That left the question of where the atmospheric mercury was coming from in the first place.

An engineering firm was contracted to do an emissions inventory-looking at medical and municipal waste incinerators, for example-but, as Atkeson explained, historical reconstructions revealed peak emissions in the region in the 1970s and 80s.

"Two main things had happened," said John Glunn, Air Toxics Program Manager for DEP. "For one, there was a reduction of mercury in the waste stream. In the past, pretty much all batteries, for instance, had some mercury in them, but now it's pretty well nonexistent. Also, EPA developed regulations during the '90s that required municipal waste incinerators to install carbon-injection control devices; mercury adheres to the carbon, and the particles are trapped and removed."

"By 1992 or 93, mercury emissions had declined by 90-plus percent," Atkeson said. "But when mercury is deposited in sediments, it exerts its effects for years. So there's a long lag time between peak emissions and when we began to see fish come down."

In other words, there's a correlation between what's lofted into the air over South Florida, what's dropped into the Glades by rainfall and what ends up at the other end of your line. It's just that the effects of reductions take time.

The observed decline may be analagous to one that Atkeson says has occurred in northern Europe. There, a chemical industrial process-chloralkali-had been a major contributor to mercury deposition.

"Since the cleanup of a lot of this eastern European industrial complex, the deposition of mercury and bioaccumulation in fish in popular vacation spots-like mountain lakes between Norway and Sweden-has begun to decline as well," said Atkeson.

While it's encouraging to see regional solutions, Atkeson cautioned that there are still global and natural deposition sources that are not yet fully understood.

And of course there are those cobia and seatrout.

Marine fish from state waters that make the hot list are sampled by the Florida Marine Research Institute (FMRI) in St. Petersburg, then sent to a DEP lab in Tallahassee for analysis. The effort has been commendable, if somewhat sporadic. According to FMRI senior research scientist George Henderson, the state doesn't spe-cifically fund the collection of marine fish for mercury testing purposes. Instead, fish are gathered through fisheries independent monitoring programs-like trammel net sets in Tampa Bay-and the dockside intercepts conducted by fisheries dependent monitoring staff.

For the most part, marine fish seem to be safe for consumption by any standards. But some have turned up with methylmercury levels officials say could pose risks.

"What we've found so far we feel is certainly sufficient to give advice," said Henderson. But he added that he would like to see a more comprehensive sampling regime, one that would shed light on mercury accumulation trends from year to year, in various marine species, sizes and locations.

Henderson noted that so far there don't seem to be geographic "hot spots" of mercury contamination in marine fish. With a few exceptions, uniform distribution seems to be the rule. This begs the question of whether levels of methylmercury showing up in marine fish today are in fact increases or merely reflections of something that's been with us all along.

"The ability to look back is difficult and controversial," said DEP's Atkeson. "But it would be powerful if we can understand where we are today in relation to what went on in the past."

The problem is one of sampling, as there aren't too many frozen fish fillets from the 1900s. Atkeson said there is ongoing debate over whether the feathers of seabirds could be used to provide an accurate picture of methylmercury trends in the marine environment. A provocative study by Portuguese and Scottish researchers asserts this connection; it's based on data collected at seabird breeding sites on the Azores, Madeira and Salvages islands in the north Atlantic. The researchers compared methylmercury levels in feather samples with those from skins of birds taken from the same sites and kept in museums. Their conclusion was that mercury levels in the marine environment have indeed risen at rates of from 1.1 to 4.8 percent per year since the 1880s.