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 relationshipmodified Multimedia Urban Model (ppLFER-MUM) in Toronto, Canada, as a case study. Modeled air emissions of ∑ 6 OPEs of 3300 (190−190 000) kg yr −1 were 10− 100 times higher than emissions of polychlorinated biphenyls (∑ 5 PCBs) and polybrominated diphenyl ethers (∑ 5 PBDEs). Model results suggested that measured ∑ 6 OPE 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 ∑ 6 OPEs to Lake Ontario from wastewater treatment plants, streams, and atmospheric deposition were 70%, 18%, and 13%, respectively, of ∑ 6 OPE 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(1,3dichloroisopropyl)phosphate (TDCiPP), fit the profile of PMOCs due to their mobility and persistence in surface waters.

Tris(chloropropyl) phosphate (TCPP) is an environmentally abundant organophosphate ester (OPE). TCPP is comprised of four isomers with seven possible structures, eight CAS numbers, and even more common names. A review of 54 studies reporting one or more TCPP isomers confirmed that the most abundant and most often reported TCPP isomer was tris(2-chloro-1-methylethyl) phosphate, also known as tris(chloroisopropyl) phosphate (TCiPP, referred to hereafter as TCPP1). Full-scan gas chromatography-mass spectrometry (GC-MS) was used to identify the other three isomers numbered here according to their elution order on a non-polar GC column (DB-5): bis(2-chloro-1-methylethyl) (2-chloropropyl) phosphate (TCPP2), bis(2-chloropropyl)(2-chloro-1-methylethyl) phosphate (TCPP3), and tris(2-chloropropyl) phosphate (TCPP4). GC with a flame ionization detector (FID) was used to identify the relative abundances of the isomers in commercially available standards with unknown isomer composition. In technical TCPP, TCPP1-4 isomers averaged 71 ± 1, 26 ± 0.4, 3 ± 0.5, and 0.1 ± 0.02%, respectively. When these percent masses are incorporated into GC-MS quantification, response factors (RFs) for TCPP1 and TCPP2 are significantly different from TCPP3 and TCPP4, indicating that the multiple RF approach is more accurate than the commonly employed single RF method. Samples from urban streams and wastewater treatment plant (WWTP) effluent from Toronto, Canada, had isomeric ratios of TCPP1/2 that were not significantly different from a technical mixture whereas rain had a significantly different ratio indicating enrichment in the more volatile TCPP1 isomer. Reporting TCPP isomers can provide insight into sources, transport, and fate of TCPP in the environment. Graphical Abstract ᅟ.