Association between long-term occupational exposure to PM10 and allergic diseases in subway workers

Background: Long-term exposure to ambient particulate matter (PM) in adults increases the risk of allergic diseases exacerbation. We evaluated whether a long-term occupational exposure to subway PM10 is associated with the prevalence of atopic sensitization and allergic diseases (i.e., current asthma, current rhinitis or current eczema) and whether the latter are associated with biomarkers measured in exhaled breath condensate (EBC) of subway workers.

Methods: Participants were randomly selected from a 15,000-subway worker cohort. Individual inhaled PM10 mass (iPM10) per shift at work was estimated using a company-specific job-exposure-matrix based on PM10 measurements conducted between 2004 and 2019. iPM10 was modelled as function of PM10 exposure averaged over the participant’s employment in the Parisian subway, inhalation rate, and filtration efficiency of the respiratory protection used. Atopic sensitization was tested using skin prick tests. Allergic diseases were assessed using self-administered questionnaire. Associations were assessed using multivariable logistic regression models adjusted for potential confounders.

Results: Amongst 287 participants, 39% had an atopic sensitization, 25% a poly-atopic sensitization, 5% a current asthma, 35% a current rhinitis and 12% a current eczema. Mean exposure duration of PM10 was 23.3 years at a mean estimated concentration of 76.7µg/m3. This corresponds to an iPM10 of 0.6 µg/shift. Nitrite concentration in EBC was associated with atopic and poly-atopic sensitization, and current asthma (adjusted OR=2.95 [95%CI 1.21-7.19], 3.94 [95%CI 1.35-11.54] and 9.13 [95%CI 1.23-67.96] per µmol/L, respectively). iPM10 was associated with an increased risk of current asthma among locomotive operators OR=1.05 [95%CI 1.00-1.10] per 10 ng/shift.

Conclusion: This study showed for the first time the relationship between long-term exposure to subway PM10 and prevalence of asthma in some categories of subway workers. It also confirmed nitrite in EBC as a biomarker of atopy and current asthma, indicating its diagnostic interest. Our findings pave the way for future targeted interventions and further research in the field of occupational allergology. In particular, it highlights the potential for specific preventive measures to address occupational health risks of PM10. However, the study sample was small, and these findings need further confirmation.