Selenium in Nutrition, Revised Edition (1983) / Chapter Skim
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3 DISTRIBUTION
3 DISTRIBUTION
Pages 10-39
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From page 10... ...
Considerable variation has been found in the selenium content of sulfide minerals (Lakin and Davidson, 1967) , with values ranging from 0 to 2,100 10
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From page 11... ...
However, selenium concentrations found in members of the Pierre formation that have actually weathered to seleniferous soil are much higher (Moxon et al., 1939~. Shales are also the principal sources of selenium-toxic soils in Ireland, Australia, and several other countries of the world (Johnson, 1975~.
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From page 12... ...
In 1973, total free world production of selenium was 1.1 million kg, with Japan, the United States, and Canada the leading producers in that order. The principal commercial selenium compounds are selenides of aluminum, arsenic, bismuth, cadmium, calcium, copper, and indium; ammonium selenite and sodium selenite; selenates of copper, potassium, and sodium; selenium dioxide; selenium disulfide; selenium hexafluoride; and selenium monosulfide.
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From page 13... ...
The total selenium content of many toxic seleniferous soils is appreciably lower than that of some nontoxic soils. Because of the high levels of selenium in sedimentary rocks and the importance of such rocks as soil-forming materials, the processes contributing to high selenium concentrations are of interest.
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From page 14... ...
The average selenium content of 500 samples of soil from seleniferous areas in the western United States was 4.5 ppm, with a maximum of 80 ppm (Trelease, 19454. Seleniferous soils supporting toxic vegetation in Canada are associated with Cretaceous rocks in large areas of Alberta, Saskatchewan, and Manitoba (Rosenfeld and Beath, 19641.
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From page 15... ...
Low total selenium concentrations in the tertiary volcanic rocks of Arizona and New Mexico are suspected to be the cause of the low selenium levels in crops in this part of the United States. The soil-forming materials of the northeastern United States are derived primarily from sedimentary rocks that predate the major Cretaceous period of selenization of the North American continent.
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From page 16... ...
and the complexities of soil systems (Rosenfeld and Beath, 1964~. The forms of selenium generally considered to be present in soil are selenides, elemental selenium, selenites, selenates, and organic selenium compounds.
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From page 17... ...
or a transitory constituent of neutral and acid soils during the reduction of selenites under acid conditions (Allaway et al., 19671. There are indications that significant amounts of elemental selenium may be oxidized by microorganisms in neutral and alkaline soils (Geering et al., 1968~.
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From page 18... ...
· Where rocks with a high content of selenium weather to form soils in humid areas, slightly soluble complexes of ferric oxide or hydroxide and selenite ions will be formed. These soils will also be slightly to strongly acid, and the plants produced on them will not contain toxic concentrations of selenium, but they may contain sufficient selenium to protect livestock consuming them from selenium deficiency.
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From page 19... ...
Applying manure to low-selenium soils from animals fed imported selenium-adequate feeds increases the soil selenium content slightly. Superphosphate fertilizers contain selenium, but the extent of their contribution to soil selenium is not known.
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From page 20... ...
(1941) have published data on the selenium contents of wheat and feed grains produced in the high-selenium areas of the United States.
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From page 21... ...
Since then many other selenium compounds have been isolated from plants, including Se-methylselenomethionine, the glutamyl peptide of selenocystathionine, selenohomocystine, selenocystine and its oxides, selenomethionine selenoxide, selenoglutathione, selenite, selenate, selenocysteic acid, selenocysteine seleninic acid, dimethyl selenide, and dimethyl diselenide (Moxon and Olson, 1970;
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From page 22... ...
Our understanding of the metabolic pathways for selenium in plants remains very limited. SELENIUM IN ANIMAL FEEDSTUFFS The selenium content of feedstuffs varies with plant species and geographical area of production.
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From page 23... ...
when grown on low-selenium soil. In the United States, alfalfa accumulated more selenium than red clover, timothy, or bromegrass from soils containing moderately low selenium concentrations, but differences among forage species have not been consistent when the soils contained very low levels of available selenium.
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From page 24... ...
ADEQUATE-80% OF ALL FORAGES AND GRAIN CONTAIN>0.10 PPM SELENIUM (INCLUDES HAWAII) FIGURE 2 Regional distribution of forages and grain containing low, variable, or adequate levels of selenium in the United States and Canada.
