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Mercury, the liquid metal, has been used for centuries due to its unique properties in items such as thermometers and tooth fillings although its use has declined as we have become aware of its toxic side effects. However, it is still commonly found in energy saving light bulbs, computers and smartphones. So what toxic effect does mercury have? Well, many of you will be familiar with the expression ‘Mad as a Hatter’, popularized by Lewis Carols’ Hatter character in Alice in Wonderland, these hat makers were thought to be insane because they were exposed to high amounts of mercury used in the felt treatments for hats. While the term and the character make the condition seem like a lot of fun, it is not an accurate portrayal of mercury toxicity. Insanity is a condition of mercury poisoning in humans, however, people suffering from mercury poising usually show signs of depression, anxiety, social awkwardness, and loss of motor control (body movements). Mercury poisoning has a similar influence on animal behaviour, it can cause social fish to stop shoaling together and birds to neglect care of their young, and these behavioural changes can be detrimental to the species’ survival. Extreme cases of mercury poisoning can lead to death in both humans and animals.

Mercury in our environment

It may seem obvious how people working with mercury get toxic exposures, but you’re probably wondering how animals get exposed to mercury? Do we eat these animals and is it toxic to us if we do eat them? Well, plenty of research here at Trent University looks into just those questions!

Mercury occurs naturally in the earths crust and is released into the air mainly by volcanic activity and natural breakdown of soils. However, as with many processes, humans have significantly changes the cycle of mercury since the industrial revolution by increasing outputs of mercury through coal-power generation, metal smelting and mining. It is estimated that up to 50% of total mercury released yearly comes from human activity.

Once mercury is deposited into the sediments of lakes bacteria can transform it into a form known as methyl-mercury, its most toxic form. Methyl-mercury then moves into animals increasing in concentration the longer the animal lives for, a process known as bioaccumulation. In addition, as larger animals eat smaller prey, mercury increases in concentration as is moves up the food chain, known as biomagnification. By the time it reaches predatory fish the mercury can be concentrated up to ten million times its original environmental concentrations. These contaminated fish pose a severe health hazard to predatory mammals and birds, which feed on them and accumulate this toxin into their bodies.

People that consume these fish as a large part of their diet, such as in Northern Canada, are also at risk. Unfortunately, the risk of mercury poisoning became clear in the 1950s when a chemical plant in Minamata, Japan expelled mercury waste into Minamata Bay where many people ate the local fish; close to 1800 people died and more than 10,000 suffered symptoms of mercury poisoning. Discovery of this problem drastically changed regulations for the dumping of metallic wastes by the chemical industry. However, atmospheric inputs of mercury into aquatic environments, though regulated, are harder to control since it is transported over long distances in the air and cannot be separated from the natural input. Current research, at Trent University, aims to improve this bleak picture by investigating methods of identifying mercury from human versus natural sources.

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How to track mercury

How can we track mercury from different sources? Our research explores the identification and potential use of chemical “fingerprints” to track human sources of mercury pollution. The mercury atom has seven different masses, called isotopes of mercury, which are present in different proportions within the environment and get separated and changed as the mercury moves from one state to another. Certain materials, such as coal, have unique proportions of mercury isotopes that are associated with particular biochemical processes within their region of origin. By studying the different proportions of isotopes inside a single sample we can develop techniques to trace the origin of its mercury components.

What does this mean for you? The potential for improved guidelines and predications regarding the mercury content of fish, which will allow for both recreational fisherman and isolated communities to plan ahead and source the right types of fish. These guidelines could help decrease human exposure to mercury in food and protect vulnerable individuals from this toxin.

At an ecological level more accurate identification of mercury sources can lead to improve understanding regarding, which regions and species are most at risk. Mercury stable isotope fingerprinting could enable us to identify local mercury sources, which would result in greater industry accountability for pollution control. On a global scale this new fingerprinting technique could allow us compare our pollution control methods with other nations and compare the best results. Accurate knowledge of system processes and sources is an important component of any international trade deals and negotiation processes.