May 16, 2011
Clearing the Air on Mercury
More fish are added to the mercury hot list, but troubles may actually be abating in some areas. The full story for Florida anglers.
If you could get over the shock of seeing cobia and seatrout on the latest fish consumption advisory from the Florida Department of Health, you'd read some good news between the lines. Largemouth bass in the northern two thirds of the Everglades got promoted from "No Consumption" status to "Limited Consumption."
That means state researchers saw declines in tissue concentrations of methylmercury, an especially toxic form of that silvery stuff you used to see in all thermometers.
From a peak in the mid 1990s, in 3-year-old largemouth bass mercury declined by a conservative analysis about 60 percent, maybe as much as 75 percent," said Tom Atkeson, mercury coordinator with the state Department of Environmental Protection.
Atkeson attributes the decline-specifically in the Loxahatchee National Wildlife Refuge and South Florida's Water Conservation Areas 2 and 3-to regional efforts to curtail mercury-laden air pollutants.
For those of you who haven't been reading the gloom-and-doom advisories circulating lately, a little chemistry lesson: Mercury in its elemental form occurs naturally, but when waste incinerators, powerplants, mining operations and other industrial processes disperse it into the atmosphere, it undergoes a chemical transformation into a gaseous, reactive form. Rainfall brings it back to the ground, and sulfate-reducing bacteria convert it into organic methylmercury.
The Everglades happens to be a hot zone for two reasons, Atkeson explained. One, the shallow waters and matted algae foster the growth of this kind of bacteria; and two, prevailing winds blow airborne pollutants out there most every day in the rainy season. A third factor-yet to be fully studied-is how sulfur related to agricultural practices may enhance the conversion of methylmercury.
Links in the aquatic food web give methylmercury a direct route to predatory fish like bass. The toxin "bioaccumulates" over time, meaning older, higher level predators tend to store higher concentrations. The danger to humans is that methylmercury is readily absorbed by the digestive tract-and from there it goes right to the brain and nervous system. It also has an insidious ability to affect infants in utero. If consumed in large enough quantities, methylmercury can inflict crippling, even fatal, damage.
That methylmercury is potentially dangerous to consumers of fish has been known for decades. In the 1950s, hundreds of villagers in coastal Japan died after eating fish and shellfish tainted with mercury pollution. Many others were afflicted with neurological symptoms ranging from numbness in lips and limbs, to loss of control of muscles, to brain damage. Many infants there were born with mental retardation and other birth defects.
Florida health officials began issuing dietary consumption advisories in the late 1980s, after researchers discovered high levels of methylmercury in Everglades bass and some other fish.
But unlike the case in Japan-where a plastics factory had been pouring mercury-laden sludge into a bay for years-in Florida there was no smoking gun (nor was there anything that could even be remotely termed a public health crisis). As it turns out, explained Atkeson, changes in industry and waste management, on a local and regional scale, had by 1990 already reduced the deposition of mercury in the South Florida environment.
"We were in the middle of the movie; we couldn't see the beginning," said Atkeson, a biologist by training, hired by the state in the early '90s to study the mercury problem.
One of the first Florida studies determined that rainfall, not surface runoff, was the primary vehicle carrying mercury to the Everglades. "Fresh mercury loads each year were dominated by rainfall deposition," said Atkeson.
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.
Gulf Oil Rigs Implicated
Closer to home, an investigative report by the Mobile Register newspaper, in Alabama, turned up compelling evidence that oil drilling in the Gulf of Mexico may be linked to elevated mercury levels in fish-and worse-local fishermen.
The Register sponsored testing of samples of grouper, cobia, amberjack, king mackerel and other species commonly associated with the reef-like ecosystem that's grown up around the rigs. Unsafe levels of mercury, as stipulated by the FDA, turned up in nearly all the samples, the Register reported. Subsequent testing of Gulf Coast residents who said they'd eaten fish at least once a week revealed that 51 out of 65 sampled had levels of methylmercury in their bodies above 1 part per million, the threshold established by EPA as considered safe. Some had 10 or 11 times that level.
Where was the mercury coming from?
The Register cited U.S. Minerals Management Service studies showing intense concentrations of mercury within a 650-foot-diameter circle around Gulf oil rigs. There are about 4,000 such rigs out there, but none in Florida waters. The mercury concentrations, the Minerals Management Service concluded, are the byproduct of barite, a substance the oil industry employs to lubricate the huge oil well drilling bits. Mercury is contained in barite.
Scientists interviewed by the Register indicated that the same type of mercury conversion process that occurs in the Florida Everglades and elsewhere is apparently happening in the sediments surrounding the rigs. "Islands of Contamination," was the front-page headline in the Dec. 30, 2001 edition. From the base of these islands, worms, shrimp, crabs and other critters start the methylmercury on its way up the food chain.
Oil industry reps and an EPA spokesman interviewed by the Register insisted that federal regulations on barite usage had addressed the mercury problem. But could a time lag be at work here, wherein mercury levels remain elevated even after the source has been addressed? Interestingly, Minerals Management Service found dangerous levels of mercury around rigs 12 years after drilling was ceased. That's the same time frame Atkeson cited for a corresponding decline in mercury concentrations in northern Everglades largemouth bass following emissions controls.
How Much Is Too Much?
As researchers struggle to pin down the mercury problem, Florida seafood fans find themselves wading through consumption guidelines set by three agencies. The federal Food and Drug Administration (FDA) is responsible for market and restaurant fish; the Environmental Protection Agency (EPA) gives advice for recreational fishermen; and the state Department of Health rules on fish or water bodies not covered by the others.
The guidelines are easy to read, if sometimes hard to find (you'd think a state fishing magazine would be the first to receive bulletins from the Department of Health, but not so).
According to Dr. David Johnson, bureau chief of environmental epidemiology for the Florida Dept. of Health, fillets of fish are tested for methylmercury concentrations, and consumption guidelines set at levels he described as "somewhat conservative; levels at which there would be no risk to sensitive populations like women and fetuses."
Over time, Johnson said, the body can rid itself of methylmercury. The stuff has a half-life of about 44 days. Eating two tainted fish today, for example, would result in a higher net accumulation of mercury in your system than, say, eating one today, one next week. Still, consuming too much too quickly could overrun the body's defensive mechanisms.
Johnson would not say for certain that immediate sickness would result from flouting state consumption advisories, but he urged anglers to abide by the guidelines.
"We want people to use these," he said, "but we get the feeling many aren't."
To be sure, there have been cases in which symptoms have arisen from relatively low levels of methylmercury exposure-though none to date that stand out in Florida. In the Amazon River basin, where methylmercury levels are thought to be rising because of soil erosion, Canadian researchers discovered impaired motor skill and perception skills among people who tested below 50 parts per million. That figure is a World Health Organization threshold that supposedly represents "no significant health risk" to adults. Children and the unborn apparently are affected by even lower concentrations. Levels of 11 ppm resulted in developmental problems among some Iraqi children born to women who'd eaten mercury-tainted grain.
Our advice, until we hear otherwise, is to follow the published consumption advisories.