Annals of Occupational Hygiene Advance Access first published online on January 23, 2008
This version published online on February 4, 2008
Annals of Occupational Hygiene, doi:10.1093/annhyg/mem063
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A Population-Based Study on Welding Exposures at Work and Respiratory Symptoms
1 Department of Occupational and Environmental Medicine, Sahlgrenska University Hospital, Göteborg, Sweden
2 Centre for Research in Environmental Epidemiology (CREAL)/Municipal Institute of Medical Research (IMIM), Barcelona, Spain
3 CIBER Epidemiology and Public Health, Spain
4 Institute for Risk Assessment Sciences, Utrecht University, The Netherlands
5 Department of Respiratory Epidemiology and Public Health, National Heart and Lung Institute, Imperial College, London, UK
6 Department of Allergology Sahlgrenska Academy at Göteborg University
7 Department of Social Medicine, Medical School, University of Crete, Heraklion, Greece
* Author to whom correspondence should be addressed. Tel: +46-31-786-6289; Fax: +46-31-40-9728; E-mail: linnea.lillienberg{at}amm.gu.se
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONAIMSMETHODSRESULTSDISCUSSIONCONCLUSIONFUNDINGREFERENCES |
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In the first European Community Respiratory Health Survey (ECRHS I), an excess asthma risk was associated with high exposure to gases and fumes, mineral and biological dusts. In a 9-year follow-up study (ECRHS II), the aim was to study if welding at work increases the risk of asthma symptoms, wheeze and chronic bronchitis symptoms. The study also aimed to identify specific welding risk factors. In a random population sample of individuals from 22 European centres in 10 countries, 316 males reported welding at work during the follow-up period. These individuals responded to a supplemental questionnaire about frequency of welding, use of different methods and materials, welding environment and respiratory protection. Cumulative exposure to welding fumes for the follow-up period was estimated by using a database on welding fume exposures. Log-binomial regression models were used to estimate prevalence ratios (PR) with 95% confidence intervals (CIs) for prevalence of asthma symptoms or asthma medication, wheeze and chronic bronchitis symptoms in relation to welding methods and welded materials as well as estimated cumulative welding fume exposure compared to an external reference group. In the study population of 316 males, 62% performed welding <1 h day–1, 23% 1–3 h day–1 and 15% >4 h day–1. Welding was a common task in many occupations and only 7% of the individuals actually called themselves welders and flame cutters, while the largest groups doing welding worked in construction or were motor, agricultural and industrial mechanics and fitters. Welding at work was not associated with an increased prevalence of asthma symptoms or wheeze but there was an association with chronic bronchitis symptoms (PR = 1.33, 1.00–1.76). Using assigned cumulative exposure in tertiles showed that the lowest exposed tertile had the highest PR of bronchitis symptoms. Chronic bronchitis symptoms was significantly higher in those frequently welding in galvanized steel or iron (PR = 2.14, 1.24–3.68) and in those frequently manual welding stainless steel (PR = 1.92, 1.00–3.66). There was also an increase in the prevalence of wheeze in individuals welding painted metal (PR = 1.66, 0.99–2.78; PR = 1.83, 0.90–3.71). Welding with manual metal arc technique <1 day week–1 showed a prevalence risk of 1.69 for wheeze (CI = 1.16–2.46). In conclusion, the present study shows an association between welding in galvanized material and stainless steel and chronic bronchitis symptoms. There was also an increased prevalence of wheeze and welding in painted metal. The results support that welding in coated material is a respiratory hazard underscoring the importance of preventive actions.
asthma medication • asthma symptoms • chronic bronchitis symptoms • epidemiology • male • stainless steel • welding • welding techniques • wheeze
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INTRODUCTION |
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Welding and welding fumes are associated with occupational asthma, metal fume fever, chronic bronchitis and lung function abnormalities (Antonini, 1983; Sferlazza and Beckett, 1991). The type and amount of welding fumes and respiratory symptoms depend on duration of welding, welding method, welding material, ventilation facilities and respiratory protection.
There are very few population-based studies on welding exposures and health effects in the general population. In the European Community Respiratory Health Survey (ECRHS I), the occupational group of welders was too small to be analysed separately (Kogevinas et al., 1999). In another population-based study (Torén et al., 1999) exposure to welding fumes was associated with an increased odds ratio for ‘physician diagnosed asthma’ as well as increased risks of ‘asthma like symptoms’.
