Background
In 1989 a three-agency monitoring project found high levels of mercury in fish from the Everglades. Mercury is a human neurotoxin, and its consumption in contaminated food has caused illness and death around the world.
Finding high mercury levels in fish led the State Health Officer to issue a series of Health Advisories urging anglers not to eat some species of fish caught in the Everglades, and to sharply limit consumption of largemouth bass taken from other fresh waters in Florida.
Five years later, we know that about one million acres of the Everglades drainage system contain fish with very high levels of mercury: largemouth bass that average over 2 parts per million mercury (which exceeds all health-based standards). More than another million acres of Florida waters contain largemouth bass with elevated, but lesser, levels of mercury. When sampling is complete we expect that mercury problems in bass will be found in one half to two thirds of Florida's lakes and streams.
High levels of mercury in fish is not limited to Florida. Thirty-four states have issued health advisories restricting consumption of fish, and similar problems are found widely spread throughout North America, Europe and Asia. Most lakes in southern Canada and Scandinavia, for example, show mercury contamination. It is generally accepted that this widespread mercury problem is caused by atmospheric pollution.
Major sources to the atmosphere are mining and smelting of metals, coal-fired utilities and industry, and the use and disposal of mercury in commercial products. Both long distance trans-port and localized deposition around some types of sources may be important.
The unusually severe problem in the Everglades may be from several factors. The principal concerns in the Everglades focus on local effects of municipal incinerators and other emissions sources on Florida's southeast coast, increased release of mercury from the soils of the Everglades Agricultural Area promoted by drainage and soil disturbance, or because of hydrologic changes from the Flood Control Project.
Environmental Controls
Our lack of knowledge of the causes limits our ability to correct the problem of too much mercury in fish, but one generalized solution is
clear: we must limit mercury emissions to the environment. Florida has increased controls on mercury releases through:
Pollution Prevention -- Florida's solid waste law requires mercury to be eliminated from some commercial products. Other provisions ban mercury in packaging, prohibit incineration of mercury-containing lamps and devices, promote recycling, and phase out the use of mercury batteries.
Waste Disposal -- Hazardous waste regula-tions now require stricter control of wastes that contain mercury. Proper disposal minimizes the long-term releases of mercury into the environ-ment. An unintended but beneficial side effect of stricter regulation is to encourage elimination of mercury from some commercial products and industrial processes.
Emissions Control -- A 1991 emissions in-ventory for Florida found that the major sources of mercury to the atmosphere were municipal solid waste incinerators, electric utilities, and medical waste incinerators. Under its authority to control toxic air emissions the DEP has adopted the first US rules to limit emissions of mercury from municipal solid waste incinerators.
Although aggregate emissions of mercury from incinerators are small in comparison to the global mercury budget, facilities in south Florida emit amounts that may be significant for the region. Proven, cost-effective control technology is available, and will be required of these facilities when necessary to comply with standards, although some facilities may meet the new standard by recycling and waste control alone. Rules governing emissions from medical waste incinerators are under development.
Research
We do not understand the dynamics of mercury in the atmosphere or its effects on aquatic systems in general, much less of the specific causes of the unusually severe problem in the Everglades. Before environmental controls can be developed to address the broader aspects of the problem, we must know the relationships between sources, transport
mechanisms and the dynamics of mercury in the watershed-sediment-waterbody system.
The Governor's Mercury in Fish and Wildlife Task Force adopted a research plan to clarify these uncertainties. The research falls into three areas:
Trend Monitoring -- To properly understand today's mercury problem, we must be able to put it into historical perspective. Have mercury burdens in fish truly increased, or are the high levels in bass from the Everglades a reflection of natural mercury in the organic soils of that area?
Studies elsewhere indicate that deposition from the atmosphere has increased 2- to 5-fold since the Industrial Revolution. But, while regional or local phenomena may cause differ-ences, Florida seems to fit this pattern. Analysis of mercury in Everglades sediments shows that mercury accumulation in the surface layers is about five times higher today than in 1900. Another research project will measure historical trends in Florida wildlife by analysis of museum specimens.
Despite the insight that understanding historical trends gives us, perhaps the more urgent question is: Are mercury burdens of Florida fishes stable, increasing or decreasing? The Florida Game and Fresh Water Fish Commission is monitoring fish from several waterbodies to answer that question.
Atmospheric Fluxes -- Although we believe that much if not most of the the broad-scale mercury problems are the result of airborne mercury, We have little reliable data on mercury in air or on deposition to the earth's surface.
Atmospheric concentrations of elemental mercury vapor are thought to be relatively uniform, but most of the good data is from remote sites at higher latitudes and may not be applicable to Florida as a whole or the South Florida region specifically. Relatively little work has been done on the emission, fate and transport of other forms of mercury in the atmosphere.
Before air sources can be invoked as the explanation for the particularly severe problems in the Everglades, we must measure the distribution, over space and time, of atmospheric mercury burdens and deposition. To that end, a network of air monitoring stations--The Florida Atmospheric Monitoring Study--was built to measure mercury in the air, as well as wet and dry deposition.
The most dense network is in south Florida--seven sites--to map the fine-scale relationships between the Everglades and several types of emissions sources. Two other sites will determine the importation of mercury into Florida from global or regional sources, and measure local atmospheric fluxes at the sites of aquatic studies.
This work needs to be complemented by intensive studies to measure and model mercury emissions and deposition from the urban areas of South Florida to estimate the proportion of the deposition that comes from local and regional sources. Other work will continue to refine emissions estimates from Florida sources and examine emerging technological options for emissions control.
Aquatic and Wetlands Studies -- The Everglades' mercury problem, as opposed to that of lakes and rivers elsewhere in Florida, likely has somewhat different causes, requiring separate studies of these different types of aquatic systems.
The initial effort in the Everglades is to develop a finer picture of where mercury is in Everglades water, sediment, and biota by random sampling in the canals and marshes, augmented by monitoring mercury inputs and outputs to the system to construct a crude mass balance. Together, these should help develop additional hypotheses about the causes of the Everglades' unusually severe mercury problem.
More intensive, process-oriented studies will be done at the Everglades Nutrient Removal Project, a 2,740-acre experimental treatment area. These studies will begin with the determination of a precise mercury budget for the Project, and go on to process-oriented studies in test cells that permit replication and control of water and chemistry variables.
Other work will concentrate on mercury cycling in lakes and streams for later application to the Everglades.
Additional studies will determine long-term trends of mercury accumulation in sediments; interactions between the watershed, air, sediments and water; the changes in the chemical forms of mercury within the waterbodies; how this affects its uptake into fish and other aquatic organisms; and what risk this poses to wildlife and man.
The planned research will be pursued through a state-federal-private consortium with total funding needs of $12-15 million over 5 years. About a third will come from federal agencies, one third from private sources, and the balance from state sources.
For Further Information, please contact
Thomas D. Atkeson, Ph.D., DEP Mercury Coordinator, (904) 921-0884. For information about the Mercury Health Advisories, contact Roger Inman, HRS Toxicology and Hazard Assessment Program, (904) 488-3385.
6/22/94