Reducing mercury pollution entering lakes lowers how much harmful mercury is found in freshwater fish destined for consumers’ plates.
This is according to a new paper, published today in Nature. During the study, conducted over 15 years, scientists intentionally added a traceable form of mercury to an experimental lake and its watershed.
The interdisciplinary research team, including Western University’s Brian Branfireun, discovered that the new mercury they added quickly built up in fish populations, and then declined almost as quickly once they stopped additions.
Notably, the fish populations were able to recover from mercury much quicker than previously understood, which suggests that curbing mercury pollution through policy initiatives now will have a rapid and tangible benefit on the quality of fish we consume.
The findings provide indisputable, science-based support for necessary regulations on mercury emissions that have been weakened in recent years, especially in the United States. They also support the efficacy of existing and new policies around the globe that seek to curb how much mercury ends up in the environment.
Branfireun, a professor in Western’s department of biology who specializes in ecohydrology and biogeochemistry, worked with collaborators to lead a team of graduate and undergraduate students to investigate the role of wetlands and forest soils in storing, processing and transporting ‘new’ mercury currently being deposited on watersheds.
They found that the way that soils, mercury and water runoff interact significantly influences the timing of recovery of mercury-contaminated fish in response to reductions in mercury deposits to the landscape.
“The gains we made in understanding the role of the watershed in regulating the movement of mercury from the atmosphere to lakes and fish were gigantic,” said Branfireun. “These scientific advances will allow policy-makers, resource managers and communities dependent on subsistence fishing to make better lake-specific predictions about the magnitude and timing of mercury reductions.”
The study was carried out at IISD Experimental Lakes Area in Ontario, which is one of the only facilities in the world where lakes and their watersheds can be experimentally manipulated to determine the many ways in which humans are impacting lakes.
“None of this would have been possible without this experiment, this team, and the Experiment Lakes Area,” said Branfireun.
The team applied about one teaspoon of a special form of mercury to a lake and its watershed, at a cost of more than $1 million.
They were able to measure this mercury as methylmercury in the ecosystem and to track its rapid decline in fish once they stopped adding it to the environment. Methylmercury is a much more toxic form of mercury that accumulates to high concentrations in many freshwater fishes leading to many adverse, and even life-threatening, symptoms in humans.
“Showing that reducing mercury inputs to a lake will lower mercury concentrations in fish sounds simple,” said Paul Blanchfield of the Department of Fisheries and Oceans and Queen’s University, the lead author of the paper and a lead investigator of the Mercury Experiment to Assess Atmospheric Loading in Canada and the United States (METAALICUS).
“But it required a dedicated team effort, including academic, government and NGO researchers from across North America, during the 15-year, whole-ecosystem study to arrive at this conclusion.”