of carbonic acid on man. Journal of Physiology 18, 430-462; Henderson, Y., H.W. Haggard, M.C. Teague, A.L. Prince and R.M. Wunderlich, 1921. Physiological effects of automobile exhaust gas and standards of ventilation for brief exposures. Journal of Industrial Hygiene 3, 79-92. Test Species/Strain/Sex/Number: Nelson (2005a): Humans/not applicable/both sexes/~3010 subjects Chiodi et al. (1941), Haldane (1895), Henderson et al. (1921): Humans (healthy young males) / not applicable / males / 4 (total) Exposure Route/Concentrations/Durations: Inhalation /Nelson (2005a) reported COHb levels iff [ Formatted Table deceased subjects poisoned by inhalaling CO; Chiodi et al. (1941): repeated test on three subjects that reached COHb of 27-52% at the end of exposure; individual COHb values were 31, 32, 32, 33, 39, 41, 42, 43, 45 and 52 % in subject H.C., 27, 35, 41, 43 and 48 % in subject F.C. and 41, 42 and 44 % in subject S.H.; Haldane (1895): repeated exposure of one subject reaching the following COHb at the end of exposure (time in min): 13 % (240 min), 14 % (210 min), 23 % (240 min), 27 % (24 min), 35 % (29 min), 37 % (29 min), 37 % (120 min), 39 % (30.5 min), 49 % (71 min), 56 % (35 min). Effects: At a COHb of about 40-56 %, Haldane (1895) described symptoms included hyperpnea, confusion of mind, dim vision and unsteady/inability to walk. Chiodi et al. (1941) found no effect on oxygen consumption, ventilation, pulse rate, blood pressure and blood pH; the cardiac output increased 20-50 % at COHb >40 %, while the changes were negligible at COHb of <30 %. Nelson (2005a) reported COHb measurements in lethal poisoning human cases and the data indicated that most lethal poisoning cases occurred at COHb levels higher than 40% and that survival of CO-exposed humans were likely to be seen at levels below 40%. Endpoint/Concentration/Rationale: The derivation of AEGL-3 values was based on observations in humans. Analysis of lethal cases reported by Nelson (2005a) indicated that most lethal poisoning cases occurred at COHb levels higher than 40% and that survival of CO-exposed humans were likely to be seen at levels below 40%. Thus, 40%COHb level seems a reasonable threshold for lethality. This level is supported by experimental studies performed in healthy human subjects. Studies by Chiodi et al. (1941), Henderson et al. (1921), and Haldane (1895) suggest that a COHb of about 34-56 % does not cause lethal effects in healthy individuals. Further support come from the studies by Kizakevich et al. (1994), Stewart et al. (1970), and Nielsen (1971) that reported headache as the only symptom when subjects were exposed to 20-33 % COHb. The point of departure of 40% COHb is also supported by studies in animals 88 ------- CARBON MONOXIDE FINAL: 07/2008 reporting minimum lethal COHb levels in rats and mice of about 50-70 % (E.I. du Pont de Nemours and Co., 1981; Rose et al., 1970). Further support comes from published cases of myocardial infarction that measured COHb levels after transport to the hospital: 52.2 % (Marius-Nunez, 1990), 30 %, 22.8 % (Atkins and Baker, 1985), 21 % (Ebisuno et al., 1986), 15.6 % (Grace and Platt, 1981). Uncertainty Factors/Rationale: Total uncertainty factor: 3 Interspecies: Not applicable Intraspecies: 3 - an intraspecies uncertainty factor of 3 was supported by information on effects, such as myocardial infarction and stillbirths, reported in more susceptible subpopulations. Modifying Factor: Not applicable Animal to Human Dosimetric Adjustment: Not applicable Time Scaling: A mathematical model (Coburn et al., 1965; Peterson and Stewart, 1975) was used to calculate exposure concentrations in air resulting in a COHb of 40 % at the end of exposure periods of 10 and 30 minutes and 1, 4 and 8 hours. Data Adequacy: AEGL-3 values were based on 40% COHb levels derived from the analysis of clinical cases of lethal and non-lethal poisoning. The AEGL-3 values derived using an intraspecies uncertainty factor of 3 (corresponding to an COHb of about 15 %) are supported by the available case reports of lethal effects (myocardial infarction, stillbirths) in more susceptible subpopulations. Lethal effects from myocardial infarction in hypersusceptible patients with coronary artery disease at even lower CO concentrations, which could be at the upper end of the range of CO concentrations found inside buildings and in ambient air outside, cannot be excluded. 89 ------- |