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Estimating mercury concentrations and fluxes in Lake Ontario water and sediment with HERMES

Estimating mercury concentrations and fluxes in Lake Ontario water and sediment with HERMES. Adrienne Ethier *, Joseph Atkinson, Joseph DePinto and David Lean.

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Estimating mercury concentrations and fluxes in Lake Ontario water and sediment with HERMES

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  1. Estimating mercury concentrations and fluxes in Lake Ontario water and sediment with HERMES Adrienne Ethier*, Joseph Atkinson, Joseph DePinto and David Lean

  2. The symbol for Mercury may represent the caduceus staff or the circle might be mercury’s head and the two “horns” might be wings on his head. HERMES Hermes (Roman: Mercury) is the Greek god of boundaries and travelers who cross them. A messenger with a winged hat and shoes. Similar to the symbol for woman (♀). Pregnant women are the most at risk group for Hg exposure since Hg can cross placental membrane causing birth defects and neurological damage in fetus.

  3. Hg is conserved Approach taken... • Hg concentration and / or flux rates are commonly measured in the environment *** not interconversion or reaction rates among Hg species • Attempts are often made to relate these measurements to other physical and / or chemical parameters of the watershed or lake (e.g. DOC versus Hg) Reaction Why?

  4. Mercury species modelled Hg0: Elemental Hg Main species found in atmosphere MeHg: Methyl Hg Organic fraction of Hg that bioaccumulates in food webs Hg(II) : Inorganic Hg Main species found in sediment and water

  5. Some equations from model... • Log10 (Suspended particulate matter (mg L-1)) = 1.56 x Log (Total phosphorus (μg L-1)) – 1.69 • Log10 (Suspended particulate matter (mg L-1)) = -1.123 x (Log Secchi depth (m)) +0.993 • Solid settling rate (g m-2day-1) = 1.04 - (0.07 x Mean depth (m)) • Resuspension rate (% of settling) = 90 x (850 - ((Mean depth (m) - 8.5) x 70)) / 850 • Vapour Pressure (Pa) = P1 x exp (- (ΔHvap / R) (1 / T2 – 1 / T1)) • Water solubility (mg L-1) = 8000000 x 10 (-122.911 + (4475.3 / T2) + (40.2205 x Log (T2)))

  6. Hg estimation methods... • Ln (Concentration of Hg in inflow water (ng L-1)) = 2.02 – 0.063 x Ln (Watershed area (km2) x 100) • Log10 (Sediment MeHg : THg) = -1.9025 - 0.0086 x TOC (%) + 0.0011 x Redox potential (mV) • For summer and DOC < 20 mg L-1: Water MeHg : THg = (-0.4 + 0.128 x DOC (mg L-1)) / (0.48 x DOC (mg L-1)) • Water inflow MeHg : THg = 10 ((% Wetland x 0.056)-1.12) / e (2.02 – 0.063 x Ln (Watershed area (km2) x 100)) • Sediment with TOC < 20%: sediment THg (ng g-1) = 4.4215 x TOC (%) + 16.225 • Water with DOC < 20 mg L-1: water THg (ng L-1) = 0.48 x DOC (mg L-1)

  7. HERMES model input Location or lake-specific variables Model input driving variables

  8. ESTIMATION METHODS MODEL OUTPUT ‘DOUBLE-CHECK’ MeHg : THg RATIOS click

  9. ModelComparison LOTOX 2 HERMES No rate constants used

  10. Lake Ontario versus smaller lakes Small Large Concentration of Hg in air (ng/m3) <0.1 <0.1

  11. References Model theory and development: Ethier, A.L.M., Mackay, D., Toose-Reid, L.K., O’Driscoll, N.J., Scheuhammer, A.M. The development and application of a mass balance model for mercury (total, elemental and methyl) using data from a remote lake (Big Dam West, Nova Scotia, Canada) and the multi-species multiplier method. ApplGeochem 2008; 23(3): 467-481. Model estimation methods: Ethier, A.L.M., Lean, D.R.S., Scheuhammer, A.M., Bodek, T., Sosso-Kolle, K. Predicting mercury concentrations and fluxes in the water column and sediment of lakes with a limited dataset. Environ Toxicol & Chemin press – available online

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