At one point or another, most people have been told to be wary of how much tuna they consume due to excessive mercury content, but is there any truth in that? A study coming out of the University of Montreal’s Department of Biological Sciences decided to go fishing for the truth.
The study combined data on the amount of mercury fished out of oceans and seas from 1950 to 2014 and the weekly consumption rate of fish and seafood by the populations of 175 countries between 1971 and 2011. The findings left researchers more concerned than previously thought.
With a vast quantity of populations around the world relying on food from the sea as their primary source of protein – 3 billion according to WWF – excessively high levels of methylmercury is particularly unsettling.
Postdoctoral fellow, Raphaël Lavoie, was able to estimate these populations’ per capita intake of methylmercury (MeHg), which is a highly toxic form of mercury, under the direction of Professor Marc Amyot. He approximates that the people of 38 per cent (66 of 175) of the countries examined by the study might be exposed to methylmercury levels higher than the maximum deemed safe for foetal development. The highest-risk countries include the Maldives, Iceland, Malaysia, Lithuania, Japan, Barbados and South Korea.
Industrialisation has released mass quantities of mercury into the air that settles in oceans and waterways that, ultimately, are absorbed by sea creatures and in turn humans if ingested. This toxin has the potential to penetrate the blood-brain barrier and impact cerebral development when consumed, especially in children and foetuses.
Since the 1950’s, demand for seafood products has been on the rise, and with modern technology enabling more intensive forms of industrial fishing, it has gradually migrated to deep-sea and international waters.
“The global marine catch totals 80 million tonnes of fish per year, which means that we are also pulling out increasingly large amounts of mercury,” says Amyot.
Of the industrial fishing areas listed by the FAO, the Northwest Pacific currently exports the most fish – and the most methylmercury. The Western Central Pacific holds second place, while the Indian Ocean ranks third.
“Together, these three fishing areas exported 60 per cent of the mercury resulting from global seafood production in 2014,” says Lavoie.
The people in these regions are some of the world’s top seafood consumers. Species high up on the food chain contain the highest concentrations of mercury. From 1950 to 2014, large fish represented approximately 60 per cent of the global catch (by weight) and nearly 90 per cent of the mercury ingested by consumers from fish.
To be safe for foetal development, the threshold for methylmercury consumption is 1.6 micrograms for each kilogram of a person’s body weight per week (1.6 μg/kg/week).
“By comparing FAO data on global seafood consumption, we observed that from 2001 to 2011 the populations of 38 per cent of the 175 countries we analyzed would have been exposed to weekly doses of methylmercury far above the maximum safe level of consumption for foetal development,” says Lavoie. “Many of these populations are in coastal and island nations, especially developing countries.”
For instance, the Maldivians during that 10-year period consumed an average of 23 micrograms of methylmercury per kilogram of body weight each week, or more than 14 times what’s deemed safe. The next highest-ranking were people in Kiribati (8 μg/kg/week), Iceland (7.5 μg/kg/week), Malaysia and Samoa (6.4 μg/kg/week), French Polynesia (5 μg/kg/week), Lithuania, Japan and Barbados (4.8 μg/kg/week) and South Korea (4.7 μg/kg/week).
By contrast, the global average for mercury exposure over the same 2001-2011 period was estimated at 1.7 μg/kg/week. In Canada, exposure totalled 1 μg/kg/week.
Lavoie and Amyot say that their estimates are conservative. The global catch by the fishing industry, including artisanal and illegal fishing, is probably 50 per cent higher than the Food and Agriculture Organization of the United Nations (FAO) data indicates.
Hopefully, these estimates will help authorities find ways to mitigate risk of mercury exposure, especially for vulnerable populations, across the world.