Human exposure to green spaces and monoterpenes: discovery and use of α-pinene metabolites as biomarkers.

Exposure to green spaces has been linked to numerous health benefits, including a reduction in the risk of cardiovascular disease and lower mortality rates. However, to better understand how green spaces influence human health, it is essential to have valid, quantitative measures of greenness exposure. Building on our previous identification of urinary limonene metabolites as potential biomarkers of exposure, we now investigate α-pinene, another abundant plant-emitted monoterpene, to identify and quantify its urinary metabolites and evaluate their suitability as biomarkers. We used liquid chromatography-high resolution mass spectrometry (LC-HRMS) to analyze samples of human urine collected following either controlled α-pinene inhalation or real-world greenness exposure. Through a combination of pseudo-targeted and untargeted analyses, we discovered 22 α-pinene metabolites post-inhalation including nine novel structures, with two confirmed against synthetic standards. Relative quantitation of the urinary levels of the metabolites was used to estimate their kinetic parameters. A 4 h exposure to a forest environment resulted in significant increases in the most abundant metabolites. This suggests that α-pinene metabolites, specifically myrtenic acid glucuronide and dihydromyrtenic acid glucuronide, may serve as valid biomarkers when assessing individual exposure to green environments. When combined with other subjective and objective measures, these novel urinary biomarkers promote a more comprehensive assessment of exposure to greenness.