A survey to evaluate the association
between blood lead level and blood pressure among workers employed in factory
manufacturing lead acid-storage batteries
Kalahasthi R.B, PhD *, Barman T, MPharm, Rajmohan
HR, M.B.B.S, DNB (Occupational Health)
Regional Occupational Health Centre
(Southern) , Nirmal Bhavan, ICMR Complex, Kannamangala (Post), Devanahalli,
Bangalore-562110, Karnataka,
India.
Abstract
Received: September 2012, Accepted: December
2013
Background: There are
many controversies reported about the association between blood lead levels
and blood pressure among lead exposed workers. Studies have suggested
incorporating lifestyle factors along with blood lead levels. The present
study aimed to evaluate the effect of lead exposure on blood pressure changes
among lead exposed workers in contemplation of lifestyle factors. Materials and methods: Study design
is descriptive. Three hundred ninety one male lead exposed workers were
enrolled. The subjects were categorized into four groups according to their
blood lead levels by using quartile distribution. Blood lead levels were
measured by using an atomic absorption spectrophotometer. Blood pressure was measured by using a
standard mercury sphygmomanometer. Data were analyzed by using SPSS (Version 7.5).
Results: The mean systolic blood pressure in
quartile-2 blood lead levels and the prevalence of hypertensive in quartile-4
blood lead levels were significantly increased as compared to quartile-1
blood lead levels. Multiple regression analysis found no significant
association between blood pressure and blood lead levels among lead exposed
workers. The lifestyle factors such as alcohol consumption, smoking, body
mass index and chewing of tobacco products were significantly associated with
blood pressure changes among lead exposed workers. Conclusion: The findings of the present study
showed that there was a significant association noticed between blood
pressure and lifestyle factors. |
Keywords: Lead, workers, blood pressure
Hazardous chemicals
used in manufacturing of lead-batteries are lead oxide (PbO2),
spongy lead (Pb) and sulfuric acid (H2SO4). The workers
engaged in those processes are exposed to Pb through inhalation, ingestion and
dermal contact. Lead enters into the body of workers by inhalation, ingestion
and dermal contact. After entry into the body, lead will be accumulated in
erythrocytes, soft and mineralized tissue. Occupationally exposure to Pb has a
higher risk of cardiovascular disease as compared to the general population (1)
and predicted the left ventricular diastolic dysfunction and local arterial*
stiffness (2). Acute exposure of Pb has elevated the arterial blood pressure
due to disorder of intracellular calcium ions, increased activities of
angiotensin-converting enzyme, Na (+), K (+)-ATPase, matrix metalloproteinase
and decreased activity of nitric oxide synthase (3-5). Occupational exposure to
Pb had the dose response association between BLL and blood pressure changes in
workers employed in galleries of mine (3), battery recycling (6), automobile
(7), tile factory (8), apprentices in lead exposed plants (9), crystal glass
(10) bus drivers (11), firearm instructors (12), exhaust battery storage (13), and
crystal toy making (14). Some of the studies have reported the relation between
blood lead and blood pressure in lead battery workers (15-17). Navaho et al.
(18) have reported that the BLL had no clinically significant effect on blood
pressure and suggested following up of lifestyle predictors to be evaluated.
Therefore, in this study, we decided to find the correlation between BLL with
blood pressure changes among workers employed in a lead battery factory with
contemplation of lifestyle factors.
Materials and Methods
The
present study was carried out in male lead exposed subjects engaged in a lead
acid-storage battery manufacturing plant located in Tamil Nadu (India).
Research design is a descriptive study. For this study, sample sizes of 391
male lead exposed subjects were obtained by using target population 400,
confidence level 99% and margin of error 1%. The study subjects were
categorized into four groups according to their BLL using quartile
distribution. Informed consent was obtained from the subjects included in the
study.
A
pre-designed pro-forma was used to collect the information related to
socio-demographic characteristics, personal habits like alcohol consumption,
smoking, dietary pattern, chewing of tobacco products and details of
occupational history. Body mass index (BMI) was calculated by using height and
weight of each subject and expressed as Kg/m2.
Three
ml of venous whole blood was collected in heparinized vacutte from the workers
and stored at -20oC until taken for analysis. Two ml of blood were
digested using ETHOS-D, milestone microwave system (Italy) with two ml of
nitric acid (HNO3) and 0.2 ml of hydrogen peroxide (H2O2)
by maintaining power, temperature and duration of time. The digested samples
were made up to five ml using triple distilled water and centrifuged. The
concentration of lead in blood was measured by using an atomic absorption
spectrophotometer (GBC-Avanta P. Australia). A known concentration of lead
standard solution was digested and analyzed to serve as internal quality
control. The recovery rate of 20 µg/dL of the standard lead solution was found
in 100% with % RSD at < 0.5. The BLL was expressed as μg/dL.
