Methylmercury contamination of fish in South Florida

An article, entitled "Awfully Fishy", appeared in the New Times-Broward/Palm Beach newspaper on April 27, 2000. Below are excerpts from the article, which discusses the study conducted by Bill Orem, USGS geochemist, on mercury accumulation and its effects on the South Florida canals and Everglades. The complete article is located on the newspaper's web site.

"This is the stuff that can kill," says Bill Orem, a career scientist for the U.S. Geological Survey in Washington, D.C. ... the 47-year-old Orem is a midcareer scientist ... not an office scientist or a bureaucrat. Orem travels regularly from his office in Reston, Virginia, to South Florida to study mercury accumulation and its effects here. A calm, articulate admirer of the vast Everglades region, Orem explains that methylmercury, the organic form of the metal, springs from a bacterium that does not require oxygen to live. Found in underwater peat sediment or mats of algae, the bacteria use sulfur to respire, using it as other organisms use oxygen.

Orem became unpopular with farmers late last year when his research traced the major source of sulfur in the Everglades to sugar and vegetable farmers north and east of the region. Orem believes that, by loading large quantities of sulfur onto their fields to help crops absorb nutrients, the farmers may unknowingly nurture methylmercury farther south.

Orem thinks most of the sulfur runs off the fields and into the canals after rains or flooding. Florida Farm Bureau spokesmen say there is no evidence to suggest that, and attribute Everglades sulfur levels to natural evolution in ground water.

"I got blasted at the January meeting of the [Southwest Florida Water Management District] by agricultural people who don't think we have enough evidence to blame the sulfur they use," Orem says. "They think it comes from ground water."

But ground water accounts for only a small percentage of water that comes into the Everglades and surrounding areas, so Orem believes it probably isn't the primary source. "Before our study no one realized how much sulfur the farmers really use," he says.

Later this year he will conduct tests in the Everglades and in parts of WCA 2 and 3 to determine if sulfur levels vary with seasons and with periodic fertilizing in the fields to the north. "I certainly don't want to be seen as blaming the farmers, because I'm not blaming them," Orem insists, reflecting the opinions of state-agency scientists who say it is far too early to begin asking farmers to find crop stimulants other than sulfur.

"This isn't something they could have known, it isn't something they did purposely," Orem says. And if state scientists accept his studies as conclusive proof that sulfur stimulates methylmercury in the Everglades region, Orem is confident that farmers will adjust their level of use. He points to a precedent: the phosphorus problem. Farmers stopped using phosphorus in their fields after scientists demonstrated the huge damage it caused in the Everglades. But that took painstaking research and legal pressure before an $8 billion Everglades restoration project was planned to clean up the Everglades and remove phosphorus -- a project still not fully under way. Phosphorus helps create explosions of exotic species that are destroying the native flora and fauna of the Everglades.

Orem, a scientist of the senses, followed his nose to the sulfur problem. He decided to investigate the sulfur connection one day in 1994 when he was wandering along the Hillsboro Canal. "I smelled a distinct odor of rotten eggs, which doesn't go with a freshwater environment," he said. The odor characterizes salt marshes where sulfur exists naturally. In a freshwater environment, the smell suggests an unnatural source of sulfur, which led to Orem's research. The rotten-egg odor, Orem explains, is the sign that bacteria are using sulfur by "breathing in sulfate and breathing out sulfide -- these same bacteria are also the guys that methylate the mercury."

When methylation occurs -- when mercury metals fall to earth in the rain and become organic -- it threatens all the animals and people in the food chain who consume it, by destroying body tissue. But it is most dangerous to animals at the top of the food chain because it "bioaccumulates" rather than breaking down.

Orem explains how this works: "You might start out with methylmercury being one unit in [algae]. Something that eats that might have 10 units, the guy that eats him might have 100 units, and the larger fish might have 1000 units." By the time a bird eats the fish, a raccoon eats the bird, and a panther eats the raccoon, a million units of methylmercury might accumulate. If people continue to eat fish poisoned by methylmercury, it accumulates in them as well.