- Email: [email protected]
Blood cadmium levels in non-occupationally exposed adult subjects in Singapore
the Science of the Total Environment la~rutklmadka.m,ad ~ r ,Stiemif l t Rt.llllu~h
ELSEVIER
The Science of the Total Environment 145 (1994) 119-123
Blood cadmium levels in non-occupationally exposed adult subjects in Singapore S i n - E n g C h i a *a, O i - Y o k e C h a n b, C h e u c k - T a t t
S a m c, B e e - H o o n H e n g d
aDepartment of Community, Occupational and Family Medicine, National University of Singapore, Lower Kent Ridge Road, Singapore 0511, Singapore ~Department of Industrial Health, Ministry of Labour, Singapore, Singapore "Department of Scientific Services, Institute of Science and Forensic Medicine, Ministry of Health, Singapore, Singapore aQuarantine and Epidemology Department, Ministry of the Environment, Singapore, Singapore
(Received 2 January 1993; accepted 9 February 1993)
Abstract Cadmium concentrations in whole blood were measured in subjects with no occupational exposure to cadmium. The study covered 128 males and 150 females from the three main ethnic groups in Singapore (namely Chinese, Malays and Indians). The geometric means (GM) of blood cadmium (CdB) levels of non-smoking males and females were 0.21 #g/1 and 0.26/~g/1, respectively. Smokers had higher GM CdB levels than non-smokers. Significant ethnic differences were observed in both sexes, with Indian males having the highest GM CdB level of 0.48 #g/l. Among the females, the Chinese had the highest GM CdB level: 0.33 #g/l. Differences in dietary habits may have contributed to the observed ethnic differences in blood cadmium levels. Key words," Blood cadmium; Singapore; Population; Chinese; Malay; Indian
1. Introduction It is a well-known phenomenon that blood cadmium (CdB) levels vary considerably among the general population in different countries. Friberg and Vahter [1] in a global UNEP/WHO pilot project on assessment of human exposure to lead and cadmium, reported geometric mean values for CdB that ranged from 0.5 #g/1 in Stockholm and Jerusalem to 1.2 #g/l in Brussels and Tokyo [1]. * Corresponding author.
There are a number of reasons for this wide variation. Tobacco contains relatively high cadmium concentrations, varying between 1.0 and 2.0/~g/cigarette in cigarette brands usually smoked in the Western European countries; 10% of this cadmium is inhaled during smoking [2]. Smokers have, on the average, higher levels of cadmium in blood [3-5,]. Smoking patterns may differ from country to country. Individuals from heavily industrialised countries generally have higher mean CdB levels [ 11. Dietary
0048-9697/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved. SSDI 0048-9697(94)03663-M
120
habit, which to some extent is linked to environmental pollution, also determines the level of intake of cadmium [6,7]. Vegetables can have a higher content of cadmium if grown in land contaminated with cadmium as a result of uncontrolled waste disposal [8,9]. Similarly, some seafoods could be contaminated by industrial waste containing cadmium [10]. The wide variation in the CdB levels among different countries makes it difficult for any one country to adopt the standards or norms of another. It is therefore important for countries to determine and monitor levels of cadmium in their own populations. Such an approach may help to prevent trends of rising exposure, which could, if left unchecked, ultimately reach levels which have direct implications for human health. This study was conducted with the objectives of reporting the mean CdB levels among adult subjects in Singapore who have no known occupational exposure and determining if there are significant differences in CdB levels between the three major ethnic groups (namely Chinese, Malay and Indian). 2. Materials and methods
2.1. Study subjects The population covered comprised employees from government organisations and statutory boards, production workers, as well as individuals attending government health clinics. None of the subjects was known to have any specific exposure to cadmium other than those present in the general environment. In addition to their personal particulars, smoking history and details to determine possible cadmium exposure in the workplace as well as home environment were obtained by the interview method using a formally structured questionnaire. Smoking history was categorised as follows: (1) non-smokers, inclusive of ex-smokers who have stopped smoking for more than 1 year; (2) light smokers, subjects who smoked 1-10 cigarettes/day; (3) moderate smokers, subjects smoking 10-20 cigarettes/day; and (4) heavy smokers, those smoking more than 20 cigarettes/day.
