Overview

Over the past decade, high concentrations of mercury contamination have appeared in higher organisms in the Florida Everglades. In some locations ("hot spots"), game fish contain mercury levels that require warnings to the public about the hazards of mercury contamination. The waters at these hot spots contain higher levels of methylmercury (CH₃Hg⁺), the species of mercury that accumulates in organisms. Methylmercury is produced by methylation of the mercuric ion (Hg²⁺) by sulfate-reducing bacteria. Strong complexation of the mercuric ion limits the rate of mercury methylation and uptake by organisms. Our research focuses on the ability of natural organic matter to strongly bind mercuric ions. We've been studying the interactions of natural organic matter from the Everglades and other locations with mercury in aqueous solutions and in sulfide minerals (HgS; cinnabar). 

This work was initiated by George Aiken and Michael Reddy at the U.S. Geological Survey (USGS) laboratory in Boulder, Colorado, as part of the Aquatic Cycling of Mercury in the Environment (ACME) project and the South Florida Ecosystem Program.  Drs. Aiken and Reddy recruited Mahalingam Ravichandran to work on their project.  The NSF Environmental Geochemistry and Biogeochemistry grant received by Joe Ryan, George Aiken, and Kathy Nagy of the Department of Geological Sciences at the University of Colorado follows up on ideas initiated by the USGS work.

Projects

• The Role of Organic Matter in the Fate of Mercury in the Florida Everglades
  PI: Joe Ryan
  Colorado Water Resources Research Institute/U.S. Geological Survey/U.S. Environmental Protectional Agency, 1995 to 1998.
• Interactions of Mercury with Organic Matter in Water and Soil
  PIs: Joe Ryan, George Aiken (USGS), and Kathy Nagy (Geological Sciences, University of Colorado)
  National Science Foundation, Environmental Geochemistry and Biogeochemistry Program (EAR-9807735), September 1998 to August 2001.

Collaborators

• Dr. George Aiken, U.S. Geological Survey, Boulder, Colorado
• Prof. Kathy Nagy, Department of Geological Sciences, University of Colorado, Boulder
• Dr. Michael Reddy, U.S. Geological Survey, Boulder, Colorado
• Appathurai Vairavamurthy, Brookhaven National Laboratory, Brookhaven, New York

Students and Theses

• Mahalingam Ravichandran, Ph.D., 1999, Interactions between Mercury and Dissolved Organic Matter in the Florida Everglades. "Ravi" tested the hypothesis that dissolved organic matter from the Everglades could compete with sulfide for the mercuric ion by testing the effect of organic matter on the dissolution and precipitation of cinnabar (HgS).  The organic matter, which XANES (x-ray absorption near-edge spectroscopy) analysis showed to contain significant amounts of reduced sulfur moieties, enhanced dissolution following adsorption to the cinnabar surface (Ravichandran et al., 1998).  Cinnabar precipitation was prevented if the amount of mercury was less than the amount of reduced sulfur (Ravichandran et al., 1999).
• Todd Drexel, M.S., 2000, Mercury(II) Sorption to Two Florida Everglades Peats: Effects of pH, Ionic Strength, Calcium, Chloride, and Dissolved Organic Matter. Todd worked under the supervision of George Aiken and Joe Ryan on the binding of the mercuric ion by two peats from the Everglades.  Todd's work showed that strong and weak binding sites, thought to correspond with reduced sulfur and carboxyl/phenol functional groups, must be considered to describe mercury binding by the peat.
• Jake Waples, M.S., in progress. Jake is working under the supervision of Kathy Nagy on the mechanism of organic matter enhancement of cinnabar dissolution.
• Jarrod Gasper, M.S., in progress. Jarrod is working under the supervision of George Aiken and Joe Ryan on the binding of the mercuric and methylmercury ions by natural organic matter using ion exchange, liquid-liquid extraction, and dialysis techniques.

