Occup. Med. Vol. 48, No. 6, pp. 369-373, 1998
Copyright © 1998 Lippincott Williams & Wilkins lor SOM
Printed in Great Britain. All rights reserved
0962-7480/98
Lead exposure in the lead-acid
storage battery manufacturing
and PVC compounding
industries
S. F. Ho,* C. T. SamJ G. Bin Embi*
* Department of Industrial Healthy Ministry of Manpower, Singapore;
^Industrial Health Laboratory, Department of Scientific Services, Institute
of Science and Forensic Medicine, Ministry of Health, Singapore
This study was conducted as part of the Human Exposure Assessment Location (HEAL) Project
which comes under the United Nations Environment Programme/World Health Organisation
(UNEP/WHO) Global Environmental Monitoring System (GEMS). The objective of the study was
to evaluate workers' exposure to lead in industries with the highest exposure. All subjects were
interviewed about their occupational and smoking histories, the use of personal protective
equipment and personal hygiene. The contribution of a dietary source of lead intake from
specified foods known to contain lead locally and personal air sampling for lead were assessed.
A total of 61 workers from two PVC compounding and 50 workers from two lead acid battery
manufacturing plants were studied together with 111 matched controls. In the PVC
compounding plants, the mean lead-in-air level was 0.0357 mg/m 3 , with the highest levels
occuring during the pouring and mixing operations. This was lower than the mean lead-in-air
level of 0.0886 mg/m 3 in the lead battery manufacturing plants where the highest exposure was
in the loading of lead ingots into milling machines. Workers in lead battery manufacturing had
significantly higher mean blood lead than the PVC workers (means, 32.51 and 23.91 mcg/100
ml respectively), but there was poor correlation with lead-in-air levels. Among the lead workers,
the Malays had significantly higher blood lead levels than the Chinese (mean blood lead levels
were 33.03 and 25.35 mcg/100 ml respectively) although there was no significant difference
between the two ethnic groups in the control group. There were no significant differences
between the exposed and control group in terms of dietary intake of specified local foods
known to contain lead. However, Malays consumed significantly more fish than the Chinese
did. There were no ethnic differences in the hours of overtime work, number of years of
exposure, usage of gloves and respirators and smoking habits. Among the Malays, 94.3% eat
with their hands compared with 9.2% of the Chinese. Workers who ate with bare hands at least
once a week had higher blood lead levels after adjusting for lead-in-air levels (mean blood
lead was 30.2 and 26.4 mcg/100 ml respectively). The study indicated that the higher blood
lead levels observed in the Malay workers might have been due to their higher exposure and
eating with bare hands.
Key words: Absorption; ethnic differences; dietary intake; lead.
Occup. Med. Vol. 48, 369-373, 1998
Received 13 October 1997; accepted in final form 11 May 1998.
INTRODUCTION
Since 1985, workers in Singapore who are exposed to
inorganic lead are required to go for compulsory pre-
Correspondence and reprint requests to Dr Ho Sweet Far, Department
of Industrial Health, 18 Havelock Road, #05-01, Singapore 056497.
Tel: (+65)5397117; Fax: (+65)5395140; email: Sweet-Far-Ho@
MOM.GOV. SG
employment and 6-monthly examinations. These examinations include a clinical examination and an estimation
of the blood lead and haemoglobin levels.1 About 1,500
workers were examined in 1996.2 Factories with significant lead exposure are monitored regularly by the
Department of Industrial Health of the Ministry of Labour. It has been frequently observed that the levels of
,
^
d
R
}
J
*
2 3
correlated w i t h the lead-in-air concentrauons. The
results obtained f r o m occupational health surveillance o f
{
d
^
±
^
d
f
370 Occup. Med. Vol. 48, 1998
lead-exposed workers in Singapore have also shown an
apparent incongruity between environmental and biological monitoring data. Many workers with excessive lead
absorption do not have corresponding environmental
data that indicate a high degree of contamination of the
inspired air. The diagnosis of excessive lead absorption
was based on a blood lead level of 50 meg/100 ml or more
and the absence of signs and symptoms of lead poisoning.
