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* From the Department of Thoracic Medicine (Drs. Tzanakis, Bouros, Samiou, and Siafakas), Medical School, University of Crete, Heraklion, Crete; and General Hospital of Rethymnon (Dr. Kallergis), Crete, Greece.
Correspondence to: Nikolaos Tzanakis, MD, Senior Registrar in Respiratory Medicine, Department of Thoracic Medicine, University Hospital of Heraklion, PO Box 1352, 71110 Heraklion, Crete, Greece; e-mail: tzanakis{at}med.uoc.gr
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Abstract |
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Patients and setting: A total of 22 charcoal workers (mean age, 41 years; 9 current smokers, 5 ex-smokers, and 8 nonsmokers) were studied and compared with a control group of 35 farmers residing in Perama, Rethymnon, Crete.
Results: The charcoal workers were exposed to wood smoke for an average of 14 h/d during a mean of 23.7 days required for the burning of kilns. The workers under study were found to have significantly more cough (odds ratio [OR], 4.8; 95% confidence interval [CI], 1.2 to 19.7), sputum production (OR, 6; 95% CI, 1.4 to 26.5), wheezing (OR, 7.7; 95% CI, 1.4 to 41.5), dyspnea (OR, 28.7; 95% CI, 5.4 to 153), and hemoptysis (OR, 2.7; 95% CI, 0.7 to 55) than the control group. The prevalence of respiratory symptoms such as cough, sputum production, wheezing, and dyspnea in the charcoal workers was significantly elevated during the exposure period (OR, 5.4; 95% CI, 1.1 to 17.7; OR, 5.7; 95% CI, 1 to 31; OR, 9.8; 95% CI, 1 to 88; and OR, 36.7; 95% CI, 1 to 327, respectively). The mean ± SD percent of predicted values of FVC, FEV1, FEV1/FVC ratio, and forced expiratory flow at 25 to 75% of FVC during the exposure period were significantly lower than those before exposure: 106 ± 10.8 vs 101 ± 11.9, p < 0.01; 104 ± 16 vs 97 ± 15, p < 0.001; 81 ± 9 vs 78 ± 8, p < 0.001; and 95 ± 27 vs 80 ± 25, p < 0.01, respectively. The mean ± SD value of peak expiratory flow at midday and in the evening during the exposure were significantly lower than before: 524 ± 131 L/min vs 548 ± 108 L/min, p = 0.03; and 521 ± 135 L/min vs 547 ± 131 L/min, p = 0.02, respectively.
Conclusions: Our results suggest that wood smoke exposure in charcoal workers is associated with increased respiratory symptoms and decreased pulmonary function. Longitudinal studies are needed to determine potential long-term adverse respiratory effects.
Key Words: charcoal production • occupational exposure • wood smoke
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Introduction |
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Open charcoal production is a traditional seasonal job still existing in certain rural areas in Crete. Charcoal production is the process of pyrolyzing wood under controlled conditions to produce charcoal. It involves cutting wood, assembling it into cone-shaped piles, covering it with soil, and, finally, letting it burn until charcoal is produced. Kiln sizes vary between 15 m3 and 90 m3. Many of the tasks involved could be regarded as potentially hazardous. During the burning period of production, workers are exposed to incomplete combustion of wood burning and noxious smoke gases for several hours per day. In this study, we investigated the short-term respiratory effects of occupational heavy wood smoke exposure in these traditional charcoal workers. To the best of our knowledge, there has been no study in the literature investigating the short-term respiratory effects of this occupational exposure.
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Materials and Methods |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Study Design
The study involved three visits that took place in the local
rural medical offices. At the first visit, a history (including
questions on occupational exposure) was taken and a physical
examination and spirometry were performed. All subjects
completed a self-administered Greek version of the internationally
accepted British Medical Research Council respiratory
questionnaire,13
supplemented with questions on
work-related symptoms. Symptoms were considered as work related if
subjects reported them as being provoked by contact with relevant
respirable agents during the working period. At the same visit, the
charcoal workers were instructed to perform peak expiratory flow (PEF)
measurements and complete a diary card with their respiratory symptoms
and PEF measurements. Details of the exposure to wood smoke in the
kilns, such as hours per day of exposure, were also recorded in the
diary. At the second visit, which took place after 10 to 14 days of
exposure, a check of the diaries was done and a second spirometry was
performed. Finally, during the third visit, a reassessment of the
subjects, including a respiratory physical examination, took place and
the diaries were collected.
