Urinary Pyrene Carboxylic Acid as a Novel Exposure Biomarker of Woodsmoke

Quantifying people's exposure to wildfires is essential for assessing related health risks. While hydroxyl metabolites of polycyclic aromatic hydrocarbons (PAHs) are commonly used exposure biomarkers of combustion-originated air pollutants, methylated PAHs are more abundant in woodsmoke than other sources. Thus, urinary PAH carboxylic acids, which are metabolites of methylated PAHs, may serve as more sensitive biomarkers of wildfire exposure. In this exploratory study, we developed an LC-MS/MS method to simultaneously quantify hydroxylated and carboxylic metabolites of PAHs and methyl-PAHs in urine. This method was then applied to 56 urine samples collected from 8 campers before, during, and after a 4-hour exposure to campfire. Campers also wore silicone wristbands to monitor ambient PAHs. We found that 1-pyrenecarboxylic acid (1-PYRCA) levels increased significantly at 4 h (96.9%, 95% CI: 2.60-101%), 6 h (96.8%, 95% CI: 5.85-107%), and 8 h (92.5%, 95% CI: 3.59-99.2%), and returned to baseline levels at 24 h. In contrast, the campfire exposure did not significantly increase other urinary PAH metabolites. Wristband PAHs also significantly increased during the 4-hour exposure. These results suggest the use of urinary 1-PYRCA as a sensitive exposure biomarker for woodsmoke and potentially for assessing exposure to wildfires.