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Redox Potential Effects on Mercury Complexation with DOC by Chase Gerbig Advisor: Dr. Stefan Grimberg

Redox Potential Effects on Mercury Complexation with DOC by Chase Gerbig Advisor: Dr. Stefan Grimberg. Complexation and Availability. Aqueous Hg involved in methylation DOC strongly complexes with many metals, Hg included DOC is heterogeneous, with oxygen and sulfur functional groups

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Redox Potential Effects on Mercury Complexation with DOC by Chase Gerbig Advisor: Dr. Stefan Grimberg

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  1. Redox Potential Effects on Mercury Complexation with DOC by Chase GerbigAdvisor: Dr. Stefan Grimberg

  2. Complexation and Availability • Aqueous Hg involved in methylation • DOC strongly complexes with many metals, Hg included • DOC is heterogeneous, with oxygen and sulfur functional groups • Increased DOC levels would significantly impact free aqueous Hg levels

  3. Complexation and Availability

  4. Complexation and Availability

  5. Complexation and Availability

  6. Redox Potential • Varies with sediment depth • Potentially affects DOC functional groups • Methylation only occurs in anaerobic regions • DOC-Hg complexes at low redox potentials of special interest

  7. Hypothesis The availability of mercury for methylation is effected by Hg complexation with DOC which is dependant on the redox potential of the environment.

  8. Variables • Redox Potential • Aerobic Conditions – high redox • Denitrifying Conditions – midrange redox • Sulfur Reducing Conditions – low redox • DOC Source from Sunday Lake • Inlet • Outlet • Surface

  9. Method - EDLE (Haitzer, Aiken, Ryan. ES&T, 2002, 36) • Significance of competing ligand (EDTA in this case) • Free movement of EDTA • Free movement of Hg(II) • Limited movement of DOC • Known amount of EDTA, measure Hg concentration, determine Hg-DOC complexation • Accounting for additional complexes (OH-, HS-) Free Hg(II) Free DOC Hg-DOC Free Competing Ligand Hg-Ligand

  10. Method - EDLE Initial Final [Hg-DOM] K= Hg Hg Hg DOM DOM Hg Hg DOM Hg Hg DOM DOM HgHg HgDOM DOM Hg HgDOM Hg HgDOM DOM [Free Hg]

  11. Method - EDLE (Haitzer, Aiken, Ryan. ES&T, 2002, 36) • Significance of competing ligand (EDTA in this case) • Free movement of EDTA • Free movement of Hg(II) • Limited movement of DOC • Known amount of EDTA, measure Hg concentration, determine Hg-DOC complexation • Accounting for additional complexes (OH-, HS-) Free Hg(II) Free DOC Hg-DOC Free Competing Ligand Hg-Ligand

  12. Controls and Quality Assurance • Hg movement across membrane without DOC present • DOC movement across membrane • Maintenance of constant redox potential • Reproduction of published data for variable pH • Triplicate analysis

  13. Results to Date • Water Source not significant • Stronger complexation in lower redox potentials • Mercury recovery poor in sulfur environments pH=6.8

  14. Next Steps • Mass Balance of DOC and Hg – minimal recovery of Hg in sulfur redox system • Hg:DOC ratio changes • within range of previous body of work • within range of Sunday Lake • Add aerobic condition

  15. Questions Sunday Lake Inlet, 10/04

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