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Northern Ontario fish showing increasing mercury levels says U of T study

“If levels continue to rise it could pose significant health risks to both the fish and the people consuming them.”
walleye on ice

A just released study shows mercury levels in Ontario fish are on the rise and if that trend continues it will have considerable health and economic consequences  in the upcoming decades according to a new U of T study.

Northern Ontario lakes in particular are showing trends of increasing fish mercury levels.  If the levels continue to increase at this pace, Walleye (pickerel) at almost all monitored Northern Ontario lakes will suffer sublethal effects including an inability to reproduce. 

Walleye is a key sport fish in Lake Nipissing, and for years has drawn anglers lured by its reputation for fishing. It has many islands, weed beds and shoals that are perfect for walleye.

"Walleye, Northern Pike and Lake Trout were chosen as subjects because they are a top predatory fish and as a result tend to accumulate higher concentrations of mercury from eating contaminated prey lower in the food chain," says a news release from the university. 

"The fish are also extremely popular among anglers and contribute significantly to Ontario’s commercial, sport fishing and tourism industries, which add $2.2 billion to Ontario’s economy annually. Walleye in particular is also a popular fish to eat among First Nations living in Northern Ontario," notes Dr. Satyendra Bhavsar, a research scientist with Ontario’s Ministry of the Environment and Climate Change.

“Fish mercury levels actually declined during the 1970s and 1980s, but mercury levels in Walleye and Pike increased between 1995 and 2011,” says U of T Scarborough Professor George Arhonditsis.

“If levels continue to rise it could pose significant health risks to both the fish and the people consuming them.”    

Authored by a team of researchers including Arhonditsis, Bhavsar, and Dr. Nilima Gandhi. The study looked at trends in mercury levels found in Ontario Walleye, Northern Pike and Lake Trout over the past 15 years while projecting where levels will be in 2050. 

"For Lake Nipissing, the observed fish mercury trends are similar to the majority of the monitored Ontario waterbodies.  That means, it’s good news – fish mercury levels are similar or lower at present than those during the 1970's.  However, the levels have been increasing in recent years. For both Walleye and Northern Pike, which are popular for human consumption, mercury levels are increasing," explained Dr. Gandhi.

"I would like to note though that there may be natural variability within a system and that may show a temporary increase in fish mercury concentrations - they may either remain unchanged or even decline over a long term period. We can hope that Lake Nipissing fish mercury levels will trend towards the lower levels observed during the 1990s.  Important to notice though, is that the strength of our study lies in the above mentioned findings for tens of locations for two key fish species: Walleye and Northern Pike."

The study is unique because of the richness of data obtained through the Province’s long-running Fish Contaminant Monitoring Program. Not only did it cover a large geographical area but more than 200,000 measurements of fish mercury levels were taken across the province, even including remote locations only accessible by plane. 

“There’s never been a study that tracked changes in fish mercury concentrations over a long period while also projecting levels for the future,” says Gandhi. 

"It is a common misperception that northern Ontario waterbodies would have less mercury in fish," Gandhi told BayToday. "This misunderstanding originates mainly from our common knowledge that environmental pollution primarily occurs due to human activities, and as such, urbanized areas would be more polluted and remote locations would be more or less free of contamination.  We tend to extend this common belief for fish mercury levels as well. 

"However, mercury is a natural element and although it can be enhanced in the environment due to human activities such as coal burning, a large portion can be due to natural events such as forest fires, volcanos etc.  Further, accumulation of mercury in fish also depends on a variety of factors including characteristics of the surrounding environment, such as acidity of water. For example, the Canadian Shield region has certain features such as increased tendency for acidification, which likely results in higher fish mercury levels in the region compared to off-Shield locations.  Since the majority of northern Ontario is on the Canadian Shield, it could be a major reason behind observed higher mercury levels in northern Ontario fish."

The findings, which are published in journal Environmental Science & Technology, build on a 2014 study by Gandhi, Bhavsar, and Arhonditsis that found mercury levels in the same fish have been on the rise over the last 15 years.

Mercury is a highly toxic pollutant. It’s been shown to disrupt sex hormones in fish while in humans can cause damage to the neurological, immune, genetic, cardiovascular, respiratory and gastrointestinal systems. A fetus and children are particularly vulnerable because mercury can hamper the neurological development of the brain.

The study also looked at the impact rising mercury levels will have on fish consumption advisories. It shows that by 2050 only 1 per cent to 33 per cent of monitored Ontario lakes may have Walleye in which mercury levels could be deemed safe to eat twice a week, which is the recommended serving of fish by Health Canada to maintain a healthy diet.

“Clearly this shows there’s a health risk to the people eating these fish, ironically who are doing it for better health,” says Gandhi.

Although only about one third of mercury emissions are emitted from human activities, about 60 per cent results from ‘re-emissions’ of mercury stored in soil and oceans from past human activity over the last decades and centuries.

The way in which mercury cycles around in the environment means it can spend a long time as a contaminant once it’s emitted, and that any action taken on reductions will only see results after a decade or longer, notes Gandhi.  

Mercury emissions in North America have been in decline, especially in Canada where rates fell 90 per cent between 1970 and 2011.  North American emissions now represent only about 3 per cent of human caused global mercury emissions. Global coal burning and mercury emissions have actually gone up in the last 20 years mostly due to greater industrialization in China and India. Current global emissions of mercury stand at about 2,000 metric tons annually.   

“A recent study showed that if dramatic actions were to be taken even the most hopeful estimate shows emissions can realistically only be reduced to about 800 metric tons by 2050. If it’s business as usual, emissions will likely increase to 3,400 metric tons annually,” says Arhonditsis.

“That means the fish mercury projections in this study are entirely possible.” 

Jeff Turl

About the Author: Jeff Turl

Jeff is a veteran of the news biz. He's spent a lengthy career in TV, radio, print and online, covering both news and sports. He enjoys free time riding motorcycles and spoiling grandchildren.
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