S.-E. Chia et al./ Sci. Total Environ. 145 (1994) 119-123
2.2. Blood cadmium estimation About 2 ml of whole blood was obtained by venipuncture with informed consent from each participating subject. The samples were collected in heparinised tubes and subsequently analysed at the Industrial Health Laboratory of the Department of Scientific Services, Institute of Science and Forensic Medicine. Cadmium in blood was determined by graphite furnace atomic absorption spectroscopy using an external standard. A 400-#1 each of control blood (for 3 standards), blood blank, sample blood and reagent blank (distilled-deionised water) were added to each Corning (75 x 12 mm) test tube containing 400/~1 of concentrated nitric acid. The contents in the tubes were mixed thoroughly prior to heating on a block-heater at 50°C for 1 h followed by 3 h at l l0°C. Quantities of 10, 20 and 30 #1 of a 0.5 p.p.m. cadmium standard solution (cadmium nitrate) were added to each of the three tubes containing a control blood and mixed thoroughly. A 100-/~1 quantity of 60% perchloric acid was added to all the test tubes (standards, blood bank, regeant blank and samples) followed by heating at 130°C for 3 h and finally at 160°C for I h. A 2-ml quantity of distilled, deionised water was added to each tube, agitated on a vortex mixer and centrifuged. A 0.8-ml aliquot of a clear supernatant solution was transferred from each tube to a corresponding autosampler vial. The reagent blank was used to autozero the instrument. Analysis was carried out using the absorbance mode. The limit of detection was 0.2/~g/1. For computation purposes, CdB values which were below the detection limit were taken to be at half the detection limit. Quality assurance for the laboratory was through participation in external programmes with two centres: Centre de Toxicologie du Quebec (Canada) and the Health and Safety Executive (UK). 2.3. Statistics Statistical analysis was carried out on the IBM mainframe computer 3081 with the Statistical Analysis System (SAS). Logarithms of CdB levels were used to ensure a more normal distribution of
121
S.-E. Chia et al. / Sci. Total Environ. 145 (1994) 119-123
tory. The mean age o f the subjects was 36.0 years with a range o f 1 6 - 6 0 years. N o n e o f the w o m e n studied were smokers. There were m o r e smokers a m o n g the I n d i a n and M a l a y male subjects than the Chinese males. Age was not significantly c o r r e l a t e d (r = 0.01) with CdB levels. N o significant sex differences were noted in the geometric m e a n ( G M ) CdB. The 95th percentile CdB levels for males (inclusive o f smokers) and females were 2.4 #g/1 a n d 2.0/xg/l, respectively. However, significant ethnic differences were observed a m o n g b o t h males a n d females. Indian males h a d the highest G M CdB level o f 0.48/~g/1, while a m o n g the females, the Chinese had the highest G M CdB, at 0.33 #g/l (Table 2). CdB levels showed a positive association with smoking history a m o n g the males. This correlation was especially evident a m o n g the I n d i a n males. A m o n g the non-smokers, significant ethnic differences were observed in some o f the groups for b o t h sexes (Table 2).
Table 1 Sex, ethnic group, age and smoking profiles of subjects Ethnic Group
All subjects Chinese Malay Indian
Male
Female
No a
Ageb
No a
Age b
128 [441 41 [9] 45 [19] 42 [161
38.0 (10.4) 37.8 (11.7) 37.0 (8.5) 39.4 (11.1)
150 [0] 51 [0] 59 [0] 40 [0]
34.2 ( 12.1) 36.5 (13.8) 30.0 (9.3) 35.1 (11.5)
aNumber of subjects in brackets [ ] refers to smokers. bMean age and standard deviation, in parentheses (), are given in years. the data. N o r m a l i t y o f the d a t a set was tested with P R O C U N I V A R I A T E before p r o c e e d i n g to further analysis. P R O C C O R R E L A T E was used to determine the correlation between variables. Differences in b l o o d c a d m i u m levels between ethnic groups were tested with P R O C G L M .