There are several cross-sectional and case studies on welders reporting respiratory symptoms. In case studies, occupational asthma has been reported in workers welding in aluminium (Vandenplas et al., 1988) and stainless steel (Keskinen et al., 1980; Hannu et al., 2005). In a study by Wang et al. (1994), they found no difference in asthma incidence for workers welding in stainless steel compared to welding in mild steel but higher prevalence of airway symptoms as compared to a referent group. In a group of 134 stainless steel welders, a higher prevalence of cough or sputum production was found (Sobaszek et al., 1998). An increased prevalence of chronic cough, phlegm and wheeze has also been shown in young shipyard welders and caulkers/burners (Chinn et al., 1995). In a cross-sectional study of welders in New Zealand (Bradshaw et al., 1998), symptoms of chronic bronchitis were more common in current welders than non-welders and those with higher total lifetime welding fume exposure index. A longitudinal study of apprentice welders showed a significant association between welding-related metal fume fever and respiratory symptoms as well as a decrease in lung function values after 15 months in welding school (El-Zein et al., 2003, 2005). In a 2-year follow-up study of pulmonary function values among welders, no overall difference was found compared to a referent group of non-welders. If the analyses were restricted to only smokers the welders had a significantly greater annual decline in forced expiratory volume in 1 s (Erkinjuntti-Pekkanen et al., 1999). Welding in painted metal will give low exposure to irritating degradation products like formaldehyde, alkylbenzenes, chlorendic anhydride and airborne hydrogen chloride (Engstrom et al., 1988; Pfäffli et al., 2002).
This study is an investigation within the 9-year follow-up study of the ECRHS of individuals who reported welding at work during the follow-up period. Contrary to most studies on welders, we asked about welding at work regardless of occupation, which comprised a more extensive group of workers actually welding at work and not only individuals who have welding as their occupation.
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AIMS |
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The purpose of the investigation was to study if welding at work increased the prevalence of asthma symptoms, wheeze or chronic bronchitis symptoms and if so to identify which specific welding factors were responsible.
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METHODS |
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European Community Respiratory Health Survey
A European population-based cohort study comprising 28 study centres in 13 countries was started in 1991 (Burney et al., 1994). In 1998–1999, there was a follow-up in 22 centres in 10 countries (ECRHS II). In the follow-up, each individual completed an interview-administered main questionnaire, including a survey about respiratory symptoms and asthma therapies, filtering questions asking if they performed seven specific activities: cleaning (professionally or at home), disinfecting, nursing, metal working, soldering or welding. Individuals giving positive answers to any of the specific activities had to respond to a short supplemental questionnaire (module) about selected tasks and duration of activities for each relevant job held during the follow-up. Information about the set-up of the survey has been published (ECRHS II Steering Committee, 2002).
Study population
In the random population of the ECRHS II, there were 316 men who reported that they had been doing welding at work during the follow-up period and had answered at least one questionnaire (module) on welding activities. If the individuals performed welding at work in another time period between ECRHS I and ECRHS II with essentially different working tasks, they had to complete another welding module. For individuals with two or more modules, the highest frequencies of welding exposures were selected. The estimation of cumulative welding fume exposure, however, did incorporate multiple welding modules.
For comparison, we selected all male from the random sample answering any module except welding at work or home, resulting in 2610 men. These individuals had filled in at least one module where they reported that they had performed cleaning, disinfecting, nursing, metal working or soldering for at least 3 months during the follow-up period or doing the cleaning and/or washing at home.
Occupational history
In the main questionnaire, all subjects were asked about different jobs (job title, company or organization, start and stop year) during the follow-up period starting with the current job. Professional and/or administrative jobs were classified according to the International Standard Classification of Occupations (ISCO) codes (International Standard Classification, 1990) in four-digit codes together with the information given about job title and branch in the free text. Three subjects in the final group had not filled in their job history with job duration and type of job in the main questionnaire and no cumulative exposure could be estimated, which gives 313 individuals with cumulative exposure.
Welding modules
Subjects welding at work filled in a welding module with nine questions about welding tasks and activities (complete questionnaire publicly available on www.ecrhs.org). They were asked about hours per day and days per week they carried out welding, frequencies of using different welding methods and materials. They answered questions on frequencies performing welding by hand and/or operating a fully automated machine, how many days per week they were welding in confined spaces, workshops, shipyards and outdoors. They were also asked about type of ventilation and use of respiratory protection. To create exposure variables, we dichotomized the frequency of welding methods and welding materials in <1 day week–1 and 
1 day week–1. Duration of exposure in years of welding at work was only taken into account in the calculation of cumulative exposure.
