The amount of poisonous mercury measured in fish and birds in the Everglades has dropped by more than 60 percent over the past decade, according to a study by state environmental officials.
The decrease is being generally attributed to a drop in emissions from municipal garbage incinerators and medical waste incinerators.
The findings are from an ongoing decadelong effort by the state Department of Environmental Protection to determine the maximum amount of mercury that can be present in the Everglades under federal clean water laws. Even an environmental group that has been critical of the state found promise in the findings.
Mercury is toxic, and eating mercury-contaminated food can be fatal. Its presence in certain amounts has in the past led to health advisories against eating fish caught in the Everglades and other Florida waters.
The amount of the toxic metal found in largemouth bass and certain wading birds as part of the study is still higher than the amount officials are aiming for, but considerably less than it was a decade ago, said Don Axelrad, environmental administrator of DEP's mercury program.
"When we first started measuring this stuff it was pretty uniformly high," Axelrad said. "Now you see the decline. It is very good news the mercury level's come down. It is still a threat."
In 1989 when state officials first started trying to measure mercury levels in the Everglades, some areas had concentrations above 2 milligrams per kilogram in fish. Now measurements are ranging from 0.2 milligrams to 1.5 milligrams per kilogram, depending on the location in the Everglades.
"In general we're talking 0.6, 0.7 is the average for the Glades," Axelrad said.
The state's target is 0.5 milligrams, although when officials adopt new federal measuring guidelines the target is likely to drop.
Axelrad said the decline represented a success story for regulators who required tougher emissions standards for solid waste and medical waste incinerators.
Holly Binns, the clean air specialist for Florida Public Interest Research Group, one of the most vocal critics of what the group says are lax emissions standards, agreed with the assessment and echoed Axelrad's attribution of the cause.
"Surprisingly, I agree with them," said Binns. "Primarily because there have been tight regulations put on municipal waste incinerators. The other piece of the puzzle is a lot of the power plants in South Florida burn oil rather than coal," which leads to mercury emissions.
"I think it's strong evidence that you can reduce mercury if you regulate mercury from the source," Binns said.
Mercury doesn't harm fish and other animals at the bottom of the food chain but can build up to dangerous levels in larger animals.
In 1989, a 4-year-old female panther, known as No. 27, was found dead of mercury poisoning in the Shark River Slough area of Everglades National Park.