Synopsis: Researchers will examine in detail the dynamics of mercury being washed off of urban surfaces during rain events. Several rain events will be examined in the Toronto metropolitan area. For each event, the rainfall and runoff dynamics over a surface will be studied by high-frequency water sampling, rain gauging and measurement of numerous water quality parameters. Water samples will be assessed for total, reactive and methyl mercury. Mercury in samples will also be assessed for bioavailability. The outcomes of this study will include a much improved understanding of the dynamics leading to mercury washoff during rain events, will be applicable to other urban areas in the region, and may have significant implications for efforts to reduce mercury flows into urban waterways, as well as the Great Lakes.

Chemicals Studied: The study will focus on mercury, a substance of high concern within the Great Lakes region due to its high toxicity and tendency to accumulate at high levels within fish. The analysis approaches used will allow differentiation among the various mercury species commonly found in the atmosphere and in the region’s waters.

Geographic Area: The studies will take place in the Toronto metropolitan area and the results will be broadly applicable to other urban areas throughout the region, as well as elsewhere in the world.

Project Duration: The project will begin in the Spring of 2006 and will complete in the Spring of 2007.

Methods Used: During several rain events, a high-frequency acoustic Doppler flow meter will be used to characterize the flow of precipitation over an urban surface. Simultaneously, a high-frequency water quality meter will be used to determine the chemical characterization of the water and frequent samples will be taken at high frequency for mercury (inorganic and methyl) analysis. In addition, the surface will sampled for mercury content before and after the rain event and frequent rain samples will be analyzed to allow determination of the relative contribution of wet-deposited and dry-deposited mercury in the urban rain runoff. Finally, the samples will be assessed to determine the reactivity and availability of the mercury for uptake by biota and ultimately accumulation in the food chain.

Potential Results and Implications: This study will provide essential information for determining relative origin of mercury in urban rainwater. It will distinguish between previously deposited mercury that is washed off an urban surface and that depositing with the rain event itself. In addition, it will provide a thorough temporal profile of the mercury and related water quality dynamics during an urban rain event. Finally, the project will provide an assessment of the relative reactivity and bioavailability of mercury from such rain events, which is important for assessing its eventual accumulation in the aquatic food chain.

Project Contact:
Brian Branfireun, Ph.D.
University of Toronto at Mississauga
Phone: (905)569-4649
Email: brian.branfireun@utoronto.ca