Trace Essential Elements

Iron is, as part of several proteins, such as hemoglobin, essential for vertebrates. The element is not available as ion but mostly as the protein ligands transferrin (transport), lactoferrin (milk), and ferritin (storage), and cytochromes (electron transport) (Alexander 1994). Toxicity due to excessive iron absorption caused by genetic abnormalities exists. For the determination of serum Fe a spectrophoto-metric reference procedure exists. Urine Fe can be determined by graphite furnace (GF)-AAS, and tissue iron by GF-AAS and SS-AAS (Alexander 1994 Herber 1994a). Total Iron Binding Capacity is determined by fuUy saturated transferrin with Fe(III), but is nowadays mostly replaced by immunochemical determination of transferrin and ferritin. 

Copper appears as the a2-globulin ceruloplasmin in the human body (Sarkar 1994). Deficiency of this protein in serum is characteristic of both Menkes and Wilson s diseases. Wilson s disease is an abnormal storage of Cu(II) in body tissues. Cu(II) in biological material can be determined by spectrophotometry or by FAAS, ceruloplasmin in serum by a spectrophotometric method. 

Selenium is required, but levels must fall into a narrow window. Both deficiency and toxicity symptoms occur. The element is also used therapeutically in cancer treatment. It is the co-factor of the enzyme glutathione peroxidase which is thought to play an important role in oxygen toxicity. The determination of Se in blood or serum is not easy, as many incorrect, inaccurate and imprecise methods have been published (Magee and James 1994). A suggested procedure for Se in body fluids is based on GF-AAS (Thomassen et al. 1994)- For tissues SS-AAS may be used (Fler-ber 1994a). Recent developments by Turner et al. (1999) show that LC-ICP-MS is sensitive and reproducible at low levels. 

Cobalt is present in animals in vitamin B12 (cyanocobalamine) and thus is essential for humans (Thunus and Lejeune 1994). The determination of Co has little significance for the diagnosis of deficiency of cyanocobalamine. Instead, cyanocobalamine itself must be determined in serum. The determination of methyl malonic acid in urine seems more reliable (McCann et al. 1996). 

Chromium deficiency may be related to the glucose tolerance factor (Herold and Fitzgerald 1994). The determination of this deficiency, however, is questioned, because the lack of accuracy of the Cr determination in the earlier publications. 

The order of increase in volume requirements also reflects to a certain degree the difficulties of analysis, but this will be modified by matrix interferences and volatilisation problems. The calculations do indicate however that ETA—AAS should never be the method of choice for serum Zn analysis. The problems of contamination associated with such large dilutions can only lead to poor precision. 

PHYSIOLOGICAL CONCENTRATIONS OF ESSENTIAL TRACE ELEMENTS IN BODY FLUIDS AND SAMPLE VOLUMES REQUIRED FOR ANALYSIS BY ETA-AAS 

NOTE The reference ranges for Mo, Co, and V and possibly Cr may prove to be lower than the quoted values (see Sections IV.F to IV.1). 

The measurement of Zn in body tissues or fluids for clinical purposes does not require the sensitivity of ETA—AAS. The very early methods using carbon-rod atomisers required only 0.5 pi serum for direct analysis of Zn [48], and current techniques require 0.1 pi. The measurement of Zn in cerebrospinal fluid (CSF) by ETA—AAS [49] could have just as easily been determined using pulsed —nebulisation FAAS with 100 pi sample volumes. 

The most useful role for ETA—AAS will be measuring the various low molecular weight and protein bound Zn species in body fluids and the 

Copper is necessary, together with iron, for hematopoiesis, probably partly because it is needed for the synthesis of fer-roxidase (ceruloplasmin). Many enzymes require copper for activity. Examples of some of the copper-enzymes and their functions are given in Table 37-5. Mitochondrial iron uptake may be blocked by deficiency of a cuproprotein, perhaps cytochrome oxidase. Several inherited diseases involving abnormalities in copper metabolism (Wilson s disease, Menkes syndrome) or copper enzymes (X-linked cutis laxa, albinism) occur in human and in several animal species. 

