Journal of the New Zealand Medical Association, 07-May-2004, Vol 117 No 1193
Respiratory symptoms and lung function change in welders: are they associated with workplace exposures?
David Fishwick, Lisa Bradshaw, Tania Slater, Andrew Curran, and Neil Pearce
Previous studies have documented excesses of chronic bronchitis and other respiratory symptoms in welders.1 More recently, in the same group of workers,4 we have described2 both across-shift changes in FEV1 in welders (and partially exposed non-welders working adjacent to a weld site),2 chronic bronchitis,3 and accelerated longitudinal decline in FEV1.4
However, our previous study of welders2,3 did not include a hygiene assessment of the workplace. Current welding-fume exposure was assessed using a combination of workplace factors and the use of respiratory protection or local extraction ventilation, but detailed exposure information was not available.
Therefore, we revisited four of the original eight work sites, to carry out a full hygiene assessment of total fume and metal exposure, in order to ascertain which agents were candidates for producing the adverse health effects seen in the previous study.
Approximately 11 months following our first study, 2,3 four of the original eight welding sites were re-visited. In brief, 137 welders and non-welders (comprising the consenting population of eight welding sites) were surveyed. In this study, we documented respiratory symptoms; baseline, pre-shift, lung function; and across-shift FEV1 (forced expiratory volume in 1 second, in litres), FVC (forced vital capacity in litres), PEF (peak expiratory flow in litres/minute), and FEF25–75 (forced expiratory flow25–75 in litres/minute). In addition, we measured FEV1 change after 15 minutes of work (in both welders and non-welders).
The four welding sites (re-visited for the current study) constituted a total available study population of 85, and 75 individuals consented to participate.
Previous welding exposure was calculated for each individual as previously described.2 Briefly, a cumulative index of previous fume exposure (expressed in years) was calculated for all workers—by summing all occupations in years associated with welding exposure, and multiplying by the proportion of time in each job spent welding.
All hygiene data was generated from site visits to the four chosen factories (factories 1, 2, 3 and 5 from our first study).
At each site, workers were approached and asked to wear personal samplers (GilAir 5, Gilian, USA) on their belt. IOM sampling heads5 were used to store pre-weighed 25-mm diameter microfibre filters, and sampling was carried out for variable sample lengths (approximating 4 hours). Flow rates were assessed at regular intervals throughout the sample period, and the total volume was calculated as the product of flow rate and time.
Gravimetric analysis (re-weighing the filters) was used to calculate total fume (expressed in mg/m3) for all workers. In addition, the filter was used to calculate specific metal levels.
All air samples were collected on 0.8 um MCE (metraccil) filters, and subsequently digested in nitric acid. Aliquots were then analysed by an inductively coupled plasma mass spectrometer.
For all 75 individuals in the study, a personal level of exposure to all the above parameters was estimated (shown in more detail in Table 1).
All 34 workers who were directly sampled were ascribed their own individual exposure value for all measured parameters. All values were expressed in mg/m3. Workers (welders and non-welders) who did not form part of the sampling exercise were ascribed an exposure value according to the following method.
All workers in the study were categorised as either: currently welding, not welding but in the vicinity of a welder, or not welding and not in the vicinity. For each separate work site, the mean (of all measurements in each of these three categories) was calculated and used as the exposure level for the remaining workers in those categories not yet ascribed. The majority of welders carried out metal inert gas (MIG) welds on a mild steel base.
Respiratory symptoms and pulmonary function
All workers had previously completed an interviewer-led respiratory questionnaire, and this data was again used for analysis. If an individual was new to the study (ie, had not been previously studied), the same investigator (DF) administered the identical questionnaire.
The study questionnaire included demographic data, current smoking habits, and questions about work-related and non-work-related respiratory symptoms. We recorded reports of current or recent cough, phlegm, wheeze, chest tightness, and shortness of breath—and whether these symptoms were related to work (this was defined as a symptom worse at work or improving on rest days). For the purposes of analysis, work-related symptoms were defined as the presence of any work-related lower respiratory tract symptom.
As previously described,2 all pulmonary function testing was performed for those workers who were new to the study when seen during the hygiene exercise. For those workers who had previously been studied, that data was used to assess possible FEV1 change at 15 minutes of work.
In brief, measurements were taken before shift (time 0), at 15 minutes after the start of a weld (or at a corresponding time for those workers not welding), and again at 7 hours into the working shift. On the study day, all pre-shift values occurred prior to any exposure to welding fume, and at least 16 hours after any previous weld.
FEV1, FVC, PEF, and FEF25–75 were measured using the best value of three forced expiratory manoeuvres in the standing position. For the purposes of analysis, those workers who sustained a 5% or greater fall in FEV1 after 15 minutes of work were regarded as having developed a clinically significant fall in lung function, and those workers with lesser degrees of fall, had not. All pulmonary function was measured using a calibrated portable spirometer (Alpha Spirometer, Vitalograph). A small number of workers did not complete three measurements for reasons of work commitment, and these have been excluded from the analysis of lung function.
