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Background: Millions of workers worldwide are exposed to diesel engine exhaust (DEE), a known genotoxic carcinogen. Alu retroelements are repetitive DNA sequences that can multiply and compromise genomic stability. There is some evidence linking altered Alu repeats to cancer and elevated mortality risks. However, whether Alu repeats are influenced by environmental pollutants is unexplored. In an occupational setting with high DEE exposure levels, we investigated associations with Alu repeat copy number., Methods: A cross-sectional study of 54 male DEE-exposed workers from an engine testing facility and a comparison group of 55 male unexposed controls was conducted in China. Personal air samples were assessed for elemental carbon, a DEE surrogate, using NIOSH Method 5040. Quantitative PCR (qPCR) was used to measure Alu repeat copy number relative to albumin (Alb) single-gene copy number in leucocyte DNA. The unitless Alu/Alb ratio reflects the average quantity of Alu repeats per cell. Linear regression models adjusted for age and smoking status were used to estimate relations between DEE-exposed workers versus unexposed controls, DEE tertiles (6.1-39.0, 39.1-54.5 and 54.6-107.7 µg/m 3 ) and Alu/Alb ratio., Results: DEE-exposed workers had a higher average Alu/Alb ratio than the unexposed controls (p=0.03). Further, we found a positive exposure-response relationship (p=0.02). The Alu/Alb ratio was highest among workers exposed to the top tertile of DEE versus the unexposed controls (1.12±0.08 SD vs 1.06±0.07 SD, p=0.01)., Conclusion: Our findings suggest that DEE exposure may contribute to genomic instability. Further investigations of environmental pollutants, Alu copy number and carcinogenesis are warranted., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2021. No commercial re-use. See rights and permissions. Published by BMJ.)

Objectives: Occupational asbestos exposure is causally linked to mesothelioma. However, whether exposure to only chrysotile asbestos is associated with mesothelioma risk, and the heterogeneity in risk by different fibre types/lengths remains unclear. We investigated whether mesothelioma risk differs among workers exposed to only chrysotile asbestos compared with chrysotile and ≥1 amphibole (ie, amosite, tremolite, anthophyllite and crocidolite) over the working lifetime., Methods: We analysed next-of-kin interview data including occupational histories for 580 white men (176 cases and 404 controls) from a case-control study of mesothelioma conducted in the USA in 1975-1980. Asbestos exposure was determined by an occupational hygienist using a job-exposure matrix and exposure categories included chrysotile only and nine chrysotile-amphibole mixtures. Logistic regression models were used to estimate the ORs and 95% CIs of mesothelioma, comparing each asbestos category to the unexposed group, adjusted for age at death and data source. Analysis of contrasts was used to assess overall heterogeneity and pair-wise differences in risk., Results: Exposure to long and short chrysotile only was associated with increased mesothelioma risk compared with the unexposed (OR=3.8 (95% CI 1.3 to 11.2)). The complex mixture of extra-long amosite, short and long chrysotile, tremolite and anthophyllite was associated with the highest risk (OR=12.8 (95% CI 4.1 to 40.2)). There was evidence for overall heterogeneity among the asbestos exposure categories (p heterogeneity=0.02). However, the lower risk observed for exposure to chrysotile only compared with the complex mixture was not significant (p difference=0.10)., Conclusions: Our findings suggest that policies aimed at regulating asbestos should target both pure chrysotile and mixtures that include amphibole., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2020. No commercial re-use. See rights and permissions. Published by BMJ.)

Objectives: Foundry work is a risk factor for lung cancer; however, the association with welding is unclear, as smoking is common among metalworkers and may mask the relationship. We evaluated whether history of welding and foundry work, independently and jointly, and employment duration were associated with lung cancer risk in heavy smokers., Methods: We analysed data from the National Lung Screening Trial, a prospective randomised trial of 53 454 heavy smokers (>30 pack-years) in the USA. Cox regression models were used to estimate the HRs and 95% CIs of medically/histologically confirmed incident lung cancer during the follow-up period (2002-2009) in relation to history and duration of welding and foundry work assessed via questionnaires, adjusted for screening arm, component study, sex, age, race/ethnicity, education, smoking status and pack-years, body mass index and personal/family medical history., Results: There were 2034 incident lung cancer cases throughout the follow-up. Increasing years of employment in welding (p-trend =0.039) and foundry work (p-trend =0.005) were related to increased lung cancer risk among heavy smokers. Having ever been employed (≥1 yr) as either a welder or foundry worker alone was associated with non-significant increased risks of lung cancer (HR=1.12 (95% CI 0.91 to 1.37) and HR=1.09 (95% CI 0.85 to 1.39), respectively). Further, there was a joint-effect in that those who were ever employed in both occupations had significantly increased risks (HR=1.48 (95% CI 1.08 to 2.04))., Conclusions: Our findings provide further evidence that exposure to welding/metal fumes may be associated with elevated lung cancer risk., Trial Registration Number: NCT00047385., Competing Interests: Competing interests: None declared., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.)