Insights into the Atmospheric Persistence, Transformation, and Health Implications of Organophosphate Esters in Urban Ambient Air

Abstract

Transformation of organophosphate esters (OPEs) in natural ambient air and potential health risks from coexposure to OPEs and their transformation products are largely unclear. Therefore, a novel framework combining field-based investigation, in silico prediction, and target and suspect screening was employed to understand atmospheric persistence and health impacts of OPEs. Alkyl-OPE transformation products ubiquitously occurred in urban ambient air. The transformation ratios of tris(2-butoxyethyl) phosphate were size-dependent, implying that transformation processes may be affected by particle size. Transformation products of chlorinated- and aryl-OPEs were not detected in atmospheric particles, and atmospheric dry deposition might significantly contribute to their removal. Although inhalation risk of coexposure to OPEs and transformation products in urban ambient air was low, health risks related to OPEs may be underestimated as constrained by the identification of plausible transformation products and their toxicity testing in vitro or in vivo at current stage. The present study highlights the significant impact of particle size on the atmospheric persistence of OPEs and suggests that health risk assessments should be conducted with concurrent consideration of both parental compounds and transformation products of OPEs, in view of the nonnegligible abundances of transformation products in the air and their potential toxicity in silico.

Keywords: inhalation risk; novel organophosphate esters; particle size; suspect screening; transformation products.

Figure 1

Particulate and gaseous concentrations (pg m^–3) of traditional and novel organophosphate esters (OPEs) in urban ambient air of three different urban areas, three sewage treatment plants (STP), and a landfill [bar-chart] and the relative abundance (%) of individual traditional OPEs in the particulate and gaseous phases [pie-charts].

Figure 2

(a) Geometric mean diameters (μm) of particulate OPEs in different types of ambient air and (b) mean dry deposition velocities (cm s^–1) of particulate OPEs in different settings.

Figure 3

(a–c) Correlations between log-transformed concentrations of TBOEP and its transformation products in the atmospheric particles and (d–f) correlations between transformation ratios of TBOEP and particle diameters, estimated with the mean values using polynomial regression. Significant level was set at 0.05. The red shadow represents the 95% confidence interval.

Figure 4

(a) Spline curves show the mean deposition concentrations of total particulate OPEs in head airway (HA), tracheobronchial (TB), and alveolar (AR) regions of the human respiratory tract; solid and dotted lines represent occupational and nonoccupational exposure. (b) Box-whisker plots show the estimated daily intake (pg kg bw^–1 d^–1) of total OPEs and their transformation products (TPs) via inhalation; black dots represent the minimum and maximum values, and dash lines represent the mean values. (c) Cumulative probability (%) of hazard index for inhalation exposure to OPEs and TPs.