1. Basic Chemical Principals of Mercury

2. Solid-Water Interface
Mineralogical transformation
biomineralization
dissolution
precipitation
Mn+
Oxidation
Reduction
Mn+x
release
Bacteria
deposition
Organic
Matter
Mineral
adsorption
Organic ligand
desorption
Soil Profile
complexation
Aqueous Metal Ion
degradation
Metal-Organic Complex
Surface complex

4. Air Water Hg(II) (s) Hgo (g) Hg(II) Hgo (aq) Hgo (l) deposition
volatilization
Water
reduction
Hg(II)
Hgo (aq)
Hgo (l)
oxidation
dissolution
Natural concentrations: 5 to 100 pM
(1 – 20 ng /L)
ng/L = ppt; µg/L = ppb; mg/L = ppm

5. Air Water Hg(II) (s) Hgo (g) Hg(II) Hgo (aq) Hgo (l)
deposition
Air
volatilization
Water
reduction
Hg(II)
Hgo (aq)
Hgo (l)
oxidation
dissolution
Hgo (l)  Hgo (aq) K = (mol/L)
Hgo (g)  Hg (aq) K = 2.56 x (mol / L · atm)

6. Morel et al., 2002

7. Air Water Hg(II) (s) Hgo (g) Hg(II) Hgo (aq) Hgo (l) reduction
oxidation
dissolution

8. Oxidation-Reduction Reactions
Hg(II)
Hgo (aq)
Microbially mediated (dominant)
Photoreduction
oxidation
Hgo (aq)
Hg(II)
Limited in freshwater
Particle surfaces catalyze O2 oxidation of Hg-halides (HgCl2, for example)

9. Air Water Hg(II) (s) Hgo (g) Hg(II) Hgo (aq) reduction oxidation
Hg2+, HgCl2o, Hg(OH)2o, Hg(SH)2o, HgS(SH)-, CH3Hg(SH)o
Natural concentrations: 5 to 100 pM
(1 – 20 ng /L)

10. Ion Coordination: Hg(II)
Hg2+ · nH2O

11. Solutions Speciation: Differences in molecular configuration
Hg2+, HgCl2o, Hg(OH)2o, Hg(SH)2o, HgS(SH)-, CH3Hg(SH)o

12. Ion Complexes Cation + Anion (termed ligand) => Complex
Hg Cl-  HgCl- Keq = 107.2
(association reaction)
Hg(SH)2o  Hg HS- log K = -36.6
(dissociation reaction)
Kdiss = (Hg2+) (HS-)2 / (Hg(SH)2o)
DG = -RT ln K

13. Oxic (Aerated) Waters
Morel et al. (2002)

14. Sulfide and Methyl Mercury
SO42-
HgS(HS)-
Hg(HS)2
Hg(Sn)HS-
reduction
MeHg
SRB
Hg(II)
Hgo (aq)
oxidation
H2S, HS-

15. Guadalupe River Watershed

16. San Francisco Bay, ‘Stinky Mud’

17. Energy Electron Donor Electron Acceptor Yield (food) (breathing)
CH2O  CO2
DGdonor - DGacceptor
SO42-  H2S
NH4+  NO3-
Fe3+  Fe2+
Fe2+  Fe3+
NO3-  NH4+
H2S  SO42-
O2  H2O
Energy
Energy

18. Sulfide Complexes of Hg
Hg(SH)2o
HgS(SH)-
Hg(Sn)SH-
Hg HS-

19. Methyl Mercury (MeHg) Hg(HS)2 SRB HgS(HS)- MeHg MeHg: CH3HgS- CH3HgCl
CH3HgOH

20. Methylated Species of Hg

21. Air Water Interaction with Solids Sediment Hg(II) (s) Hgo (g) Hg(II)
deposition
volatilization
Water
reduction
Hg(II)
Hgo (aq)
Hgo (l)
oxidation
Dissolution/precipitation
HgS
Sediment

22. Mineral Solubility HgS = Hg2+ + S2- log Ksp = -53
What about other Hg(II) species?

23. Role of Sulfide
with So

24. Interaction with Solids

25. Ion Retention
adsorption
desorption
Aqueous Metal Ion

26. Adsorption: Chemical versus Electrostatic
(strong) (weak)
Hg2+

27. Cylcing of Mercury

29. Mineral Solubility Concentration vs Activity
HgS = Hg S2- log Ksp = -53
Ksp = (Hg2+) (S2-)
Concentration vs Activity

30. Calculating Activity Coefficients
Debye-Hueckel Limiting Equation:
log g = Z2 I1/2 for I < 0.01
Extended Debye-Hueckel Equation:
  for I < 0.1
Davies Equation:
for I < 0.5
B is a temperature dependent constant 25 °C)
a is an effective ion size parameter