ORIGINAL ARTICLE
The Impact of Reduced Dust Exposure on Respiratory Health Among Cement Workers An Ecological Study Alexander Mtemi Tungu, MD, Magne Br˚atveit, PhD, Simon H. Mamuya, PhD, and Bente E. Moen, PhD
Objectives: To compare total dust exposure, prevalence of chronic respiratory symptoms, lung function, and chronic obstructive pulmonary disease (COPD) among Tanzanian cement workers before (2002) and after (2010–2011) establishment of dust-control measures. Methods: Personal total dust-exposure measurements, questionnaire assessment for chronic respiratory symptoms, and spirometry were conducted in both examination periods. Results: Total dust exposure was lower in 2010–2011 than in 2002. The prevalence of most chronic respiratory symptoms and COPD was lower in 2010 than in 2002. Forced expiratory volume in 1 second (FEV1 ), percentage predicted FEV1 , and percentage predicted forced vital capacity were higher among cement workers in 2010 than in 2002. Conclusions: There was reduced total dust exposure level, lower prevalence of chronic respiratory symptoms and COPD, and higher lung function among cement workers in 2010 than in 2002.
P
revious studies have suggested a relationship between dust exposure and adverse respiratory health effects among workers in cement factories.1–5 A multicenter cross-sectional study among European cement workers found a higher prevalence of chronic respiratory symptoms among cement workers compared with controls.4 A higher prevalence of chronic respiratory symptoms and chronic obstructive pulmonary disease (COPD) were found among Tanzanian cement production workers compared with maintenance and administrative controls.5 Few follow-up studies on respiratory health and dust exposure exist in cement factories.6,7 A prospective follow-up study among highly exposed Ethiopian cement workers reported an increase in prevalence of chronic cough (with or without phlegm) and dyspnoea, as well as reduction of lung function (forced expiratory volume in 1 second [FEV1 ], and the ratio of FEV1 to forced vital capacity [FEV1 /FVC]) among the exposed after only 1 year, but not among controls.8 Some studies conducted in developed countries found no association between dust exposure and adverse chronic health effects.9–12 This could be due to low dust-exposure levels as a result of more efficient dust-control measures in these factories. Nevertheless, none of the previous studies in cement factories have assessed the impact of reducing personal dust exposure levels on the prevalence From the Department of Global Public Health and Primary Care (Drs Tungu, Br˚atveit, and Moen), Occupational and Environmental Medicine, University of Bergen, Bergen, Norway; Department of Environmental and Occupational Health (Dr Mamuya), School of Public Health and Social Sciences, Muhimbili University of Health and Allied Sciences, Dar es Salaam, Tanzania; and Department of Occupational Medicine (Dr Moen), Haukeland University Hospital, Bergen, Norway. A.M.T. planned the study, collected and analyzed data, and revised the manuscript after consultation with the other authors. M.B., S.H.M., and B.E.M. participated in planning, collection, and analysis of data, provided scientific support throughout the study, and reviewed and commented on the manuscript. All authors have read and approved the final manuscript for publication. No conflicts of interest were declared. Address correspondence to: Alexander Mtemi Tungu, MD, Department of Global Public Health and Primary Care, Occupational and Environmental Medicine, Kalfarveien 31, N-5018, Bergen, Norway ([email protected]). C 2013 by American College of Occupational and Environmental Copyright Medicine DOI: 10.1097/JOM.0000000000000057
of chronic respiratory symptoms, lung function, and/or COPD. A follow-up study among Austrian workers exposed to quartz demonstrated a slowing of the annual decrease in FEV1 and FVC after implementation of a Threshold Limit Value (TLV) of 10 mg/m3 for inhalable dust.13 Nevertheless, the Austrian study has no personal dust exposure levels and the type of exposure is different from that in this study. Dust exposure among workers in cement factories occurs in all stages of cement production.14,15 High dust-exposure levels exceeding recommended international exposure levels16 have been reported in several studies.17,18 In a Tanzanian cement factory, the highest dust-exposure levels were found in the crane, packing, and crusher in 2002.18 Conditions related to high dust-exposure levels among workers were reportedly defective doors and windows of crane cabins, and lack of or poor ventilation systems in the packing areas and open flow lines.18 A reduction of dust-exposure levels among factory workers was recommended in this factory. As part of the recommended measures, maintenance and repair activities were carried out in the cement factory (Table 1). In addition, a new production line was established alongside the old cement factory and started production in early 2010. In this study, we have used group-based data from two crosssectional studies to evaluate the effect of the collective measures19,20 in reduction of exposure levels and the targeted respiratory health outcomes. We compared baseline data collected in 2002 and the data obtained after intervention (8 years after the baseline study) in the same cement factory. We aimed at comparing total dust-exposure levels, prevalence of chronic respiratory symptoms, lung function, and COPD among Tanzanian cement production workers in 2002 and 2010–2011.
METHODS Study Design and Setting This study compared data collected in 2002 with similar data obtained in 2010–2011 among workers in the production line (exposed) at a Portland cement factory in Tanzania. Because of the absence of individual data obtained in 2002, we compared summarized data between 2002 and 2010–2011 (an ecological analysis). In 2002, all exposed workers (n = 120) were included in respiratory health examinations.5 The controls were maintenance and administrative workers (n = 107) in the same cement factory in 2002. The 2002 data on total dust exposure, chronic respiratory symptoms, lung function, and COPD among cement workers have been published previously.2,5,18 In 2010, a total of 210 out of 411 exposed workers were randomly selected and invited to participate in the study.14 Thirtynine exposed workers did not participate giving a response rate of 82.4%. A total of 105 out of 349 production workers in the mineral water factory were randomly selected to form the control group in 2010. Seven controls did not participate giving a response rate of 93.3% in 2010. Data were collected (same variables as in 2002) from exposed workers and controls in 2010. In 2011, additional data
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TABLE 1. Comparison of Work Conditions Between 2002 and 2010–2011 in Different Sections of a Tanzanian Cement Factory Working Conditions in 2010–11 Section(s)
Working Conditions in 2002 Old Factory
Old Plant
New Plant
Crusher
The crusher and the conveyor belts were not enclosed; the crusher and the belt had a roof to provide protection from rain.