4. Discussion
3. Results
The results o f o u r study indicate that the geometric mean CdB levels o f n o n - s m o k i n g males and females in Singapore (0.21 #g/1 a n d 0.26/zg/1, respectively) are lower than those o f subjects in a
Table 1 shows the distribution o f the study subjects by sex, ethnic group, age and s m o k i n g his-
Table 2 Blood cadmium (CdB) levels of subjects by sex, ethnic group and smoking history Ethnic group
All subjects Chinese Malay Indian
Male
Female
All males
Non-smokers
Light smokers
Moderate smokers
All non-smokers
0.25 (1.17)
0.21 (1.08)
0.30 (1.35)
1128]
(84]
[19]
0.14 (0.88) [411 0.22 (1.18) [45] 0.48 (1.10) [421
0.15 (0.98) [32] 0.19 (1.02) [26] 0.35 (1.09) [261
0.1 ( - - ) [3] 0.31 (1.50) 1121 0.60 (0.87) [41
0.36 (1.27) [251 0.10 ( - - ) [6] 0.24 (1.16) [7] 0.85 (0.99) [ 121
0.26 (1.14) [1501 0.33 (1.16) [51] 0.18 (0.90) [591 0.26 (0.90) 1401
Geometric mean and geometric standard deviation ( ) of CdB in #g/1 and No. of subjects [ ] are given. Statistically significant differences were noted in CdB among males between (i) Chinese and Malays (P < 0.03), (ii) Chinese and Indians (P < 0.0001), and (iii) Malays and Indians (P < 0.001); among females between Chinese and Malays (P < 0.01); and among male non-smokers between (i) Chinese and Indians (P < 0.002), and (ii) Malays and Indians (P < 0.03).
122
number of major cities in the industrialised countries. Friberg and Vahter [1] reported GM CdB levels of 0.9/zg/l and 1.1 /zg/l, respectively, among non-smoking Japanese males and females in Tokyo, while non-smoking Belgian males and females in Brussels had GM CdB levels of 1.0/~g/1 and 0.9/~g/1, respectively. The levels found in our study are similiar to those reported among nonsmoking Swedish males and females in Stockholm: GM CdB levels of 0.1 /~g/1 and 0.3 /xg/1, respectively. Chia et al. [11] reported a mean CdB level of 7.57 t~g/l among workers exposed to cadmium in a nickel-cadmium battery factory in Singapore. Compared with our subjects, the levels of the cadmium-exposed workers show a 30-fold increase. As Singapore's industrialisation activities intensified in the early 1970s, one of the government's main concerns was the need to address the potential problem of environmental pollution. Since 1970, strict control of air and water pollution and the management of solid wastes have been top priorities, currently under the purview of the Ministry of the Environment. While air pollution levels at the time were in fact below those found in cities of the highly industrialised countries, new laws were, none the less, enacted to ensure effective emission control at source [12]. Existing factories were required to install pollution control equipment, while new factories were not allowed to operate until they complied with similar requirements. Thus, in spite of rapid industrialisation, Singapore has been able to keep environmental pollution under control. In 1990, overall air pollution levels remained low, well within the World Health Organisation (WHO) and US Environmental Protection Agency (EPA) standards [12]. This is reflected in the low CdB levels in our study population. With regard to smoking, the findings of the present investigation are consistent with those of previous reports which showed that smokers have higher levels of cadmium than non-smokers [3-5]. We noted a dose-effect relationship among the smokers for CdB concentration (Table 2). This observation was also made by Moreau et ai. in their study of 440 French civil service employees [13].
S.-E. Chia et al. / Sci. Total Environ. 145 (1994) 119-123
The reason for the ethnic differences observed in the CdB levels is not clear. One possible factor is the dietary habit of the subjects which may differ substantially between the Chinese, Malays and Indians. For example, the latter are known to consume large amounts of spices, more so than the other two ethnic groups. Sattar et al. [14] assayed different spices, dry fruits and plant nuts commonly consumed in Pakistan for cadmium, lead, copper, zinc, iron and manganese. They found that mixed spices generally exhibited higher values for trace metals, specifically cadmium, lead, iron and zinc. An analysis of some common spices consumed by local Indians in Singapore showed cadmium concentrations in cumin, turmeric, coriander, chilli and mustard of 0.009 mg/kg, 0.011 mg/kg, 0.012 mg/kg, 0.01 mg/kg and 0.013 mg/kg, respectively [ 15]. These values are higher when compared with cadmium concentrations reported in rice, which is the staple food for Chinese, Malays and Indians in Singapore. Wolnik et al. quoted in Ref. [161 reported a median cadmium concentration of 0.0045 mg/kg in rice from various regions in the USA. Another interesting finding was the relatively higher cadmium levels among the Chinese females of 0.33 #g/1 compared with 0.26/~g/1 among the Indian females, although the difference was not significant. Differences in dietary habit may also have contributed to this finding. Certain herbal tonics are popular among the local Chinese females and are quite widely consumed, particularly at the end of the menstrual period. An analysis of some of these common herbal preparations showed cadmium concentrations ranging from 0.008 mg/kg to 0.016 mg/kg [171. Unfortunately, in our study, details regarding the consumption of spices and herbal preparations among our subjects were not obtained. Further studies would be needed to confirm these hypotheses.
