Everglades Mercury In Sharp Decline, UF Researchers Say

July 15, 2004

GAINESVILLE, Fla. — By analyzing nearly a century of data, University of Florida researchers have been able to prove definitively that mercury levels in the Everglades have dropped dramatically during the last decade after reaching dangerously high levels in the early 1990s.

The researchers say the study confirms what earlier findings had suggested: that controls on emissions from waste incinerators, combined with a reduction in the use of mercury in household items, are helping eliminate the toxin from the massive wetland. They say their findings may also shed light on the ongoing debate over expanding emissions controls to other industries.

“This is a triumph of regulation, which is something you don’t hear about very often,” said Peter Frederick, an associate professor of wildlife ecology at UF’s Institute of Food and Agricultural Sciences.

Frederick, a specialist in wetland ecology who has long been concerned about wading birds in the Everglades, led a team of researchers who measured mercury levels over the past century using feathers from museum specimens of Everglades wading birds. Their findings appeared in the June issue of the journal Environmental Toxicology and Chemistry.

Bird populations in the marsh declined by 90 percent between the 1950s and the 1980s, and Frederick believes high mercury levels played a part in that decline.

Mercury, which is found in a wide variety of products from medical thermometers to electrical switches, is a toxin that causes reproductive and behavioral problems in birds. The metal also is toxic to humans, causing serious neurological damage in people who ingest it.

When materials containing mercury are burned, particles of the metal are released into the air. But mercury becomes most hazardous when those particles settle into water bodies. When fish ingest mercury, either by absorbing it through their gills or by eating smaller contaminated fish, the element is stored in their bodies for life. Wading birds, which consume large amounts of fish, are particularly at risk from mercury contamination.

In the late 1980s and early 1990s, various states and the federal government tried to stop the contamination of the Everglades and other water bodies by imposing limits on mercury emissions from medical and municipal waste incinerators. Use of incinerators to burn garbage – including mercury-laden household products such as flashlight batteries – boomed nationwide in the 1980s.

But there was still some doubt about whether South Florida’s waste incinerators were to blame for the rise in mercury in the Everglades. Because airborne mercury particles can travel hundreds or thousands of miles before settling to a body of water, scientists said it was possible the pollution was coming from smokestacks in other countries.

One way to settle the question, Frederick said, was to look at the history of Everglades contamination. A slow, steady increase over the course of the 20th century would reflect the global increase in use of mercury, indicating that global sources were to blame. If levels increased sharply during the incineration boom, local sources were probably to blame, he said.

To construct such a history, the researchers took feathers from specimens of Everglades wading birds stored in museums around the country. They tested the feathers, 73 in all, for mercury content.

“When birds ingest mercury, some of it will bind in a durable form with their growing feathers, which leaves a record of their (birds’) exposure,” Frederick said.

The museum specimens were from four species – anhingas, great egrets, white ibises and great blue herons – and were collected between 1905 and 1990. The researchers examined feathers they collected from live birds in the Everglades of the same types after 1990.

They found mercury levels remained consistently low in the feathers of the Everglades birds until the 1970s. They increased sharply during a period beginning in the late 1970s and ending in the early 1990s, roughly coinciding with the nationwide growth in the use of incineration, Frederick said. And they dropped sharply after 1994, reflecting the delayed effect of emissions regulations, he said.

“There’s a certain amount of lag time, up to seven years, between the passage of the regulations and the changes we observed in the field,” Frederick said. “But that lag time was actually predicted because it takes some time for existing mercury to cycle through the environment.”

Tom Atkeson, coordinator of the mercury program at the Florida Department of Environmental Protection, said the study presents “very convincing” evidence that reduced incinerator emissions are responsible for the drop in mercury levels in Everglades birds.

Atkeson said state and federal governments can’t take all the credit for the cut in mercury emissions. Several large battery manufacturers voluntarily phased out the use of the mercury in the 1980s, dramatically reducing the amount of the toxin in the waste burned in incinerators, he said.

“At one time, 85 percent of the mercury in municipal solid waste came from household batteries,” Atkeson said. “So our regulations have had an effect, but we’ve also gotten a boost from manufacturers.”

Frederick’s research team included Marilyn Spalding, an assistant scientist in the UF College of Veterinary Medicine’s pathobiology department; Julie Heath, a former UF graduate student who now is an assistant professor at Hofstra University in New York; and UF graduate student Becky Hylton.