Crushers 1 and 2 each have a production capacity of 156 t/hr Bag filters for dust suppression are under installation. The crusher and the conveyor belts were not enclosed; the crusher and the belt had a roof to provide protection from rain. Airtight crusher operating rooms with an air conditioning system are present. Manual removal of lodged bulky raw materials.
Crusher production capacity was 700 t/hr Bag filters for dust suppression present The crusher and the conveyor belts were partially enclosed; the crusher had larger openings to provide free airflow. The crusher had a “hammer breaker,” which was used to break the lodged bulky raw material in the crusher into smaller pieces. Crusher operators stayed in the “hammer breaker” cabin which was airtight and had an air conditioning system.
Crane
The gantry was an open building with only a roof. The crane cabins had defective glass windows and doors.
Ongoing gantry enclosure process. Defective glass window and doors were repaired. Air conditioning system was installed in the crane cabins.
The gantry was partially enclosed with large openings at both ends, which provided natural air ventilation No cranes. Automatic feeding of the raw materials into the conveyor belt system using two “stacker” machines replacing the cranes. The stackers can also be operated manually, and their operating rooms were airtight and had an air conditioning system.
Raw mill/Kiln
The raw mill machinery was enclosed indoors and the workers mainly operated the mill from a control room. The rotary kiln was located outdoors, but workers operated the kiln from a control room and made regular visits to the kiln.
Raw mill production capacity was 50 t/hr Kiln production capacity was 40 t/hr No precalcination of material before they enter the kiln. Bag filters for dust suppression were installed in the raw mill. No cross belt analyzer.
Raw mill production capacity was 250 t/hr Kiln production capacity was 2500 t/day Precalcination of material to give material short resident time in the kiln. A cross belt analyzer added before raw mill to control the quality of the raw mill input. Used bag filters for suppression of dust.
Cement mill
Same working conditions as for the raw mill
Cement mill production capacity Cement mill 1 was 20 t/hr, cement mill 2 is 30 t/hr, and cement mill 3 was 45 t/hr. No bag filters after the separators of the cement mills. Used electrostatic precipitator (ESP) dust suppression system.
Cement mill production capacity was 120 t/hr. Bag filters present after the separator of the cement mills for dust suppression.
Packing
The packing area was an enclosed large room without obvious ventilation except for the main entrance. There was no local exhaust ventilation on the packing machine and no enclosure for the conveyor belts.
Conveyor belts not enclosed with an opening on one end. Packing plant 1 was partially enclosed. Local exhaust ventilation on the packing machine was installed in both packing plant 1 and 2.
Partially enclosed with large openings at both ends to allow natural air ventilation. Bag filters present. Conveyor belts not enclosed.
for personal total dust exposure alone were collected for the same months (June to August) as in 2002. All participants in both 2002 and 2010–2011 were males. The cement factory18 and mineral water factory14 were located in Dar es Salaam, Tanzania.
Exposure Assessment In both sampling periods (2002 and 2010–2011), personal total dust samples were collected on preweighed 37-mm cellulose acetate filters with a pore size of 0.8 μm in a closed faced three-piece Millipore-cassette connected to an SKC pump (Sidekick Casella; SKC Limited, Blandford Forum, United Kingdom) with a flow rate of 2.0 L/min. The analysis of total dust samples was performed using similar methods in both periods. Nevertheless, the analysis was performed at the X-lab AS laboratory in Bergen, Norway, in 102
200218 and at the Eurofins Product Testing in Denmark in 2010– 2011, as the X-lab had been sold to the Eurofins laboratory.14 In 2002, a total of 79 dust samples were collected from 52 exposed workers,18 whereas among controls, 24 samples from 16 maintenance workers and 17 samples from administrative controls were collected in 2002. In 2010–2011, a total of 192 dust samples were collected from 115 exposed workers, whereas 47 dust samples were collected from 43 mineral water factory controls. Nevertheless, 13 dust samples from the exposed workers and 3 dust samples from controls were not analyzed in 2010–2011, leaving a total of 179 and 44 samples for final analysis among the exposed workers and controls, respectively. Reasons for exclusion in the analysis were low pump flow rate for nine exposed workers and three controls. Four samples obtained from cleaning workers using vacuum cleaners were
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JOEM r Volume 56, Number 1, January 2014
also excluded because these appliances were used in multiple sections of the cement factory.
Questionnaire Chronic respiratory symptoms among study participants were assessed using a modified British Medical Research Council questionnaire21 in both examination periods. The questionnaire was translated from English to Swahili and back to English, using two independent translators. Questions used in the assessment of chronic respiratory symptoms are shown in Table 2. The questionnaire also comprised sociodemographic data, occupational history, past chest illnesses, use of respiratory protective equipment (RPE), and smoking habits. Current smokers or those who had stopped smoking less than 1 year ago were categorized as smokers, whereas never-smokers or those who had stopped smoking more than 1 year ago (ex-smokers) were categorized as nonsmokers. The pack years of smoking were calculated as the number of cigarettes per year divided by 20. In 2002, participants self-administered the questions and returned the completed questionnaire to the investigator on the next day. In 2010, the first author administered the questionnaire by interviewing each participant.
Spirometry Lung function tests were performed in accordance with the American Thoracic Society recommendations for spirometry22 in both examination periods. In 2002, a Vitalograph Spirometer was used,2 and in 2010 a digital Spirare Spirometer (SPS310) was used. The Vitalograph spirometer was calibrated daily using a 2L syringe, whereas no calibrations were required for the Spirare Spirometer. Lung function examinations were conducted between 10:00 AM and 12:30 PM in 2002 and between 14:00 PM and 16:00 PM in 2010.
