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Scientists in search of the sources of mercury pollution in the Arctic

Polar bears, toothed whales and humans in the Arctic have higher levels of mercury than anywhere else on the planet. A new research project will use mercury isotopes to gain new knowledge about the cycle of mercury in the Arctic. This knowledge may provide a better understanding of the sources and processes that lead to the high levels.

Polar bear captured on camera close to the breeding grounds of harp seals and hooded seals in Northeast Greenland in the spring of 2007. These species are increasingly replacing the ringed seals as diet due to climate change. This may explain an increasing mercury input to polar bears because the new seal species have high mercury. Photo: Rune Dietz

When we pollute in North America and Eurasia toxic substances are transported north to the Arctic. This also applies to mercury.

Despite that the liquid metal has been phased out in many places, it is still used for a number of purposes around the world – for example in gold mining in third world countries. Mercury is also released when we burn fossil fuels, especially coal.

Part of the mercury is transported to the Arctic either by atmosphere or ocean currents, where it is taken up in the food web and biomagnified.

Until now, researchers have used computer models to simulate the atmospheric dispersion of mercury to explain the sources and processes underlying the high mercury concentrations in animals. However, this new research project will provide more detailed knowledge that can supplement the models describing spatial-temporal development of mercury in biota in different species and tissues.

Professor Rune Dietz from the Department of Ecoscience at Aarhus University, together with a number of colleagues, has received funding from Denmark's Independent Research Fund Denmark (DFF) for the project. The plan is for them to examine mercury isotopes in biological samples from a number of key species such as polar bears, ringed seals, toothed whales and various fish species, as well as in sediments and peat to gain more knowledge of the mercury cycle in the Arctic. The analyzes will be conducted on equipment granted by the Carlsberg Foundation in 2020.

- One of the reasons we look at the mercury isotopes is that we can potentially say something about the pollution sources. When we know where the mercury comes from, we can also do more to reduce the emissions that end up in the Arctic area, says Rune Dietz and continues:

- However, there is still very limited knowledge of the mercury isotopes in the global pollution sources, and therefore it will be a challenge to completely map this.

Isotopes - A natural fingerprint

All elements have isotopes – including mercury. Isotopes are variations of an element that differ by having more or fewer neutrons in the nucleus. Mercury has seven stable isotopes.

The isotopes can be considered a kind of a fingerprint. The composition of isotopes can be completely unique from source to source, just as the biogeochemical processes of which mercury plays a part in nature cause a change in the isotope composition.

- We plan to use the composition of isotopes in the mercury to learn more about sources and transport to the Arctic, explains senior researcher Jens Søndergaard from Aarhus University, who is one of the researchers behind the new project.

Using a unique data bank of Arctic animals, collected by Aarhus University over the past four decades, as well as sediments and peat collected by the University of Copenhagen, which is also a partner in the project, the researchers will analyze the mercury isotopes in these samples. They hope it will allow them to follow both natural and anthropogenic releases and deposits of mercury in the Arctic over thousands of years.

Leading researchers in mercury pollution

Rune Dietz's group of researchers from Aarhus University has considerable experience when it comes to mercury pollution in the Arctic area. He himself has been responsible for investigating mercury pollution through his work in making extensive international assessment reports under the Arctic Monitoring and Assessment Program, AMAP.

At the Department of Ecoscience, he has also, for the past 40 years been involved in systematically and regularly collecting and taking samples of arctic animals.

- 40 years is completely unique. There are virtually no other animal tissue time series of this kind that have been collected so consistently. It gives us the opportunity to investigate how the pollution has developed over time, he says.

However, this does not mean that no further samples will be collected. Rune Dietz and his colleagues are determined to investigate the mercury pollution as thoroughly and widely as possible, he emphasizes.

- We will go to Greenland and collect samples from toothed whales in the autumn in Tasiilaq in Southeast Greenland, and next spring we will travel to Ittoqqortoormiit in central East Greenland when the hunting season for polar bears is peaking.

- In addition the plan is to obtain more samples to elucidate the effects of pollution with, among other things, mercury. In addition, we are already in the process of discussing deliveries of key samples from Canada, Alaska and Svalbard with our international network.

The transport routes must be mapped

The many biological and geological samples collected during the project will, among other things, help to map how much mercury has been transported to the Arctic over time.

- Samples from sediment and peat allow us to map mercury levels thousands of years back in time. We have no doubt that most of the pollution is caused by humans, but we get a clearer picture of when the development takes off, explains senior researcher Jens Søndergaard from the Department of Ecoscience. He is the chemical expert responsible for analyzing the mercury isotopes in the project.

- In addition, there is also mercury bound in the permafrost in the Arctic. The permafrost is thawing these years, and this may cause more mercury to be released into the Arctic environment. But we don't know very much about how much and how quickly mercury can be released from areas with thawing permafrost, says Professor Bo Elberling, who has been in charge of sediment and permafrost collection at the basic research center CENPERM (Center for Permafrost).

The idea is to use measurements of mercury isotopes from the permafrost to investigate whether it is possible to distinguish this mercury from recently deposited mercury.

- If we succeed, we will be able to say if this 'old' mercury is starting to play a larger role in the high mercury loads we observe in Arctic top predators, he explains.

Can help us to live up to the MINAMATA Convention

In 2013, 140 countries (including Denmark) decided to limit the release of mercury into nature. It happened in Minamata in Japan, where in the 1950s it was discovered that a chemical factory was discharging large amounts of mercury into the bay.

The Minamata Convention obliges countries to stop emitting mercury and to find alternative substances in products where possible. More knowledge about where the mercury comes from and how it travels north can therefore help us live up to the convention, explains Rune Dietz.

- When we know where the mercury comes from – whether it is from the sea or the atmosphere – we have a better basis for making the right decisions to stop mercury from entering nature, he concludes.

About the research project

The Department of Ecoscience (ECOS), Roskilde, AU, has just been granted the project 'Greenland Mercury Stable Isotopes: from Holocene Sources to Modern Time-series and Pathways (GreenPath)' by the Independent Research Fund Denmark (DFF) - (Case number: 4258-00004B).

The grant is DKK 6,189,553, and Professor Rune Dietz is leading the project. In addition to AU (Rune Dietz, Jens Søndergaard and Christian Sonne), collaborators from the University of Copenhagen (Bo Elberling) and from research institutions in France (Jeroen Sonke) and Canada (John Chetelat) participate in the project. There will also be a Ph.D. and a postdoc working on the project.

AU has for more than four decades led the collection and analysis of mercury in Greenlandic environmental samples, as in the past 25 years has been a part of the Arctic Monitoring and Assessment Program (AMAP). Some of these biological samples will be examined in more detail as described above in GreenPath.
The project will be coordinated with two other recently granted projects WhaleAdapt (Lead: McGill University) and ArcSolution (EU project).