It has been reported that parenteral intake from leadcontaminated hands and fingernails is an important cause
of lead absorption in the local lead-exposed workers,
especially since Malay and Indian workers customarily
eat with their bare hands, that is, without the use of
utensils.4 This study was conducted as part of the Human
Exposure Assessment Location (HEAL) Project which
comes under the UNEP/WHO Global Environmental
Monitoring System (GEMS). The objective was to evaluate workers' exposure to lead in industries and the contribution from dietary sources.
MATERIALS AND METHODS
Study subjects
A total of 111 male lead-exposed workers from the two
main ethnic groups (Malay and Chinese) and another
111 matched controls by ethnicity and within 5 years of
age were studied. The exposed workers were selected
from two lead-storage battery manufacturing factories
and two polyvinyl chloride (PVC) compounding plants.
These factories were selected from a total of 67 factories
as they represent the highest exposure situations locally
based on blood lead results. The risk of lead exposure in
these two types of industries comes from the smelting of
lead ingots and the handling of lead paste in battery
manufacturing, and the weighing and pouring of lead
power in the PVC compounding plants.
was utilized for the determination of lead in blood. In this
analysis, 100 ul heparinized whole blood were diluted
1:10 in an ammonium dihydrogen phosphate matrix
modifier containing 0.5% v/v Triton X-100, 0.2% w/v
ammonium dihydrogen phosphate and 0.2% v/v nitric
acid. Aqueous standards of lead nitrate, 20 ug/dl,
40 ug/dl, 50 ug/dl and 60 ug/dl diluted in the chemical
matrix modifier were used for calibration purposes. 12 ul
of the diluted blood, standards and chemical modifier
blank were dispensed by an autosampler on the L'vov
platform of a pyrolytically coated graphite THGA tube
for analysis. External quality assurance was carried out in
collaboration with the Centre de Toxicologie du Quebec,
Canada.
Environmental monitoring
Lead-in-air monitoring for the lead-exposed workers was
conducted by personal sampling, with the sampling
head attached to the subject's lapel. For each subject
monitored, two consecutive samples were taken to cover
the 6 h workshift. Lead levels of the non-exposed controls
and those in ambient air were monitored by static (area)
sampling, with the sampling head placed at a representative work locations. At each location monitored, a single
6 h sample was collected. The sampler consisted of
a mixed cellulose-ester filter (37 mm diameter, 0.8 micron pore size) mounted on a three-piece cassette holder
and connected by a plastic tubing to a sampling pump.
The pumpflowrate was regulated at 1.5 litres per minute
and checked at least hourly using a calibrated rotameter.
The lead content of the filters was analyzed at DSS,
ISFM, using flame ionization atomic absorption spectrophotometry. External quality assurance was carried out in
collaboration with the Health and Safety Executive
(United Kingdom), Workplace Analysis Scheme for
Proficiency.
Statistical analysis
Questionnaire
All subjects were interviewed with regard to their occupational and smoking histories, usage of personal protective
equipment and personal hygiene practices such as hand
washing before meals. To quantify the lead contribution
from dietary sources, the types and frequency of food or
drink (known to contain lead in the local context) consumed and the usage of glazed crockery during a 24-hour
period over the past workweek was noted (Appendix 1)
using photographs and pictures. Data on overtime work
was obtained from the factories.
Blood lead estimation
About 2 ml of heparinized blood was collected from each
worker and submitted for lead analysis by the Industrial
Health Laboratory of the Department of Scientific Services, Institute of Science and Forensic Medicine (DSS,
ISFM). Strict precautions were taken to avoid sample
contamination. A rapid Zeeman graphite furnace atomic
absorption spectrometric method with L'vov platform
The data were analyzed using the Statistical Analysis
System (SAS) software package. Step wise multiple linear
regression analysis was used to evaluate the proportions
of the variance in blood lead that were explained by
factors related to lead exposure.
RESULTS
A total of 61 workers from two PVC compounding and
50 workers from two lead acid battery manufacturing
plants were studied together with 111 matched controls.
Their mean age was 38.33 years (range = 19-62 years).
The exposed workers, comprised 76 Chinese and 35
Malays, had worked an average of 119.44 months in their
respective sections (range = 2-313) on a weekly rotating
8 h shift. Eating, drinking and smoking were prohibited
during work.