The oxidation state of copper in biological systems is -1-1 or +2. Copper(III) is found in inorganic systems and may occur as a reaction intermediate in galactose oxidase, laccase (a plant enzyme), and perhaps other enzymes. The coordination number of copper in these enzymes ranges from two to six and occasionally higher. 

The average adult human contains 70-100 mg of copper. The highest concentrations (in decreasing order) are in liver, brain, heart, and kidney. Muscle contains about 50% 

Human erythrocytes contain 1.0-1.4 /zg of copper per milliliter, of which more than 60% is in superoxide dismu-tase. Normal serum contains of copper and 200-400 mg/L of ceruloplasmin. Whether copper is released from ceruloplasmin by endocytosis or by conformational change following binding of ceruloplasmin to a membrane receptor remains unknown. 

Copper is absorbed from food in the upper small intestine. The absorption is primarily dependent on the quantity of the copper present in the diet. High intake of zinc diminishes copper absorption by inducing metallothionein formation in the mucosal cells. Metallothioneins, due to their high affinity for copper, bind it preferentially and the bound copper is lost during the sloughing of cells from the villi. Copper accumulation in patients with Wilson s disease can be reduced by giving oral zinc acetate, which decreases absorption (discussed later). Absorbed copper is transported to the portal blood where it is bound to albumin (and probably transcuprein), amino acids, and small peptides. Copper binds to albumin at the N-terminal tripeptide (Asp-Ala-His) site. The recently absorbed copper is taken up by the liver, which plays a central role in copper homeostasis. 

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Elemental selenium has been said to be practically nontoxic and is considered to be an essential trace element however, hydrogen selenide and other selenium compounds are extremely toxic, and resemble arsenic in their physiological reactions. 

Bloremedia.tlon. Cmde oil and refined products are readily biodegradable under aerobic conditions, but they are only incomplete foods siace they lack any significant nitrogen, phosphoms, and essential trace elements. Bioremediation strategies for removing large quantities of hydrocarbon must therefore iaclude the addition of fertilisers to provide these elements la a bioavailable form. 

Molybdenum, recognized as an essential trace element for plants, animals, and most bacteria, is present in a variety of metaHo enzymes (44—46). Indeed, the absence of Mo, and in particular its co-factor, in humans leads to severe debility or early death (47,48). Molybdenum in the diet has been impHcated as having a role in lowering the incidence of dental caries and in the prevention of certain cancers (49,50). To aid the growth of plants. Mo has been used as a fertilizer and as a coating for legume seeds (51,52) (see FERTILIZERS Mineral NUTRIENTS). 

An average of about 7 ppm of bromine is found ia terrestrial plants, and edible foods contain up to 20 ppm. Among animals the highest bromide contents are found ia sea life, such as fish, sponges, and cmstaceans (44). Animal tissues contain 1—9 ppm of bromide and blood 5—15 ppm. The World Health Organization has set a maximum acceptable bromide iatake for humans at 1 mg/kg of body weight per day. In adult males the bromine content ia semm has been found to be 3.2—5.6 p.g/mL, ia urine 0.3—7.0 p.g/mL, and ia hair 1.1—49.0 p.g/mL. Bromine may be an essential trace element as are the other hahdes (45). 

Nutrition. Chromium, in the trivalent oxidation state, is recognized as an essential trace element for human nutrition, and the recommended... 

It appears that chromium(III) is an essential trace element in mammalian metabolism and, together with insulin, is responsible for the clearance of glucose from the blood-stream. Tungsten too has been found to have a role in some enzymes converting CO2 into formic acid but, from the point of view of biological activity, the focus of interest in this group is unquestionably on molybdenum. 

