The Science of the Total Environment, 116 (1992) 53-58 Elsevier Science Publishers B.V., Amsterdam
53
Carboxyhemoglobin levels in blood donors in Bahrain Ismail M. Madany Arabian Gulf University, P.O. Box 26671, Bahrain (Received March 10th, 1991; accepted March 20th, 1991)
ABSTRACT A total of 107 venous blood samples were obtained from blood donors in Bahrain for carboxyhemoglobin (COHb) analysis. The donors were categorized according to their sex, smoking habits, occupation, place of work (indoor or outdoor), and residential area. The mean COHb levels were significantly higher in smokers (4.8%) than nonsmoking (1.5%). The mean COHb levels were higher in smoking, outdoor working donors (4.98%) and nonsmoking outdoor working donors (2.29%) than smoking indoor working donors (3.07%) and nonsmoking indoor working donors (1.04%). Other factors, such as sex and residential area did not influence COHb concentrations. The results indicate a possible influence of the levels of environmental carbon monoxide on the COHb in the blood of the Bahraini population.
Key words." carbon monoxide; carboxyhemoglobin; blood donors; Bahrain
INTRODUCTION
Carbon monoxide is a well-recognized widespread air pollutant emanating from many sources to which people may be exposed in various ways. Numerous investigators have documented the deleterious effects of exposure to high concentrations of carbon monoxide (Goldsmith and Aronow, 1975; Stewart et al., 1970; Kleinman et al., 1989; Christine and Halton, 1990). With respect to the Bahraini people, there are various sources of exposure to carbon monoxide. The first and major source are the exhaust products of motor vehicles, which amounts to - 89% of the total emissions (Madany et al., 1991). Other sources include power generators and industrial processes such as a crude oil refinery, an aluminium smelter, and a methanol and ammonia plant. The ambient carbon monoxide level in Bahrain ranges from 0.2 to 2.3 ppm with an average of 0.7 ppm (Madany and Danish, 1988). Indoor sources of carbon monoxide include the use of liquefied petroleum gas (LPG) in cooking, and cigarette smoking. Carbon monoxide can be pro0048-9697/92/$05.00
© 1992 Elsevier Science Publishers B.V. All rights reserved
54
I.M.MADANY
duced endogenously from the normal breakdown in the body of blood pigments giving carboxyhemoglobin values of 0.1 to 1.0% (World Health Organization, 1979). Other studies report mean values of 0.45% (Stewart et al., 1974) and 0.5% (Lynch and Moede, 1972). Human exposure to carbon monoxide can be estimated either by its measurement in the air or by measurement of carboxyhemoglobin (COHb) in the blood. This investigation was undertaken to determine the COHb levels in the Bahraini blood donors, and to study the difference in the carboxyhemoglobin concentration between smokers and nonsmokers, and indoor and outdoor working donors. Moreover, this study will establish the range of CO exposure experienced by the Bahraini citizens, and provides a basis for establishing ambient air quality standards for carbon monoxide. MATERIALS AND METHODS A total of 107 samples were collected from the Salmania Medical Centre blood-bank collection site in Bahrain. Samples were taken from both smokers and nonsmokers, and those who work indoors and outdoors. At the time of sampling, a questionnaire was completed by the blood donors, so that the influence of the following variables could be assessed: sex, smoking habits, place of residence, occupation, and place of work (indoor or outdoor). Venous blood samples were collected in glass bottles containing EDTA, and then the whole bottle was covered with aluminium foil. Analysis was undertaken within 24 