Selenium rich area

The main environmental pathway of occupational exposure to selenium is through the air or, in some cases, by direct dermal contact. Srivastava et al. (1995) reports a worker employed in this type of job for 6 months who presented with alopecia areata, which later deteriorated to alopecia universalis. This patient s blood selenium levels were 0.5 pg/ml. Yang et al. (1983) reported mean blood selenium levels of 3.2 mg/1 in a selenium rich area in China where chronic selenosis was common. Mean normal blood selenium in different states of the U.S. and China range from 0.082 mg/ml to 0.206 mg/1. In spite of much work, knowledge about the health effects of occupational exposure to selenium is far from complete (Srivastava et al. 1995). Since alopecia areata is common in 1.7% of the population studied (Jackow et al. 1998), this report requires follow-up before a cause and effect relationship can be assumed. 

The behavior of selenium in soils mirrors that of the pure oxides (Goldberg, 1985). In acid soils, selenium is likely to occur mainly as Se(lV) strongly adsorbed to iron oxides. Less commonly, Se(IV) may form highly insoluble iron compounds such as ferric selenite (Fe2(0H)4Se03) or iron selenide (FeSe). In alkaline, oxidized and selenium-rich soils, most of the selenium is likely to be present as Se(Vl) which is very weakly adsorbed. Furthermore, there are no common insoluble selenate minerals. Hence, selenate accumulates in soluble form particularly in arid and semi-arid areas where evaporation tends to concentrate selenium along with other soluble salts (Deverel et al., 1994). 

The selenium content of soils ranges from 0.1 ppm (S) in a selenium-deficient area of New Zealand to 1200 ppm in an organic-rich soil in a toxic area of Ireland (14). Soils of Hawaii that contain 6-15 ppm selenium do not produce seleniferous vegetation (15). In contrast, soils of South Dakota and Kansas that contain less than 1 ppm selenium do produce seleniferous (toxic) vegetation (16). 

In large areas of the world, the soils contain very little selenium in forms that can be taken up by plants. Crops produced in these areas are, therefore, very low in selenium. A selenium (deficiency in livestock is a serious problem. A deficiency causes a form of muscular dystrophy in younger animals and poor reproductive qualities in the adult animals. For prevention, sodium selenate or sodium selenite, sometimes augmented with vitamin E. is added in proper proportions to feedstuffs Some areas, including the Plains and Rocky Mountain states in the United States have soils that are rich in available selenium. Tn regions like these, selenium toxicity is a problem. The situation is particularly senous in Arizona, California, Montana, Nevada, New Mexico, and South Dakota. 

As discussed in a previous section, organoselenium chemistry has recently evolved into an area which is rich and varied. Synthetic organic chemists have been instrumental in stimulating the interest in research concerning selenium analogues of natural products which contain sulfur. The biological activity of many of these molecules has also been an area of growing interest. 

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