Quantitative assignment of welding fume exposure
A welding fume database built from exposure measurements collected over a 20-year period (1983–2003) in the Netherlands was used in the calculation of cumulative exposure of welding fumes (Kromhout et al., 2004). Part of this database has successfully been used previously for the construction of a welding fume-exposure matrix for a multicentre study on lung cancer among European welders (Gérin et al., 1993). Briefly for the current study, a linear mixed effects model algorithm derived from the database was used with time trend, welding method, effect of presence of general ventilation, local exhaust ventilation and use of helmet with fresh air supply as factors affecting welding fume exposure. The algorithm together with information about welding tasks and activities from the modules and job history from the main questionnaire were used to create a record per year resulting in a cumulative welding fume exposure (mg m–3 week-years) for each individual.
Health outcome
- Asthma symptoms or medication was defined as a positive response to ‘Have you had an attack of asthma in the last 12 months’ and/or ‘Have you been woken by an attack of shortness of breath at any time in the last 12 months’ and/or ‘Are you currently taken any medications for asthma’.
- Wheeze was defined as a positive answer to the question ‘Have you had wheezing or whistling in your chest in the last 12 months when you did not have a cold’.
- Chronic bronchitis symptoms was defined as a positive answer to ‘Do you usually cough for as much as 3 months each year’ and/or ‘Do you usually bring up phlegm from your chest on most days for as much as 3 months each year’.
Statistical analysis
Statistical analyses were done using SAS statistical package version 8 and Stata software version 8. An algorithm based on a linear mixed effects model was used to assign welding fume exposure. Log-binomial regression models were used to estimate prevalence ratios (PR) with 95% confidence intervals (CIs) for welding characteristics and respiratory outcome. All PR were adjusted for age, smoking status at follow-up, geographical area and asthmagens including high molecular weight agents and low molecular weight agents assessed by a job-exposure matrix (Kogevinas et al., 2007).
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RESULTS |
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The mean age of the welders was slightly lower and current and former smokers slightly higher compared to the reference group (Table 1). In the welding group, the percentage of individuals from north Europe was higher and from middle Europe lower compared to the reference group. Among the welders, 7.7% reported asthma symptoms or medication, 17.0% wheezing and 15.8% chronic bronchitis symptoms compared to 9.6, 13.9 and 11.1% in the referent group, Table 1.
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Welding at work was an activity performed in many occupations (Table 2). In total, 102 different ISCO codes were registered. The subjects could be grouped in 17 different occupational categories, where welders and flame cutters only comprised 7%. Welding was a common task among, e.g. construction workers (20%), motor vehicle, agricultural and industrial mechanics and fitters (17%) and plant and machine operators (11%).
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In the study group of male welding at work, more than half performed welding <1 h day–1, about one-fourth performed welding 1–4 h day–1 and 15% >4 h day–1. About two-thirds of the men used manual metal arc (MMA) welding but only 10% applied MMA
4 days week–1. About half of the men performed welding with metal active/inert gas welding, one-fourth reported tungsten inert gas welding while submerged arc welding and flux cored welding were more seldom used, Table 3. Most individuals used more than one welding technique. Welding by hand was performed by 96% of the subjects compared to 13% reporting welding by a fully automated welding machine. Only 13 men (4%) never performed manual welding. Most of the subjects performed welding in several different materials. In the study group, 37% of the men welded in stainless steel but only eight (2.6%) performed welding in only stainless steel. Most men performed welding in mild steel and galvanized iron or steel and almost half of the study group also did welding in painted material.
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Most men (85%) performed welding in workshops but they could also be welding at other locations. At the workplaces, more than half of the subjects had general mechanical ventilation, 37% had local exhaust ventilation at fixed places, 20% had mobile exhaust systems and 9% exhaust ventilation on-tool tip. Less than 10% of the subjects used face mask with filter or face shield with fresh air supply during welding. The differences in exhaust ventilation and use of respiratory protection between those welding <1 day week–1, 1–3 days week–1 and >3 days week–1 were relatively small. Those welding <1 day week–1 used less frequent local mobile exhaust ventilation (14.5% compared to 21%) and face mask with filter and face shield with fresh air supply (8 and 5% compared to 10–11% and 8–9%, respectively), but most individuals did not use mobile exhaust ventilation or respiratory protection.