h of collection. Carboxyhemoglobin was measured in duplicate on all samples and in a single analytical run, using a IL 282 CO-Oximeter system (Allied Instrumentation Laboratory, Lexington, MA, USA). The CO-Oximeter was calibrated before analysis against a IL Caldye reference standard sample. The Student's t-test was used to assess the observed difference between mean COHb levels. RESULTS The characteristics of the 107 subjects under investigation are presented in Tables 1 and 2 according to their smoking habits and working places (indoor or outdoor). Out of the 107 subjects, only three were females, due to the small number of females donating blood. Number of smokers was 56, of whom 25 were working indoors, and the nonsmokers were 51, of whom 30 were working indoors. The results of the concentration of carboxyhemoglobin in the blood of 107 subjects are shown in Tables 1 and 2. The results for percentage COHb are
55
C A R B O X Y H E M O G L O B I N LEVELS IN B A H R A I N I B L O O D D O N O R S
TABLE ! Carboxyhemoglobin levels in the blood of 107 subjects according to smoking habits COHb (%)
Smoking N
0.1-1.0 1.1-2.0 2.1-3.0 3.1-4.0 4.1-5.0 5.1-9.1 Total Mean S.D. Range
Nonsmoking %
N
%
3
5.4
18
35.3
6 6 14 9 18
10.7 10.7 25.0 16.0 32.0
19 11 3 0 0
37.2 21.6 5.9 0 0
56
100
4.8 4.7 0.2-9.1
51
100
1.5 0.8 0.1-3.3
divided into six groups according to their smoking habits (Table 1). The first group has COHb levels ranging from 0.1 to 1.0%. In this category, there are three smokers (5.4%) and 18 nonsmokers (35.3%). The second group which had COHb ranging from 1.1 to 2.0%, comprised six smokers (10.7%) and 19 nonsmokers (37.2%). In group three (COHb 2.1-3.0%), the number of smokers was 6 (10.7%) while that of nonsmokers was 11 (21.6%). The fourth group (COHb 3.1-4.0%) had 14 smokers (25.0%) and 3 nonsmokers (5.9%) while in group 5 (COHb 4.1-5.0%) there was only smokers (N = 9, 16%). The last group, which had COHb ranging from 5.1 to 9.1%, consisted only of smokers (N = 18, 32%). The mean COHb level in the 107 subjects was 4.8% (S.D. = 4.7, range 0.2-9.1) for smokers, and 1.5% (S.D. = 0.8, range 0.1-3.3) for nonsmokers, as shown in Table 1. TABLE 2 Levels of carboxyhemoglobin in the blood of 107 subjects according to place of work and smoking habits COHb (%)
Mean S.D. Range
Smoking
Nonsmoking
Indoor (N = 25)
Outdoor (N = 31)
Indoor (N = 30)
Outdoor (N = 21)
3.07 1.57 0.2-6.4
4.98 1.96 2.4-9.1
1.04 0.58 0.1-2.7
2.29 0.58 1.4-3.3
56
I.M.MADANY
Table 2 presents COHb levels in the blood of 107 donors with respect to smoking habits and place of work (indoor or outdoor). The mean COHb level for indoor smoking subjects was 3.07% (N = 25, S.D. = 1.57, range 0.2-6.4) and for outdoor smoking subjects 4.98 (N = 30, S.D. = 1.96, range 2.4-9.1). For indoor nonsmoking donors the mean COHb level was 1.04% (N = 30, S.D. -- 0.58, range 0.1-2.7), and for outdoor nonsmoking donors was 2.29% (N = 21, S.D. = 0.58, range 1.4-3.3). Student's t-test showed significant differences between the means of COHb levels in smoking and nonsmoking donors (P < 0.001), in smoking (indoor workers) and smoking (outdoor workers) (P < 0.001), and in nonsmoking (indoor workers) and nonsmoking (outdoor workers) (P < 0.001). DISCUSSION
