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Mercury in Aquatic Ecosystems in Florida

Mercury (Hg) is a chemical element - a dense, silver-colored liquid in its pure metallic form - that also occurs in other forms such as in some minerals in the rocks which make up the Earth’s crust, as a gas in the atmosphere, and dissolved in minute quantities in the ocean. Because mercury can both evaporate into air, and, dissolve into water, it cycles between land, the atmosphere, lakes, and oceans.

Mercury may be converted into methyl-mercury (methylmercury or MeHg) by certain groups of naturally occurring bacteria in water bodies. MeHg is both a very toxic mercury compound, and it may be strongly concentrated up the aquatic food chain.

Atmospheric deposition of mercury (from rainfall and the settling of dust) is the predominant source of mercury to water bodies in Florida. Although the concentration of mercury in waters of lakes, streams and coastal waters is usually very low, levels in fish may be 100,000 or 1,000,000 times higher, and reach concentrations that may be toxic to humans who consume fish. MeHg exposure to women of childbearing age and young children poses increased risk of learning disabilities in children, and MeHg may increase the rate of heart attacks in adults.

While a portion of the mercury present in the atmosphere is due to natural processes (e.g., emissions from volcanoes), about two-thirds is from human activities which release mercury to the air such as combustion of fossil fuels, mining and smelting of mineral ores, and waste incineration. The sources of mercury to our waterbodies via deposition from the atmosphere may arise from half way around the world, or from local sources.

Florida is a state that is particularly susceptible to mercury contamination of its fish, due in part to the state’s latitude, geographical setting, and meteorology, which allow a high rate of mercury deposition from the atmosphere onto Florida lands and waters. Further, the chemistry of many of Florida’s water bodies is conducive to the conversion of mercury from atmospheric deposition, to the more toxic and bioaccumulative mercury form, MeHg.

Americans are exposed to MeHg almost exclusively through consumption of fish; predominantly from consumption of marine and estuarine fish. There are currently over 300 fresh water waterbodies in Florida with a Human Health Fish Consumption Advisory urging limited or no consumption of recreationally caught fish. Furthermore, the entire coast of Florida, as well as the coasts of neighboring states, is under advisory due to mercury in fish. In all, 20 species of freshwater fish and over 60 species of marine fish in Florida are under some level of advisory.

Besides human health concerns regarding MeHg, there are concerns regarding wildlife in the aquatic food web (e.g. otters, egrets, ibis, ospreys, eagles, panthers). About two-thirds of all fish analyzed in Florida exceed the U.S. Environmental Protection Agency (USEPA) MeHg criterion for the protection of fish-eating wildlife.

The Florida Department of Health has advised the public to limit their consumption of fish from hundreds of waterbodies throughout the State due to unacceptable risk of MeHg exposure. As a result, these waterbodies have been listed as “impaired” for mercury, requiring that a Total Maximum Daily Load (TMDL) for mercury be conducted.

Florida Statewide Freshwater Mercury TMDL

Because of the high proportion of Florida’s lakes, rivers and streams that are impaired due to elevated MeHg levels in fish, FDEP is conducting a statewide mercury TMDL study, scheduled for completion in 2012. The project consists of collecting and assessing data on mercury emissions, atmospheric deposition, and aquatic cycling, and conducting modeling to quantify how mercury emission reductions to the atmosphere (sources both within and outside State) may be achieved to reduce MeHg levels in fish in the State’s water bodies to safe levels.

Gulf of Mexico Mercury TMDL

The Gulf of Mexico is a very significant fishery, and in 2008, accounted for 15% of the nation’s marine commercial fish landings, and 42% of the marine recreational fish catch. Further, MeHg levels in a high proportion of Gulf of Mexico (GoM) fish exceed the proposed USEPA fish tissue criterion. Because the Gulf is a single waterbody with fish moving from one State’s waters to another’s, with water currents moving mercury around the Gulf, with atmospheric emissions of mercury from one State being deposited in other States’ waters, a Gulf-wide research and TMDL approach is needed.

Florida Fish Consumption Advisory Committee

This committee, formed in 1989, includes representatives from the FDEP, the Department of Health, the Fish and Wildlife Conservation Commission, and the Department of Agriculture, who cooperate to sample fish from Florida waters, analyze these for mercury and other pollutants, and issue Fish Consumption Advisories to the public on safe fish consumption.

Everglades Mercury and Sulfur Research Project

The Everglades is a unique wetland of national and international importance; the Everglades National Park was created because of its “spectacular plant and animal life that distinguishes this place from all others in our country" (President Truman). Yet the Everglades has among the highest MeHg levels in freshwater fish in the nation. FDEP and the South Florida Water Management District (SFWMD), collaborating with the USEPA, U.S. Geological Survey (USGS), and the Florida Fish and Wildlife Conservation Commission (FWCC), are continuing efforts to better understand the sources, transformations, and toxicity of mercury and sulfur in the Everglades.

The FDEP takes the lead in writing the Mercury and Sulfur Chapter (3B) of the SFWMD’s annual South Florida Environmental Report.

South Florida Environmental Report, (SFER) Chapter 3B, Mercury and Sulfur Monitoring, Research and Environmental Assessment in South Florida.

New! Sulfur in the South Florida Ecosystem

2008 SFER: Sulfur as a Regional Water Quality Concern in South Florida

Everglades Mercury TMDL Pilot Study Integrating Atmospheric Mercury Deposition with Aquatic Cycling in the Florida Everglades: An Approach for Conducting a Total Maximum Daily Load Analysis for an Atmospherically Derived Pollutant.

Related Mercury Web Sites

U.S. Geological Survey

U.S. Environmental Protection Agency

Florida Fish and Wildlife Conservation Commission

For more information, contact Don Axelrad, Ph.D., (850) 245-8072; Barbara Donner, (850) 245-8453; or Russel Frydenborg (850) 245-8063.

Water Quality Standards Program
Florida Department of Environmental Protection
2600 Blair Stone Road - M.S. 6511
Tallahassee, FL 32399
Contact Us

Freshwater Mercury TMDL

Gulf of Mexico Mercury Research

Fish Advisories

Everglades Mercury Research


Last updated: June 30, 2015

  2600 Blair Stone Road M.S. 3500   Tallahassee, Florida 32399   850-245-8336 (phone) / 850-245-8356 (fax) 
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