1. Adrienne Ethier*, Joseph Atkinson, Joseph DePinto and David Lean

2. 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. 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.

3.  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 Hg is conserved

4. Hg 0 : 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.  Log 10 (Suspended particulate matter (mg L -1 )) = 1.56 x Log (Total phosphorus ( μ g L -1 )) – 1.69  Log 10 (Suspended particulate matter (mg L -1 )) = -1.123 x (Log Secchi depth (m)) +0.993  Solid settling rate (g m -2 day -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) = P 1 x exp (- ( Δ H vap / R) (1 / T 2 – 1 / T 1 ))  Water solubility (mg L -1 ) = 8000000 x 10 (-122.911 + (4475.3 / T 2 ) + (40.2205 x Log (T 2 )))

6.  Ln (Concentration of Hg in inflow water (ng L -1 )) = 2.02 – 0.063 x Ln (Watershed area (km 2 ) x 100)  Log 10 (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 (km 2 ) 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. Model input driving variables Location or lake- specific variables

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

9. HERMES No rate constants used Model Comparison LOTOX 2

11. Small Large Concentration of Hg in air (ng/m 3 )<0.1<0.1 Lake Ontario versus smaller lakes

12. 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. Appl Geochem 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 & Chem in press – available online