The aim of this investigation was to determine the magnitude of exposure of the Bahraini population to carbon monoxide by measuring the concentration of COHb in the blood of 107 Bahraini blood donors. Also, the influence of several variables such as smoking habit, geographical locations, occupation, and place of work (indoor or outdoor) on the levels of carboxyhemoglobin was studied. In general smokers had higher levels of carboxyhemoglobin than those of nonsmokers. From Table 1, it can be seen that the mean COHb% in smokers was 4.8, which is significantly higher than the nonsmokers (COHb 1.5%). Seventy-three percent of the smokers had COHb ranging from 3.1 to 9.1%, whereas only 5.9% of the nonsmokers had COHb falling within this range. Our data is consistent with the literature which has reported that smokers had statistically higher COHb levels than nonsmokers (Cole, 1974; Castleden and Cole, 1975; Stewart et a1.,1974; Khan et a1.,1974). The results also indicate that cigarette smoking contributes more than other sources, such as motor vehicle to exposure to carbon monoxide, which results in elevated COHb levels in the blood of the Bahraini population. With respect to indoor and outdoor workers, the results (Table 2) show marked differences between the two categories. Smoking donors who worked outdoors had mean COHb levels of 4.98% compared with 3.07% for nonsmokers. This trend was also observed for nonsmokers who work outdoors (COHb 2.29%) and those who work indoors (COHb 1.04%). Among those outdoor workers who had the highest COHb levels were taxi drivers, dock workers, air port workers, and policemen. This observation has also been reported by other workers (Stewart et al., 1974; Petrov, 1968; Chovin, 1967). The lowest levels of COHb in the blood of Bahraini population were in nonsmoking indoor workers. For this category, there might be two sources
CARBOXYHEMOGLOBIN LEVELS IN BAHRAINI BLOOD DONORS
57
of exposure to carbon monoxide. The endogenous CO produced in the body, and exogenous atmospheric sources. The contribution to the second CO source originates mainly from automobile exhausts, which is causing major concern regarding the quality of air in Bahrain. This result may indicate a possible relationship between carbon monoxide in air and COHb concentration in the blood of the population. With regard to other variables, namely place of residence and sex, no important variations were found in the COHb levels. The recommended concentration set by the National Institute for Occupational Safety Health, 1972 and the American Conference of Governmental Industrial Hygienists, 1986 for occupational exposure to carbon monoxide should not result in COHb levels exceeding 5 and 8%, respectively. Our investigation shows that 18 (32.0%) of the smokers exceed the 5% limit (Table 1). However, for the general population, a carboxyhemoglobin level of 2.5-3.0% is recommended by the World Health Organization (1987). This level is exceeded by 41 (73%) smokers and only 3 (5.9%) nonsmokers (Table 1). CONCLUSIONS
Our investigation provides base line data concerning exposure of the general population of Bahrain to CO by measuring the levels of COHb. The results demonstrate that the mean COHb level in smokers is significantly higher than those of nonsmokers, which indicate that smoking is the main contributor to exposure to CO. Moreover, the present study shows that place of the work (indoor or outdoor) markedly change the concentration of COHb, with outdoor workers having the highest COHb levels. We can conclude that there is a possible relationship between carbon monoxide in the air and COHb in the blood of the Bahraini population. ACKNOWLEDGMENT
The author is indebted to M.A.R. AL-Khayat for his valuable assistance during this work. REFERENCES American Conference of Governmental Industrial Hygienists: Carbon Monoxide, 1986. In Documentation of the Threshold Limit Values and Biological Exposure Indices. 5th ed. (BE17-BEI 10). Cincinnati, Ohio, pp. 106-107. Castleden, C.M. and P.V. Cole, 1975. Carboxyhemoglobin levels of smokers and nonsmokers working in the city of London. Br. J. Indust. Med., 32:115-118.
