This is the outcome of a study published a few weeks ago in Nature. During the study, conducted over 15 years, scientists intentionally added a traceable form of mercury to a lake and its watershed. They discovered that the new mercury they added quickly built up in fish populations, and then declined almost as quickly once they stopped additions.
Background:Every year, about 2000 tons of gaseous mercury are released into the atmosphere by human activities such as coal power plant operation, waste incineration or cement production. The harmful substance then is partly transformed to various species as it circulates between the air, soil and water in a complex biogeochemical cycle. Reaching the aquatic environment, it gets particularly dangerous, entering the food web where it accumulates in fish in the form of methylmercury. Human exposure is mainly via the consumption of contaminated fish, creating adverse effects on brain development in children or causing cardiovascular diseases in adults. Simply avoiding fish is not a good solution, since Fish is a source of high-quality protein that is beneficial to many people, providing that it is low in methylmercury.
The Minamata Convention on Mercury is an international treaty that aims to protect human health and the environment from adverse effects of methylmercury by controlling mercury emissions, which should then decrease deposition and loading of anthropogenic mercury to aquatic environments. Since the biogeochemical cycling of mercury in the environment is rather complex, influenced by many environmental and anthropogenic factors, little is known about how quickly fish contamination will decline following reductions in anthropogenic mercury emissions.
The new study:The study was carried out at
IISD Experimental Lakes Area (IISD-ELA) in Ontario, Canada, which is one of the few facilities in the world where lakes and their watersheds can be experimentally manipulated to determine the many ways in which humans are impacting lakes.
“Showing that reducing mercury inputs to a lake will lower mercury concentrations in fish sounds simple,” said Dr. Paul Blanchfield of Fisheries and Oceans Canada and Queens University 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.”
Photo: An aeroplane that sprays mercury into the experimental lake area (Credit: IISD Experimental Lakes Area)
The team applied about one teaspoon of an isotopically enriched mercury to a lake and its watershed, at a cost of over one million CAD. 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.
“Whole-ecosystem experiments are incredibly powerful because they examine the effects of a single factor at a time and provide solutions to globally-important issues in a real-world setting,” said Dr. Carol Kelly, who has spent decades conducting research on the experimental lakes.
Part of that real-world setting was working with natural fish populations.
“Studying fish only in laboratories was not revealing the full story,” said Lee Hrenchuk, a Biologist with IISD-ELA. “Individual fish retain mercury they have previously accumulated for a long time, and so it could be assumed that decreasing mercury input to a lake might not be very beneficial. However, we discovered that the hatching of new fish into a lower mercury environment was sufficient to lower the mercury level of the population as a whole in a short period of time”.
“The near-term value of reducing mercury inputs to freshwater lakes was not a sure thing, because large masses of old mercury always exist in lakes from decades past,” said Mr. Reed Harris, of Reed Harris Environmental, one of the founders of the study.
“So, it was critical for the experiment that the isotopic form of mercury we added could be distinguished from older mercury in the ecosystem.” As new mercury inputs to the experimental lake were increased and then decreased in a controlled manner, the methylmercury in the lake water, surface sediments, invertebrates and fish both increased and decreased quickly. This was true whether the mercury ‘rained’ directly onto the lake surface or entered the lake from the surrounding watershed in streams.
“While mercury exported to lakes from their watersheds may not decline exactly in step with lowering atmospheric deposition rates, this experiment clearly demonstrates that any reduction in the amount of mercury entering lakes will have immediate benefits to fish consumers,” said Dr. John Rudd, former Chief Scientist at the Experimental Lakes Area and a principal investigator on the study.
Source:
This article has been republished from material presented by
IISD. Note: material may have been edited for length and content.
The original publication
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