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
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
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
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
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.
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.