58
I.M. MADANY
Chovin, P., 1967. Carbon monoxide: analysis of exhaust gas investigations in Paris. Environ. Res., 1: 198-216. Christine, A.N. and D.M Halton, 1990. Is carbon monoxide a workplace teratogen? A review and evaluation of the literature. Ann. Occup. Hyg., 34: 335-347. Cole, P.V., 1974. Uptake of CO by man: a population survey of COHb levels. Proceedings Health effect of Carbon monoxide Environmental Pollution. Commission of the European Communities, Luxembourg, EUR 5242 (d, e, f, i, n). Goldsmith, J.R. and W.S. Aronow, 1975. Carbon monoxide and coronary heart disease: a review. Environ. Res., 10: 236-248. Khan, A., R.B. Rutledge, G.L. Davis, A. Altes, G.E. Gantner, C.A. Thornton and N.D. Wallace, 1974. Carboxyhemoglobin sources in the metropolitan St. Louis population. Arch. Environ. Health, 29: 127-135. 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. Environ. Health, 44: 361-369. Lynch, S.R. and A.L Moede, 1972. Variation in the rate of endogenous carbon monoxide production in normal human beings. J. Lab. Clin. Med., 79: 85-95. Madany, I.M., S. Khalfan, H. Khalfan, J. Jiddah and M.N. Aladin, 1991. Occupational exposure to carbon monoxide during charcoal meat grilling. Sci. Total Environ., in press. Madany, I.M. and S. Danish, 1988. Measurement of air pollution in Bahrain. Environ. Int., 14: 49-58. National Institute for Occupation and Health, 1972. Occupational exposure to carbon monoxide (HSM 73-11000). Washington D.C., Government Printing Office, pp. 1-1, XI-2. Petrov, P., 1968. Chronic CO intoxications in workers engaged in loading and loading processes. Transp. Med. Vesti., 4: 24-27. Stewart, R.D., E.D. Baretta, L.R. Platte, E. B. Stewart, J. H. Kalbfleisch, B.V. Yserloo and A.A. Rimm, 1974. Carboxyhemoglobin levels in American blood donors. J. Am. Med. Assoc., 229: 1187-1195. 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. Arch. Environ. Health, 21: 154-164. World Health Organization-Regional Office of Europe, 1987. Air quality guideline for Europe. WHO Regional Publications, European series No. 23, Copenhagen, p. 217. World Health Organization, 1979. Enviromental Health Criteria, No. 13: Carbon Monoxide. Geneva, p. 35.
53
Carboxyhemoglobin levels in blood donors in Bahrain Ismail M. Madany Arabian Gulf University, P.O. Box 26671, Bahrain (Received March 10th, 1991; accepted March 20th, 1991)
ABSTRACT A total of 107 venous blood samples were obtained from blood donors in Bahrain for carboxyhemoglobin (COHb) analysis. The donors were categorized according to their sex, smoking habits, occupation, place of work (indoor or outdoor), and residential area. The mean COHb levels were significantly higher in smokers (4.8%) than nonsmoking (1.5%). The mean COHb levels were higher in smoking, outdoor working donors (4.98%) and nonsmoking outdoor working donors (2.29%) than smoking indoor working donors (3.07%) and nonsmoking indoor working donors (1.04%). Other factors, such as sex and residential area did not influence COHb concentrations. The results indicate a possible influence of the levels of environmental carbon monoxide on the COHb in the blood of the Bahraini population.
