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Does Everglades Restoration Mean More Florida Bay Mercury?

Scientists are trying to determine if the largest ecological restoration project ever attempted – now underway in Florida’s Everglades, the largest remaining subtropical wilderness area in the U.S. – will lead to increased human exposures to toxic mercury concentrations from seafood in Florida Bay.

Researchers from NOAA’s National Centers for Coastal Ocean Science laboratory in Beaufort, N.C., and from the South Florida Water Management District (SFWMD) have teamed up to determine whether redirected freshwater flows aimed at restoring damaged habitats and supplying water to adjoining coastal areas will increase human and wildlife exposure to methylmercury. Although many of the changes in water deliveries to Florida Bay planned as a result of the Comprehensive Everglades Restoration Plan (CERP) have already taken place, there are scenarios under consideration which would provide substantial additional deliveries in order to restore the southern Everglades and Florida Bay to a more natural condition existing before flood control and diversions were implemented. These additional flows would change the spatial patterns of inundation in the Everglades wetlands with the possibility that more methylmercury could be produced there and delivered to Florida Bay.

Florida Bay has been identified as one of two regional “hotspots” for mercury accumulation in fish from the Gulf of Mexico in the Environmental Protection Agency’s Gulf of Mexico Program report, A Survey of Mercury in the Fishery Resources of the Gulf of Mexico. Unlike the other hotspot at a Superfund site in Texas, there are no known industrial point sources of mercury in Florida Bay.

The researchers’ preliminary findings suggest that high mercury concentrations in many Florida Bay fish result from multiple runoff sources and atmospheric deposition combined with special environmental conditions in Florida Bay and its watershed. These conditions facilitate the transformation of inorganic mercury from external sources into methylmercury which is readily bioaccumulated by fish and other organisms in their food web.

Concern over methylmercury concentrations in south Florida is not a new phenomenon, and Florida Bay since 1995 has been under a health advisory concerning limited fish consumption because of elevated mercury levels. Neither are mercury concerns limited to south Florida. As of December 2000, mercury contamination had led to issuance of more than 2,200 fish consumption advisories in 41 different states, increasing 149 percent from the 899 mercury-related advisories issued in 1993.

Methylmercury Sources and Risks

View of Florida Bay

View of Florida Bay

What makes the issue of increasing public health concern is the possibility that increased methylmercury flows could be directed toward Florida Bay and its numerous recreational fishers, potentially increasing total human exposures.

Methylmercury, an organic form of mercury derived from inorganic mercury released into the environment, accumulates up the food chain, reaching high concentrations in predatory fish and leading to increased risks to humans when they consume those fish.

“Methylmercury biomagnifies up the food chain as it is passed from a lower food chain level to a subsequently higher food chain level through consumption of prey organisms by predators,” the U.S. Environmental Protection Agency has reported. “Fish at the top of the aquatic food chain

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