Health outcome
Welding at work did not increase the prevalence of asthma symptoms or medication or wheeze compared to the reference group independently of duration of exposure per day (Table 4). There was a significant increase in prevalence of chronic bronchitis symptoms in the study group (PR = 1.33, 1.00–1.76), with almost the same PR for welding <1 h day–1, 1–4 h day–1 or >4 h day–1 (PR, respectively, 1.35, 1.26 and 1.33).
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Asthma symptoms or medication was increased, however, without statistical significance, among those frequent welding in stainless steel (PR = 1.37, 0.46–4.15). Chronic bronchitis symptoms was significantly increased in those welding in galvanized steel or iron
1 day week–1 (PR = 2.14, 1.24–3.68), increased in those frequent welding in stainless steel (PR = 1.82, 0.96–3.44) and significantly increased in those infrequent welding in painted metal (PR = 1.79, 1.06–3.02) (Table 5). An increased prevalence of wheeze was seen in those welding in painted metal (PR = 1.83, 0.90–3.71; PR = 1.66, 0.99–2.78) as well as in those infrequent welding in galvanized steel or iron (PR = 1.56, 0.98–2.48). Welding in mild steel showed a significant decrease in the prevalence of chronic bronchitis symptoms independent of duration of welding.
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If the 13 men who answered that they never did manual welding but operated fully automated welding machines were excluded, the PR and confidence intervals were almost identical. The PR of chronic bronchitis symptoms among those welding in galvanized steel or iron remained similar (PR = 2.05, 1.18–3.55) and for those welding in stainless steel
1 day week–1 the association was stronger (PR = 1.92, 1.00–3.66).
Welding with the MMA technique <1 day week–1 increased significantly the prevalence of wheeze (PR = 1.69, CI = 1.16–2.46), while the same effect was not seen for MMA welding 1 day week–1 (Table 6). No significant increase in the prevalence of asthma symptoms or medication, wheeze or chronic bronchitis symptoms could be seen for any of the other welding methods.
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Using tertiles of the assigned cumulative exposure (cut-off points 0.02–0.31, 0.31–1.67, 1.67–30.88 mg m–3 week-years), there was a significant increase in the prevalence of chronic bronchitis symptoms in the lowest tertile (PR = 1.57, CI = 1.04–2.37) (Table 7). Prevalence of wheeze tended to be higher in the lowest cumulative exposure tertile (PR = 1.32, CI = 0.89–1.95).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONAIMSMETHODSRESULTSDISCUSSIONCONCLUSIONFUNDINGREFERENCES |
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In this 9-year follow-up study of male individuals performing welding at work, we could not show an increased prevalence of asthma symptoms or medication independent of frequency of welding. In the ECRHS I, Kogevinas et al. (1999) showed increased (not significant) asthma for 100 welders compared to a large reference group of professional, administrative and clerical workers. In the same study, a job-exposure matrix with exposure to gases and fumes showed a significant increase of asthma in the group with high exposure to gases and fumes. It is difficult to compare the specific findings for welders from the ECRHS I with this follow-up study as ‘welders’ in ECRHS I only comprised <10% of those performing welding at work as we found out during the follow-up study. In addition, the individuals exposed to gases and fumes in ECRHS I were a much more heterogeneous group than those doing welding at work.
Frequent manual welding in stainless steel or frequent welding in galvanized steel or iron increased (not significantly) the PR of asthma symptoms or medication compared to the reference group. The PR of asthma in the total group of welding at work was 0.77 compared to the reference group. This indicates that individuals welding at work are healthier than people in general or that those with asthma symptoms stop welding at work. The number of individuals doing frequent welding in stainless steel or frequent welding in galvanized steel or iron was rather low (43 and 59 individuals), why it might be difficult to demonstrate significant relations even if they exist.
Chronic bronchitis symptoms was significantly increased in the whole study group as well as in those frequent welding in stainless steel or galvanized steel or iron. Welding in galvanized steel or iron and increased risk of chronic bronchitis has been shown in other studies (Chinn et al., 1995; Bradshaw et al., 1998). El-Zein et al. (2003) showed a strong relation between at least one welding-related respiratory symptom (cough, wheezing or chest tightness) and having had metal fume fever, which indicated welding in galvanized material. The prevalence of wheeze was increased for individuals frequent and infrequent welding in painted material. This health effect might depend on contaminants generated from the coated material and is something that should be more investigated. Even if it is recommended that dry paint coating should be removed from an area around the seam before welding (Pfäffli et al., 2002), it might not always be done or not carefully enough.