Key words." carbon monoxide; carboxyhemoglobin; blood donors; Bahrain
INTRODUCTION
Carbon monoxide is a well-recognized widespread air pollutant emanating from many sources to which people may be exposed in various ways. Numerous investigators have documented the deleterious effects of exposure to high concentrations of carbon monoxide (Goldsmith and Aronow, 1975; Stewart et al., 1970; Kleinman et al., 1989; Christine and Halton, 1990). With respect to the Bahraini people, there are various sources of exposure to carbon monoxide. The first and major source are the exhaust products of motor vehicles, which amounts to - 89% of the total emissions (Madany et al., 1991). Other sources include power generators and industrial processes such as a crude oil refinery, an aluminium smelter, and a methanol and ammonia plant. The ambient carbon monoxide level in Bahrain ranges from 0.2 to 2.3 ppm with an average of 0.7 ppm (Madany and Danish, 1988). Indoor sources of carbon monoxide include the use of liquefied petroleum gas (LPG) in cooking, and cigarette smoking. Carbon monoxide can be pro0048-9697/92/$05.00
© 1992 Elsevier Science Publishers B.V. All rights reserved
54
I.M.MADANY
duced endogenously from the normal breakdown in the body of blood pigments giving carboxyhemoglobin values of 0.1 to 1.0% (World Health Organization, 1979). Other studies report mean values of 0.45% (Stewart et al., 1974) and 0.5% (Lynch and Moede, 1972). Human exposure to carbon monoxide can be estimated either by its measurement in the air or by measurement of carboxyhemoglobin (COHb) in the blood. This investigation was undertaken to determine the COHb levels in the Bahraini blood donors, and to study the difference in the carboxyhemoglobin concentration between smokers and nonsmokers, and indoor and outdoor working donors. Moreover, this study will establish the range of CO exposure experienced by the Bahraini citizens, and provides a basis for establishing ambient air quality standards for carbon monoxide. MATERIALS AND METHODS A total of 107 samples were collected from the Salmania Medical Centre blood-bank collection site in Bahrain. Samples were taken from both smokers and nonsmokers, and those who work indoors and outdoors. At the time of sampling, a questionnaire was completed by the blood donors, so that the influence of the following variables could be assessed: sex, smoking habits, place of residence, occupation, and place of work (indoor or outdoor). Venous blood samples were collected in glass bottles containing EDTA, and then the whole bottle was covered with aluminium foil. Analysis was undertaken within 24 h of collection. Carboxyhemoglobin was measured in duplicate on all samples and in a single analytical run, using a IL 282 CO-Oximeter system (Allied Instrumentation Laboratory, Lexington, MA, USA). The CO-Oximeter was calibrated before analysis against a IL Caldye reference standard sample. The Student's t-test was used to assess the observed difference between mean COHb levels. RESULTS The characteristics of the 107 subjects under investigation are presented in Tables 1 and 2 according to their smoking habits and working places (indoor or outdoor). Out of the 107 subjects, only three were females, due to the small number of females donating blood. Number of smokers was 56, of whom 25 were working indoors, and the nonsmokers were 51, of whom 30 were working indoors. The results of the concentration of carboxyhemoglobin in the blood of 107 subjects are shown in Tables 1 and 2. The results for percentage COHb are
55
C A R B O X Y H E M O G L O B I N LEVELS IN B A H R A I N I B L O O D D O N O R S
TABLE ! Carboxyhemoglobin levels in the blood of 107 subjects according to smoking habits COHb (%)
Smoking N
0.1-1.0 1.1-2.0 2.1-3.0 3.1-4.0 4.1-5.0 5.1-9.1 Total Mean S.D. Range
Nonsmoking %
N
%
3
5.4
18
35.3
6 6 14 9 18
10.7 10.7 25.0 16.0 32.0
19 11 3 0 0
37.2 21.6 5.9 0 0
56
100
4.8 4.7 0.2-9.1
51
100
1.5 0.8 0.1-3.3
