Strong inorganic acid mists and respiratory tract cancers: a meta-analysis

Background: Exposure to strong inorganic acid mists (SIAMs) in the workplace has been linked to respiratory tract cancers. Aims: We conducted a meta-analysis of cohort and case-control studies examining the association between occupational SIAMs and respiratory tract cancers other than laryngeal cancer, which is already established. Methods: Studies mentioned in the 1992 IARC Monograph on carcinogenicity of SIAMs were combined with later studies identified from a systematic search of Scopus, PubMed and Embase. Forest plots of relative risks (RR) and odds ratios were constructed for the 34 identified studies. A random-effects model was used to address heterogeneity. Results: An association between the roles associated with occupational SIAMs exposure and risk of lung (RR = 1.17; 95% confidence interval [CI] = 1.05-1.32), and nasal cancers (RR = 3.30, 95% CI = 1.16-9.41) was found. The risk of oral and pharyngeal cancer was also associated with SIAMs exposure-related roles (RR = 1.59, 95% CI = 0.98-2.57). Results did not differ by study design, gender or outcome for all three cancers. A positive association for lung cancer was found with chemical (RR = 1.25, 95% CI = 1.13-1.38), and metal and steel industries (RR = 1.19, 95% CI = 1.04-1.37), as well as for oral and pharyngeal cancer with chemical industry (RR = 1.72, 95% CI = 1.57-1.89). We checked publication bias for lung (p = 0.35), oral and pharyngeal (p = 0.02) and nasal cancer (p = 0.40). Conclusions: Our study showed an association between occupational SIAM exposure and risk of lung, nasal, and possibly oral and pharyngeal cancers. However, weaknesses in the recording of confounding and exposure data in the currently available literature were found.