Impact of Reduced Dust Exposure: Ecological Study
The lung function examinations were performed in a sitting position without a nasal clip in both periods. Participants performed three to eight spirometric tests. For comparison purposes, the choice of the lung function indices in 2010 was based on the indices examined in 2002. The lung function indices included FVC, FEV1 , percentage predicted FVC (FVC%), percentage predicted FEV1 (FEV1 %), and FEV1 /FVC ratio. The maximum values for FVC and FEV1 were used in the statistical analysis. Predicted values for FVC and FEV1 in both periods were calculated on the basis of the regression equations for Tanzanian male adults as follows: FVC(l) = 0.0604H − 0.016A − 6.14, and FEV1 (l/s) = 0.046H − 0.022A − 3.864, where H is height (cm) and A is age (years).23 In 2010, nine spirograms (six unacceptable and three missing data) among exposed workers and five spirograms among controls were excluded, leaving 162 and 93 spirograms among the exposed workers and controls, respectively, for statistical analysis.
Diagnosis of COPD In both examination periods, all participants with airflow limitation (FEV1 /FVC ratio < 0.70) were considered to have COPD based on the Global Initiative for Chronic Obstructive Lung Disease (GOLD) criteria.24
Ethical Clearance The study was approved by the Western Norway Regional Committee on Medical Research Ethics and the Muhimbili University of Health and Allied Sciences Research and Ethics Committee, in both 2002 and 2010–2011. Each study participant gave a written informed consent. No information about the individuals was available to the employers at any time during the study.
Statistical Analysis TABLE 2. Questions Used in Assessment of Chronic Respiratory Symptoms in 2002 and 2010 Symptom(s)
Questions
Chronic cough (If yes to all four questions)
Chronic sputum production (If yes to all four questions)
Dyspnoea Work-related shortness of breath Wheeze Chronic bronchitis
a) Do you usually cough first thing in the morning? b) Do you usually cough during the day or night? c) Do you cough as much as four to six times a day in a week? d) Do you cough like this on most of days for as much as 3 consecutive months during the year? a) Do you usually cough with sputum first thing in the morning? b) Do you usually cough with sputum during the day or night? c) Do you usually cough with sputum as much as four to six times a day in a week? d) Do you cough with sputum on most of days for as long as 3 consecutive months during the year? Do you get shortness of breath when walking at your own pace on level ground? Do you usually experience chest tightness while at work or just after work? Does your chest ever sound wheezy (whistling sound)? During the last 3 years have you had any periods with increased cough and/or cough with sputum production lasting for 3 months or more?
Total dust-exposure levels were skewed and were logtransformed before analysis. The geometric mean (GM) and geometric standard deviation for total dust exposure in 2010–2011 were calculated. The GM for total dust exposure from each section of the production line in the cement factory in 2002 was obtained from a previous publication.18 Statistical testing of the overall GM for total dust exposure between the two time periods was not possible because of missing geometric standard deviation in 2002. In 2010–2011, the dust exposure levels in the raw mill and kiln were combined because workers in these sections worked interchangeably; hence, they were not compared with the dust levels in 2002. An independent t test was used for comparison of continuous variables. A two-sample t test was used for comparison of summarized data between the two time periods. A chi-squared test was used to compare categorical variables. Linear regression analysis was used to compare FVC, FEV1 , and the FEV1 /FVC ratio between the exposed workers and controls in the respective years, adjusting for age, height, duration of employment, and pack years. Additional linear regression analysis was used to compare FVC%, FEV1 % while adjusting for pack years of smoking and duration of employment. A chi-squared test with a Breslow-Day test of homogeneity of the odds ratios (ORs) was used to compare the difference in risks (unadjusted OR) of chronic respiratory symptoms between 2002 and 2010. Logistic regression analysis was used in the comparison of chronic respiratory symptoms between the exposed workers and controls within the same time period of examination while adjusting for age, duration of employment, education level, and pack years of smoking. Among the exposed workers, a subgroup analysis of chronic respiratory symptoms and lung function among workers who had less than 8 years at work (examined in 2010 only) and those with 8 years or more at work (examined in both 2002 and 2010)
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was performed. Statistical analyses were performed using Statistical Package of Social Sciences, version 19 (International Business Machines [IBM] SPSS Statistics, NY) for Windows and statistical significance was reached at 95% confidence interval (CI).
RESULTS Study Participants A total of 120 exposed workers and 107 controls participated in the study in 2002 (Table 3). In 2010, a total of 171 exposed workers and 98 controls participated in the study (Table 3). Age, duration of employment, and education level were lower among the exposed workers than among maintenance and administrative controls in 2002. These characteristics were similar among the exposed workers and controls in 2010, except for height where the exposed workers were significantly shorter than controls (P < 0.001) (Table 3). Height and duration of employment among the exposed workers were significantly lower in 2010 than in 2002 (Table 3). The proportion of the exposed workers who reported using RPE was lower in 2002 than in 2010 (38% vs 91%). Age, education, pack years of smoking, and weight among the exposed workers did not differ significantly between the two periods. Among controls, age and duration of employment were significantly lower in 2010 than in 2002, whereas height and pack years of smoking did not differ significantly between the two periods. In 2010, five exposed workers and four controls reported a history of tuberculosis but had been treated and declared cured. Six exposed workers and eight controls had a history of asthma.
Exposure Assessment The number of personal total dust-exposure levels obtained in the cement factory in 2002 and 2010–2011 were 79 and 179, respectively (Table 4). In 2002, the overall GM for total dust exposure among exposed workers was 10.6 mg/m3 . The proportion of dust levels above TLV of 10 mg/m3 for particles not otherwise specified (PNOS) in 2002 was 58.2%. The highest exposure levels in 2002 were found in the crane followed by packing and crusher (Table 4). In 2010, the overall GM for total dust exposure was 5.8 10 mg/m3 , and the proportion of the dust levels above the TLV16 value of 10 mg/m3 were 31% (Table 4). The highest exposure level was found in the packing, followed by crusher and cement mill. Among the exposed workers, the overall dust exposure levels were significantly lower in 2010–2011 than in 2002. Similarly, the dust-exposure levels were consistently lower among the exposed job groups in 2010–2011 than in 2002. Nevertheless, there were significantly higher dust-exposure levels in the cement mill in 2010– 2011 than in 2002 (Table 4). Among controls, total dust exposure among maintenance workers (GM: 1.16 mg/m3 , range 0.11 to 10.23) was higher than that among administrative workers (GM: 0.29 mg/m3 , range: 0.01 to 2.36) and among mineral water factory controls (GM: 0.36 mg/m3 , range: 0.05 to 1.8). Nevertheless, the dust exposure levels among controls did not differ significantly.