divided into six groups according to their smoking habits (Table 1). The first group has COHb levels ranging from 0.1 to 1.0%. In this category, there are three smokers (5.4%) and 18 nonsmokers (35.3%). The second group which had COHb ranging from 1.1 to 2.0%, comprised six smokers (10.7%) and 19 nonsmokers (37.2%). In group three (COHb 2.1-3.0%), the number of smokers was 6 (10.7%) while that of nonsmokers was 11 (21.6%). The fourth group (COHb 3.1-4.0%) had 14 smokers (25.0%) and 3 nonsmokers (5.9%) while in group 5 (COHb 4.1-5.0%) there was only smokers (N = 9, 16%). The last group, which had COHb ranging from 5.1 to 9.1%, consisted only of smokers (N = 18, 32%). The mean COHb level in the 107 subjects was 4.8% (S.D. = 4.7, range 0.2-9.1) for smokers, and 1.5% (S.D. = 0.8, range 0.1-3.3) for nonsmokers, as shown in Table 1. TABLE 2 Levels of carboxyhemoglobin in the blood of 107 subjects according to place of work and smoking habits COHb (%)
Mean S.D. Range
Smoking
Nonsmoking
Indoor (N = 25)
Outdoor (N = 31)
Indoor (N = 30)
Outdoor (N = 21)
3.07 1.57 0.2-6.4
4.98 1.96 2.4-9.1
1.04 0.58 0.1-2.7
2.29 0.58 1.4-3.3
56
I.M.MADANY
Table 2 presents COHb levels in the blood of 107 donors with respect to smoking habits and place of work (indoor or outdoor). The mean COHb level for indoor smoking subjects was 3.07% (N = 25, S.D. = 1.57, range 0.2-6.4) and for outdoor smoking subjects 4.98 (N = 30, S.D. = 1.96, range 2.4-9.1). For indoor nonsmoking donors the mean COHb level was 1.04% (N = 30, S.D. -- 0.58, range 0.1-2.7), and for outdoor nonsmoking donors was 2.29% (N = 21, S.D. = 0.58, range 1.4-3.3). Student's t-test showed significant differences between the means of COHb levels in smoking and nonsmoking donors (P < 0.001), in smoking (indoor workers) and smoking (outdoor workers) (P < 0.001), and in nonsmoking (indoor workers) and nonsmoking (outdoor workers) (P < 0.001). DISCUSSION
The aim of this investigation was to determine the magnitude of exposure of the Bahraini population to carbon monoxide by measuring the concentration of COHb in the blood of 107 Bahraini blood donors. Also, the influence of several variables such as smoking habit, geographical locations, occupation, and place of work (indoor or outdoor) on the levels of carboxyhemoglobin was studied. In general smokers had higher levels of carboxyhemoglobin than those of nonsmokers. From Table 1, it can be seen that the mean COHb% in smokers was 4.8, which is significantly higher than the nonsmokers (COHb 1.5%). Seventy-three percent of the smokers had COHb ranging from 3.1 to 9.1%, whereas only 5.9% of the nonsmokers had COHb falling within this range. Our data is consistent with the literature which has reported that smokers had statistically higher COHb levels than nonsmokers (Cole, 1974; Castleden and Cole, 1975; Stewart et a1.,1974; Khan et a1.,1974). The results also indicate that cigarette smoking contributes more than other sources, such as motor vehicle to exposure to carbon monoxide, which results in elevated COHb levels in the blood of the Bahraini population. With respect to indoor and outdoor workers, the results (Table 2) show marked differences between the two categories. Smoking donors who worked outdoors had mean COHb levels of 4.98% compared with 3.07% for nonsmokers. This trend was also observed for nonsmokers who work outdoors (COHb 2.29%) and those who work indoors (COHb 1.04%). Among those outdoor workers who had the highest COHb levels were taxi drivers, dock workers, air port workers, and policemen. This observation has also been reported by other workers (Stewart et al., 1974; Petrov, 1968; Chovin, 1967). The lowest levels of COHb in the blood of Bahraini population were in nonsmoking indoor workers. For this category, there might be two sources
CARBOXYHEMOGLOBIN LEVELS IN BAHRAINI BLOOD DONORS
57
