Fluorogenic Polymer Can Detect Mercury Levels in Fish

A novel fluorescent polymer that lights up when it makes contact with mercury that may be present in fish could be used to reduce the sale and consumption of fish containing mercury levels deemed to be unsafe by the European Food Safety Authority (EFSA) and U.S. Food & Drug Administration (FDA).

A swordfish auction in the fish market of Vigo, Spain. Courtesy of José Antonio Gil Martínez.

The fluorogenic polymer, JG25, can detect the presence of mercury in its organic form (MeHg+) and as an inorganic salt (Hc2+). The presence of mercury in fish comes from natural sources in the environment and from industrialized waste.

Researchers at the University of Burgos used a portable polymeric probe in situ to apply the polymer to two-gram samples from a range of fish species. The polymer emitted blue light when irradiated with UV light proportional to the quantity of mercury, whether MeHg+ or Hg2+, present in the fish. The quantitative relationship between the concentration of mercury in the fish and the increase of fluorescence in the polymer in contact with fish samples was confirmed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS).

“The polymer remains in contact with samples extracted directly from the fish for around 20 minutes. Then, while (it) is being irradiated with ultraviolet light, it emits a bluish light, which varies in intensity proportionally to the quantity of methylmercury and inorganic mercury present in the fish,” said researcher Tomás Torroba.

The research showed that the larger the fish, the higher the levels of mercury. The researchers found between 1.0 and 2.0 parts per million (ppm) in swordfish, tuna and dogfish; around 0.5 ppm in conger eels; and around 0.2 ppm in panga. No mercury was found in farmed salmon.

“Contamination of above 0.5 ppm in a food is already thought to be a considerable level,” Torroba said. “Several of the fresh tuna and swordfish samples we analyzed exceed and even double this amount. This is why experts recommend that pregnant women reduce their weekly intake of certain types of fish, such as swordfish, due to possible risks to the fetus.”

The research was published in Chemical Communications (doi: 10.1039/C6CC05977E).