Methods of chemical hazard ranking and toxic impact assessment estimate fate and toxicity assuming the chemical exists in dissolved and particulate phases and, for metals, that all dissolved species are equally bioavailable. This treatment of metals, similar to organic chemicals, introduced a significant error in their estimates of hazard ranking since metal bioavailability and ecotoxicity are related to truly dissolved phase and specifically free metal ion within it. My thesis addressed this concern by developing a new method that introduced Bioavailability Factor (BF) to the calculation of Comparative Toxicity Potentials (CTPs) for hazard ranking of chemicals; also known as Characterization Factors for use in Life Cycle Impact Assessment (LCIA). First, the metal speciation/complexation was incorporated into fate calculations by loosely coupling commercial geochemical metal speciation model, WHAM, with a multimedia fate model, USEtoxTM, which is originally designed to calculate CTPs for organic chemicals. Second, Biotic Ligand Model (BLM) was used to calculate the bioavailability-corrected adverse toxic effects of metals.
This new method was applied to assess the implications of choosing environmental characteristics, notably freshwater chemistry, by calculating BFs and CTPs of several cationic metals (e.g., Cd, Cu, Co, Pb, Ni and Zn) using 12 European, 24 Canadian ecoregions, several distinct freshwater-types selected from large river and lake systems world-wide. The newly estimated metal CTPs (i.e., ecotoxicity potentials) are up to ~1000 times lower than previous values used in LCIA. Notably the model results showed that the absolute values of CTPs, and their relative ranking amongst chemicals, are a product of the characteristics of a receiving environment. Hence it is crucial to select a generic freshwater archetype on which this analysis should be based. Finally, the new model framework was extended to apply within the Unit World Model (UWM) framework to estimate critical loads (CLs) of cationic metals to surface aquatic systems.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/31758 |
| Date | 09 January 2012 |
| Creators | Gandhi, Nilima |
| Contributors | Diamond, Miriam L. |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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