5. Acknowledgments We would like to thank Mr W.K. Chua, Ms B.T. Tan and Mrs S.L. Poon of the Department of Scientific Services, Institute of Science and Forensic Medicine, as well as Mrs M.H. Yeo and Ms
123
S.-E. Chia et al. / Sci. Total Environ. 145 (1994) 119-123
P.G. Koh of the Department of Industrial Health, Ministry of Labour, for their invaluable assistance in the study. This study was supported in part by Research Grant RP900339 from the National University of Singapore. We wish to record our appreciation for the generous cooperation of all subjects who participated in the study. 6. References 1 L. Friberg and M. Vahter, Assessment of exposure to lead and cadmium through biological monitoring: results of a UNEP/WHO global study. Environ. Res., 30 (1983) 95-128. 2 L. Fribeig, M. Piscator, G.F. Nordberg and T. Kjellstrom, Cadmium in the Environment, 2nd edn. C.R.C. Press, Cleveland, 1976, pp. 18-19. 3 A. Ulander and O. Axelson, Measurement of blood cadmium levels. Lancet, i (1974) 682. 4 R.L. Zielhuis, E.J. Struik, R.F.M. Herber, H.J.A. Salle, M.M. Verberk, F.D. Psoma and J.H. Jager, Smoking habits and levels of lead and cadmium in blood of urban women, Int. Arch. Occup. Environ. Health, 39 (1977) 53-58. 5 A. Brockhaus, I. Freier, U. Ewers, E. Jermann and R. Dolgner, Levels of cadmium and lead in blood in relation to smoking, sex, occupation and other factors in an adult population of the F.R.G. Int. Arch. Occup. Environ. Health, 52 (1983) 167-175. 6 J.P. Creason, D.I. Hammer, A.V. Colucci, L. Preister and J. Davis, Blood trace metals in military recruits. South. Med. J., 69 (1976) 289-293.
7
8 9
10 11
12
13
14
15 16
17
R.P. Sharma, T. Kjellstrom, J.M. McKenzie, Cadmium in blood and urine among smokers and non-smokers with high cadmium intake via food. Toxicology, 29 (1983) 163-171. M. Hutton, Sources of cadmium in the environment. Ecotoxicol. Environ. Safety, 7(I)(1983)9-24. M. Shariatpanahi and A.C. Anderson, Accumulation of cadmium, mercury and lead by vegetables following longterm land application of wastewater. Sci. Total Environ., 52(1-2) (1986) 41-47. J.C. Sherlock, Cadmium in foods and the diet. Experientia Suppl., 50 (1988) 177-183. K.S. Chia, C.N. Ong, H. Y. Ong and G. Endo, Renal tubular function of workers exposed to low levels of cadmium. Br. J. Ind. Med., 46 (1989) 165-170. Inter-Ministry Committee for the U.N.C.E.D. Preparatory Committee, Singapore, Singapore's National Report for the 1992 U.N. Conference on Environment and Development Preparatory Committee. Points Prespress Services Pte Ltd., Singapore, 1992, pp. 19-20. T. Moreau, J. Lellouch, B. Juguet, B. Festy, G. Orssaud and J.R. Claude, Blood cadmium levels in a general male population with special reference to smoking. Arch. Environ. Health 38 (1983) 163-167. A. Sattar, M. Wahid and S.K. Durrani, Concentrations of selected heavy metals in spices, dry fruits and plant nuts. Plant Foods Hum. Nutr., 39(3) (1989) 279-286. Department of Scientific Services; Institute of Science and Forensic Medicine, Singapore. Unpublished data, 1992. L. Friberg, C.G. Elinder and T. Kjellstrom, Cadmium. Environmental Health Criteria 134, World Health Organisation, Geneva, 1992, p. 56. Department of Scientific Services, Institute of Science and Forensic Medicine, Singapore. Unpublished data, 1992.
