Comparative test results for swordfish. (Photo: Stock File/FIS)

Fluorescent polymer detects mercury contamination in fish

SPAIN
Saturday, February 18, 2017, 01:50 (GMT + 9)

Researchers at the University of Burgos have manufactured a fluorescent polymer, called JG25, capable of detecting the presence of mercury, in both organic and inorganic form, in fish.

According to the researchers, mercury is a toxic metal that can reach the environment from natural sources, but in recent decades its concentrations have soared in marine and land areas by industrial discharges.

In the food chain it is present diluted in organic form, as methylmercury (MeHg +), or inorganic, as the cation Hg2 +.

"The polymer contacts samples extracted directly from fish for about 20 minutes and, after being irradiated with ultraviolet light, emits a bluish light whose intensity is proportional to the amount of methylmercury and inorganic mercury present in the fish," explains lead author, Tomas Torroba.

The technique was applied by a portable polymer probe that can be used in situ, in samples of 2 grams extracted from various species.

The quantitative relationship between mercury levels in fish and the increase in fluorescence was verified with a chemical analysis (called ICP-Mass).

The results, published in Chemical Communications journal, show that larger fish have higher amounts of mercury: Between 1.0 and 2.0 parts per million in swordfish, tuna and school shark; about 0.5 ppm in conger and 0.2 ppm in pangasius, Agencia Sinc reported.

However, this harmful substance was not found in farmed salmon, since although they are fish of great size and in the upper part of the trophic chain, in captivity there is no presence of the metal.

The authors point out that the amount of mercury in fish and what a person eats determines its toxicity.

The European Food Safety Authority (EFSA) recommends that the tolerable weekly intake of methylmercury be no more than one serving containing amounts in excess of 1,6 μg/kg (micrograms per kilogram of fish) and 4 μg/Kg for the case of inorganic mercury, an amount higher than that detected.

For its part, FDA food safety agency goes further and recommends not to consume more than one serving of fish per week containing concentrations greater than 1 μg/kg.

"It is considered that above 0.5 ppm food contamination is already considerable," explains Torroba.

That amount is surpassed and even doubled by several of the analyzed samples of fresh tuna and swordfish. Hence, experts advise pregnant women to reduce the weekly consumption of certain types of fish, such as swordfish, because of the risk it could pose to the fetus.

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