Scripps Scientists Develop New "Kit" To Screen Mercury In Fish

The article, "Practical Screening of Mercury Contamination in Fish Tissue," by Oliver Brummer, James J. La Clair, and Kim D. Janda, is published in the April 2001 issue of Bioorganic & Medicinal Chemistry.

"It's fast and very inexpensive," Janda says, adding that more than one million assays can be prepared in less than a week for just a few hundred dollars. For consumers, he continues, the method could be safe and easy to use. "You could buy your fish in the morning and have tested it by the time you're ready to cook that evening."

Mercury in fish is a serious health hazard, 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. There, aquatic organisms convert normal mercury ions into methlymercury 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 the most risky because they eat smaller fish and have longer life spans during which the methylmercury can build up.

In recent months, the Environmental Protection Agency (EPA) has issued a warning to women who are pregnant or who are considering becoming pregnant. The EPA cautions them to avoid eating the larger, high-risk fish, such as swordfish, king mackerel and tilefish. The Food and Drug Administration (FDA), which works with state regulators and commercial fisheries to monitor methylmercury levels, also has issued a warning in recent months. The agency has recommended a mercury limit of no more than 1 part per million for human consumption.

Janda's method uses a solution that changes color if there is even half the recommended FDA limit on mercury levels in fish. Basically, a tiny pellet of fish is placed in a tube with a few drops of an acid and enzyme solution, which digests the tissue for a few hours, in a way similar to human digestion. Then the mixture is stirred with a special dipstick coated with a "chelating" 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, which pulls the mercury off the resin, and then a few drops of lightly colored 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 color, becoming clear. The addition of a drop of dye allows a quantitative measure of the concentration of mercury in the fish.

Janda believes that the colorimetric assay could be a boon to field environmentalists, since their current mercury detection procedures demand that they catch whole fish and bring them into the laboratory for slow, expensive and complicated testing.

"This method could be made field ready," he says. "Environmental professionals could test the fish and then release them back into the water."

The research was funded by The Skaggs Institute for Research and Deutsche Forschungsgemeinschaft.