ELSEVIER
The Science of the Total Environment 145 (1994) 119-123
Blood cadmium levels in non-occupationally exposed adult subjects in Singapore S i n - E n g C h i a *a, O i - Y o k e C h a n b, C h e u c k - T a t t
S a m c, B e e - H o o n H e n g d
aDepartment of Community, Occupational and Family Medicine, National University of Singapore, Lower Kent Ridge Road, Singapore 0511, Singapore ~Department of Industrial Health, Ministry of Labour, Singapore, Singapore "Department of Scientific Services, Institute of Science and Forensic Medicine, Ministry of Health, Singapore, Singapore aQuarantine and Epidemology Department, Ministry of the Environment, Singapore, Singapore
(Received 2 January 1993; accepted 9 February 1993)
Abstract Cadmium concentrations in whole blood were measured in subjects with no occupational exposure to cadmium. The study covered 128 males and 150 females from the three main ethnic groups in Singapore (namely Chinese, Malays and Indians). The geometric means (GM) of blood cadmium (CdB) levels of non-smoking males and females were 0.21 #g/1 and 0.26/~g/1, respectively. Smokers had higher GM CdB levels than non-smokers. Significant ethnic differences were observed in both sexes, with Indian males having the highest GM CdB level of 0.48 #g/l. Among the females, the Chinese had the highest GM CdB level: 0.33 #g/l. Differences in dietary habits may have contributed to the observed ethnic differences in blood cadmium levels. Key words," Blood cadmium; Singapore; Population; Chinese; Malay; Indian
1. Introduction It is a well-known phenomenon that blood cadmium (CdB) levels vary considerably among the general population in different countries. Friberg and Vahter [1] in a global UNEP/WHO pilot project on assessment of human exposure to lead and cadmium, reported geometric mean values for CdB that ranged from 0.5 #g/1 in Stockholm and Jerusalem to 1.2 #g/l in Brussels and Tokyo [1]. * Corresponding author.
There are a number of reasons for this wide variation. Tobacco contains relatively high cadmium concentrations, varying between 1.0 and 2.0/~g/cigarette in cigarette brands usually smoked in the Western European countries; 10% of this cadmium is inhaled during smoking [2]. Smokers have, on the average, higher levels of cadmium in blood [3-5,]. Smoking patterns may differ from country to country. Individuals from heavily industrialised countries generally have higher mean CdB levels [ 11. Dietary
0048-9697/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved. SSDI 0048-9697(94)03663-M
120
habit, which to some extent is linked to environmental pollution, also determines the level of intake of cadmium [6,7]. Vegetables can have a higher content of cadmium if grown in land contaminated with cadmium as a result of uncontrolled waste disposal [8,9]. Similarly, some seafoods could be contaminated by industrial waste containing cadmium [10]. The wide variation in the CdB levels among different countries makes it difficult for any one country to adopt the standards or norms of another. It is therefore important for countries to determine and monitor levels of cadmium in their own populations. Such an approach may help to prevent trends of rising exposure, which could, if left unchecked, ultimately reach levels which have direct implications for human health. This study was conducted with the objectives of reporting the mean CdB levels among adult subjects in Singapore who have no known occupational exposure and determining if there are significant differences in CdB levels between the three major ethnic groups (namely Chinese, Malay and Indian). 2. Materials and methods
2.1. Study subjects The population covered comprised employees from government organisations and statutory boards, production workers, as well as individuals attending government health clinics. None of the subjects was known to have any specific exposure to cadmium other than those present in the general environment. In addition to their personal particulars, smoking history and details to determine possible cadmium exposure in the workplace as well as home environment were obtained by the interview method using a formally structured questionnaire. Smoking history was categorised as follows: (1) non-smokers, inclusive of ex-smokers who have stopped smoking for more than 1 year; (2) light smokers, subjects who smoked 1-10 cigarettes/day; (3) moderate smokers, subjects smoking 10-20 cigarettes/day; and (4) heavy smokers, those smoking more than 20 cigarettes/day.