Chronic Respiratory Symptoms In 2002, the exposed workers had a significantly higher prevalence of chronic respiratory symptoms than controls (Table 5). In 2010, work-related shortness of breath was the only symptom that was significantly higher among the exposed workers than among controls (OR: 3.3; 95% CI 1.3 to 8.3) while adjusting for age, duration of employment, educational level, and pack years of smoking. Among the exposed workers, the prevalence of chronic cough, chronic sputum production, and chronic bronchitis were considerably lower in 2010 than in 2002 (Table 5). Among controls, there was a 104
lower prevalence of chronic cough and chronic sputum production in 2010 compared with 2002. The OR for developing chronic bronchitis among the exposed workers compared with controls was significantly lower in 2010 than in 2002 (P = 0.022) (Table 5). No significant difference in the ORs between 2002 and 2010 for the remaining symptoms was found. In a subgroup analysis among the exposed workers, there was no significant difference in chronic respiratory symptoms between those who had worked less than 8 years and those who had worked for 8 years or more (Table 5).
Spirometry In 2002, a total of 115 and 102 spirometric results among exposed workers and controls were analyzed, respectively. In 2010, the spirometric results analyzed were 162 and 93 among exposed workers and controls, respectively. The exposed workers had significantly lower FVC, FEV1 , FVC%, FEV1 %, and FEV1/FVC ratio than controls in 2002 (Table 6). In 2010, there was no significant difference in FVC, FEV1 , and FEV1/FVC ratio, whereas FVC% and FEV1 % were significantly higher among the exposed workers than among controls. Among the exposed workers, FEV1 , FVC%, and FEV1 % were lower in 2002 than in 2010, while FVC and the FEV1 /FVC ratio did not differ significantly between the two periods (Table 6). The fraction of airflow limitation (FEV1 /FVC < 0.7) was significantly higher among the exposed workers in 2002 than in 2010 (23% and 2.7%, respectively; P = 0.003). Among controls, there was no difference in lung function indices between the two periods except for FVC%, which was significantly lower in 2002 than in 2010 (P < 0.001). A subgroup analysis for lung function indices revealed no significant differences between the exposed workers who had worked less than 8 years and those with 8 years or more in the cement factory (Table 6).
COPD Diagnoses In 2002, there was a significantly higher prevalence of COPD among the exposed workers than among controls (Table 6). The prevalence of COPD did not differ significantly between the exposed workers and controls in 2010. Among the exposed workers, the prevalence of COPD was higher in 2002 than in 2010 (Table 6). All the exposed workers who had COPD in 2010 had worked less than 8 years in the cement factory. Two of seven exposed workers (28.6%) who had COPD in 2010 were smokers. The prevalence of COPD among controls did not differ significantly between the two periods (Table 6).
DISCUSSION Total dust-exposure level in the cement factory was considerably lower in 2010–2011 than in 2002. The exposed workers had a considerably lower prevalence of chronic cough, chronic sputum production, chronic bronchitis, and COPD in 2010 than in 2002. The OR for chronic bronchitis among the exposed workers was significantly lower in 2010 whereas FEV1 , FVC%, and FEV1 % were significantly higher in 2010 than in 2002. We observed an overall reduction in personal total dustexposure levels in 2010–2011 compared with the dust levels reported previously in the same cement factory.18 The exposure level in 2010– 2011 (GM: 5.8 mg/m3 ) was considerably lower than that reported among Ethiopian cement cleaners8 (GM: 549 mg/m3 ) but was still higher than those among Norwegian12 (GM: 2.3 mg/m3 ), German25 (GM: 3.0 mg/m3 ), and American10 (GM: 2.9 mg/m3 ) cement workers. In this study, the reduction of dust-exposure levels in the crusher may have resulted from the installation of an air conditioning system in the crusher control room in the old factory and the use of bag filters for dust suppression in the new production line. Nevertheless,
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40.4 (8.2) 14.8 (8.2) 169.6 (6.0) 73.2 (14.1) 2.6 (6.1) n (%) 41 (38.3) 79 (73.8) 16 (14.9) 11 (10.3) 20 (23.5)
n (%) 65 (54.2) 80 (66.7) 16 (13.3) 24 (20) 45 (37.5)
Controls (N = 107)
35.7 (8.7) 11.0 (8.2) 169.5 (6.5) 74.2 (14.1) 1.9 (4.6)
Exposed (N = 120)
*Values represent mean (standard deviation). †Independent t test between the exposed and controls. ‡Independent t test between exposed subgroups in 2010. §Two-sample t tests between controls in 2002 and 2010, P < 0.001. ||Two-sample t test between exposed workers in 2002 and 2010, P < 0.05. ¶Chi-squared test between the exposed and controls. #Chi-squared test between exposed subgroups in 2010.
Primary education only Smoking habits Never-smokers Current smokers Ex-smokers Respiratory protective equipment‡
Age, yr* Duration of employment, yr* Height, cm* Weight, kg* Pack years of smoking*
Variable(s)
2002
0.239 0.726 0.726
P¶ 0.017
0.001 0.001 0.901 0.579 0.309
P†
121 (70.8) 34 (19.8) 16 (9.4) 156 (91.2)
n (%) 95 (55.6)
34.4 (9.7) 8.1 (9.4)|| 164.2 (7.0)|| 70.7 (13.5) 1.1 (3.7)
Exposed (N = 171)
69 (70.4) 19 (19.4) 10 (10.2) ...
n (%) 53 (54.1)
32.6 (7.0)§ 7.5 (5.9)§ 168.6 (6.8) 68.8 (12.6) 1.0 (3.8)
Controls (N = 98)
2010
Year of Examination
0.951 0.762 0.697 ...
