An assessment of selenium to mercury in Greenland marine animals
Introduction
The accumulation, toxicity and effects of mercury and selenium have been documented in the scientific literature and been reviewed extensively (e.g. WHO, 1976, WHO, 1987, WHO, 1989, WHO, 1990, WHO, 1991). The most relevant results of mercury poisoning in most animal groups are the adverse effects on reproduction, immune response, neurological impairment, as well as damage to organs like the central nervous system, the liver and kidney. Additional effects in invertebrates and fish include reduced growth and cardiac activity, as well as extended developmental times. Recent investigations from the Faeroe Islands indicate that the present methylmercury intake is high enough to cause cognitive deficits in children from this area (Grandjean et al., 1997).
Less information is available on the toxicity of selenium. Liver and kidney congestion, hair loss, erosion of bone joints, emaciation, as well as effects on the central nervous system have been reported for a number of species. As for mercury, selenium also has an adverse effect on reproduction (Hansen and Deguchi, 1996). The results of some studies seem to indicate that selenium compounds are less toxic to animals which normally have a high dietary intake of selenium.
High concentrations of mercury and selenium have been documented in Arctic marine biota, (e.g. Dietz et al., 1996, Dietz et al., 1998a) as well as the Greenland Inuit population (e.g. Hansen, 1981, Hansen, 1990, Hansen et al., 1984a, Hansen et al., 1984b, Hansen and Pedersen, 1986). A recent evaluation of the estimated contaminant input for the Greenland Inuit population is dealt with elsewhere in this issue (Johansen et al., 2000).
It has been shown that marine mammals, having the highest mercury burdens in the marine biota, are able to detoxify methylmercury by a specific chemical mechanism involving selenium (Koeman et al., 1973, Koeman et al., 1975). This relation has also been documented in Arctic marine mammals (e.g. Hansen et al., 1990, Paludan-Müller et al., 1993, Dietz et al., 1995, Dietz et al., 1998b).
All our available data on mercury and selenium from the Greenland marine environment have been compiled in the present paper in order to elucidate whether selenium is found in a molar surplus to mercury in other tissues and groups beside the liver of marine mammals. Further details of the species have been presented previously (e.g. Nielsen and Dietz, 1989, Dietz et al., 1990, Dietz et al., 1995, Dietz et al., 1996, Dietz et al., 1998a, Dietz et al., 1998b, Dietz et al., 2000, Hansen et al., 1990, Paludan-Müller et al., 1993, Riget et al., 1997, Riget et al., 2000).
Some concerns have been raised as to whether mercury is increasing in the Arctic due to the increased global energy consumption, involving burning of coal and fossil fuels (Pacyna, 1996). It is, therefore, of major importance to monitor ecosystems in which mercury concentrations are high, to assess whether selenium is present in concentrations sufficient to detoxify increased methylmercury concentrations.
Section snippets
Sample selection
The mercury and selenium data were compiled from 2510 analysed samples of 48 different Greenland marine animal species obtained during the last two decades. The data were grouped into eight animal groups and three different tissue groups. The number of species and mercury concentrations for each are listed in Table 1. The species represented in each of the animal groups are: molluscs: blue mussel (Mytilus edulis); crustaceans: Calanus finmarchicus, Parathemisto libellula, Euphausiacea sp.,
Results and discussion
The molar concentrations of mercury were all below 10 nmol/g (equivalent to 2.0 μg/g wet wt.) in the 939 samples of muscle, maktak (i.e. whale skin) or whole organisms analysed, representing 48 different marine species (Fig. 1). Average concentrations were, therefore, all well below this limit. In some samples the molar concentrations of selenium were as much as 100 times higher than those of mercury. This was particularly so for mollusc soft tissue and harbour porpoise maktak (Fig. 1). The
Acknowledgements
The majority of the external funding was provided by the Commission for Scientific Research in Greenland, the Danish Natural Science Research Council, and Aage V. Jensens Foundation, which are gratefully acknowledged. In addition to some of the authors, a large number of colleagues and assistants participated in the sample collections together with Greenland Inuit, who are all acknowledged. We also want to thank our laboratory technicians Jørgen Brøndum Andersen and Sigga Joensen, who carried
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