Lomonosov Ridge off Greenland (LOMROG) 2007: Accumulation of mercury in the Arctic Ocean12 August 2007 - 17 September 2007
Emissions of mercury
As a consequence of long-range transport of manmade emissions into the atmosphere, the Polar Regions are nowadays contaminated with highly neurotoxic mercury (Hg). About 6 000 tonnes of Hg are present in the atmosphere today, mainly originating from anthropogenic emissions in the industrialized part of the world. Mercury is one of the most dangerous environmental pollutants, and since it is an element, it cannot be destroyed. Mercury poisoning of the planet could best be reduced by curbing pollution from power stations, since coal-fired power stations and waste incinerators account for around 70 percent of new, quantified manmade mercury emissions to the atmosphere (UNEP, 2002).
Mercury is biomagnified in marine wildlife
The most toxic form of mercury is monomethylmercury (MMHg), which is formed in aquatic environments after deposition of inorganic mercury. MMHg is bioaccumulated in fish, and fish contaminated with MMHg is hazardous to eat because MMHg passes the blood brain barrier and the placenta in pregnant women, and can therefore be dangerous to the foetus.
The level of Hg found in marine mammals in the Canadian Arctic exceeds guideline limits for Hg contamination of food for human consumption. Moreover, Hg levels in Arctic ringed seals and beluga whales have increased by a factor of up to four over last the 25 years and the levels recorded in indigenous people living in the Arctic exceed those in people from more temperate, industrial regions. In a study on 7-year-old children in the Faeroe Islands, it has been shown that prenatal methyl mercury exposure may lead to neuropsychological dysfunctions, such as problems in language acquisition, attention and memory deficit (Grandjean, 1997). According to exposure data published by the U.S. Center for Disease Control and Prevention, the number of babies at risk in the U.S. could be as high as 300,000. On a global scale, that number can be increased to several million (UNEP, 2002).
Long-range transport and chemical transformation contributes to deposition of mercury in the Arctic
Atmospheric deposition of Hg in the Arctic is post-industrially driven, and high Hg concentrations in the upper layer of polar lake sediments have been found (Steffen et al. 2007 and references therein). Ice core samples confirm these results, and the same trends are also observable in, for example, peat from southern Greenland.
Enhanced mercury deposition is observed in the arctic environment, and one important factor influencing the deposition of the species is so-called atmospheric mercury depletion events (AMDE). These events occur during the polar spring and a substantial amount of the global atmospheric Hg pool, that is to say, approximately 300 tonnes per year, is deposited in the arctic environment (Ariya et al., 2004, Skov et al., 2004, Sommar et al., 2007). In addition to atmospheric deposition of Hg, the species may also enter the polar basin via oceanic currents and river input. However, while land based measurements of Hg species are represented in literature, information is lacking on the relative importance of various sources of mercury to the polar basin today. Our work contributes to an extensive investigation on water and air masses, aiming at an assessment of mercury sources and sinks in the Polar Basin. The measurements have been conducted under the umbrella of the LOMROG and Beringia expeditions, both arranged by the Swedish Polar Research Secretariat in 2007 and 2005 respectively.
Mercury sampling in Arctic seawater and air
To estimate the input and accumulation of mercury in Arctic marine waters, about 200 samples for determination of total mercury (Hgtot) and MMHg were taken at some 20 stations along the LOMROG 2007 expedition route, and around 500 samples were taken for the same species at 48 stations during the expedition Beringia 2005. Continuous measurements of total gaseous mercury (TGM) in air were also conducted during both expeditions using a Tekran 2537A mercury vapour detector, and a portable mercury analyser i.e. LUMEX Mercury Analyzer RA-915+. Figure 1 presents data on concentrations of elemental mercury in air recorded during the LOMROG expedition over a period of 22 days, between 15 August and 6 September 2007. The average concentration of TGM during this period was 1.3 ± 0.2 ng/m3. The data will be further analysed with respect to a number of ambient parameters, such as wind conditions and sea ice coverage.
The mercury sampling in water was designed as profile measurements at various latitudinal sites at the LOMROG and Beringia CTD water stations sites respectively, and will be analysed in combination with data on movements of the water masses. In addition, a transect for sampling of surface water using the water sample system in the boat were performed when crossing the Greenland Sea from 76°44’N and 1°22’E to 78°06’N and 13°24’E off the west coast of Svalbard. For each sample, 125 ml of seawater was collected in acid washed Teflon bottles and these are currently being analysed for Hgtot by purge and trap technique as described in Gårdfeldt (2002). Determination of MMHg content in the samples is conducted after derivatisation by an ethylating agent using the gas chromatography CVAFS technique as described in Lee et al. (1994).
During the Beringia 2005 expedition continuous measurements of dissolved gaseous mercury (DGM) were performed using a new method first described in Andersson et al. (2007a). Part of the data from these measurements is presented in figure 1, and is thoroughly described in Andersson et al. (2007b and 2007c).
Multiphase investigations combining oceanography and mercury speciation, as performed during the LOMROG 2007 and Beringia 2005 expeditions, comprise a unique series of Hg sampling. The data archived will help to assess the Hg sources, the accumulation and the long-term fate of mercury in the polar ecosystem. Preliminary results from our measurements show that the enhanced deposition and river input of mercury species, in combination with restricted evasion at northern latitudes compared to more southern latitudes, result in an accumulation of mercury in the polar water body. For example, the concentration of dissolved gaseous mercury is up to ten times higher in the Arctic Basin compared to the North Atlantic Ocean.
- Andersson, M.E., Gårdfeldt, K. and Wängberg, I. 2007a. A description of an automatic continuous equilibrium system for measurement of dissolved gaseous mercury. Analytical and Bioanalytical Chemistry.
- Andersson, M.E., Sommar, J. and Gårdfeldt, K. and Lindqvist, O. 2007b. Accumulation of mercury in the Arctic Ocean. Submitted to Marine Chemistry.
- Andersson, M.E., Sommar, J. and Gårdfeldt, K. 2007c. Air-Sea flux of volatile mercury over the North Atlantic Ocean. Manuscript.
- Ariya, P., Dastoor, A., Amyot, M., Schroeder, W., Barrie, L., Anlauf, K., Raofie, F., Ryzhkov, A., Davignon, D., Lalonde, J. and Steffen, A. 2004. The Arctic: A sink for mercury, TELLUS B, 56 (5), 397–403.
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- Grandjean, P., Weihe, P., White, R., Debes, F., Araki, S., Yokoyama, K., Murata, K., Sorensen, N., Dahl, R. and Jorgensen, P. 1997 Cognitive deficit in 7-year-old children with prenatal exposure to methylmercury. Neurotoxicology and Teratology 19, 417–428.
- Lee, Y., Munthe, J. and Iverfeldt, Å. 1994. Experiences on analytical procedures for the determination of methylmercury in environmental samples. Applied Organometallic Chemistry 8, 659–664.
- Skov, H., Christensen, J.H., Heidam, N.Z., Jensen, B., Wahlin, P. and Geernaert, G. 2004. Fate of elemental mercury in the Arctic during atmospheric depletion episodes and the load of atmospheric mercury to the Arctic. Environment Science and Technology 38, 2373–2382.
- Sommar, J., Wangberg, L., Berg, T., Gardfeldt, K., Munthe, J., Richter, A. Urba, A. Wittrock, F. and Schroeder, W.H. 2007. Circumpolar transport and air-surface exchange of atmospheric mercury at NyÅlesund (79°N), Svalbard, spring 2002. Atmos. Chem. Phys. 7 (1), 151–166.
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- UNEP 2002. Global Mercury Assessment report