Form Of Elements Research Articles

Genetic and nongenetic factors affecting the elemental composition of human and other animal tissues--a review.

The genetic and nongenetic factors affecting the elemental composition of animal and human tissues are presented. Genetic factors include: (1) some well-known inherited diseases that affect copper, zinc, iron, magnesium, manganese and selenium metabolism; (2) animal species differences and (3) breed differences within animal species. The nongenetic factors include regional variation, dietary concentration of elements, interactions between elements, dietary concentration of other nutrients, chemical form of elements, age, sex, hormones, pregnancy, disease, temperature and altitude.

The characterizations of solid specimens: Approaching the whole problem

The purpose of this paper is to demonstrate that complicated mixtures of solids can be characterized to a rather high degree if a coordinated examination by non-destructive methods is used. The techniques discussed are X-ray fluorescence, scanning electron microscopy, photoelectron spectroscopy, transmission electron microscopy, electron diffraction and X-ray diffraction. The application of these methods to the characterization of corrosion scale on an inconel coupon is illustrated. The types of information accumulated were elemental composition, chemical forms of elements, special distributions of elements and compounds in the scale, sizes of particles that made up the scale, variations in composition of particle surfaces from that of their interiors, and composition of scale-alloy interface.

On the development of the chemical arts, during the last ten years

From the time selenium was discovered in 1817 by Berzelius and Gahn [1] until the recognition in the mid 1950s of its toxicity and, subsequently, its essentiality for animal well-being, a large number of its properties have been elucidated. This element ranks seventieth in abundance among the elements and constitutes approximately 105% of the earth's crust. Selenium is located in the VIa Group of the Periodic Table between sulphur and tellurium, and its chemical and physical properties are between these elements, i.e. intermediate between nonmetals and the metals, although similarity in behaviour of selenium and sulphur is more pronounced than that of selenium and tellurium. Its atomic number is 34 and its mass of 78.96 results from the six natural isotopes which exist under normal conditions 74Se (0.87%), 76Se (9.02%), 77Se (7.58%), 78Se (23.52%), 80Se (49.82%) and 82Se (9.19%). Other artificial short-lived man-made isotopes such as 75Se, 77Se are utilized in neutron activation and radiology [2]. Selenium has a melting point of 217 °C and a boiling point of 685 °C. Like sulphur it can exist in three allotropic forms: a gray or “metallic”,thermodynamically stable, hexagonal form; a red monoclinic form; and a vitreous amorphous form. Selenium is mainly found in metal sulphide deposits, mostly of the metals Cu, Zn, Ag, Hg, and Pb and is obtained industrially as a by-product of the processing of these elements. It is mainly used in the electrical and electronic (23%), rubber, plastics and lubricants (13%), ceramics and glass 27%) and other chemical industries [3], Table 1. Selenium pollution is caused by these industries and by fossil fuel combustion which releases the element into the atmosphere.Analytical methodologies and applications for the determination of total selenium at trace level have been developed and used extensively in the last thirty years. The reason for determining selenium are multiple: a) the long established selenium poisoning of domestic animals foraging on seleniferous plants, b) disorders in humans and animals resulting from selenium deficiencies and excesses, c) the nutritional essentiality of the element, d) the protective effect of selenium against the toxicity of the metals such as Hg and As, e) the metabolic interaction between selenium and vitamin E and other antioxidants and f) the reported carcinogenicity, anticarcinogenicity, antimutagenicity and anticlastogenicity and its effect on dietary intake of selenium [4] (Fig.l). Table 1: Industrial uses of different Se compounds (adapted from ref. [3])It is now well known that it is the chemical form of elements rather than their concentration which determines their role in the living organism. This is particularly so for elements such as, Se, Hg, etc., which exist in many different forms and oxidation states.Natural waters, sediments and air are the most commonly studied environmental media. Robberecht and Van Grieken [5] have extensively reviewed the literature on total selenium in natural waters of river (content 0.016-20 ng.l1), lake (0.1-1.85ng.11), open ocean (0.025-0.2ng.11)and coastal or harbour environments, but an exhaustive review of selenium species in environmental samples has not yet been published.