Data
were analyzed by using SPSS (version 7.5). The student-t test was used to
compare the mean levels of blood lead, age, BMI, experience, systolic and
diastolic blood pressure among lead exposed workers. A chi-square test was used
to compare the proportion of alcohol consumption, smoking habits and prevalence
of systolic and diastolic blood pressure among lead exposed workers. Stepwise
multiple regression analysis was used to assess the effect of blood lead and
lifestyle factors on blood pressure among lead exposed workers.
Results
Descriptive
characteristics of lead exposed workers are presented in table 1. The mean and
standard deviation of blood lead levels, age, experience, BMI and proportions
of alcohol consumption and smoking habits were reported in lead exposed
workers. The mean blood lead levels of Q2, Q3 & Q4 were significantly
increased as compared to BLL of Q1. The means quartiles of blood-lead levels of
Q1 to Q4 were ranged from15-44µg/dL. The proportions of smoking habits were not
significantly associated. Alcohol consumption proportion in Q4 blood lead
levels was significantly (P=0.048) associated as compared to the lowest
quartile.
Table
1: Descriptive characteristics of lead exposed workers
Characteristics |
Total (N-391) |
Blood lead Quartile |
|||
Quartile1 (N=101) |
Quartile 2 (N=107) |
Quartile 3 (N=90) |
Quartile 4 (N=93) |
||
Blood lead levels (µg/dL) |
27.6 ± 11.4 |
15.1 ± 1.3 |
22.0 ± 2.5 |
31.3 ± 3.1 |
44.0 ± 6.3 |
Age(years) |
34.5 ± 4.5 |
35.5 ± 3.4 |
34.6 ± 4.7 |
35.1 ± 4.5 |
32.5 ± 4.9 |
Body mass index (Kg/m2) |
24.7 ± 2.7 |
24.9 ± 2.4 |
25 ± 2.7 |
24.8 ± 2.6 |
24.8 ± 2.9 |
Experience (Years) |
11.3 ± 3.0 |
12.4 ± 1.9 |
11.3 ± 3.2 |
11.4 ± 2.8 |
10.0 ± 3.4 |
Alcohol consumption (%) No |
37.0 63.0 |
31.0 69.0 |
29.0 71.0 |
45.0 55.0 |
46.0* 54.0 |
Smoking habit (%) Yes No |
19.0 80.0 |
15.0 85.0 |
19.0 81.0 |
23.0 77.0 |
22.0 78.0 |
*P<0.05
Table
2 shows the mean systolic and diastolic blood pressure and its prevalence of
hypertension in lead exposed workers according to their BLL. Mean SBP in
Quartile2 blood lead levels was significantly (P=0.020) increased as compared
to the quartile1. The prevalence of systolic hypertension was significantly
(P=0.032) increased in Q4 blood lead levels as compared to the Q1. The mean
diastolic blood pressure and its prevalence of hypertension were not
significantly associated in Q2, Q3 & Q4 blood lead levels as compared to the Q1.
A difference in blood-lead levels between the lowest Q1 and Q2, Q3 and Q4 was
associated with a difference of 4.3, 1.5 and 3.0 mmHg in SBP and 2.2, 1.0 &
1.0 mmHg in DBP.
Table
2: Distribution of blood pressure-related variables in lead exposed workers
Characteristics |
Total (N-391) |
Blood lead Quartile |
|||
Quartile1 (N=101) |
Quartile 2 (N=107) |
Quartile 3 (N=90) |
Quartile 4 (N=93) |
||
Blood
pressure Systolic (mmHg) Diastolic( mmHg) |
125.7 ± 13.8 79.5 ± 7.8 |
123.5 ± 11.6 78.5 ± 7.3 |
127.8 ± 14.7 80.7 ± 8.0 |
125.0 ± 13.0 79.4 ± 7.8 |
126.5 ± 15.5 79.4 ± 7.9 |
Hypertension
(%) Systolic
≥140 mmHg Diastolic
≥90 mmHg |
20.0 15.0 |
13.0 11.0 |
22.0 16.0 |
20.0 18.0 |
26.0* 16.0 |
*P<0.05
Table 3 shows the multiple regression analysis of
variables effect on the systolic and diastolic blood pressure among lead
exposed workers. The variables, included in the regression model, were systolic
(SBP) and diastolic (DBP) pressure used as dependent variables and age, alcohol
consumption, BLL, BMI, experience, smoking and chewing of tobacco products were
used as independent variables. The multiple regression analysis showed that the
alcohol consumption influences 13% on SBP in Q1 BLL. In Q2, blood-lead levels
in the alcohol consumption, BMI, smoking and chewing of tobacco products
influenced the 20% on SBP. In Q4 BLL, the BMI and chewing of tobacco products
were associated with 17% for SBP. Chewing of tobacco products influences 14% on
DBP in Q2 BLL. BMI influences 9.1% on DBP with BLL of Q4.
.