P¶ 0.815
0.096 0.596
The Impact of Reduced Dust Exposure on Respiratory Health Among Cement Workers An Ecological Study Alexander Mtemi Tungu, MD, Magne Br˚atveit, PhD, Simon H. Mamuya, PhD, and Bente E. Moen, PhD
Objectives: To compare total dust exposure, prevalence of chronic respiratory symptoms, lung function, and chronic obstructive pulmonary disease (COPD) among Tanzanian cement workers before (2002) and after (2010–2011) establishment of dust-control measures. Methods: Personal total dust-exposure measurements, questionnaire assessment for chronic respiratory symptoms, and spirometry were conducted in both examination periods. Results: Total dust exposure was lower in 2010–2011 than in 2002. The prevalence of most chronic respiratory symptoms and COPD was lower in 2010 than in 2002. Forced expiratory volume in 1 second (FEV1 ), percentage predicted FEV1 , and percentage predicted forced vital capacity were higher among cement workers in 2010 than in 2002. Conclusions: There was reduced total dust exposure level, lower prevalence of chronic respiratory symptoms and COPD, and higher lung function among cement workers in 2010 than in 2002.
P
revious studies have suggested a relationship between dust exposure and adverse respiratory health effects among workers in cement factories.1–5 A multicenter cross-sectional study among European cement workers found a higher prevalence of chronic respiratory symptoms among cement workers compared with controls.4 A higher prevalence of chronic respiratory symptoms and chronic obstructive pulmonary disease (COPD) were found among Tanzanian cement production workers compared with maintenance and administrative controls.5 Few follow-up studies on respiratory health and dust exposure exist in cement factories.6,7 A prospective follow-up study among highly exposed Ethiopian cement workers reported an increase in prevalence of chronic cough (with or without phlegm) and dyspnoea, as well as reduction of lung function (forced expiratory volume in 1 second [FEV1 ], and the ratio of FEV1 to forced vital capacity [FEV1 /FVC]) among the exposed after only 1 year, but not among controls.8 Some studies conducted in developed countries found no association between dust exposure and adverse chronic health effects.9–12 This could be due to low dust-exposure levels as a result of more efficient dust-control measures in these factories. Nevertheless, none of the previous studies in cement factories have assessed the impact of reducing personal dust exposure levels on the prevalence From the Department of Global Public Health and Primary Care (Drs Tungu, Br˚atveit, and Moen), Occupational and Environmental Medicine, University of Bergen, Bergen, Norway; Department of Environmental and Occupational Health (Dr Mamuya), School of Public Health and Social Sciences, Muhimbili University of Health and Allied Sciences, Dar es Salaam, Tanzania; and Department of Occupational Medicine (Dr Moen), Haukeland University Hospital, Bergen, Norway. A.M.T. planned the study, collected and analyzed data, and revised the manuscript after consultation with the other authors. M.B., S.H.M., and B.E.M. participated in planning, collection, and analysis of data, provided scientific support throughout the study, and reviewed and commented on the manuscript. All authors have read and approved the final manuscript for publication. No conflicts of interest were declared. Address correspondence to: Alexander Mtemi Tungu, MD, Department of Global Public Health and Primary Care, Occupational and Environmental Medicine, Kalfarveien 31, N-5018, Bergen, Norway ([email protected]). C 2013 by American College of Occupational and Environmental Copyright Medicine DOI: 10.1097/JOM.0000000000000057
of chronic respiratory symptoms, lung function, and/or COPD. A follow-up study among Austrian workers exposed to quartz demonstrated a slowing of the annual decrease in FEV1 and FVC after implementation of a Threshold Limit Value (TLV) of 10 mg/m3 for inhalable dust.13 Nevertheless, the Austrian study has no personal dust exposure levels and the type of exposure is different from that in this study. Dust exposure among workers in cement factories occurs in all stages of cement production.14,15 High dust-exposure levels exceeding recommended international exposure levels16 have been reported in several studies.17,18 In a Tanzanian cement factory, the highest dust-exposure levels were found in the crane, packing, and crusher in 2002.18 Conditions related to high dust-exposure levels among workers were reportedly defective doors and windows of crane cabins, and lack of or poor ventilation systems in the packing areas and open flow lines.18 A reduction of dust-exposure levels among factory workers was recommended in this factory. As part of the recommended measures, maintenance and repair activities were carried out in the cement factory (Table 1). In addition, a new production line was established alongside the old cement factory and started production in early 2010. In this study, we have used group-based data from two crosssectional studies to evaluate the effect of the collective measures19,20 in reduction of exposure levels and the targeted respiratory health outcomes. We compared baseline data collected in 2002 and the data obtained after intervention (8 years after the baseline study) in the same cement factory. We aimed at comparing total dust-exposure levels, prevalence of chronic respiratory symptoms, lung function, and COPD among Tanzanian cement production workers in 2002 and 2010–2011.
METHODS Study Design and Setting This study compared data collected in 2002 with similar data obtained in 2010–2011 among workers in the production line (exposed) at a Portland cement factory in Tanzania. Because of the absence of individual data obtained in 2002, we compared summarized data between 2002 and 2010–2011 (an ecological analysis). In 2002, all exposed workers (n = 120) were included in respiratory health examinations.5 The controls were maintenance and administrative workers (n = 107) in the same cement factory in 2002. The 2002 data on total dust exposure, chronic respiratory symptoms, lung function, and COPD among cement workers have been published previously.2,5,18 In 2010, a total of 210 out of 411 exposed workers were randomly selected and invited to participate in the study.14 Thirtynine exposed workers did not participate giving a response rate of 82.4%. A total of 105 out of 349 production workers in the mineral water factory were randomly selected to form the control group in 2010. Seven controls did not participate giving a response rate of 93.3% in 2010. Data were collected (same variables as in 2002) from exposed workers and controls in 2010. In 2011, additional data
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TABLE 1. Comparison of Work Conditions Between 2002 and 2010–2011 in Different Sections of a Tanzanian Cement Factory Working Conditions in 2010–11 Section(s)
Working Conditions in 2002 Old Factory
Old Plant
New Plant
Crusher
The crusher and the conveyor belts were not enclosed; the crusher and the belt had a roof to provide protection from rain.
