University of Sask. study finds no mercury damage from high-fish diet

A man fishes on the Pacific side of the Panama Canal in Amador, Panama City, Thursday, April 7, 2022. (AP Photo/Arnulfo Franco)

A Saskatoon researcher has shone a bit more light on how an "enigmatic" element affects people who consume it through fish.

"Mercury is a fascinating element, I've been interested in it for more than 20 years now. Its chemistry is fascinating," said Graham George, professor and Canada Research Chair in X-ray Absorption Spectroscopy at the University of Saskatchewan.

He says clarity on the consequences of ingesting low levels of mercury from fish is an important issue for global food security, as many people worldwide rely on fish for protein. The concern over the safety of eating fish stems from the United States Environmental Protection Agency's "conservative" recommendation to avoid some species due to them containing mercury, he said.

However, the type of mercury in question is important, he said.

"So it doesn't matter what element you were you're dealing with, whether it's something that's nutritionally essential in your diet, the chemical form in which that element is presented to you in your diet, or however you ingest it, will control whether it's benign, or beneficial or harmful," he said.

Dimethyl mercury, for example, a colourless, clear liquid, is a "death sentence" if it burns through your skin into your body. But mercury sulphide, used in silver tooth fillings, isn't toxic at all, he said.

His team used the Stanford Synchrotron Radiation Lightsource in California and the Advanced Photon Source at the Argonne National Lab in Illinois to compare the form of mercury in brain samples from two people from the Republic of Seychelles who had consumed bout 12 fish meals a week over their lifetimes and samples from two people who died after accidental mercury poisoning.

The form of mercury in the brains of the people who ate fish was the same as the form found in the fish themselves — and those people showed no neuropathological consequences or neurological deficits that could be linked to mercury exposure.

"There was nothing that could be identified as something that was a health consequence of consuming all that fish and all that mercury over an entire lifetime," George said.

However, the brains of subjects poisoned with organic mercury contained mixtures of mercury compounds, including significantly elevated levels of mercury selenide.

"So the outcomes, the molecular level outcomes, were entirely different," George said.

He cautions that he's not a physician and isn't telling anyone to ignore health guidelines or how much mercury they should consume.

"What I can say is that it's not simple. I don't think you're going to find much fish for sale in the supermarket in most parts of Canada that contains very high levels of mercury."

Personally, he would avoid swordfish and shark, both because some species are endangered and because as predators they accumulate concentrated levels of mercury.

The FDA recommends avoiding shark and swordfish as well due to mercury concerns, in addition to king mackerel, marlin, orange roughy, tilefish and bigeye tuna.