Symptoms, Spirometry, and PEF Measurements
Spirometry was performed by a trained technician, using a
calibrated pneumotachograph spirometer (Flowmate, Version E2.0; Jaeger;
Wuerzburg, Germany). The device was calibrated daily, and the values
were recorded at body temperature pressure, saturated. Each
subject completed a dynamic spirometry with at least three acceptable
and two reproducible maneuvers according to standard
guidelines.14
Predicted values were obtained from the new
standardized lung function testing guidelines of the European Community
for Steel and Coal Luxembourg, 1993.14
All data were
expressed as percentages of predicted values. PEF was measured using a
peak flowmeter (Mini Wright; Armstrong Medical Industries;
Lincolnshire, IL) three times daily, at 7 AM, 2
PM, and 8 PM. Each subject recorded morning,
midday, and evening PEF readings (three blows for each measurement) for
the 2-week period before exposure and during the period of exposure.
The morning PEF measurement during the exposure period was performed
just before starting work. Participants were instructed to record the
highest of the three PEF readings in the diary card. The PEF was
expressed as measured (liters per minute) and as a percentage of the
subjects’ maximal values during the study period. Any respiratory
symptoms were also recorded. Symptoms noted in the diary were cough,
wheezing, sputum production, dyspnea, and hemoptysis.
Statistical Analysis
The data were analyzed as prevalence odds ratios (ORs) for the
presence of various respiratory symptoms among the charcoal workers
before and during the exposure period and between the charcoal workers
and the control group. Paired Student’s t test was used to
compare the variables before and during the exposure period. A
Mann-Whitney U test was drawn to compare the mean values of
spirometric variables, PEF measurements, and symptom scores between
workers and control group. A nonparametric Wilcoxon signed-rank test
was used to compare proportions. For all statistical tests, a
probability of 0.05 was taken as significant. All analyses were
performed using software (SPSS 6.0 for Windows; SPSS; Chicago, IL).
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Results |
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Symptoms
ORs and their associated 95% confidence intervals (CIs) for the
prevalence of various respiratory symptoms in the control group and in
the charcoal workers are shown in Table 1
(Wilcoxon signed rank test). The workers had significantly elevated ORs
during the exposure period for symptoms such as cough (OR, 4.8), sputum
production (OR, 6.0), wheezing (OR, 7.7), dyspnea (OR, 28.7), and
hemoptysis (OR, 12.7; Table 1
). All workers complained of headache, and
acute eye, nose, and throat irritation during the exposure period.
Table 2 shows the ORs and 95% CIs for the prevalence of respiratory symptoms
in the workers before and during the exposure period (Wilcoxon
signed-matched-pairs rank test). During the exposure period, the
workers had significantly elevated ORs for the respiratory symptoms:
cough (OR, 4.5), sputum production (OR, 5.7), wheezing (OR, 9.8), and
dyspnea (OR, 36.7). There was a trend to have more symptoms when the
workers spend more time tending the pyrolyzing procedure, but this
trend was not significantly different. Nonsignificantly elevated ORs
were found for hemoptysis (OR, 8.0). Findings of a complete checkup of
workers with hemoptysis, including bronchoscopy, sputum cytology with
microbiology, and CT of the chest, were negative for malignancy or
infection. Bronchoscopy showed no active bleeding. Endoscopic findings
of subacute bronchitis were observed. In one worker, high-resolution CT
showed bronchiectases in the left upper lobe. All three workers were
current smokers. Symptoms in current smokers and nonsmokers did not
differ in response to wood smoke.
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Discussion |
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The charcoal workers had an short-term postexposure decline in PFT indexes, including FVC, FEV1, FEV1/FVC ratio, and FEF25–75%. The exposure of the population studied is somewhat similar to the exposure to smoke produced by fires in the open country (wildland fires). Charcoal workers, like wildland firefighters, are exposed to several vegetative resinous combustion products, including CO, aldehydes, acids, respirable particulates, and semivolatile and volatile organic agents.1 15 16 Moreover, exposure patterns and work practices have remarkable similarities in both occupations. Suppression activities in open-country and forest fires have a potential for long uninterrupted periods of exposure to smoke.2 3
In this study, the workers were exposed to wood smoke for a long time, approximately 9 to 19 h/d for a total of 2 to 4 weeks. Taking into account the similarities between the exposures of wildland firefighters and charcoal workers, we could compare our data with the studies on firefighters working in forest fires. Five previous cross-seasonal studies1 2 3 6 17 of wildland firefighters have reported similar PFT declines associated with recent fire-fighting activities and smoke exposure. Our findings are in accordance with the PFT measure decline seen in these studies, but the magnitude of the decline in PFT measures of the population in our study is generally greater than in the studies of firefighters. The California Department of Health Services study18 found mean individual declines for FVC, FEV1, and FEF25–75% of 90 mL, 150 mL, and 0.44 L/s, respectively.18 The Johns Hopkins University study17 found that FVC and FEV1 declined by 130 mL and 101 mL, respectively, in the group classified in the highest exposure category, which averaged 73 h of fire fighting. The PFT decrements of charcoal workers were 157 mL for FVC, 196 mL for FEV1, and 4.4 L/s for FEF25–75%, and are comparable to those of wildland firefighters in the highest exposure categories (heavier and more prolonged exposure period). We should also note that the charcoal workers never used respiratory protective equipment at any time during the burning period of the kilns.