Crushers 1 and 2 each have a production capacity of 156 t/hr Bag filters for dust suppression are under installation. The crusher and the conveyor belts were not enclosed; the crusher and the belt had a roof to provide protection from rain. Airtight crusher operating rooms with an air conditioning system are present. Manual removal of lodged bulky raw materials.
Crusher production capacity was 700 t/hr Bag filters for dust suppression present The crusher and the conveyor belts were partially enclosed; the crusher had larger openings to provide free airflow. The crusher had a “hammer breaker,” which was used to break the lodged bulky raw material in the crusher into smaller pieces. Crusher operators stayed in the “hammer breaker” cabin which was airtight and had an air conditioning system.
Crane
The gantry was an open building with only a roof. The crane cabins had defective glass windows and doors.
Ongoing gantry enclosure process. Defective glass window and doors were repaired. Air conditioning system was installed in the crane cabins.
The gantry was partially enclosed with large openings at both ends, which provided natural air ventilation No cranes. Automatic feeding of the raw materials into the conveyor belt system using two “stacker” machines replacing the cranes. The stackers can also be operated manually, and their operating rooms were airtight and had an air conditioning system.
Raw mill/Kiln
The raw mill machinery was enclosed indoors and the workers mainly operated the mill from a control room. The rotary kiln was located outdoors, but workers operated the kiln from a control room and made regular visits to the kiln.
Raw mill production capacity was 50 t/hr Kiln production capacity was 40 t/hr No precalcination of material before they enter the kiln. Bag filters for dust suppression were installed in the raw mill. No cross belt analyzer.
Raw mill production capacity was 250 t/hr Kiln production capacity was 2500 t/day Precalcination of material to give material short resident time in the kiln. A cross belt analyzer added before raw mill to control the quality of the raw mill input. Used bag filters for suppression of dust.
Cement mill
Same working conditions as for the raw mill
Cement mill production capacity Cement mill 1 was 20 t/hr, cement mill 2 is 30 t/hr, and cement mill 3 was 45 t/hr. No bag filters after the separators of the cement mills. Used electrostatic precipitator (ESP) dust suppression system.
Cement mill production capacity was 120 t/hr. Bag filters present after the separator of the cement mills for dust suppression.
Packing
The packing area was an enclosed large room without obvious ventilation except for the main entrance. There was no local exhaust ventilation on the packing machine and no enclosure for the conveyor belts.
Conveyor belts not enclosed with an opening on one end. Packing plant 1 was partially enclosed. Local exhaust ventilation on the packing machine was installed in both packing plant 1 and 2.
Partially enclosed with large openings at both ends to allow natural air ventilation. Bag filters present. Conveyor belts not enclosed.
for personal total dust exposure alone were collected for the same months (June to August) as in 2002. All participants in both 2002 and 2010–2011 were males. The cement factory18 and mineral water factory14 were located in Dar es Salaam, Tanzania.
Exposure Assessment In both sampling periods (2002 and 2010–2011), personal total dust samples were collected on preweighed 37-mm cellulose acetate filters with a pore size of 0.8 μm in a closed faced three-piece Millipore-cassette connected to an SKC pump (Sidekick Casella; SKC Limited, Blandford Forum, United Kingdom) with a flow rate of 2.0 L/min. The analysis of total dust samples was performed using similar methods in both periods. Nevertheless, the analysis was performed at the X-lab AS laboratory in Bergen, Norway, in 102
200218 and at the Eurofins Product Testing in Denmark in 2010– 2011, as the X-lab had been sold to the Eurofins laboratory.14 In 2002, a total of 79 dust samples were collected from 52 exposed workers,18 whereas among controls, 24 samples from 16 maintenance workers and 17 samples from administrative controls were collected in 2002. In 2010–2011, a total of 192 dust samples were collected from 115 exposed workers, whereas 47 dust samples were collected from 43 mineral water factory controls. Nevertheless, 13 dust samples from the exposed workers and 3 dust samples from controls were not analyzed in 2010–2011, leaving a total of 179 and 44 samples for final analysis among the exposed workers and controls, respectively. Reasons for exclusion in the analysis were low pump flow rate for nine exposed workers and three controls. Four samples obtained from cleaning workers using vacuum cleaners were
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JOEM r Volume 56, Number 1, January 2014
also excluded because these appliances were used in multiple sections of the cement factory.
Questionnaire Chronic respiratory symptoms among study participants were assessed using a modified British Medical Research Council questionnaire21 in both examination periods. The questionnaire was translated from English to Swahili and back to English, using two independent translators. Questions used in the assessment of chronic respiratory symptoms are shown in Table 2. The questionnaire also comprised sociodemographic data, occupational history, past chest illnesses, use of respiratory protective equipment (RPE), and smoking habits. Current smokers or those who had stopped smoking less than 1 year ago were categorized as smokers, whereas never-smokers or those who had stopped smoking more than 1 year ago (ex-smokers) were categorized as nonsmokers. The pack years of smoking were calculated as the number of cigarettes per year divided by 20. In 2002, participants self-administered the questions and returned the completed questionnaire to the investigator on the next day. In 2010, the first author administered the questionnaire by interviewing each participant.
Spirometry Lung function tests were performed in accordance with the American Thoracic Society recommendations for spirometry22 in both examination periods. In 2002, a Vitalograph Spirometer was used,2 and in 2010 a digital Spirare Spirometer (SPS310) was used. The Vitalograph spirometer was calibrated daily using a 2L syringe, whereas no calibrations were required for the Spirare Spirometer. Lung function examinations were conducted between 10:00 AM and 12:30 PM in 2002 and between 14:00 PM and 16:00 PM in 2010.
