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 (HVOPM+NOx), or 2) an aftertreatment system containing a diesel oxidation catalyst and a diesel particulate filter (HVONOx). The exposure concentrations complied with current EU occupational exposure limits (OELs) of NO, NO2, formaldehyde, polycyclic aromatic hydrocarbons (PAHs), and future OELs of elemental carbon (EC) from 2023.
Exposure to HVOPM+NOx consisted of PM1 (≈90 µg m-3, 54 µg m-3 EC) and NOx (NO 3.4 ppm, NO2 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 HVOPM+NOx exhaust. Exposure to HVONOx consisted mainly of NOx (NO 2.0 ppm, NO2 0.7 ppm) with low level of PM1 (~1 µg m-3). Compared to filtered air, exposure to HVOPM+NOx and HVONOx caused higher incidence of self-reported symptoms (78%, 63%, respectively, vs. 28% for FA, p<0.03). Especially, exposure to HVOPM+NOx showed 40-50% higher eye and throat irritation symptoms. Compared to filtered air, a decrement in nasal patency was found for the HVONOx exposures (-18.1, 95%CI: -27.3 to -8.8 L min-1), and for the HVOPM+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 FEV1/FVC after exposure to HVONOx.
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.