The air levels in these plants were well below the
American Conference of Governmental Industrial Hygienists (ACGIH)5 recommended threshold limit value of
S. F. Ho et al.: Battery manufacturing and PVC compounding industries
0.15 mg/m3. In the lead battery manufacturing plants, the
mean lead-in-air was 0.0886 mg/m3 (SD = 0.1763) in the
area of highest exposure (loading of lead ingots into
milling machines). This was higher than the mean leadin-air of 0.0357 mg/m3 (SD = 0.0624) in the PVC compounding plants where the highest exposure was during
the pouring and mixing of lead powder.
The mean blood lead levels of the exposed workers and
controls were 27.78 (SD = 11.84) and 6.82 (SD = 3.23)
meg/100 ml respectively. There was no significant difference in blood lead levels between the two ethnic groups in
the control group.
The mean blood lead concentration was 32.51 and
23.91 meg/100 ml in the lead battery manufacturing and
PVC compounding workers respectively. Workers in the
lead battery manufacturing plant had significantly higher
mean blood lead than the PVC workers. This corresponded to their higher exposure. However, there was poor
correlation between the workers' blood lead and personal
lead-in-air levels (Table 1). There was no significant
difference in blood lead levels between smokers and nonsmokers. Workers with blood lead levels of more than
40 meg/100 ml were found to have done significantly
more overtime work over the last month but there was no
significant correlation with the present and total duration
of exposure (r=0.06).
Among the lead workers, more Malays were employed
in the lead battery manufacturing than the PVC compounding plants (40% in the lead battery and 24.6% in
the PVC manufacturing plants). Table 2 shows the type
of differences between the two exposed ethnic groups,
Malays and Chinese. Exposed Malays had significantly
higher blood lead levels than Chinese (mean blood lead
levels were 33.04 and 25.35 mcg/100 ml, respectively)
and higher personal lead-in-air levels. A large number of
Malays (94.3%) frequently ate with their bare hands
compared with 9.2% of the Chinese. Workers who eat
using their bare hands at least once a week had significantly higher blood lead levels after adjusting for lead-inair levels (mean levels of blood lead were 30.2 and 26.4
mcg/100 ml for those using hands and those not using
hands, respectively). Except for higher fish consumption
among the Malays, there was no significant difference in
the type of food, e.g., crabs, prawns, brinjals/egg plant,
condiments, Chinese herbal, milk or canned fruit drinks
consumed among the two ethnic groups. There were
no ethnic differences in the hours of overtime work,
number of years of exposure, number of cigarettes
smoked, usage of gloves and respirators and glazed
cookery.
Multiple linear regression analysis was used to evaluate
the proportions of variance in blood lead that were determined by lead-in-air levels, fish intake and ethnicity.
Lead-in-air exposure explained 7.6% of the variance in
blood lead levels, ethnic differences accounted for 9.2%
and washing of hands explained 4.6%, while fish consumption explained only 0.06% of this level in the exposed group (non-significant for fish consumption).
When these factors were considered together, the difference in blood lead levels could be explained by 14.24%
(Table 3). In terms of rank order, ethnic differences
ranked first, followed by air lead and washing of hands.
DISCUSSION AND CONCLUSION
In Singapore, the enforcement of hygiene and medical
surveillance programmes and the implementation of
Table 1 . Mean air and blood lead levels by industry
Industry
No.
Mean lead-in-air
(mg/m3)
r
Mean blood lead
(mcg/100 ml)
P value
PVC compounding
61
0.0357 (ND-0.2770)
0.0624*
0.33
23.91 (6.7-75.8)
13.06*
0.0094
Lead acid battery
manufacturing
50
0.0886 (ND-1.140)
0.1763*
0.26
32.51 (19.1-50.9)
8.01*
0.0707
Note: Range shown within parentheses.
ND = Not Detectable.
* = Standard Deviation.
Table 2. Differences between the two exposed ethnic groups
Nature of differences
Mean lead-in-air levels (mg/m3)
Mean blood lead (mcf/100 ml)
Percentage of workers using bare hands to eat
Mean fish consumption over the last one week
Note: * = Student's f-test.
' = Pearson's continuity correction.
