OPEs, What Do We Do? Modeling Emissions, Fate, and Mitigation of Organophosphate Esters in Urban Systems
Organophosphate esters (OPEs) are high production volume chemicals that span a broad range of physicochemical properties. Their global distribution raises concern that they could be classified as Persistent Mobile Organic Compounds (PMOCs) for which assessment tools and mitigation measures are required. This thesis has advanced the development of such tools and measures for PMOCs, using OPEs as a case study. By developing a novel workflow including a novel Bayesian model, I generated final adjusted values (FAVs) for 12 physicochemical properties of 74 compounds across nine compound classes, including OPEs, filling an important data gap. This work also found that different in silico estimation methods used to predict physicochemical properties varied widely, underlining the continued importance of measuring these properties for use both in understanding compounds fate and in further improving the in silico estimations. I developed and applied an updated polyparameter linear free energy relationships multimedia urban model (ppLFER-MUM) to better model PMOC fate and emissions in cities. Application of the model to OPEs in Toronto, Canada, I identified that chlorinated-OPEs acted as PMOCs with atmospheric deposition driven by efficient scavenging from air to receiving waters by precipitation while non-chlorinated-OPEs acted as Persistent, Bioaccumulative and Toxic (PBTs) compounds. Stormwater and treated wastewater discharges were important pathways of OPEs from Toronto air emissions to receiving waters. Using bioretention cells as an example stormwater management technology, I undertook a scoping review of bioretention research. This review found that uptake by vegetation was a potentially important pathway for the fate of PMOCs, requiring further study. I then developed a multimedia, activity-based chemical transport model called “SubsurfaceSinks” and a submodel called “BioretentionBlues” for bioretention cells. Fate in a bioretention cell was determined first by hydrology, then by sorption to soil, and finally transformation of compounds that were captured; vegetation played a minor role. Persistent compounds with soil-organic carbon distribution coefficients (log10 DOC) ≤ 2.7 were not captured and so are likely PMOCs transmitted to the environment through stormwater. Compounds with 2.7 ≤ log10 DOC ≤ 3.8 may be PMOCs transmitted to the environment through stormwater, depending on chemical- and location- specific factors.
multimedia modeling, OPEs, Persistent Organic Pollutants
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