Do Welding Fumes Cause Lung Cancer?

Do Welding Fumes Cause Lung Cancer?

1. What were the conclusions of Canadian researchers in 2017

"An excess lung cancer risk among welders is well established, but whether this is attributable to welding fumes is unclear. . . . Studies that are able to disentangle welding effects from smoking and asbestos exposure are needed. . . . This study found evidence to support the emerging hypothesis that lung cancer risk observed among welders cannot be attributed exclusively or directly to welding fume exposure, but may be largely attributable to nonwelding specific factors including possible occupational coexposures, including asbestos, or smoking." [PMID 28951802]

2. Is self-reported smoking behavior a source of error, especially in case control studies?

"Recall bias may arise because individuals with a particular exposure or adverse health outcome are likely to remember their experiences differently from those who are not similarly affected. . . . Similarly, in studies of exposures widely believed to be detrimental, such as cigarette smoking, individuals with a particular disease or other adverse health outcome might, consciously or unconsciously, tend either to exaggerate their actual level of exposure if they believe it to have caused their illness, or to minimize their exposure to appear more acceptable to the interviewers or investigators." [Hennekens, p. 35]

"Self-report is vulnerable to reporting and recall bias and has been shown to consistently underestimate total tobacco exposure, which may result in residual confounding. One way to mitigate this risk is to use an objective biochemical assay to validate self-reports of tobacco use. The most commonly used assays include exhaled carbon monoxide (eCO) or cotinine in serum, urine or saliva." [PMID 29631575]

"Thus, smokers may be more likely to exaggerate the extent to which their behavior conforms to the perceived social norm of "not smoking." [PMID 8017530]

"Cotinine is the main metabolite of nicotine, and its serum or plasma level is useful marker of tobacco smoking. . . . The Janus serum bank offers the opportunity to investigate for the first time prospectively the association between lung cancer risk and serum level of cotinine. . . . The results of this study show a strong, linear dose-response relationship between serum cotinine level and lung cancer risk among smokers." Shown below is Table 3 from this article. [PMID 16775179]

Table 3. ORs of lung cancer for serum cotinine level

Serum cotinine level (ng/mL)*

N cases

N controls

OR (95% CI)

0.1-5.0 (reference)

135

755

1.00

5.1-24.7

21

124

0.93 (0.46-1.9)

24.8-114.7

51

123

2.80 (1.55-5.05)

114.8-180.2

118

123

7.67 (4.75-12.4)

180.3-223.8

157

123

13.8 (8.70-22.0)

223.9-271.9

235

124

24.9 (14.9-39.0)

272.0-317.7

274

123

30.4 (19.5-47.3)

317.8-378.8

308

123

33.1 (21.7-51.4)

>378.8

442

123

55.1 (35.7-85.0)

*Categories are based on serum cotinine level only, not on self-reported smoking status.

3. Do studies show a dose-response relationship for exposure to welding fumes and the risk of lung cancer?

"The IARC multicentre cohort study comprised 11 092 welders employed in 135 companies in eight European countries (Denmark, England, Finland, France, Germany, Italy, Norway, Scotland, and Sweden) (Simonato et al., 1991). . . . A positive relationship was observed with time since first exposure for MS and SS welders, which was more evident for predominantly SS welders, but there was no clear positive trend with duration of employment." [IARC Monograph 118, p. 114]

"In a German study, Jöckel et al. (1998) reported a detailed assessment of exposure to welding fumes and exposure to asbestos through a set of job-specific questionnaires (around 20 questions) and a supplementary questionnaire on welding. . . . In this study, ever being exposed to welding fumes and gases was associated with a slightly elevated risk (OR, 1.25; 95% CI, 0.94–1.65), but no dose–effect relationship was seen with cumulative exposure expressed in lifetime hours of welding after adjustment for smoking and asbestos." [IARC Monograph 118, p. 158]

"A Swedish study reported that 62% of welding entailed asbestos exposure, according to a detailed exposure assessment by an industrial hygienist (Gustavsson et al., 2000). . . . Cumulative exposure was calculated as the product of intensity, probability, and duration of exposure over all job periods. In analysing the dose–effect relationship with cumulative welding exposure, Gustavsson et al. (2000) did not observe an elevated risk in the upper two quartiles of welding exposure after adjustment for asbestos and other potential confounders." [IARC Monograph 118, p. 158,182]

