1. Mercury in the Environment

2. What is Mercury (Hg) Hg is a silvery, liquid metal at room temperature "heavy metals." Like water, Hg can evaporate and become airborne. Because it is an element, mercury does not break down into less toxic substances. Once mercury escapes to the environment, it circulates in and out of the atmosphere until it ends up in the bottoms of lakes and oceans.

3. Where Does Mercury Come From? Mercury is a naturally occurring element. Mercury ore - cinnabar - is mined History of SJ

4. Mercury enters the environment from: Natural sources such as volcanoes and the weathering of rocks; Our intentional uses of mercury; Our unintentional releases of mercury from burning fossil fuels and smelting metals. CFL E-waste

5. Bioaccumulation = an increase in the concentration of a chemical in an organism over time, compared to the chemical's concentration in the environment. Occurs naturally –And necessary for certain minerals and macromolecules Problematic when bioaccumulate toxins

6. Bioaccumulation of Hg Hg enteres food chain via anaerobic bacteria (SRBs) Why does Tuna have such high [Hg]?

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

9. Morel et al., 2002

10. Hg(II)Hg o (aq) oxidation reduction - Done by bacteria Hg(II) Hg o (aq) - Limited in freshwater (since not many molecules to bond with) Oxidation-Reduction Reactions

11. Hg(II) Water Air Natural concentrations: 5 to 100 pM (1 – 20 ng /L) Hg o (aq) oxidation reduction Hg o (g) Hg(II) (s) Hg 2+, HgCl 2 o, Hg(OH) 2 o, Hg(SH) 2 o, HgS(SH) -, CH 3 Hg(SH) o Versions of Hg (II):

12. MeHg HgS(HS) - Hg(HS) 2 Hg(Sn)HS - Hg o (aq) oxidation reduction Hg(II) SO 4 2- H 2 S, HS - SRB Sulfide and Methyl Mercury SRB = Sulfide reducing Bacteria (these by-products perpetuate methylation, since they cycle back into the rxn)

13. Guadalupe River Watershed River system low [methylated] Hg since low [SRB] Bay has highest [methylated Hg] since high [SRB]

14. San Francisco Bay, ‘Stinky Mud’ Salt H 2 O has 1000x more sulfate than fresh H 2 O

15. Hg(SH) 2 o HgS(SH) - Hg(S n )SH - Hg 2+ + HS - Sulfide Complexes of Hg

16. Hg(HS) 2 HgS(HS) - SRB MeHg MeHg = CH 3 HgS - CH 3 HgCl CH 3 HgOH Methyl Mercury (MeHg) Less toxic More toxic

17. Hg(II)Hg o (aq) Hg o (g) Hg(II) (s) volatilization deposition oxidation reduction Water Air Hg o (l) Dissolution/precipitation Sediment (solid) Interaction with Solids HgS (mined mercury)

18. Interaction with Solids

19. Cylcing of Mercury