In addition to the dynamic spirometric changes, a significant postexposure decline of maximal expiratory flow rate (PEF) was observed in charcoal workers. Our results are in agreement with the data of Thomas,19 who reported a statistically significant decrease in several pulmonary indexes, including PEF, after fire fighting. The mean postexposure PEF changes in this study were 16 L/min, 24 L/min, and 26 L/min for morning, midday, and evening measurements, respectively. The PEF decline has a tendency to be greater at midday and evening. This diurnal pattern of the PEF decline may reflect that the flows were affected by the exposure time during the day. Alternatively, the decreases in flows may have been partly reversed after a relatively short period of cessation of exposure to irritants during the previous night. The data of the present study are not enough to differentiate between these two hypotheses. Moreover, it should be noted that the study was not designed to evaluate either the association between the magnitude of exposure and the pulmonary function changes or the reversibility of short-term pulmonary changes after cessation of the exposure to smoke irritants. There has been an ongoing longitudinal study of our cohort of charcoal workers for 3 years now, aiming to determine whether the short-term decrements in lung function seen in this study are causing long-term chronic respiratory effects. These long-term effects have been reported in studies of wildland firefighters7 8 and in studies of indoor firewood smoke exposure.10
An increase in reports of respiratory symptoms accompanying the decreases seen in lung function across the work shift was observed in this study. Studies of wildland firefighters showed similar cross-season changes in prevalence in one or more respiratory symptoms.2 6 17 In the study of Serra et al,3 an increased prevalence of cough and sputum production long after the fire-fighting season was reported.
We should emphasize the observed hemoptysis in three workers. On bronchoscopy, a subacute bronchitis was found. Subacute bronchitis because of the heavy wood smoke exposure may explain the increased lower respiratory tract symptoms observed in this study. We do not know whether the bronchiectasis diagnosed in one of the workers was related to long-term wood smoke exposure or was simply an incidental finding.
The mechanisms underlying the increased respiratory symptoms and lung function abnormalities to wood smoke exposure are uncertain. Wood and vegetative combustion materials emit smoke with a variety of respiratory irritants and noxious agents, such as CO, aldehydes, acids, SO2, NO2, respirable particulates, and semivolatile and volatile organic agents.16 20 Certain characteristics of the work, such as extended work demands, leading to long work shifts and increased breathing rate, enhance the toxic effects of the noxious agents on the respiratory system. High CO levels in wood smoke of open kilns have been detected in the Zambia study by Ellegard.16 Moreover, studies1 on wildland firefighters found levels of COHb to be from 5 to 9%. Inhalation of CO in combination with combusted particulates produces headaches, nausea, sore throat, and irritation.17 Complaints of daily headache and irritation were reported from all charcoal workers in this study. It has also been reported20 that aldehydes and acids reduce the ciliary activity of the respiratory tract, interfering with the ability of the airway epithelium to remove particles and microorganisms. This may explain the increased cough and sputum expectoration seen in charcoal workers. Moreover, several air pollutant components of wood smoke, such as SO2, NO2, and particulates, have been reported21 to increase respiratory symptoms and to affect lung function even in low concentrations. High concentrations of irritant gases have been reported22 23 to cause pulmonary symptoms resembling asthma, a condition known as reactive airway dysfunction syndrome (RADS). Moreover, a short-term increase of airway responsiveness has been reported in firefighters.24 We suspected RADS in two workers with a large PEF decrease (Fig 2) . Unfortunately, methacholine challenge was not applied in this study in order to assess airway hyperresponsiveness. Thus, it is unclear if these two workers in fact had RADS.
In conclusion, both increased respiratory symptoms and worsening of lung function found in this study indicate an short-term cross-season and midseason effect associated with smoke exposure because of the pyrolyzing of wood to produce charcoal. The changes in lung function seen in this study should be of concern for potential long-term adverse respiratory effects in charcoal workers. Longitudinal studies are needed to determine the long-term effects on the respiratory system in this traditional occupation.
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Footnotes |
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Received for publication February 29, 2000. Accepted for publication October 31, 2000.
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