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| Journal of the New Zealand Medical Association,
07-May-2004, Vol 117 No 1193
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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.
MethodsApproximately 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.
Exposure
Welding
history
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.
Hygiene
data
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.
Metal
analysis
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.
Exposure
attribution
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
Respiratory
symptoms
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.
Pulmonary
function
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.
Data
analysis
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
ResultsAs 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.
Exposure dataTable 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.
Respiratory symptomsSixteen 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.
Pulmonary functionAdequate 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.
DiscussionWe 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: david.fishwick@hsl.gov.uk
References:
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