All variables were then converted either into the percentage-predicted value for that individual, or as a percentage change from baseline, where the measurement at ‘time 0’ represents the baseline value.
All data were entered using dbase III (Ashton Tate, UK) and Microsoft Excel, and analysed using SPSS (version 8.0.2). Univariate analysis of the presence or absence of both respiratory symptoms (and a fall of at least 5% in FEV1) were carried out by categorising all demographic, smoking, exposure and hygiene data (dust and metal levels). In each case, a reference category was defined, and odds ratios were calculated to express the magnitude of effect for each variable.
Dividing metal exposure into high and low groups was carried out by stratifying—by using a cut-off of the mean value of all measurements in each category (where possible). If stratifying was not possible (for example, in the case of cobalt) where those with measurable exposure were placed in the high category, and those with no measurable exposure were placed in the lower category. That is, any measurable level above the limit of detection was placed in the high category. All cut-off levels between high and low exposure groups were decided a priori, and were not subsequently altered.
Logistic regression analysis was carried out using SPSS. Potentially predictor variables (including age, smoking, total fume, and other metal categories with elevated odds ratios) were entered into a logistic regression analysis. Similarly, the magnitude of effect seen for each independent variable in the logistic regression analysis was expressed by calculating an odds ratio and its associated 95% confidence limit.
All work carried out during this study was approved by the Wellington Ethics Committee, and all workers gave written informed consent to participate
As noted above, the industrial hygiene survey was carried out at four of the original eight welding sites included in the study. The working population of these 4 sites consisted of 85 workers, and 75 (89%) are included in the analysis.
The mean age of the 75 workers was 39.2 years (range 19 to 72 years). All workers were male, and 49 (65.3%) of them had only ever been a welder. Twenty-three workers were current smokers (30.7%) and 23 were ex-smokers (30.7%). The remaining workers had never smoked. The mean time spent working in the welding industry was 18.5 years.
Six of the workers reported a previous diagnosis of asthma (8%), although only one worker (1.3%) complained of an asthma attack in the previous 12 months. Of those 36 workers currently welding, 5 (13.9%) reported current use of local extraction ventilation.
Table 1 shows the mean exposure values for each work site. It is clear that there was a wide variation in all parameters measured, and that certain exposures were site-specific.
Table 1*. Hygiene assessment findings for total fume exposure and exposure to specific chemicals by welding exposure category
*Denotes not available (as no workers in this category). All data shown are in mg/m3 and represent mean values for all workers taken at each site, for each of three exposure categories. In second column, weld exposure 1 = current welding; weld exposure 2 = work adjacent to a welder; weld exposure 3 = not working as welder or adjacent to welder.
Sixteen workers (21.3%) complained of one or more work-related respiratory symptom. Univariate analysis relating to the presence or absence of work-related respiratory symptoms assigned odds ratios of unity to referent values. For example in Table 2, ‘never smoking’ is set as the referent category, and the odds ratio for ‘current’ and ‘ex’ smoking measures the effect in comparison to never smokers. Current work-related respiratory symptoms were significantly related to higher exposure to chromium, and non-significantly associated with proportion of the time spent welding in confined spaces.
Table 2 illustrates the results of the logistic regression analysis performed to investigate factors associated with the presence (or absence) of any work-related respiratory symptom, and shows a significant relationship between work-related symptoms and both nickel- and total-fume exposure.
Table 2. Odds ratios (and 95% CI) for work-related symptoms, by demographic factors and welding exposures (multivariate regression analysis)
*Adjusted for all factors in the model.
Adequate pulmonary function was available on 70 workers. The mean baseline FEV1 for all 70 workers was 4.06 litres (range 1.48–5.78, SD 0.85 litres). The mean change after 15 minutes welding/work for all workers was +1.77%, range –20.67 to +22.56). Eight workers had a fall of greater than 10% and eight had a fall of between 5 and 10%. Univariate analysis noted that a fall of at least 5% in FEV1 was significantly associated with higher aluminium exposure. In comparison to welding for less than four years, welding for between 4 and 10 years was negatively associated with this fall.
Table 3 illustrates the results of the multivariate logistic regression analysis performed to investigate factors associated with the presence (or absence) of at least a 5% fall in FEV1 after 15 minutes of welding (or after 15 minutes of work in the case of non-welders).
Table 3. Odds ratios (and 95% CI) for work-related 5% fall in FEV1 in 70 workers, by demographic factors and welding exposures (multivariate regression analysis)
*Adjusted for all factors in the model.
We have previously reported an elevated risk of chronic respiratory symptoms and acute work-related falls in lung function associated with current welding.2 The current study allowed us to return (approximately 11 months after our first cross-sectional study) to measure exposure levels at four of the eight work sites. We noted that levels of exposure were generally low, and indeed mostly fell below the recommended regulatory levels in New Zealand.6 Despite this, we found that just under a quarter of all of welders complained of work-related symptoms, and that the same proportion sustained a fall of at least 5% in FEV1 after 15 minutes of work.