S.-E. Chia et al./ Sci. Total Environ. 145 (1994) 119-123
2.2. Blood cadmium estimation About 2 ml of whole blood was obtained by venipuncture with informed consent from each participating subject. The samples were collected in heparinised tubes and subsequently analysed at the Industrial Health Laboratory of the Department of Scientific Services, Institute of Science and Forensic Medicine. Cadmium in blood was determined by graphite furnace atomic absorption spectroscopy using an external standard. A 400-#1 each of control blood (for 3 standards), blood blank, sample blood and reagent blank (distilled-deionised water) were added to each Corning (75 x 12 mm) test tube containing 400/~1 of concentrated nitric acid. The contents in the tubes were mixed thoroughly prior to heating on a block-heater at 50°C for 1 h followed by 3 h at l l0°C. Quantities of 10, 20 and 30 #1 of a 0.5 p.p.m. cadmium standard solution (cadmium nitrate) were added to each of the three tubes containing a control blood and mixed thoroughly. A 100-/~1 quantity of 60% perchloric acid was added to all the test tubes (standards, blood bank, regeant blank and samples) followed by heating at 130°C for 3 h and finally at 160°C for I h. A 2-ml quantity of distilled, deionised water was added to each tube, agitated on a vortex mixer and centrifuged. A 0.8-ml aliquot of a clear supernatant solution was transferred from each tube to a corresponding autosampler vial. The reagent blank was used to autozero the instrument. Analysis was carried out using the absorbance mode. The limit of detection was 0.2/~g/1. For computation purposes, CdB values which were below the detection limit were taken to be at half the detection limit. Quality assurance for the laboratory was through participation in external programmes with two centres: Centre de Toxicologie du Quebec (Canada) and the Health and Safety Executive (UK). 2.3. Statistics Statistical analysis was carried out on the IBM mainframe computer 3081 with the Statistical Analysis System (SAS). Logarithms of CdB levels were used to ensure a more normal distribution of
121
S.-E. Chia et al. / Sci. Total Environ. 145 (1994) 119-123
tory. The mean age o f the subjects was 36.0 years with a range o f 1 6 - 6 0 years. N o n e o f the w o m e n studied were smokers. There were m o r e smokers a m o n g the I n d i a n and M a l a y male subjects than the Chinese males. Age was not significantly c o r r e l a t e d (r = 0.01) with CdB levels. N o significant sex differences were noted in the geometric m e a n ( G M ) CdB. The 95th percentile CdB levels for males (inclusive o f smokers) and females were 2.4 #g/1 a n d 2.0/xg/l, respectively. However, significant ethnic differences were observed a m o n g b o t h males a n d females. Indian males h a d the highest G M CdB level o f 0.48/~g/1, while a m o n g the females, the Chinese had the highest G M CdB, at 0.33 #g/l (Table 2). CdB levels showed a positive association with smoking history a m o n g the males. This correlation was especially evident a m o n g the I n d i a n males. A m o n g the non-smokers, significant ethnic differences were observed in some o f the groups for b o t h sexes (Table 2).
Table 1 Sex, ethnic group, age and smoking profiles of subjects Ethnic Group
All subjects Chinese Malay Indian
Male
Female
No a
Ageb
No a
Age b
128 [441 41 [9] 45 [19] 42 [161
38.0 (10.4) 37.8 (11.7) 37.0 (8.5) 39.4 (11.1)
150 [0] 51 [0] 59 [0] 40 [0]
34.2 ( 12.1) 36.5 (13.8) 30.0 (9.3) 35.1 (11.5)
aNumber of subjects in brackets [ ] refers to smokers. bMean age and standard deviation, in parentheses (), are given in years. the data. N o r m a l i t y o f the d a t a set was tested with P R O C U N I V A R I A T E before p r o c e e d i n g to further analysis. P R O C C O R R E L A T E was used to determine the correlation between variables. Differences in b l o o d c a d m i u m levels between ethnic groups were tested with P R O C G L M .
