Mercury is a poison, but how toxic is it really when ingested in varying quantities through seafood? Voices in the scientific community offer conflicting answers. Many authorities assert that the metal has been associated with memory loss, fatigue, numbness in the extremities, blindness and depression. Others suggest that reported negative health effects blamed on mercury are false or imagined, and a developing theory even suggests that simultaneous consumption of selenium will protect the body and brain against any negative effects of the infamous heavy metal.

Dr. Philip Davidson of the University of Rochester has closely observed children in the Seychelles Islands since 1990 in a generational study of those reared on a fish-heavy diet. Davidson says that mercury contamination and mercury poisoning are very different things. He asserts that only two cases of severe mercury poisoning caused by fish consumption have ever occurred, each in Japan in the 1950s after local industries dumped huge amounts of highly contaminated refuse into the ocean.

"Generally, the levels of mercury found in fish are way, way below what are needed to poison a person," he says. "In the Seychelles, we've found no consistent adverse effects in the children we've studied in a period of almost 20 years."

Dr. Nicholas Ralston of the University of North Dakota's Energy and Environmental Research Center (EERC) supports a theory that suggests that sufficient dietary selenium will counter potential threats of ingested mercury. Through experimentation on nonhuman subjects, Ralston has found that selenium molecules bind tightly to mercury within the body, rendering the toxic heavy metal inert and harmless. Ralston believes that the public has not caught on due to a general misconception about selenium.

"People aren't excited about this because they often believe that selenium itself is a toxin," he says. "It's actually a required nutrient for neural development, and if this was better understood I think people would be more enthusiastic about its role in protecting against mercury."

Selenium naturally occurs in high densities in such ocean fish as tuna, salmon, swordfish and many others. Selenium facilitates brain development, strengthens the immune system and detoxifies free radicals in the body. But actually barring mercury from imparting any damage to the body and brain is the most dramatic, if debated, attribute of this element. If real, this could reshape how we've been trained to think about such fish as tuna and swordfish, notorious for their high mercury levels.

In May 2006, Frontier GeoSciences Inc., an independent laboratory in Seattle, tested 142 samples of 18 species of fish. Ninety-seven percent of the individual samples contained far more selenium than mercury; even tuna and swordfish were found to carry as much as 25 times more selenium than mercury, a ratio exceedingly sufficient for safeguarding against mercury poisoning according to Dr. Ralston.

But not all experts trust his theory. Kimberly Warner, a marine-pollution scientist with the nonprofit environmental advocacy group Oceana, says that multiple published studies demonstrate negative effects on the human body due to mercury consumption. At the University of British Columbia, Warner says, professor of pediatrics Dr. Sheila Innis has reported an influx in various physical symptoms among Asian Canadians, a large fish-eating population, serious enough to send concerned parents to hospitals with their affected kids.

Warner also points toward a 2006 paper authored by M. Saldana published in the British Journal of Ophthalmology that details the case of an individual who nearly went blind while indulging regularly in mercury-laden Caribbean red snapper. Those on the other side of the argument can just as readily rattle off the names and affiliations of various studies which back their own claim that mercury is not the devil we have come to think it is. But Jackie Savitz, pollution campaign director for Oceana, is immediately skeptical of researchers who discount mercury as a danger to human health.

"When I hear people say that mercury is not as damaging as once thought, then I begin to wonder where their funding is coming from," she says. "If you follow the money, you will find the tuna industry behind a lot of studies."

For example, in October of 2005, serious questions arose about the validity of a study released by the Harvard Center for Risk Analysis. That particular paper stated that the benefits of eating fish far outweigh any risks presented by mercury. The fishy part? Harvard accepted approximately $500,000 in research funding from the National Fisheries Institute and the United States Tuna Foundation.

The University of North Dakota's EERC also receives a portion of its selenium-mercury research funding from the tuna industry. Annual grants of $200,000 from the EPA keep Ralston's project afloat, but the Tuna Foundation caught wind of the good news emanating from his laboratory after Ralston's first year of research. The foundation promptly began donating, as did the U.S. Department of Energy, with each offering $100,000 over a three-year period.

"It doesn't mean that anyone's lying," Savitz concedes. "It just raises a red flag, since he's putting forth a serious question that is totally inconsistent with the consensus in the scientific community. It doesn't mean he's spinning the science, but it could suggest that the results are driven to some degree by the funding."

Ralston defends the validity of his research. "Nobody's allowed to have a say in our results and findings," he says. "People who start making accusations about this kind of thing just don't understand the basic respect that most scientists have toward scientific integrity."

He also insists that the idea of mercury "poisoning" is far more conceptual than factual.

"Where all this fear has come from, it's hard to say. Except in a few extreme cases, serious mercury poisoning has never even happened."

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