Impact of Reduced Dust Exposure: Ecological Study
The lung function examinations were performed in a sitting position without a nasal clip in both periods. Participants performed three to eight spirometric tests. For comparison purposes, the choice of the lung function indices in 2010 was based on the indices examined in 2002. The lung function indices included FVC, FEV1 , percentage predicted FVC (FVC%), percentage predicted FEV1 (FEV1 %), and FEV1 /FVC ratio. The maximum values for FVC and FEV1 were used in the statistical analysis. Predicted values for FVC and FEV1 in both periods were calculated on the basis of the regression equations for Tanzanian male adults as follows: FVC(l) = 0.0604H − 0.016A − 6.14, and FEV1 (l/s) = 0.046H − 0.022A − 3.864, where H is height (cm) and A is age (years).23 In 2010, nine spirograms (six unacceptable and three missing data) among exposed workers and five spirograms among controls were excluded, leaving 162 and 93 spirograms among the exposed workers and controls, respectively, for statistical analysis.
Diagnosis of COPD In both examination periods, all participants with airflow limitation (FEV1 /FVC ratio < 0.70) were considered to have COPD based on the Global Initiative for Chronic Obstructive Lung Disease (GOLD) criteria.24
Ethical Clearance The study was approved by the Western Norway Regional Committee on Medical Research Ethics and the Muhimbili University of Health and Allied Sciences Research and Ethics Committee, in both 2002 and 2010–2011. Each study participant gave a written informed consent. No information about the individuals was available to the employers at any time during the study.
Statistical Analysis TABLE 2. Questions Used in Assessment of Chronic Respiratory Symptoms in 2002 and 2010 Symptom(s)
Questions
Chronic cough (If yes to all four questions)
Chronic sputum production (If yes to all four questions)
Dyspnoea Work-related shortness of breath Wheeze Chronic bronchitis
a) Do you usually cough first thing in the morning? b) Do you usually cough during the day or night? c) Do you cough as much as four to six times a day in a week? d) Do you cough like this on most of days for as much as 3 consecutive months during the year? a) Do you usually cough with sputum first thing in the morning? b) Do you usually cough with sputum during the day or night? c) Do you usually cough with sputum as much as four to six times a day in a week? d) Do you cough with sputum on most of days for as long as 3 consecutive months during the year? Do you get shortness of breath when walking at your own pace on level ground? Do you usually experience chest tightness while at work or just after work? Does your chest ever sound wheezy (whistling sound)? During the last 3 years have you had any periods with increased cough and/or cough with sputum production lasting for 3 months or more?
Total dust-exposure levels were skewed and were logtransformed before analysis. The geometric mean (GM) and geometric standard deviation for total dust exposure in 2010–2011 were calculated. The GM for total dust exposure from each section of the production line in the cement factory in 2002 was obtained from a previous publication.18 Statistical testing of the overall GM for total dust exposure between the two time periods was not possible because of missing geometric standard deviation in 2002. In 2010–2011, the dust exposure levels in the raw mill and kiln were combined because workers in these sections worked interchangeably; hence, they were not compared with the dust levels in 2002. An independent t test was used for comparison of continuous variables. A two-sample t test was used for comparison of summarized data between the two time periods. A chi-squared test was used to compare categorical variables. Linear regression analysis was used to compare FVC, FEV1 , and the FEV1 /FVC ratio between the exposed workers and controls in the respective years, adjusting for age, height, duration of employment, and pack years. Additional linear regression analysis was used to compare FVC%, FEV1 % while adjusting for pack years of smoking and duration of employment. A chi-squared test with a Breslow-Day test of homogeneity of the odds ratios (ORs) was used to compare the difference in risks (unadjusted OR) of chronic respiratory symptoms between 2002 and 2010. Logistic regression analysis was used in the comparison of chronic respiratory symptoms between the exposed workers and controls within the same time period of examination while adjusting for age, duration of employment, education level, and pack years of smoking. Among the exposed workers, a subgroup analysis of chronic respiratory symptoms and lung function among workers who had less than 8 years at work (examined in 2010 only) and those with 8 years or more at work (examined in both 2002 and 2010)
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Tungu et al
was performed. Statistical analyses were performed using Statistical Package of Social Sciences, version 19 (International Business Machines [IBM] SPSS Statistics, NY) for Windows and statistical significance was reached at 95% confidence interval (CI).
RESULTS Study Participants A total of 120 exposed workers and 107 controls participated in the study in 2002 (Table 3). In 2010, a total of 171 exposed workers and 98 controls participated in the study (Table 3). Age, duration of employment, and education level were lower among the exposed workers than among maintenance and administrative controls in 2002. These characteristics were similar among the exposed workers and controls in 2010, except for height where the exposed workers were significantly shorter than controls (P < 0.001) (Table 3). Height and duration of employment among the exposed workers were significantly lower in 2010 than in 2002 (Table 3). The proportion of the exposed workers who reported using RPE was lower in 2002 than in 2010 (38% vs 91%). Age, education, pack years of smoking, and weight among the exposed workers did not differ significantly between the two periods. Among controls, age and duration of employment were significantly lower in 2010 than in 2002, whereas height and pack years of smoking did not differ significantly between the two periods. In 2010, five exposed workers and four controls reported a history of tuberculosis but had been treated and declared cured. Six exposed workers and eight controls had a history of asthma.
Exposure Assessment The number of personal total dust-exposure levels obtained in the cement factory in 2002 and 2010–2011 were 79 and 179, respectively (Table 4). In 2002, the overall GM for total dust exposure among exposed workers was 10.6 mg/m3 . The proportion of dust levels above TLV of 10 mg/m3 for particles not otherwise specified (PNOS) in 2002 was 58.2%. The highest exposure levels in 2002 were found in the crane followed by packing and crusher (Table 4). In 2010, the overall GM for total dust exposure was 5.8 10 mg/m3 , and the proportion of the dust levels above the TLV16 value of 10 mg/m3 were 31% (Table 4). The highest exposure level was found in the packing, followed by crusher and cement mill. Among the exposed workers, the overall dust exposure levels were significantly lower in 2010–2011 than in 2002. Similarly, the dust-exposure levels were consistently lower among the exposed job groups in 2010–2011 than in 2002. Nevertheless, there were significantly higher dust-exposure levels in the cement mill in 2010– 2011 than in 2002 (Table 4). Among controls, total dust exposure among maintenance workers (GM: 1.16 mg/m3 , range 0.11 to 10.23) was higher than that among administrative workers (GM: 0.29 mg/m3 , range: 0.01 to 2.36) and among mineral water factory controls (GM: 0.36 mg/m3 , range: 0.05 to 1.8). Nevertheless, the dust exposure levels among controls did not differ significantly.
