Natural
Match: Mercury & The Everglades
If mercury had a choice about where to set up shop in the environment, chances are it would pick the Florida Everglades hands down.
Everything it could possibly need for its wicked business is right there, and in spades. Year-round great climate, beaucoup friendly molecules, an energetic food chain that feeds everything from bacteria to panthers--it’s a made-to-order factory for creating a phenomenon scientists call “biomagnification.” Mercury’s power lies in being biomagnified.
Mercury enters the food chain in an organic form called methylmercury, although scientists still don’t know precisely how the process works. This compound can form whenever inorganic mercury--a vaporized form of the silvery metal--mixes with organic matter dissolved in water. This reaction is particularly brisk when there’s plenty of warmth, sunlight and a particular kind of bacteria around.
Permanently awash in a sunny, semi-tropical setting, the ‘Glades has no shortage of any of the above. Most of its mercury arrives via breezes, and is deposited by near-daily downpours. Swampy conditions provide a perfect habitat for sulfate-reducing bacteria, which readily absorb rainwater mercury--and turn it into its hazardous methylated form.
Here’s where the poison enters the food chain and biomagnification begins. Plankton organisms eat the methylmercury-loaded bacteria, which in turn are eaten by larger invertebrate animals. These become fodder for even larger spineless critters such as snails and freshwater shrimp, favorite diets of small fish such as bluegill. These fall prey to such top-of-the-line predators as gar, bowfin, warmouth, largemouth bass, and in particular, birds such as kingfishers, egrets and herons who eat almost nothing else.
Sitting at the apex of this feeding pyramid are raccoons, otters, alligators, panthers and ultimately humans, who are the unwitting beneficiaries of a biomagnification process that can see methylmercury concentrations increase 10-fold at every step of the food chain.
This exponential growth in potency is the consequence of methylmercury’s habit of accumulating in animal tissue once its there. Wetland-dependent animals simply can’t get rid of the stuff as fast they consume it, and the resulting accumulation can be devastating.
Several Everglades fish and all alligators today are officially branded too dangerous for humans to eat in any quantity. A 1995 study showed that Everglades great egrets fed mercury-tainted fish lost their reproductive capacity in lab tests. Dozens of emaciated cormorants and mergensers near Florida Bay were found to have high mercury in their tissues in 1994. Wading bird populations in the ‘Glades today are a fraction of what they were in the 1950s, although there’s no hard evidence that mercury has played a significant role in the decline.
Whatever the case, with its inexhaustible supply of organic material, mostly in the form of peat--the decayed remnants of millions of acres of sawgrass--the Everglades represents an enormous reservoir of energy for perpetuating mercury’s natural fondness for building up in the flesh of fish and other watery wildlife.
For all its incredible power to rid itself of so many insults thrown its way by humans, this magnificent system would appear to have met its match in mercury from the skies. --F.S.