4. Discussion
3. Results
The results o f o u r study indicate that the geometric mean CdB levels o f n o n - s m o k i n g males and females in Singapore (0.21 #g/1 a n d 0.26/zg/1, respectively) are lower than those o f subjects in a
Table 1 shows the distribution o f the study subjects by sex, ethnic group, age and s m o k i n g his-
Table 2 Blood cadmium (CdB) levels of subjects by sex, ethnic group and smoking history Ethnic group
All subjects Chinese Malay Indian
Male
Female
All males
Non-smokers
Light smokers
Moderate smokers
All non-smokers
0.25 (1.17)
0.21 (1.08)
0.30 (1.35)
1128]
(84]
[19]
0.14 (0.88) [411 0.22 (1.18) [45] 0.48 (1.10) [421
0.15 (0.98) [32] 0.19 (1.02) [26] 0.35 (1.09) [261
0.1 ( - - ) [3] 0.31 (1.50) 1121 0.60 (0.87) [41
0.36 (1.27) [251 0.10 ( - - ) [6] 0.24 (1.16) [7] 0.85 (0.99) [ 121
0.26 (1.14) [1501 0.33 (1.16) [51] 0.18 (0.90) [591 0.26 (0.90) 1401
Geometric mean and geometric standard deviation ( ) of CdB in #g/1 and No. of subjects [ ] are given. Statistically significant differences were noted in CdB among males between (i) Chinese and Malays (P < 0.03), (ii) Chinese and Indians (P < 0.0001), and (iii) Malays and Indians (P < 0.001); among females between Chinese and Malays (P < 0.01); and among male non-smokers between (i) Chinese and Indians (P < 0.002), and (ii) Malays and Indians (P < 0.03).
122
number of major cities in the industrialised countries. Friberg and Vahter [1] reported GM CdB levels of 0.9/zg/l and 1.1 /zg/l, respectively, among non-smoking Japanese males and females in Tokyo, while non-smoking Belgian males and females in Brussels had GM CdB levels of 1.0/~g/1 and 0.9/~g/1, respectively. The levels found in our study are similiar to those reported among nonsmoking Swedish males and females in Stockholm: GM CdB levels of 0.1 /~g/1 and 0.3 /xg/1, respectively. Chia et al. [11] reported a mean CdB level of 7.57 t~g/l among workers exposed to cadmium in a nickel-cadmium battery factory in Singapore. Compared with our subjects, the levels of the cadmium-exposed workers show a 30-fold increase. As Singapore's industrialisation activities intensified in the early 1970s, one of the government's main concerns was the need to address the potential problem of environmental pollution. Since 1970, strict control of air and water pollution and the management of solid wastes have been top priorities, currently under the purview of the Ministry of the Environment. While air pollution levels at the time were in fact below those found in cities of the highly industrialised countries, new laws were, none the less, enacted to ensure effective emission control at source [12]. Existing factories were required to install pollution control equipment, while new factories were not allowed to operate until they complied with similar requirements. Thus, in spite of rapid industrialisation, Singapore has been able to keep environmental pollution under control. In 1990, overall air pollution levels remained low, well within the World Health Organisation (WHO) and US Environmental Protection Agency (EPA) standards [12]. This is reflected in the low CdB levels in our study population. With regard to smoking, the findings of the present investigation are consistent with those of previous reports which showed that smokers have higher levels of cadmium than non-smokers [3-5]. We noted a dose-effect relationship among the smokers for CdB concentration (Table 2). This observation was also made by Moreau et ai. in their study of 440 French civil service employees [13].
S.-E. Chia et al. / Sci. Total Environ. 145 (1994) 119-123
The reason for the ethnic differences observed in the CdB levels is not clear. One possible factor is the dietary habit of the subjects which may differ substantially between the Chinese, Malays and Indians. For example, the latter are known to consume large amounts of spices, more so than the other two ethnic groups. Sattar et al. [14] assayed different spices, dry fruits and plant nuts commonly consumed in Pakistan for cadmium, lead, copper, zinc, iron and manganese. They found that mixed spices generally exhibited higher values for trace metals, specifically cadmium, lead, iron and zinc. An analysis of some common spices consumed by local Indians in Singapore showed cadmium concentrations in cumin, turmeric, coriander, chilli and mustard of 0.009 mg/kg, 0.011 mg/kg, 0.012 mg/kg, 0.01 mg/kg and 0.013 mg/kg, respectively [ 15]. These values are higher when compared with cadmium concentrations reported in rice, which is the staple food for Chinese, Malays and Indians in Singapore. Wolnik et al. quoted in Ref. [161 reported a median cadmium concentration of 0.0045 mg/kg in rice from various regions in the USA. Another interesting finding was the relatively higher cadmium levels among the Chinese females of 0.33 #g/1 compared with 0.26/~g/1 among the Indian females, although the difference was not significant. Differences in dietary habit may also have contributed to this finding. Certain herbal tonics are popular among the local Chinese females and are quite widely consumed, particularly at the end of the menstrual period. An analysis of some of these common herbal preparations showed cadmium concentrations ranging from 0.008 mg/kg to 0.016 mg/kg [171. Unfortunately, in our study, details regarding the consumption of spices and herbal preparations among our subjects were not obtained. Further studies would be needed to confirm these hypotheses.
