New Study Shows Form of Mercury in Fish Different From Previous Studies

Summary

A new study at the Stanford Synchrotron Radiation Laboratory (SSRL) makes use of X-ray absorption spectroscopy (XAS) to identify the exact form of mercury found in two widely consumed species of fish, swordfish, and orange roughy. The results are featured in the August 29, 2003, issue of Science. The researchers found that mercury was present not as methylmercury chloride, but rather as a methylmercury compound in which the mercury atom is also bound to a sulfur atom, probably in the amino acid cysteine. The authors suggest that the health risk of eating fish contaminated with mercury should be determined based the toxicity of methylmercury cysteine, rather than calculated on the assumption that the mercury is present as methylmercury chloride. There is considerable public health interest in mercury. The element is associated with several diseases, notably the Minamata disease, a neurological disorder caused by eating fish highly contaminated with mercury. The toxicity of mercury depends on the chemical form of the element. Methylmercury chloride is considered to be especially toxic compared with, for example, elemental mercury and many other compounds of mercury. Thus it is essential not only to measure the amount of mercury in fish or other foodstuffs, which is not hard to do, but also to determine the amounts in its various chemical forms, which is much more difficult. (XAS) is one of the few techniques that can identify the species of elements such as mercury without extensive sample preparation.