Chronic Respiratory Symptoms In 2002, the exposed workers had a significantly higher prevalence of chronic respiratory symptoms than controls (Table 5). In 2010, work-related shortness of breath was the only symptom that was significantly higher among the exposed workers than among controls (OR: 3.3; 95% CI 1.3 to 8.3) while adjusting for age, duration of employment, educational level, and pack years of smoking. Among the exposed workers, the prevalence of chronic cough, chronic sputum production, and chronic bronchitis were considerably lower in 2010 than in 2002 (Table 5). Among controls, there was a 104
lower prevalence of chronic cough and chronic sputum production in 2010 compared with 2002. The OR for developing chronic bronchitis among the exposed workers compared with controls was significantly lower in 2010 than in 2002 (P = 0.022) (Table 5). No significant difference in the ORs between 2002 and 2010 for the remaining symptoms was found. In a subgroup analysis among the exposed workers, there was no significant difference in chronic respiratory symptoms between those who had worked less than 8 years and those who had worked for 8 years or more (Table 5).
Spirometry In 2002, a total of 115 and 102 spirometric results among exposed workers and controls were analyzed, respectively. In 2010, the spirometric results analyzed were 162 and 93 among exposed workers and controls, respectively. The exposed workers had significantly lower FVC, FEV1 , FVC%, FEV1 %, and FEV1/FVC ratio than controls in 2002 (Table 6). In 2010, there was no significant difference in FVC, FEV1 , and FEV1/FVC ratio, whereas FVC% and FEV1 % were significantly higher among the exposed workers than among controls. Among the exposed workers, FEV1 , FVC%, and FEV1 % were lower in 2002 than in 2010, while FVC and the FEV1 /FVC ratio did not differ significantly between the two periods (Table 6). The fraction of airflow limitation (FEV1 /FVC < 0.7) was significantly higher among the exposed workers in 2002 than in 2010 (23% and 2.7%, respectively; P = 0.003). Among controls, there was no difference in lung function indices between the two periods except for FVC%, which was significantly lower in 2002 than in 2010 (P < 0.001). A subgroup analysis for lung function indices revealed no significant differences between the exposed workers who had worked less than 8 years and those with 8 years or more in the cement factory (Table 6).
COPD Diagnoses In 2002, there was a significantly higher prevalence of COPD among the exposed workers than among controls (Table 6). The prevalence of COPD did not differ significantly between the exposed workers and controls in 2010. Among the exposed workers, the prevalence of COPD was higher in 2002 than in 2010 (Table 6). All the exposed workers who had COPD in 2010 had worked less than 8 years in the cement factory. Two of seven exposed workers (28.6%) who had COPD in 2010 were smokers. The prevalence of COPD among controls did not differ significantly between the two periods (Table 6).
DISCUSSION Total dust-exposure level in the cement factory was considerably lower in 2010–2011 than in 2002. The exposed workers had a considerably lower prevalence of chronic cough, chronic sputum production, chronic bronchitis, and COPD in 2010 than in 2002. The OR for chronic bronchitis among the exposed workers was significantly lower in 2010 whereas FEV1 , FVC%, and FEV1 % were significantly higher in 2010 than in 2002. We observed an overall reduction in personal total dustexposure levels in 2010–2011 compared with the dust levels reported previously in the same cement factory.18 The exposure level in 2010– 2011 (GM: 5.8 mg/m3 ) was considerably lower than that reported among Ethiopian cement cleaners8 (GM: 549 mg/m3 ) but was still higher than those among Norwegian12 (GM: 2.3 mg/m3 ), German25 (GM: 3.0 mg/m3 ), and American10 (GM: 2.9 mg/m3 ) cement workers. In this study, the reduction of dust-exposure levels in the crusher may have resulted from the installation of an air conditioning system in the crusher control room in the old factory and the use of bag filters for dust suppression in the new production line. Nevertheless,
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40.4 (8.2) 14.8 (8.2) 169.6 (6.0) 73.2 (14.1) 2.6 (6.1) n (%) 41 (38.3) 79 (73.8) 16 (14.9) 11 (10.3) 20 (23.5)
n (%) 65 (54.2) 80 (66.7) 16 (13.3) 24 (20) 45 (37.5)
Controls (N = 107)
35.7 (8.7) 11.0 (8.2) 169.5 (6.5) 74.2 (14.1) 1.9 (4.6)
Exposed (N = 120)
*Values represent mean (standard deviation). †Independent t test between the exposed and controls. ‡Independent t test between exposed subgroups in 2010. §Two-sample t tests between controls in 2002 and 2010, P < 0.001. ||Two-sample t test between exposed workers in 2002 and 2010, P < 0.05. ¶Chi-squared test between the exposed and controls. #Chi-squared test between exposed subgroups in 2010.
Primary education only Smoking habits Never-smokers Current smokers Ex-smokers Respiratory protective equipment‡
Age, yr* Duration of employment, yr* Height, cm* Weight, kg* Pack years of smoking*
Variable(s)
2002
0.239 0.726 0.726
P¶ 0.017
0.001 0.001 0.901 0.579 0.309
P†
121 (70.8) 34 (19.8) 16 (9.4) 156 (91.2)
n (%) 95 (55.6)
34.4 (9.7) 8.1 (9.4)|| 164.2 (7.0)|| 70.7 (13.5) 1.1 (3.7)
Exposed (N = 171)
69 (70.4) 19 (19.4) 10 (10.2) ...
n (%) 53 (54.1)
32.6 (7.0)§ 7.5 (5.9)§ 168.6 (6.8) 68.8 (12.6) 1.0 (3.8)
Controls (N = 98)
2010
Year of Examination
0.951 0.762 0.697 ...
P¶ 0.815
0.096 0.596
