New Tests Measure Mercury Contamination in Fish and Water

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By Mike Howie

Mercury is a toxic metal many recognize as the reason why doctors tell pregnant women not to eat sushi. Fish are commonly contaminated with mercury and, when ingested, the metal can cause long-term neurological illnesses. In pregnant women, mercury can lead to reduced placental and fetal growth as well as small head circumferences. While these are not the most common risks that a mother and unborn child can face, they are still risks. Reduced placental size has been linked to high blood pressure in adulthood, and reduced head circumference is associated with cognitive development deficits.

Testing the Food

In the food chain, mercury is typically found in two forms: as organic methylmercury (MeHg+) or as an inorganic salt (the cation Hg2+). Researchers at the University of Burgos in Spain recently developed a fluorescent polymer called JG25 that can detect both of these chemicals. According to Tomás Torroba, the lead author of the study, the polymer is placed into contact with a sample for approximately 20 minutes and then irradiated with ultraviolet light. The fluorescence appears as a bluish light that varies in intensity in proportion to the amount of mercury present.

Larger fish tend to have higher concentrations of mercury.

After testing a range of species, the researchers concluded that larger fish tend to have higher concentrations of mercury. They detected as much as 2ppm in swordfish, tuna and dogfish, and as little as 0.2ppm in panga. As Torroba noted, “contamination of above 0.5ppm in a food is already thought to be a considerable level.” The United States Food and Drug Administration (FDA) states that people should not consume more than one serving per week of fish with a concentration of over 1μg of mercury per kilogram of fish.

Testing the Water

Earlier, another team of chemists at the same university developed a method of quickly testing for mercury contamination in water. They created an indicator sheet that turns red after just five minutes in water if mercury is present above a certain concentration. The sheet is calibrated to detect concentrations of 2ppb of divalent mercury (the EPA limit for potable water), but the composition of the indicator can be adjusted for other levels.

“Changes can be seen by the naked eye and anyone, even if they have no previous knowledge, can find out whether a water source is contaminated with mercury above determined limits,” said José Miguel Garcia, one of the authors of the study. For a more precise reading, one can simply take a picture of the sheet and then look at the color values in an image manipulation program like Photoshop.

The timing of these new tests is important: in 2013, more than 125 countries signed the Minamata Convention on Mercury, a treaty designed to protect humans and the environment from mercury and named for the Japanese city where hundreds died from mercury poisoning in the 1950s. With an additional 40 countries now committed to the treaty, these testing methods can help to support the convention and its goals for human safety.


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