Handy test to detect mercury

A new kit to detect contamination in fish

Published: Thursday 31 May 2001

scientists at the us -based Scripps Research Institute have developed a screening method, similar to a home pregnancy test, that can detect mercury contamination in fish. Inventors of the device say that the method is fast and inexpensive.

Mercury contamination in fish is a serious health concern, especially for children and pregnant women, because one particularly poisonous form, methylmercury, interferes with developing nervous systems and can cause birth defects. Methylmercury contamination occurs when mercury pollution from automobile emissions or industrial waste washes into the ocean or groundwater. The aquatic organisms convert normal mercury ions into methylmercury and release the compound into the water. Fish absorb it through their gills, or through their digestive tracts when they feed, and the poison accumulates in their tissue. Larger fish are more risky to eat because they prey upon smaller fish and have longer life spans during which methylmercury can build up in their systems.

The new method for mercury detection uses a solution that changes colour if mercury traces occur in the fish. To test, a tiny pellet of fish tissue is placed in a tube with few drops of an acid and enzyme solution, which digests the tissue for a few hours, in a manner similar to human digestion. Then the mixture is stirred with a special dipstick coated with a resin. If there is any mercury in the fish it sticks to the resin. The dipstick is then plunged into a second tube containing a mild acid that pulls the mercury off the resin, and then a few drops of lightly coloured detector solution is added. This solution has a molecule that precipitates when it binds to the mercury. If the fish is contaminated, the liquid changes colour, becoming clear. The addition of a drop of dye allows one to quantify the mercury contamination in fish. Researchers believe that the colorimetric assay test, as it is called, could be a boon to field researchers, since the current mercury detection procedures demand that they catch whole fish and bring them into the laboratory for slow, expensive and complicated tests.

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