The stunning reversal of mercury levels in the Everglades probably won’t be repeated in the Tampa Bay region, according to Tom Atkeson, mercury coordinator for the Florida Department of Environmental Protection. On the other hand, levels in Tampa Bay and its tributaries were never so high that the state imposed a blanket “no consumption” recommendation for certain fish either.
“It would be hard to repeat the unlikely and dramatic changes in the Everglades because that region was at risk for several reasons,” he notes. “The difficulty of siting landfills in South Florida meant it had an atypically high reliance on waste combustion, the highest in the nation in fact.”
The effects of mercury also were more pronounced in the Everglades – it’s downwind of a major metropolitan area, and it’s a large, shallow waterbody where atmospheric deposition can enter and interact with sediments, which transforms mercury to a form that is more bioavailable to fish and birds.
New regulations that became fully effective in 2000 helped to push a large number of medical incinerators out of business, he notes. “Until 1994, there was basically no regulation of small incinerators – they just notified us of what they were doing,” he said.
Mercury levels in fish and some wading birds in the Everglades dropped 60 to 70% between 1994 and 2003 as emissions from municipal and medical incinerators were regulated.
A naturally occurring metal, mercury is liquid at normal temperatures and easily transforms into a gas. Like many heavy metals, it is toxic in large doses to mammals, birds and fish, and can cause severe damage to the nervous system, particularly in unborn babies, infants and young children.
In Tampa Bay, most of the mercury probably comes from coal-powered electrical generation and that should drop significantly as Tampa Electric Company repowers its Gannon plant and installs new scrubbers at Big Bend. Only the Alafia River is listed as a river of special concern although the Florida Department of Health recommends limited consumption of certain fish in all Florida water bodies.
“From 1990 through 2000 we haven’t seen any change in Tampa Bay, but sampling is not set up to detect those changes either,” said George Henderson, a biologist at the Florida Fish and Wildlife Research Institute. Fish are sampled strictly so the health department can issue appropriate warnings, he adds.
“There really isn’t a research program per se to look at the ramifications of mercury in fish,” he adds. “We have all kinds of great ideas for research projects, but it hasn’t been a priority for the legislature.”
Most of the research has focused on freshwater ecosystems, where fish are more easily contained, but marine fish – particularly large predators like shark and mackerel – also are affected, he notes. “The marine system is very much open and water and organisms easily move from place to place so it’s much more difficult to track.”
Some of the results are counter-intuitive because mercury may attach to sediments, he adds. “There’s actually more mercury at the mouth of Tampa Bay where the water is cleaner than in the Hillsborough River.”
And even fish with very high levels of mercury – so high that entire zones are closed to fishing – exhibit no signs of mortality or even decreases in population in other parts of the country. “The levels that are potentially harmful to people don’t seem to cause harm to fish,” Henderson said.
* See http://www.doh.state.fl.us/environment/hsee/fishconsumptionadvisories/FWFGuide.htm for specific recommendations on each waterbody.