Effects of Renewable Diesel Exhaust on Lung Function and Self-rated Symptoms for Healthy Volunteers in a Human Chamber Exposure Study

Abstract Background: Diesel engine exhaust causes adverse health effects. Meanwhile, the impact of renewable diesel exhaust on human health is less known. In this study, nasal patency, pulmonary function, and self-rated symptoms were assessed in 19 healthy volunteers after two separate 3-hour exposures to renewable diesel (hydrotreated vegetable oil [HVO]) exhaust, and exposure to filtered air (FA) for comparison. The HVO exposures were generated with two modern non-road vehicles (2019) having either: 1) no aftertreatment system (HVO PM+NOx ), or 2) an aftertreatment system containing a diesel oxidation catalyst and a diesel particulate filter (HVO NOx ). The exposure concentrations complied with current EU occupational exposure limits (OELs) of NO, NO 2 , formaldehyde, polycyclic aromatic hydrocarbons (PAHs), and future OELs of elemental carbon (EC) from 2023. Results: Exposure to HVO PM+NOx consisted of PM1 (≈90 µg m -3 , 54 µg m -3 EC) and NO x (NO 3.4 ppm, NO 2 0.6 ppm). The average total respiratory tract deposition of PM1 was 27 µg h -1 . The deposition fraction of HVO PM1 was 40-50% higher compared to diesel exhaust PM1 from an older vehicle, due to smaller particle sizes of the HVO PM+NOx exhaust. Exposure to HVO NOx consisted mainly of NO x (NO 2.0 ppm, NO 2 0.7 ppm) with low level of PM1 ( ~ 1 µg m -3 ). Compared to filtered air, exposure to HVO PM+NOx and HVO NOx caused higher incidence of self-reported symptoms (78%, 63%, respectively, vs. 28% for FA, p<0.03). Especially, exposure to HVO PM+NOx showed 40-50% higher eye and throat irritation symptoms. Compared to filtered air, a decrement in nasal patency was found for the HVO NOx exposures (-18.1, 95%CI: -27.3 to -8.8 L min -1 ), and for the HVO PM+NOx (-7.4 (-15.6 to 0.8) L min -1 ). Overall, no change was indicated in the pulmonary function tests (spirometry, peak expiratory flow, forced oscillation technique), except a slight increase in FEV 1 /FVC after exposure to HVO NOx . Conclusion: Short-term exposure to HVO exhaust below the EU OELs did not cause severe pulmonary function changes in healthy subjects. However, an increase in self-rated mild irritation symptoms, and mild decrease in nasal patency after two HVO exposures may indicate irritative effects from exposure to HVO exhaust from modern non-road vehicles below future OELs.