of exposure to carbon monoxide. The endogenous CO produced in the body, and exogenous atmospheric sources. The contribution to the second CO source originates mainly from automobile exhausts, which is causing major concern regarding the quality of air in Bahrain. This result may indicate a possible relationship between carbon monoxide in air and COHb concentration in the blood of the population. With regard to other variables, namely place of residence and sex, no important variations were found in the COHb levels. The recommended concentration set by the National Institute for Occupational Safety Health, 1972 and the American Conference of Governmental Industrial Hygienists, 1986 for occupational exposure to carbon monoxide should not result in COHb levels exceeding 5 and 8%, respectively. Our investigation shows that 18 (32.0%) of the smokers exceed the 5% limit (Table 1). However, for the general population, a carboxyhemoglobin level of 2.5-3.0% is recommended by the World Health Organization (1987). This level is exceeded by 41 (73%) smokers and only 3 (5.9%) nonsmokers (Table 1). CONCLUSIONS
Our investigation provides base line data concerning exposure of the general population of Bahrain to CO by measuring the levels of COHb. The results demonstrate that the mean COHb level in smokers is significantly higher than those of nonsmokers, which indicate that smoking is the main contributor to exposure to CO. Moreover, the present study shows that place of the work (indoor or outdoor) markedly change the concentration of COHb, with outdoor workers having the highest COHb levels. We can conclude that there is a possible relationship between carbon monoxide in the air and COHb in the blood of the Bahraini population. ACKNOWLEDGMENT
The author is indebted to M.A.R. AL-Khayat for his valuable assistance during this work. REFERENCES American Conference of Governmental Industrial Hygienists: Carbon Monoxide, 1986. In Documentation of the Threshold Limit Values and Biological Exposure Indices. 5th ed. (BE17-BEI 10). Cincinnati, Ohio, pp. 106-107. Castleden, C.M. and P.V. Cole, 1975. Carboxyhemoglobin levels of smokers and nonsmokers working in the city of London. Br. J. Indust. Med., 32:115-118.
58
I.M. MADANY
Chovin, P., 1967. Carbon monoxide: analysis of exhaust gas investigations in Paris. Environ. Res., 1: 198-216. Christine, A.N. and D.M Halton, 1990. Is carbon monoxide a workplace teratogen? A review and evaluation of the literature. Ann. Occup. Hyg., 34: 335-347. Cole, P.V., 1974. Uptake of CO by man: a population survey of COHb levels. Proceedings Health effect of Carbon monoxide Environmental Pollution. Commission of the European Communities, Luxembourg, EUR 5242 (d, e, f, i, n). Goldsmith, J.R. and W.S. Aronow, 1975. Carbon monoxide and coronary heart disease: a review. Environ. Res., 10: 236-248. Khan, A., R.B. Rutledge, G.L. Davis, A. Altes, G.E. Gantner, C.A. Thornton and N.D. Wallace, 1974. Carboxyhemoglobin sources in the metropolitan St. Louis population. Arch. Environ. Health, 29: 127-135. 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. Environ. Health, 44: 361-369. Lynch, S.R. and A.L Moede, 1972. Variation in the rate of endogenous carbon monoxide production in normal human beings. J. Lab. Clin. Med., 79: 85-95. Madany, I.M., S. Khalfan, H. Khalfan, J. Jiddah and M.N. Aladin, 1991. Occupational exposure to carbon monoxide during charcoal meat grilling. Sci. Total Environ., in press. Madany, I.M. and S. Danish, 1988. Measurement of air pollution in Bahrain. Environ. Int., 14: 49-58. National Institute for Occupation and Health, 1972. Occupational exposure to carbon monoxide (HSM 73-11000). Washington D.C., Government Printing Office, pp. 1-1, XI-2. Petrov, P., 1968. Chronic CO intoxications in workers engaged in loading and loading processes. Transp. Med. Vesti., 4: 24-27. Stewart, R.D., E.D. Baretta, L.R. Platte, E. B. Stewart, J. H. Kalbfleisch, B.V. Yserloo and A.A. Rimm, 1974. Carboxyhemoglobin levels in American blood donors. J. Am. Med. Assoc., 229: 1187-1195. 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. Arch. Environ. Health, 21: 154-164. World Health Organization-Regional Office of Europe, 1987. Air quality guideline for Europe. WHO Regional Publications, European series No. 23, Copenhagen, p. 217. World Health Organization, 1979. Enviromental Health Criteria, No. 13: Carbon Monoxide. Geneva, p. 35.
