The nonprofit Center for Consumer Freedom, in Washington, D.C., for example, has accused the U.S. Geological Survey of conducting a misleading study, published in May 2009, about mercury in the Pacific Ocean. The dispute centers on the argument that the study may have tested ocean water, but didn't measure mercury in any actual fish, leaving consumers confused about seafood-consumption practices.
"No matter how much mercury is in ocean water, the levels in actual fish aren't increasing," maintains David Martosko, CCF director of research, "and the entire medical literature still contains zero U.S. mercury-poisoning cases related to eating commercial fish."
If there is contamination, how bad is it? Not bad enough to affect people at all, or can it be dangerous to lethal for humans sooner or later? And are all fish affected?
Adam Rowden, director of the division of toxicology at the Albert Einstein Medical Center in Philadelphia, says that "there is some mercury in all of our waters, but the sea, as opposed to most bodies of freshwater, is so big that some mercury is lost before it can get into a fish. All fish are affected somewhat, but the levels of contamination are different in different parts of the U.S. and in different parts of the world.
"Freshwater contamination is worse in the U.S. because of industrial runoff, so freshwater fish, for example, are at higher risk in the industrial Northeast, while parts of Northern California and the Northwest are a little less contaminated."
The same goes for areas of Asia "while parts of Latin America are more contaminated," he adds.
The extent of mercury contamination worldwide, Rowden continues, depends on fish species and on how big the fish is -- the larger and older the fish, the more mercury it contains since the buildup accumulates over time.
"We're not sure about the levels, so the debate ... that may never end with questions that may never be answered," says Rowden.
On the One Hand ...
There's no debate that mercury is not good for a person. But do the benefits of consuming fish outweigh the mercury fear?
"There is no biological need for mercury, but the oil in fish is good for our brains and hearts; however, mercury can't be soaked out of fish, and it can't be cooked out," adds the doctor.
His advice is to follow the Centers for Disease Control and Prevention's recommendations -- available at: www. cdc.com -- about how much fish to consume.
"Everyone should eat fish in moderation," he says, while warning that "pregnant women should avoid eating tuna, a big fish, because it has one of the highest concentrations of mercury."
An innovative way to check mercury levels in seafood comes from GotMercury.org, which introduced a Web- and cell phone-based mercury calculator in 2004.
At Pediatric Medical Associates, in Rydal, Steven Shapiro, chairman of pediatrics at Abington Memorial Hospital, offers insight into what to feed children.
"Methyl mercury builds up in the body of a fish and is absorbed as a toxic compound if a child eats enormous amounts, but even though kids can't metabolize it out, trace amounts are not going to bother little babies and little kids," he says. "And yet, metallic mercury, such as that found in a thermometer, will not be absorbed.
"Parents like to begin feeding kids fish products at about 6 months, but infants are very sensitive to mercury, and it does affect the kidneys," he says, adding that "all things in moderation" is the best way for everyone to go through life.
"But I would rather see kids eat moderate amounts of fish than red meat," states Shapiro.
So, what are some safe choices?
Shapiro says that "among white fish they can eat safely are fish sticks, halibut, haddock, flounder and cod; tuna can be very healthy, as long as it's consumed, of course, in moderate quantities."
Another good source of fish oil, he adds, are in over-the-counter capsule form.
A concern among physicians and others, according to Shapiro, was the use of the mercury-based preservative thimerosal in vaccines, which is no longer used: "The theory is -- and a lot of the thinking about mercury is theory -- that kids had so many exposures to that preservative because of the 32 antigens they receive by the time they're 2 years old that is was considered a potential mercury risk."
This concern was perceived as a problem, but in reality, the amount used was deemed too insignificant to pose a danger, he says.
Another place where mercury has been found is in breast milk, adds Shapiro, though most doctors believe that the benefits of breast milk far outweigh any risk: "Mothers can't metabolize it out, but I can't remember reading about any infant who was poisoned by mercury in mothers' milk."