A paper by three scientists published in the journal Science determined for the first time a new form of mercury found in fish which is said to be less toxic than other kinds.
The scientists, Dr. Graham N George, Dr. Ingrid J. Pickering and Dr. Hugh H. Harris, working at the Stanford Synchrotron Radiation Laboratory, used a technique involving high-intensity X-rays to investigate the nature of mercury molecules in samples of swordfish, orange roughy and sand sole. What they found is most likely methylmercury cysteine. Previous models of mercury toxicity has been based on methylmercury chloride.
The only evidence that this form of mercury may be less toxic, however, is that in an unrelated experiment, tiny zebra fish larvae tolerated it better than methylmercury chloride. "But fish aren't people," said George.
High levels of mercury in fish can be extremely poisonous: one episode in Japan in the 1950s and '60s caused neurological disease, birth defects and even death.
While the levels of mercury typically found in commonly eaten fish are far lower, several studies have shown a subtle loss of mental acuity in children of women who had consumed fish or whale meat while pregnant. On the other hand, at least one study found no effect.
The Food and Drug Administration recommends that children, as well as women of childbearing age, eat no more than 12 ounces of fish a week and avoid tilefish, swordfish, shark and king mackerel, all of them ocean fish known to be high in mercury.
Source: The New Sunday Times, 31 August 2003
The original study
Hugh H. Harris, Ingrid J. Pickering, and Graham N. George, The Chemical Form of Mercury in Fish, Science, 301/5637 (2003) 1203
Scientific America, August 29, 2003: Study Questions Mercury Toxicity in Fish