Publications (with links to PDF files; some PDF files are large -- 2-4 MBytes)

• Ravichandran M., Aiken G.R., Reddy M.M., and Ryan J.N., 1998. Enhanced dissolution of cinnabar (mercuric sulfide) by aquatic humic substances. Environmental Science & Technology, 32, 3305-3311.
• Ravichandran M., Aiken G.R., Ryan J.N. and Reddy M.M., 1999. Inhibition of precipitation and aggregation of metacinnabar (mercuric sulfide) by dissolved organic matter isolated from the Florida Everglades. Environmental Science & Technology, 33, 1418-1423.
• Drexel R.T., Aiken G.R., Nagy K.L., and Ryan J.N., in preparation. Mercury(II) binding by two peats from the Florida Everglades. To be submitted to Environmental Science & Technology.
• Waples J.S., Aiken G.R., Nagy K.L., and Ryan J.N., in preparation. Role of organic matter in the dissolution of cinnabar. To be submitted to Geochimica et Cosmochimica Acta.

Presentations

• Waples J.S., Nagy K.L., Aiken G.R., and Ryan J.N., Dissolution kinetics of cinnabar in the presence of dissolved organic matter. To be presented at the 11th V.M. Goldschmidt Conference, Hot Springs, Virginia, May 2001.
• Aiken G., Reddy M., Ravichandran M., Ryan J.N., Interactions between dissolved organic matter and mercury. To be presented at the 221st National Meeting of the American Chemical Society, Environmental Chemistry Division, April 2001.
• Drexel R.T., Aiken G.R., Nagy K.L., and Ryan J.N., Binding of mercury(II) by two peats from the Florida Everglades, 2000. Presented at the International Workshop on Surface Chemical Processes in Natural Environments, Monte Verita, Ascona, Switzerland, October 2000.
• Drexel R.T., Aiken G.R., Nagy K.L., and Ryan J.N., Mercury(II) sorption to two Florida Everglades peats. Abstracts of Papers of the American Chemical Society, 2000. Presented at the 220th National Meeting of the American Chemical Society, Environmental Chemistry Division, Washington, DC, August 2000.
• Ravichandran M., Aiken G.R., Ryan J.N., and Reddy M.M., 1999. Inhibition of precipitation and aggregation of metacinnabar (HgS) by humic substances isolated from the Florida Everglades. Abstracts of Papers of the American Chemical Society 217, U746, Part 1. Presented at the 217th National Meeting of the American Chemical Society, Environmental Chemistry Division, March 1999.
• Ravichandran M., Aiken G.R., Reddy M.M., and Ryan J.N., 1998. Enhanced dissolution of cinnabar (mercuric sulfide) by aquatic humic substances. Abstracts of Papers of the American Chemical Society 216, U785, Part 1. Presented at the 216th National Meeting of the American Chemical Society, Environmental Chemistry Division, August 1998.
• Aiken G.R., Ravichandran M., Reddy M.M., and Ryan J.N., 1998. Interactions of dissolved organic carbon with mercury in the Everglades, Florida. Abstracts of Papers of the American Chemical Society 216, U765, Part 1. Presented at the 216th National Meeting of the American Chemical Society, Environmental Chemistry Division, August 1998.
• Ravichandran M., Aiken G.R., Reddy M.M., and Ryan J.N., 1998. Enhanced dissolution of cinnabar (mercuric sulfide) by Florida Everglades organic matter. Eos, Transactions of the American Geophysical Union 89, S94. Presented at the Spring Meeting of the American Geophysical Union, May 1998.

"Tonight on Mutual of Omaha's Wild Kingdom: 'Mercury Sampling and Alligator Wrestling in the Florida Everglades' with your hosts, Paul Schuster (standing), a research scientist with the U.S. Geological Survey, and Mahalingam Ravichandran (seated), a PhD student at the University of Colorado."

Mahalingam Ravichandran collects surface water samples from the 2BS site in Water Conservation Area 2B in the Everglades.

Samples were collected under the longing gaze of hungry alligators.

Locations of study sites in the Florida Everglades.  Sites F1 and 2BS (not shown, about 5 miles south of site U2) were studied in our work.