For the assigned cumulative exposure, the PR for chronic bronchitis symptoms was highest in the lowest tertile indicating that those with low cumulative exposure had a higher risk of developing chronic bronchitis symptoms during follow-up. Several reasons for this phenomenon can be hypothesized. Individuals working in small workshops or at workplaces with few welding activities per day could be less motivated to use respiratory protection (Mirabelli et al. (2007). Another explanation could be that those who already have respiratory symptoms try to avoid welding activities to a greater extent than those without respiratory symptoms. Given that most of the individuals welding at work were not strictly welders, they might also have been exposed to other agents associated with respiratory health effects like wood and cement dust, for instance, for construction workers.
The reference group consisted of subjects who had answered the filtering questions and any module in the ECRHS II study except welding at work or at home. They included metal workers, solderers, nurses, cleaners, individuals using disinfectants or persons doing cleaning and washing at home, which are groups associated with elevated risks of having respiratory symptoms. In the reference group, the percentage of individuals reporting asthma symptoms or medication was higher compared to those welding at work, which might give an underestimation in the PR of asthma symptoms and welding. Exposures from soldering work might be compared with welding smoke and the same respiratory effects. If those answering soldering at work were excluded from the reference group, the differences in PR in Tables 4–7 were only marginal.
Strengths and limitations of the study
This study is probably the first population-based study to include workers doing welding from a variety of occupations and not only welders or flame cutters, which would give a more true relation between welding at work and respiratory symptoms. The external reference group belong to the same study group (ECRHS II) with the same method for health assessment. Our definition of asthma symptoms or medication has also been validated in the ECRHS I (Kogevinas et al., 1999) against bronchial responsiveness.
In the detailed questionnaire about welding tasks, methods and materials, it was possible to discriminate between large quantitative and qualitative variation in exposures. The semiquantitative measures of exposure used were hours per day welding, days per week welding with different methods, days per week welding in different materials and days per week performing manual welding and days per week a fully automated welding machine. Workers doing welding tasks either as welders or in other occupations usually have welding tasks differing from day to day and week to week, why it might be difficult to answer how many hours per day or days per week as a mean they do different welding tasks. When we compared days per week doing manual welding with hours per day welding, we got very similar numbers in the exposure groups indicating that the individuals ranked themselves in similar way independent of question format. It might also be difficult to estimate days per week using different welding methods, e.g. stainless steel and galvanized steel or iron. In order to increase the number of individuals in the subgroups and decrease uncertainties in the answers about high or fairly high exposure, we dichotomized the frequency of welding methods and welding materials in only two groups, <1 day week–1 and 1 day week–1. A limitation might be that the number of frequently doing different welding activities is small. This might decrease the possibility to detect health risks that actually exist.
This study is the first population-based study where quantitative estimates of cumulative welding fume exposure were assigned to individuals indicating that they welded at work. No clear exposure–response relation was apparent, given that the group with the lowest cumulative exposure had the highest PR for chronic bronchitis symptoms. This should not be surprising given the irregular welding practices and materials welded reported by the ECRHS II participants.
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CONCLUSION |
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TOPABSTRACTINTRODUCTIONAIMSMETHODSRESULTSDISCUSSIONCONCLUSIONFUNDINGREFERENCES |
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In this population-based study of welding at work during a 9-year follow-up, asthma symptoms or medication does not appear to relate significantly to welding. There was a significant relation to welding at work and chronic bronchitis symptoms. This could partly be explained by the increased prevalence of chronic bronchitis symptoms for those individuals frequently welding in galvanized steel or manual welding in stainless steel. At the same time, there was a significant increased PR of chronic bronchitis symptoms for those welding <1 h day–1 or with the lowest cumulative exposure. Frequent and infrequent welding in painted material increased the prevalence of wheeze, which might be an underscored health risk.
Welding at work is a common task in many occupations but the amount of time spent daily on welding is generally low. The largest groups doing welding worked in construction or were industrial mechanics and fitters, who could also be exposed to other exposures associated with respiratory symptoms.
The experiences with quantitative exposure assessment in this general population study are encouraging enough to continue to strive for more quantitative occupational exposure assessment in such studies.
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FUNDING |
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European Commission Quality of Life programme (QLK4-CT-1999-01237).
Received June 29, 2007; in final form November 1, 2007
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