5. Acknowledgments We would like to thank Mr W.K. Chua, Ms B.T. Tan and Mrs S.L. Poon of the Department of Scientific Services, Institute of Science and Forensic Medicine, as well as Mrs M.H. Yeo and Ms
123
S.-E. Chia et al. / Sci. Total Environ. 145 (1994) 119-123
P.G. Koh of the Department of Industrial Health, Ministry of Labour, for their invaluable assistance in the study. This study was supported in part by Research Grant RP900339 from the National University of Singapore. We wish to record our appreciation for the generous cooperation of all subjects who participated in the study. 6. References 1 L. Friberg and M. Vahter, Assessment of exposure to lead and cadmium through biological monitoring: results of a UNEP/WHO global study. Environ. Res., 30 (1983) 95-128. 2 L. Fribeig, M. Piscator, G.F. Nordberg and T. Kjellstrom, Cadmium in the Environment, 2nd edn. C.R.C. Press, Cleveland, 1976, pp. 18-19. 3 A. Ulander and O. Axelson, Measurement of blood cadmium levels. Lancet, i (1974) 682. 4 R.L. Zielhuis, E.J. Struik, R.F.M. Herber, H.J.A. Salle, M.M. Verberk, F.D. Psoma and J.H. Jager, Smoking habits and levels of lead and cadmium in blood of urban women, Int. Arch. Occup. Environ. Health, 39 (1977) 53-58. 5 A. Brockhaus, I. Freier, U. Ewers, E. Jermann and R. Dolgner, Levels of cadmium and lead in blood in relation to smoking, sex, occupation and other factors in an adult population of the F.R.G. Int. Arch. Occup. Environ. Health, 52 (1983) 167-175. 6 J.P. Creason, D.I. Hammer, A.V. Colucci, L. Preister and J. Davis, Blood trace metals in military recruits. South. Med. J., 69 (1976) 289-293.
7
8 9
10 11
12
13
14
15 16
17
R.P. Sharma, T. Kjellstrom, J.M. McKenzie, Cadmium in blood and urine among smokers and non-smokers with high cadmium intake via food. Toxicology, 29 (1983) 163-171. M. Hutton, Sources of cadmium in the environment. Ecotoxicol. Environ. Safety, 7(I)(1983)9-24. M. Shariatpanahi and A.C. Anderson, Accumulation of cadmium, mercury and lead by vegetables following longterm land application of wastewater. Sci. Total Environ., 52(1-2) (1986) 41-47. J.C. Sherlock, Cadmium in foods and the diet. Experientia Suppl., 50 (1988) 177-183. K.S. Chia, C.N. Ong, H. Y. Ong and G. Endo, Renal tubular function of workers exposed to low levels of cadmium. Br. J. Ind. Med., 46 (1989) 165-170. Inter-Ministry Committee for the U.N.C.E.D. Preparatory Committee, Singapore, Singapore's National Report for the 1992 U.N. Conference on Environment and Development Preparatory Committee. Points Prespress Services Pte Ltd., Singapore, 1992, pp. 19-20. T. Moreau, J. Lellouch, B. Juguet, B. Festy, G. Orssaud and J.R. Claude, Blood cadmium levels in a general male population with special reference to smoking. Arch. Environ. Health 38 (1983) 163-167. A. Sattar, M. Wahid and S.K. Durrani, Concentrations of selected heavy metals in spices, dry fruits and plant nuts. Plant Foods Hum. Nutr., 39(3) (1989) 279-286. Department of Scientific Services; Institute of Science and Forensic Medicine, Singapore. Unpublished data, 1992. L. Friberg, C.G. Elinder and T. Kjellstrom, Cadmium. Environmental Health Criteria 134, World Health Organisation, Geneva, 1992, p. 56. Department of Scientific Services, Institute of Science and Forensic Medicine, Singapore. Unpublished data, 1992.