Organophosphate Ester Transport, Fate, and Emissions in Toronto, Canada, Estimated Using an Updated Multimedia Urban Model

Organophosphate esters (OPEs), used as flame retardants and plasticizers, occur at relatively high concentrations in urban air and surface waters. We tested the hypothesis that some OPEs could be considered persistent and mobile organic compounds (PMOCs), using the poly parameter linear free energy relationship-modified Multimedia Urban Model (ppLFER-MUM) in Toronto, Canada, as a case study. Modeled air emissions of ∑6OPEs of 3300 (190–190 000) kg yr–1 were 10–100 times higher than emissions of polychlorinated biphenyls (∑5PCBs) and polybrominated diphenyl ethers (∑5PBDEs). Model results suggested that measured ∑6OPE stream concentrations of ∼2000 ng L–1 originate from emissions to urban air transferred to water mostly via precipitation. Water transport removed 7–28% of total air inputs compared to 0.1–10% for PCBs and 2–10% for PBDEs. Chlorinated OPEs were efficiently transported via surface water due to their persistence and high solubility. Loadings of ∑6OPEs to Lake Ontario from wastewater treatment plants, streams, and atmospheric deposition were 70%, 18%, and 13%, respectively, of ∑6OPE loadings of 3100 (1200–45 000) kg yr–1. Our results support the hypothesis that three chlorinated OPEs, tris(2-chloroethyl)phosphate phosphate (TCEP), tris­(chloroisopropyl)­phosphate (TCiPP), and tris­(1,3-dichloroisopropyl)­phosphate (TDCiPP), fit the profile of PMOCs due to their mobility and persistence in surface waters.