371
Chinese
(n = 35)
P value
(n = 76)
0.098 ±0.195
33.04
94.3
6.35
0.041 ± 0.078
25.35
9.2
2.65
0.0285*
0.001*
0.0001'
0.007*
Malays
372 Occup. Med. Vol. 48, 1998
Table 3. Multiple linear regression analysis of blood lead on
lead exposure variables
R2
F value
Prob > F
Race
Air lead levels
Washing of hands
Fish consumption
0.0916
0.0764
0.0455
0.0063
10.995
9.020
5.195
0.690
0.0012
0.0033
0.0246
0.4079
Total
0.1424
4.401
0.0025
Lead exposure variables
engineering control measures have markedly reduced the
incidence of lead poisoning. However, cases of lead overabsorption are still seen. Frequently, such cases occur in
areas where the environmental lead exposure is below the
recommended threshold limit value of 0.15 mg/m3.5 In
our study, the three cases of overabsorption were exposed
to air levels of between 0.004 and 1.140 mg/m3. There
was a poor correlation between blood and environmental
lead levels as reported in other studies.4'6'7 It has been
reported that other influencing factors such as ethnicity,
Chinese herbal drug consumption and dietary intake
from acidic canned food are important considerations
when examining ways to prevent overexposure to
lead.8"10
The present study showed that the higher blood lead
levels observed in local Malays may have been contributed to by their higher exposure (more Malays were
employed in the lead battery manufacturing than the
PVC compounding plants) along with their custom of
using bare hands for eating. Studies have shown significant contamination of the hands despite the use of gloves
and the apparent cleanliness of the hands.4'7 This may
explain the higher blood lead levels found in workers who
ate with their hands. The results of another study of
lead-exposed workers pointed to a strong effect of
hygienic behaviour (and in particular, ingestion-related
hygienic behaviour) on the lead-in-air and lead-in-blood
relationship.11 These observations of lead ingestion
through hand contamination are supported by the results
of previous studies in children.12"14
In this study, the lead contribution from smoking,
consumption of specific foods, Chinese herbs and the use
of glazed crockery which were reported to contain lead
were found to be insignificant compared to other studies.15"17 However, workers with higher levels of overtime
work and environmental lead exposure had significantly
higher blood lead levels. Multiple linear regression analysis used to evaluate the proportions of variance in blood
lead showed that ethnicity ranked first, followed by air
lead and washing of hands. As ethnic differences are
related to personal practices, this study confirmed that the
route of absorption in local Singapore workers is mainly
through ingestion from using bare contaminated
hands to eat. This was supported by findings in other
studies.4'7'18
These results suggest that local risk factors such as the
personal habit of eating with bare hands and environmental exposure are important influencing factors of
overabsorption of lead. Thus, to reduce the risk of lead
overabsorption, measures should be directed towards re-
ducing these risk factors. The implementation of a programme of reinforcing hand washing and mouth rinsing
(rinsing their mouth with water) before meals resulted in
a reduction of the blood lead level by 11.5% in one local
study.4
ACKNOWLEDGEMENTS
The authors are grateful to the permanent Secretary
(Labour) for permission to quote from departmental records. We would like to thank staff nurse Goh Yim Chin
for helping with the data collection. We also like to thank
Mrs Tan Wei Ling and Dr Mabel Yap of the Food
and Nutrition Department, Ministry of Health for
their assistance in planning the dietary questionnaire
survey and training on data collection. Our thanks also
to Mr Chua Wee Kian, Ms Tan Buay Ting and Mrs
Poon Siew Lan from the Department of Scientific
Services for carrying out the sample analysis. Finally, we
would like to thank the workers and management of the
factories where this study was conducted for their kind
co-operation.
REFERENCES
1. Republic of Singapore Government Gazette S4/97. The
Factories (Medical Examinations) Regulations, 1997.
2. Department of Industrial Health. Annual report 1996.
Singapore: Department of Industrial Health, Ministry of
Labour.
3. Phoon WH, Lee HS, Ho CK. Biological monitoring of workers
exposed to inorganic lead in Singapore. Singapore MedJ 1990;
31: 127-130.
4. Ho SF, Ng TP, Chan YK, Kwok SF, Chua WK, Chong KY.
An evaluation of the significance of mouth and hand contamination for lead absorption in lead-acid battery workers. IntArch
Occup Environ Health 1993; 64: 439-443.