Table
3: Un-standardized regression coefficients (β), standard error (SE) and
probability (P) for blood lead, systolic and diastolic pressure in lead exposed
workers
|
Blood lead Quartile |
|||
Quartile1 (N=101) |
Quartile 2 (N=107) |
Quartile 3 (N=90) |
Quartile 4 (N=93) |
|
Systolic blood pressure(mmHg) |
||||
R2 |
13 β
SE P |
20 β
SE P |
7 β
SE P |
17 β
SE P |
Age(years) Alcohol BLL(µg/dL) BMI(Kg/m2) Exp(years) Smoking Tobacco chewing |
0.447 (0.367) 0.223 5.144 (2.512) 0.043* 1.618 (0.900) 0.075 0.365 (0.481) 0.449 0.784 (0.646) 0.227 5.238 (3.549) 0.143 13.130 (6.875) 0.059 |
0.608 (0.322) 0.062 8.547 (2.958) 0.005* 0.288 (0.524) 0.584 0.995 (0.498) 0.048* 8.001 (0.465) 0.861 9.307 (3.531) 0.010* 15.202 (5.484) 0.007* |
0.510 (0.373) 0.174 0.742 (3.095) 0.811 0.254 (0.452) 0.575 0.834 (0.551) 0.134 7.001 (0.577) 0.897 5.160 (3.854) 0.184 3.065 (7.990) 0.702 |
1.008 (0.427) 0.965 5.079 (3.408) 0.140 0.439 (0.250) 0.083 1.451 (0.568) 0.012* 0.358 (0.599) 0.551 2.150 (4.059) 0.598 9.220 (4.315) 0.035* |
Diastolic blood pressure(mmHg) |
||||
R2 |
8 β
SE P |
14 β
SE P |
8.6 β
SE P |
9.1 β
SE P |
Age(years) Alcohol BLL(µg/dL) BMI(Kg/m2) Exp(years) Smoking Tobacco chewing |
0.007 (0.234) 0.757 2.132 (1.616) 0.190 0.823 (0.579) 0.158 0.137 (0.309) 0.659 0.553 (0.415) 0.186 4.380 (2.283) 0.058 3.707 (4.424) 0.404 |
0.262 (0.184) 0.158 2.708 (1.689) 0.112 0.223 (0.299) 0.458 0.418 (0.284) 0.144 0.121 (0.266) 0.227 5.238 (3.549) 0.649 7.591 (3.131) 0. 017* |
0.119 (0.222) 0.593 0.999 (1.843) 0.589 0.470 (0.269) 0.085 0.390 (0.328) 0.238 0.008 (0.343) 0.806 2.047 (2.294) 0.375 6.116 (4.424) 0.202 |
0.008 (0.228) 0.712 1.544 (1.824) 0.400 0.161 (0.134) 0.233 0.638 (0.304) 0.039* 0.001 (0.321) 0.953 0.995 (2.173) 0.648 1.467 (2.310) 0.527 |
*P<0.05
The present study aimed to assess the effect of lead exposure on blood
pressure changes among workers employed in a lead battery factory with
consideration of lifestyle factors. The mean SBP in Q2 and its prevalence of
hypertension in Q4-blood-lead levels were significantly increased as compared
to the lowest Q1 BLL. Multiple regressions analysis showed that lifestyle
predictors such as alcohol consumption, smoking, body mass index and chewing of
tobacco products were significantly associated with blood pressure changes, but
the BLL did not serve as a good predictor of blood pressure changes among
workers. The findings of this study were comparable with other studies reported
as no association between BLL and blood pressure changes in workers exposed to
Pb from lead battery factories was found (15-18). The significant association
was noticed between blood pressure changes and blood lead levels in workers
from galleries of mine (3), battery recycling (6), automobile workers (7), tile
factory workers (8), apprentices in lead exposed plants (9), crystal glass (10)
bus drivers (11), firearm instructors (12), exhaust battery storage (13),
crystal toy making (14), The findings of the present study showed that the only
lifestyle predictors such as alcohol consumption, smoking, body mass index and
chewing of tobacco products were significantly associated with blood pressure
changes in workers and there was no statistically significant association
between blood lead levels and blood pressure.
Conclusions
Mean SBP in Q2 blood lead levels and its prevalence of hypertensive in Q4
blood lead levels significantly increased as compared to the Q1 BLL. The
lifestyle factors such as alcohol consumption, smoking, body mass index and
chewing of tobacco products were significantly associated with systolic and
diastolic blood pressure changes among workers.
Acknowledgement
The authors
would like to thank Dr P.K Nag, the Director at the National Institute of
Occupational Health (Ahmadabad), for his encouragement and support. The authors
are also grateful to V Sehar, NSM siddaiah and N Thara for their technical
assistance. Last, but not least, the authors are grateful to the workers who
participated in the study.
Conflict of interest: Non
declared
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*Corresponding author: Ravibabu kalahasthi, Regional Occupational Health Centre, Nirmal Bhavan,
Bangalore, Karnataka, India.
E-mail: kalahasthi20012002@yahoo.co.in