Unveiling Exposure Pathways at the Oral Cavity during Firefighting Work: Salivary Metal(loid)s and Polycyclic Aromatic Hydrocarbons, Occupational and Biological Determinants, and Exploratory Health Risks

Fire emissions are environmental contaminants with hazardous effects on the environment and human health. Human exposure to fire emissions occurs mainly via inhalation and dermal contact, while buccal exposure concentrations remain largely underexplored. This work characterizes, for the first time, exposure to metal(loid)s and polycyclic aromatic hydrocarbons (PAHs) at the oral cavity during firefighting work, accounting for five occupational and personal-life variables. Paired spot saliva samples were collected by 58 firefighters [organized in 4 groups: non-smoker non-exposed (NSNE), non-smoker exposed (NSE), smoker non-exposed (SNE), and smoker exposed (SE)] pre- and post-firefighting work. About 65–67% of firefighters showed increased metal(loid) and PAH levels after firefighting, with greater increments observed in smokers than in non-smokers. ∑metal(loid)s (18.7-28.6 μg/L) were up to 1.5x increase in SE than in NSNE, with Cu and Sr as the most abundant metals; similar findings were found for toxic/carcinogenic metal(loid)s (1.06-1.75 μg/L). ∑PAHs (1.19-1.40 μg/L) were slightly increased in NSE participants with seven detected compounds (naphthalene > phenanthrene > fluorene > anthracene > fluoranthene > pyrene) in all participants. Evidence suggests the potential bioaccumulation of metal(loid)s with the increase of BMI. Participants exposed to fires for more than 1h presented up to 1.8-2.1 higher salivary metal(loid)s compared to those exposed for less than 1h. NSNE firefighters with longer careers (> 10 years) presented 2.3x increased levels than those with less than 10 years. Salivary content represents a biomonitoring exploratory screening used in a toxicological screening based on conventional environmental risk assessment. Benzo(a)pyrene total toxicity equivalent concentrations and average daily potential dose were low with negligible non-carcinogenic (<1) risks and predominantly acceptable carcinogenic risks (10 -6 – 10 -4 ). Overall, smoking and firefighting work increase salivary PAHs and meta(loid)s levels despite personal protective equipment use. These findings motivate targeted strategies to reduce exposure and promote long-term occupational and public health.