5. American Conference of Governmental Industrial Hygienists.
1997 TLVs and BEIs. Threshold limit values for chemical
substances and physical agents and biological exposure indices.
American Conference of Governmental Industrial Hygienists,
1997.
6. Booher LE. Lead exposure in a ship overhaul facility during
paint removal. Am Ind Hyg AssocJ 1988; 49: 121-127.
7. Roels HA, Butchet JP, True J, Croquet F, Lauwerys RR. The
possible role of direct ingestion on the overall absorption of
cadmium or arsenic in workers exposed to CdO or As2O3 dust.
Am J Ind Med 1982; 3: 53-65.
8. Liou SH ; Wu TN, Chiang HC, et al. Three-year study of blood
lead levels in 8828 Taiwanese adults. Int Arch Occup Environ
Health 1996; 68: 80-87.
9. Chavalitnitikul C. A study of the qualitative contribution
of the multiple sources of lead exposure in the industrial environment [Thesis]. Philadelphia, PA (USA): Drexel University,
1981.
10 Silbergeld Ellen K. The international dimensions of lead exposure. IntArch Occup Environ Health 1995; 1: 336-348.
11 Ulenbelt P, Lumens MEGL, Geron HMA, Herber RFM,
Broersen S, Zielhuis RL. Work hygiene behaviour as modifier
of the lead air-lead blood relation. Int Arch Occup Environ
Health 1990; 62: 203-207.
12 Roels HA, Buchet JP, Lauwerys RR, et al. Exposure to lead by
the oral and the pulmonary routes of children living in the
vicinity of a primary lead smelter. Environ Res 1980; 32:
81-94.
S. F. Ho et a/.: Battery manufacturing and PVC compounding industries
13. Charney E, Sayre J, Coulter M. Increased lead absorption in
inner city children. Where does the lead come from? Pediatrics
1980; 65: 226-231.
14. Lepow ML, Bruckman L, Gillette M, Makowitz S, Rabino R,
Kapish J. Investigations into sources of lead in the environment
of urban children. Environ Res 1975; 10: 415-426.
15. Gerhardsson L, Kazantzis G, Schutz A. Evaluation of selected
publications on reference values for lead in blood. ScandJ Work
Environ Health 1996; 22: 325-331.
373
16. Gonzalez de Mejia E, Craigmill AL. Transfer of lead from
lead-glazed ceramics to food. Arch Environ Contam Toxicol
1996; 31: 581-584.
17. Hernandez-Avila, Romieu I, Rios C, et al. Lead glazed ceramics: major determinants of blood lead levels in Mexican women.
Environ Health Perspect 1991; 94: 116-120.
18. Barry PSI. Lead: occupational and environmental exposure. In:
Gardner AW, ed. Current approaches to occupational medicine. Bristol, UK: John Wright and Sons Ltd, 1979: 1-17.
APPENDIX 1.
How often do you take the following types of food over the last one week?
Food
a)
b)
c)
d)
e)
f)
g)
h)
i)
j)
k)
1)
m)
n)
o)
p)
q)
Reference portion
Nuts (70 g)
Prawns (53 g)
Crabs (13 g)
Sotong (46 g)
Fish (80 g)
Milk (250 g)
Butter/margarine (5 g)
Century eggs (52 g)
Duck eggs (52 g)
Canned food e.g. sardines, curry, beans (40 g)
Canned fruit drinks/juices (9,285 g)
Lentils (90 g)
Tomato (114 g)
Brinjals (90 g)
Ladies' finger (45 g)
Cockles, clams, mussels (15 g)
Alcoholic beverages including beer
1/2 cup
5 medium
1 tablespoon
1 small
1 portion
1 glass
1 teaspoon
1
1
1
1 can
1/2 cup
1
1/2 cup
5 pods
10
1 std drink
How often do you use the following items over the last
one week?
Items
a)
b)
c)
d)
e)
f)
Condiments, pepper, spices, curry powder
Oyster sauce
Tomato ketchup
Glazed crockery
Belachan
Herbs
No. of times
used per
week
Amount taken
No. of times taken
per week