We previously concluded that the main protective factor associated with a fall in FEV1 (of at least 5%) was the use of local extraction ventilation. Whilst implying that workplace exposures were the cause of the observed effects, the data did not enable us to assess which exposures were responsible.
The current study has used the same clinical information as in the previous study (except for the FEV1 data for those workers only taking part in the second study), and has combined this with newly collected exposure data.
Stratification (by exposure) was carried out by making certain assumptions, and this will undoubtedly have led to misclassification of various workers’ exposure levels. However, unless all workers are personally sampled, creating exposure levels in this way is required, and potential mis-classification is inevitable. Furthermore, arbitrary high and low exposure groups were created from within a group of workers exposed to relatively low levels of metals. Nevertheless, the object of this study was to test the hypothesis that current respiratory symptoms and work-related falls in FEV1 were related to workplace exposures, so we feel that this form of analysis was justifiable. Indeed, due to the limitations of this study, no attempts were made in this analysis to generalise these data to all eight original factories.
The main findings of the study were that currently reported respiratory symptoms in welders related significantly only to chromium exposure—with non-significant associations (non-significant odds ratios higher than 2.5) with higher levels of confined space welding and nickel exposure. Furthermore, multivariate analysis confirmed current nickel exposure alone as the main determinant of pulmonary symptoms (correcting for the effect of total fume exposure).
Similarly, univariate analyses found that a 5% fall in FEV1 (after 15 minutes of work) was significantly related to aluminium exposure. There were non-significant associations with confined space welding. The multivariate analysis confirmed that aluminium exposure (primarily) significantly determined the fall in FEV1 (again correcting for total fume exposure). The 5% cut-off value was used as the minimum thought to be significant. Indeed, 8 of the 16 workers (recording a fall in FEV1) had a fall greater than 10%.
One other potential problem with interpretation lies in the measurement uncertainty, although we feel that ‘random’ variation in FEV1 over 15 minutes would either have no effect on the mean fall for the group.
Both these findings appear clinically relevant, as both nickel and aluminium have previously been implicated in respiratory disease.7–11 The mechanisms underpinning these workplace findings are more complex, and less well understood.
Early work by Keskinen12 suggested that stainless steel welding, and particularly chromium and nickel exposure, was likely to cause occupational asthma, although this study was only based on a small number of workers. The association between stainless steel welding and respiratory symptoms was also recorded subsequently by Sobaszek,13 although pulmonary function changes in the welders were not clearly ascribed solely to welding-fume exposure.
Recent work has also noted that stainless steel welding is associated with significant increases in serum and urinary chromium.14 The situation with aluminium exposure remains less clear again, although work with aluminium has been previously linked to occupational asthma and marked asthmatic responses on specific challenge testing).15 Furthermore, aluminium exposure has been associated with small-airway dysfunction in welders.16
Clearly, certain factors influence the strength with which these results can be interpreted. Eleven months had passed between collection of the clinical data and the hygiene data, as funding for the hygiene component of the study was not available at the time initial clinical assessments were carried out. It is possible, of course, that work practice would have changed between clinical and hygiene assessments, although none of the sites or workers reported major changes in work practice.
Again, the analysis inevitably involved multiple comparisons within small groups. Nevertheless, the findings are biologically plausible and suggest that multiple comparisons alone are not responsible for the significant findings of the study.
The metals noted in this study (to predict significant health effect) are at least consistent with the published data to date, and this study suggests that metal exposure is an important potential cause of respiratory ill-health in welders. It is critically important to keep exposures to the lowest reasonably practical levels, and particularly in situations where nickel and chromium (stainless steel welding) and aluminium (aluminium welding) are likely to be significant.
Author information: David Fishwick, Co-Director; Lisa Bradshaw, Research Nurse Specialist, Sheffield Occupational and Environmental Lung Injury Centre, Respiratory Function Unit, Royal Hallamshire Hospital, Sheffield, UK—and (formerly) Wellington Asthma Research Group, Wellington School of Medicine, Wellington South; Tania Slater, Research Assistant, formerly Wellington Asthma Research Group; Andrew Curran, Head, Health Sciences Group, HSL, Sheffield, UK; Neil Pearce, Director, Centre for Public Health Research, Massey University, Wellington.
Acknowledgements: This study was funded by a limited budget from the Health Research Council of New Zealand; David Fishwick was supported (in part) by a grant from the Northern Regional Health Authority of the United Kingdom. The authors thank all the managers, union delegates, and factory workers that took part in this study. They also thank Hazel Armstrong (Engineers’ Union of New Zealand), and Mike Ward (ESR) for his help with metal analysis.
Correspondence: Dr David Fishwick, Sheffield Occupational and Environmental Lung Injury Centre, Respiratory Function Unit, Royal Hallamshire Hospital, Glossop Road, Sheffield S10 2JF, UK. Fax: +44 114 289 2768; email: firstname.lastname@example.org
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