Characterization on Respiratory Bioaccessibility of Organophosphate Esters Based on a Mouth–Throat Model, Exhaled Breath Condensate, and Sputum

To characterize the bioaccessibility of inhaled organophosphate esters (OPEs) in the respiratory tract, we employed a highly idealized mouth-throat model to investigate the occurrence, distribution, and deposition of 17 OPEs in airborne particulate matter (PM1, PM1-2.5, and PM2.5-10; n = 80 pairs) and gas phases (n = 48) under gradient temperature and humidity. OPEs concentrations were also measured in exhaled breath condensate (EBC; n = 50) and sputum (n = 30) from 30 adults. Total median ∑17OPEs concentrations in inhaled air were 4.7 ± 0.4 ng/m3, with ∼82.7% of particle-phase OPEs deposited in the upper respiratory tract and almost all gas-phase OPEs reaching the lungs. OPEs in PM2.5-10 showed the highest deposition efficiency in the upper respiratory tract (93.8%), followed by PM1-2.5 (77.5%) and PM1 (76.2%). Humidity enhanced deposition, whereas temperature had a minimal effect. Median ∑17OPEs concentrations in EBC and sputum were 0.29 ± 0.03 ng/m3 and 0.22 ± 0.06 ng/mL, indicating that ∼20.8% of inhaled ∑17OPEs was exhaled. Significant correlations (p < 0.05) between airborne particle-phase and exhaled OPEs suggest that the exhaled fraction derives mainly from particles. Bioaccessibility of 17 OPEs ranged from 32.9% [bis(2-tert-butylphenyl)phenyl phosphate] to 92.7% [tris(1-chloromethyl-2-chloroethyl) phosphate].