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EPA Everglades Study Shows Contamination has Declined, but Risks Still Remain


The U.S. Environmental Protection Agency released a report today documenting the ecological condition of the entire 2,063-square-mile freshwater portion of the publicly- owned Everglades. The report documents the third phase of an 11-year study of the Everglades marshes, which determined that mercury in prey fish is declining, but still elevated, while phosphorous contamination of soil has increased.

“The goals of EPA’s Everglades Ecosystem Assessment Program are to first describe, then diagnose, and finally predict the status of ecosystem conditions,” said EPA Region 4 Administrator Jimmy Palmer. “The report describes the study area and will ultimately inform future decisions to restore and manage this unique environment.”

Mercury contamination was a major focus of the study, and the results are mixed. Although the concentration of mercury in mosquitofish, a key prey fish for Everglades game fish and wading birds, dropped significantly since 1995—fish in about 65 percent of the marsh were found to exceed the contaminant threshold. This poses a potential threat to fish-eating wildlife and to human health through fish consumption. People should follow applicable fish consumption advisories posted by the state of Florida.

Mercury in fish was not found to be related to concentrations of mercury in surface water, but rather declined with increased carbon and sulfur in the water. There was a slight decrease of methylmercury, a neurotoxin and the form of mercury that is most easily concentrated in organisms, in surface water as compared to 10 years ago. The total mercury concentration, however, which includes both methylmercury and atmospherically deposited mercury, increased slightly in surface water. Total mercury concentration in surface water has been below the level established to protect human health throughout the study. Changes observed in surface water mercury and other contaminants are subtle, near the limits of laboratory instruments’ ability to distinguish differences and are being studied further to see how they vary with rainfall.

Phosphorous was studied because it is a common constituent of agricultural fertilizers which, during periods of heavy rain, are discharged along with stormwater into surface water. In the Everglades, this nutrient has allowed cattails to flourish and push out native saw grass, wading birds and fish. There was a slight decline in surface water phosphorous as compared to 10 years ago. However, phosphorous in soil exceeded Florida’s impact threshold in 24 percent, and the restoration goal in 49 percent, of the Everglades as compared to 16, and 34 percent, respectively in 1995.

Sulfate contamination was also studied and, although the effects of sulfate on ecosystem health are not well understood, the U.S. Geological Survey has documented links between sulfate and high levels of methylmercury. Sulfate contamination may also be contributing to declines in native plants by altering chemical conditions in the sediments. More than half, or 57 percent, of the Everglades marsh had surface water sulfate concentrations exceeding the restoration goal, as compared to 66 percent in 1995.

Ecological stressors on the Everglades such as poor water management, soil loss, water quality degradation and mercury contamination, among other issues, are often interrelated. EPA recommends that efforts to manage water quality and pollutants such as mercury, phosphorous and sulfur be integrated to prevent further degradation.

The study is part of the Everglades Ecosystem Assessment Program, an innovative, long-term research, monitoring and assessment effort. Since 1993, three phases of marsh sampling and one phase of canal sampling have been conducted throughout the Everglades at over 1000 different locations. Its goal is to provide critical, timely, scientific information needed for management decisions on the Everglades ecosystem and its restoration.


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