Soils seleniferous

Indicator plants generally have an offensive odor, which varies with the selenium concentration. Other vegetable matter grown on seleniferous soils may have a sufficiently high selenium content to be toxic when ingested by animals or humans. Apart from appearance in these seleniferous plants, selenium has been considered as a variable contaminant. Selenium is a necessary micronutrient in living organisms, needed by humans as well as animals (see Mineral NUTHiENTs). 

Data on selenium in water are limited. The drinking water content is usually less than 1 )-lg/L, and seldom exceeds the 50 )-lg/L upper limit estabhshed in 1993 by the U.S. EPA (23). It may be higher in wells in seleniferous areas, and markedly higher in some river waters where irrigation drainage from seleniferous soil contains up to 2680 )-lg/L. 

Seleniferous formations occur in the Great Plains region from Canada to Mexico, accounting for > 700,000 km2 of the western U.S. Seleniferous soils are frequently associated with Se-containing geological formations (Boon, 1989). As discussed above, seleniferous formations occur in North Dakota, South Dakota, Montana, Wyoming, Colorado, Kansas, and New Mexico. Some soils derived from Se-rich parent materials, such as Cretaceous shales of the middle-western United States, have > 10 mg/kg Se and sometimes exceed 50 mg/kg (Reeves and Baker, 2000). 

The selenium content of a plant is dependent on the plant species and on whether it is grown in seleniferous or non-seleniferous soil. Generally, Se content in plants increases with the level of Se available and decreases with the sulphur supply. Se concen-... 

Although Se is not known to be required for the growth of plants, most assimilate it when grown on seleniferous soils, or in Se-containing... 

In the Se-deficient areas of China, Finland, and New Zealand, the Keshan disease occurs because of a low Se intake from local food. To correct soil Se deficiency in Finland, the government initiated a national program to amend agricultural soils with Se to elevate the Se content in agricultural products. As a result, the daily dietary Se intake of residents in Finland increased from approximately 30 ag (a low value as compared to the recommended US National Research Council value of 55 J,g) to 80 4g. Therefore, seleniferous soils considered as potentially Se-contaminated sites... 

Webb, J. S., Thornton, L, Fletcher, K. (1966). Seleniferous soils in parts of gland and Wales. Nature,... 

The determination of Se03- and SeOc in water with graphite furnace atomic absorption detection was investigated by Chakraborti et al. [22]. Some interference by Cl" and F was reported. DCPAE detection was used by Urasa and Ferede [23]. Results were 1000 times more sensitive than conductivity detection. One of the advantages of atomic emission detection was described in this work. Identical molar sensitivity was obtained for both species. Mehra et al. [24] developed a novel singlecolumn IC method to determine selenium species in seleniferous soil samples. The separation took about 14 minutes and there were no reported interferences. 

Populations living in the western United States in areas eating produce grown in highly seleniferous soils could be at greater risk of adverse health effects from additional environmental exposure to selenium if their selenium nutritional status is already high (see Section 6.6). 

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