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From page 25... ...
Presently, it is legally possible to provide farm animals in the United States and Canada with specific dietary selenium supplements to prevent the deficiency disorders. The preparation of countrywide and even international maps illustrating the relative concentrations of selenium in forages and grains, as in Figure 2, has become possible by integrating the results of numerous surveys conducted on specific areas of the United States and Canada, taken in conjunction with data obtained on a national basis.
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From page 26... ...
Table 3, in which data have been taken from the above published studies, indicates the variable selenium content of animal feed ingredients. BIOLOGICAL AVAILABILITY There have been several published studies illustrating differences in the biological availability of selenium occurring in various feedstuffs.
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From page 27... ...
Relative to selenium in sodium selenite (100 percent) , the effectiveness of selenium in fish meals was 32 to 60 percent, in soybean meal was 18 percent, and in corn gluten meal was 26 percent for restoration of serum gluathione peroxidase activity in selenium-depleted chicks.
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From page 28... ...
A recent bioavailability trial conducted on Finnish men of low-selenium status who were supplemented with different forms of selenium indicated that a comprehensive assessment of selenium bioavailability requires the determination of several parameters. These include a short-term platelet glutathione peroxidase activity measurement to determine immediate availability, a medium-term plasma selenium measurement to estimate retention, and a long-term platelet glutathione peroxidase measurement after discontinuation of supplements to determine the convertibility of tissue selenium stores to biologically active selenium (Levander et al., 1983~.
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From page 29... ...
found the selenium content of Animas River samples to contain 1 to 40 ,ug/liter, averaging close to 1,ug/liter. These authors observed that higher selenium levels in Colorado surface waters were correlated with higher water pH values.
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From page 30... ...
CONCENTRATIONS IN SELENIFEROUS REGIONS Smith and Westfall (1937) reported the selenium content of some foods produced on seleniferous farms in South Dakota, finding 0.16 to 1.27 ppm selenium in milk, 0.25 to 1.0 ppm in bread made from local flour, 0.25 to 9.14 ppm in eggs, and 1.17 to 8.0 ppm (dry basis)
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From page 31... ...
One of the main factors contributing to these differences is undoubtedly the use of a small number of samples from a few localized areas. Problems in analytical precision sometimes appear, particularly at low selenium levels (Schroeder et al., 1970)
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From page 32... ...
. Whey selenium concentrations generally reflect regional differences in natural selenium levels in feeds consumed by dairy cows (Hitchcock et al., 1975~.
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From page 33... ...
DIETARY SELENIUM LEVELS IN VARIOUS COUNTRIES An indication of the selenium concentration of certain selected foods for various countries is presented in Table 4. It is evident that in each country there are wide differences in the selenium level in foods, depending on the kind of food and location where it was produced.
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From page 35... ...
standards for drinking water suggest 10 ,ug selenium/liter as the acceptable upper limit (U.S. Department of Health, Education, and Welfare, 1962~.
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From page 36... ...
36 Cal A: _)
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From page 37... ...
and Figure 4 (Frost, 1973~. // // IMPLANTS ~ SOI LS¢: //\ ANIMALS J1 \\ T (~ / / AQU ATI C \ Ll FE \ / / ~/ /OCEANS, \ ~ //:ES \\\ ~ ATMOSPH E R E \ \ \ MOLTEN \ ROCK VOLCAN I SM 1 EARTH'S CORE SEDIMENTS & \ SEDIMENTARY ROCKS RUNNING\\ / and | / GROUND / WATE RS /f~' / ~ / IGNEOUS ROCKS / FIGURE 3 Cycling of selenium in nature.
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From page 38... ...
Geological processes such as wind erosion, glaciation, water erosion, and leaching all affect the selenium content of soils. Although selenium in sedimentary rocks is insoluble and unavailable to plants, chemical weathering and plant and microbial action transform much of it to soluble and available forms.
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From page 39... ...
In the biological cycling of selenium, selenite and selenate are taken up by the plant roots with much selenium subsequently reduced within the plant to the-2 oxidation state. Monogastric animals consume food containing selenium compounds in the-2 oxidation state and appear to reduce dietary selenite and selenate.
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