Chapter 6
The Moose (Alces alces L.), A Fast and Sensitive Monitor of Environmental Changes 1
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Downloaded by NORTH CAROLINA STATE UNIV on October 4, 2012 | http://pubs.acs.org Publication Date: May 5, 1997 | doi: 10.1021/bk-1997-0654.ch006
A. Frank and V. Galgan 1
Centre for Metal Biology, P.O. Box 535, S-75121 Uppsala, Sweden National Veterinary Institute, Department of Chemistry, P.O. Box 7073, S-75007 Uppsala, Sweden 2
Liver and kidney samples from 4,360 moose (Alces alces L.) were collected in the whole of Sweden in 1982 and analyzed for 14 essential and non-essential elements. The organ samples constitute a reference material, for use in future attempts to detect environmental changes with use of the moose as monitor. Changes in pH influence the mobility of metals. As a typical effect of acidification, decreasing pH in the soil results in increased uptake of cadmium, via plants, by the moose tissues. Accordingly, regional differences in the cadmium burden were observed within the reference material depending on the extent of acidification. By expressing the cadmium burden as the average renal cadmium uptake per year, different regions can be compared. In addition to comparing the cadmium burden between Swedish regions, this burden in Alaska and Canada was compared with Swedish levels by using the moose as monitor. With increasing pH, e.g. as a result of liming, levels of cadmium and other metals decrease, but molybdenum level increases, as found in the moose organs. A disturbed balance between copper and molybdenum can cause severe copper deficiency in the animals, leading to death, as reported from Sweden in the late 1980s. An environmental change within a period of only 5 years can be recognized using the the moose as monitor.
Monitors in the environmental context have been defined as organisms in which changes in known characteristics can be measured in order to assess the extent of environmental contamination, so that conclusions regarding the health implication for other species of the environment as a whole can be drawn (7). Monitors can give information about the environmental concentration both of essential and non-essential metals, in that they are able to demonstrate deficiency and toxicity, and over a period
© 1997 American Chemical Society
In Environmental Biomonitoring; Subramanian, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
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ENVIRONMENTAL BIOMONITORING
of time can also show changes in the concentrations of the metals in the environment. Environmental contamination may include contamination by metals, the origin of which may be natural and/or anthropogenic. The metals may affect life or disturb life processes on different trophic levels, which may influence the choice of suitable monitors (2). Too low or too high a concentration of essential elements, and too high a concentration of toxic elements in the bedrock or soil can cause a state of deficiency or toxicity and thus become a direct risk for human and animal health (3, 4, 5). Atmospheric deposition of oxides of sulfur and nitrogen (acid rain) may influence the weathering of bedrock and soils. A decreasing pH causes mobilization of metals in the upper soil layer, leading to greater availability of metals, via plants, to grazing animals. Elements which are easily mobilized are Ca, Mg, K, Na, Al, Cd, Mn, Ni and Zn, and to a lesser extent Hg, Pb and Cu. When the buffering capacity of the soil is insufficient, acid rain results in leaching and eluting of metals essential for plants and animals, thereby causing deficiencies of these metals in plants and, via plants, in herbivorous animals. Certain essential trace elements such as Se and Mo become less soluble in an acidic environment, which means that their availability for plants will decrease. In the case of an increasing pH, the chemical behavior of these elements will be the
reverse. A change in uptake by herbivorous animals via plants may result in a change in metal concentrations in the animal tissues as well as a change in the relationships between the concentrations of different elements in the tissues, with severe consequences for the health status of grazing animals. Selenium uptake by animals via plants is influenced by different parameters (6) such as the geochemical background, aerial deposition of selenium from natural and anthropogenic sources, the buffer capacity of the soil, and the chemical form of the selenium. In the western parts of Sweden, the atmospheric transport of organic selenium compounds from the marine environment compensates to some degree for the loss of selenium bioavailability by acidification (7). In a search for monitors of cadmium among the species of the wild Swedish fauna during 1973 - 1976, the moose (Alces alces L.) was found to be useful for this purpose (8, 9, 10) according to the above definitions (7). The moose, a large wild ruminant, is found in most parts of Sweden. It is a relatively stationary animal and its range of seasonal migration seldom exceeds 50 - 60 km. Its age is easy to determine. Tissues for investigation can be obtained through cooperation with hunters' organizations during regular hunting seasons in the autumn. Moreover, the moose acts as an integrating "sample collector" of essential and non-essential elements, browsing a great variety of plants. The moose lives in the northern hemisphere Scandinavia, Russia, Poland, Canada, Alaska, and some northern parts of the contiguous United States. From 4,360 moose, samples of liver and kidneys, and also of the left mandible for age determination, were collected in the whole of Sweden during the hunting season in 1982. All 24 counties but one participated in the sample collection. Tissue samples were pretreated by automatic wet digestion (77, 72) and submitted to simultaneous multielement analysis with respect to 13 metals using a direct current plasma-atomic emission spectrometer (DCP-AES) (75). The metals assayed were Al, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, V and Zn. Molybdenum was determined by
In Environmental Biomonitoring; Subramanian, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
Downloaded by NORTH CAROLINA STATE UNIV on October 4, 2012 | http://pubs.acs.org Publication Date: May 5, 1997 | doi: 10.1021/bk-1997-0654.ch006
6.
FRANK & GALGAN
The Moose as an Environmental Monitor
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ICP-AES. Selenium was measured by flow-injection hydride generation atomic absorption spectrometry (FI-HG-AAS) (14). The assays yielded metal concentrations in the liver and kidney samples, constituting a reference material for the year 1982 (7, 9, 15). In the present study regional differences were found, reflecting differences in the availability of metals, via plants, to the moose. The concentrations of essential and non-essential elements in the liver and kidneys provided information about normal variations in the different regions, which are important from toxicological and nutritional points of view. Comparisons of values obtained in future investigations with reference values from the same geographic region from a previous year will demonstrate changes in the environment. Among different parameters influencing the mobility of metals and their uptake by animals via plants, the pH of the soil appears to be the most important. This seems to be more significant than, for example, the decreasing rate of atmospheric deposition of heavy metals. Data of soil pH in Sweden are compiled in maps (16). At a low pH of the soil, e.g. 3.8-4.2, most of the metals, including cadmium, become mobilized, but molybdenum becomes bound to the soil. Increasing pH, e.g. when liming, has the opposite effect, molybdenum now being mobilized - as mentioned above. A n increase in pH from 5.0 to 5.5 results in an approximately 45 percent increase in Mo uptake by grasses and clovers (77). The chemistry of Se in the soil is complex (
