Mammals, essential elements

Health and Environment. Manganese in trace amounts is an essential element for both plants and animals and is among the trace elements least toxic to mammals including humans. Exposure to abnormally high concentrations of manganese, particulady in the form of dust and fumes, is, however, known to have resulted in adverse effects to humans (36,37) (see Mineral nutrients). 

Animals. Copper is an essential element and is under homeostatic control in mammals... 

Growth is rapid and many systems develop their adult cell number and composition throughout the first year of life. Optimal nutrition is thus most critical in this early period. Milk - the only source of food for the offspring of all mammals in the early months of life - cannot meet the demands of optimal growth later on in the first year of life. This is especially so with the essential elements such as iron and manganese whose low content in milk (18-23) does not meet the needs of a fast growing organism (24-27). 

The metalloid elements B, Si, and the nonmetal Se are essential elements for mammals, plants, and microorganisms. The chemistry and biology of B and Si, together with that of As, is dealt with later in this chapter, while that of Se is discussed together with S in Chapter 18. An interesting acount of biochemical selenology can be found in Flohe, 2009. 

Iodine is an essential element with an important role in mammals in the regulation of metabolism, through the action of the two related hormones produced by the thyroid gland, triiodothyronine (T3) and thyroxine (T4). Iodine, which is relatively scarce, is actively concentrated in the thyroid gland where both T3 and T4 are produced. 

Yttrium is a non-essential element for microorganisms, plants, animals, and humans. However, no adverse effects of yttrium have been reported on plants and microorganisms, nor has any mechanism of yttrium detoxification in mammals been identified (Luckey and Venugopal 1978 Deuber and Heim 1991). 

Iodine is an essential element in humans and other mammals, which is used for the synthesis of the thyroid hormones triiodothyronine (T3) and thyroxine (T4). These hormones play a prominent role in the metabolism of most cells of the organism and in the process of early growth and development of most organs, especially brain (Anderson et al., 2000). Besides T3 and T4, reverse T3 (rT3), monoiodotyrosine (MIT), and diiodotyrosine (DIT) are also synthesized and distributed in the body of humans and animals, but only T3 and T4 have a biological function. Iodine in the human body mainly comes through dietary and water intake, and inhalation of atmospheric iodine. Due to low concentrations of iodine in the air (10—20ng/m ), food and water intake form the major source of iodine for adults, while for infants it is milk. The concentration of iodine in foodstuffs is directly related to that in the environment where the foods come from. Iodine deficiency disorders are mainly found in places where the concentration of iodine in the soil and drinking water is very low. In the water, foodsmffs, and... 

The metal is oxidized by hot air and also reacts with carbon, phosphorus, sulphur, and dilute mineral acids. Cobalt salts, usual oxidation states II and III, are used to give a brilliant blue colour in glass, tiles, and pottery. Anhydrous cobalt(II) chloride paper is used as a qualitative test for water and as a heat-sensitive ink. Small amounts of cobalt salts are essential in a balanced diet for mammals (seeESSENTiAL element). Artificially produced cobalt-60 is an important radioactive tracer and cancer-treatment agent. The element was discovered by Georg Brandt (1694-1768) in 1737. 

In 1971 it was reported that a significant growth effect, in rats maintained on purified amino acid diets in a trace-element-free environment, was obtained when the diets were supplemented with tin. These studies suggested that tin was an essential trace element for mammals. The element is normally present in foods in amounts less than 1 mg/kg DM, the values in pasture herbage grown in Scotland, for example, being of the order of 300-400 pg/kg DM. The nutritional importance of this element has yet to be determined, but it is suggested that tin contributes to the tertiary structure of protein or other macromolecules. Tin is poorly absorbed... 

Cadmium has a diversity of toxic effects including nephrotoxicity, carcinogenicity, teratogenicity, and endocrine and reproductive toxicities. Although cadmium is not essential for growth and development in mammals, it generally followes the metabolic pathways of the essential elements zinc and copper. 

Cobalt is an essential element for bacteria, algae and ruminant mammals. For other organisms, including monogastric animals, cobalt is essential, in the form of the essential compound vitamin Bj2 (cobalamin). Rumen microflora of ruminants synthesises cobal-amin from cobalt in the diet. Derivatives of vitamin Bj2 cobamides are cofactors of some enzymes, for example of methyhnalonyl coenzyme A mutase, glutamate mutase and methionin synthetase. 

Zinc, a component of many metal loenzymes, is an essential element for mammals and birds it is integral to growth, dceletal development collagen formation, feathering, dermal health, wound healing, arxl reproduction. 

Arsenic is another element with different bioavailabiUty in its different redox states. Arsenic is not known to be an essential nutrient for eukaryotes, but arsenate (As(V)) and arsenite (As(III)) are toxic, with the latter being rather more so, at least to mammals. Nevertheless, some microorganisms grow at the expense of reducing arsenate to arsenite (81), while others are able to reduce these species to more reduced forms. In this case it is known that the element can be immobilized as an insoluble polymetallic sulfide by sulfate reducing bacteria, presumably adventitiously due to the production of hydrogen sulfide (82). Indeed many contaminant metal and metalloid ions can be immobilized as metal sulfides by sulfate reducing bacteria. 

Boron is an essential trace element for plants, and may well turn out to be essential for mammals as well. The boron-containing polyether-macrolide antibiotic, boromycin, was isolated as a potent anti-HIV agent. 

It is an essential trace element for mammals, but little is known about its role or requirement in human metabolism. In humans, serum levels of nickel are about 1.1 to 1.6 mcg/1. This level increases in conditions such as stroke and acute myocardial infarction. A dietary requirement for adults is about 30 meg/day. 

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