4. Do welders smoke more that the average person in the general population?

"Some population surveys in the United States have suggested that welders may smoke more than the general population (93-95), so that smoking could act as a confounder." [PMID 16539169]

"Welders have been found to smoke more than the general population." [PMID 22343633]

"A survey of the smoking habits as of 1984 indicated 10%-20% more daily smokers among the shipyard production workers than among Norwegian males." [PMID 8280640]

"Evidence from cross-sectional data from a sample of the cohort indicated that the welders smoked somewhat more than the US population and more than the nonwelders." [PMID 12109555]

5. Does welding cause lung cancer in experimental animals?

"No long-term studies on the effects of exposure to welding fumes in experimental animals treated by inhalation were available to the Working Group." [IARC Monographs - 118, p. 261]

6. What was the conclusion of IARC in 1989 about the risk of welders developing lung cancer?

Welding fumes were classified in Group 2B as "possibly carcinogenic to humans." The classification was based on "limited evidence in human beings" and "inadequate evidence" in experimental animals. The new classification in 2018 was based on "substantial new evidence" from "observational and experimental studies."

7. What is the substantial new evidence from experimental studies?

"There is strong evidence that welding fumes induce chronic inflammation and are immunosuppressive. . . . There is moderate evidence that welding fumes are genotoxic. . . . There is moderate evidence that welding fumes induce oxidative stress." [IARC Monographs - 118, p. 262-3]

8. What is the substantial new evidence from observational studies?

"Most of the more than 20 available case-control studies reported elevated risks of cancer of the lung for workers employed as welders reporting welding as their job task, or classified as or reporting to be exposed to welding fumes. The same was true for the majority of the more than 20 cohort studies that assessed the association between welding and cancer of the lung in several industries, and for 6 population-based cohort studies. Furthermore, these studies consistently observed positive associations for both arc and gas welding. In view of the constancy of these associations across different study designs, occupational settings, countries, and time periods, as well as the high quality of several positive studies, chance, information bias, or selection bias are unlikely to explain the results." [IARC Monograph 118, p. 257] In "Welding and Lung Cancer in a Pooled Analysis of Case-Control Studies" by Kendzia et al., "The database includes data on 15,483 male lung cancer cases and 18,388 male controls from 16 studies in Europe, Canada, China, and New Zealand conducted between 1985 and 2010." [PMID 24052544] All of the studies used in this meta-analysis were published after 1998.

9. Have welders' exposures to welding fumes increased or decreased since 1989?

". . . while exposure to welding fumes had decreased by 4% per year during 1983-2003, this was a lower rate of reduction than for other chemicals in the same geographic region." [IARC Monograph 118, p. 59]

10. According to IARC, do welding fumes cause lung cancer in occasional welders?

"Studies of risk estimates of occupations which may involve unspecific and infrequent welding (such as pipefitters, plumbers, and solderers), are excluded from this review; the frequency of welding in these occupations is not normally clear, and the groupings are too broad to meaningfully evaluate exposure as a welder. Studies that reported only broad occupational aggregations, combining welding with related occupations, were also excluded as they lack specificity for welding." [IARC Monographs - 118, p. 89]

11. Do welding fumes that contain Chromium VI or Nickel (known carcinogens) cause increased lung cancer?

"This meta-analysis which showed a 30% to 40% increase in the relative risk of lung cancer among welders as compared with rates in the general population, found no excess lung cancer risk among shipyard and stainless steel welders when compared with mild steel welders. " [PMID 16539169]

"Contemporary epidemiological evidence points to an increased lung cancer risk, particularly among stainless steel welders. . . . However, an increasing body of evidence has also suggested a risk among welders who work with materials other than stainless steel." [PMID 28951802]

"An analysis restricted to the two groups of ever SS welders and predominantly SS welders (potentially exposed to more Cr(VI) and Ni over time), with at least 5 years of employment and 20 years since first exposure, also failed to demonstrate a dose–response relationship." [IARC Monograph 118, p. 114]

"The excess risk did not seem to be associated with stainless steel welding." [PMID 8664959]

12. Does the fact that IARC labeled welding fumes as "possibly carcinogenic" in 1989 influence the reliability of subsequent case control studies?

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