The bad guys, shown in pink in Figure 2.8, are toxic, often lethal, even in relatively small quantities. Several of the essential trace elements become toxic if their concentrations in the body increase. Selenium is a case in point. You need about 0.00005 g/day to maintain good health, but 0.001 g/day can be deadly. That s a good thing to keep in mind if you re taking selenium supplements. 

When iodine dissolves in organic solvents, it produces solutions having a variety of colors. These colors arise from the different interactions between the I2 molecules and the solvent (Fig. 15.21). The element is only slightly soluble in water, unless I ions are present, in which case the soluble, brown triiodide ion, I,, is formed. Iodine itself has few direct uses but dissolved in alcohol, it is familiar as a mild oxidizing antiseptic. Because it is an essential trace element for living systems but scarce in inland areas, iodides are added to table salt (sold as iodized salt ) in order to prevent an iodine deficiency. 

Copper is an essential trace element. It is required in the diet because it is the metal cofactor for a variety of enzymes (see Table 50—5). Copper accepts and donates electrons and is involved in reactions involving dismu-tation, hydroxylation, and oxygenation. However, excess copper can cause problems because it can oxidize proteins and hpids, bind to nucleic acids, and enhance the production of free radicals. It is thus important to have mechanisms that will maintain the amount of copper in the body within normal hmits. The body of the normal adult contains about 100 mg of copper, located mostly in bone, liver, kidney, and muscle. The daily intake of copper is about 2—A mg, with about 50% being absorbed in the stomach and upper small intestine and the remainder excreted in the feces. Copper is carried to the liver bound to albumin, taken up by liver cells, and part of it is excreted in the bile. Copper also leaves the liver attached to ceruloplasmin, which is synthesized in that organ. 

Yoch DC (1979) Manganese, an essential trace element for N2 fixation by Rhodospirilllum rubrum and Rhodopseudomonas capsulata role in nitrogenase regulation 7 BacterioZ 140 987-995. 

A current area of interest is the use of AB cements as devices for the controlled release of biologically active species (Allen et al, 1984). AB cements can be formulated to be degradable and to release bioactive elements when placed in appropriate environments. These elements can be incorporated into the cement matrix as either the cation or the anion cement former. Special copper/cobalt phosphates/selenates have been prepared which, when placed as boluses in the rumens of cattle and sheep, have the ability to decompose and release the essential trace elements copper, cobalt and selenium in a sustained fashion over many months (Chapter 6). Although practical examples are confined to phosphate cements, others are known which are based on a variety of anions polyacrylate (Chapter 5), oxychlorides and oxysulphates (Chapter 7) and a variety of organic chelating anions (Chapter 9). The number of cements available for this purpose is very great. 

Bulk biological elements Trace elements believed to be essential [ J Possibly essential trace elements... 

The remaining 5 % includes essential bulk minerals, Na, K, Mg, Ca and Cl, plus essential trace elements, including Mn and Fe for sure, but possibly Ni, Co, MoCW) and a small amount of Zn (see Figure 2.1). The failure to understand trace element absolute requirement is a major gap in our appreciation of life as a system. 

Although zinc, cadmium, and mercury are not members of the so-called main-group elements, their behavior is very similar because of their having complete d orbitals that are not normally used in bonding. By having the filled s orbital outside the closed d shell, they resemble the group IIA elements. Zinc is an essential trace element that plays a role in the function of carboxypeptidase A and carbonic anhydrase enzymes. The first of these enzymes is a catalyst for the hydrolysis of proteins, whereas the second is a catalyst for the equilibrium involving carbon dioxide and carbonate,... 

Selenium is an essential trace element for optimal health but an excess is toxic. The British population is now reckoned to be selenium deficient because more European wheat is now used to make bread at the expense of North American wheat. The difference in the selenium content is caused by the difference in the selenium content of the soils. In geological terms, European soil is older and the selenium has washed out. 

Tin is an essential trace element for animals. It is soft, pliable and colorless and belongs to group IV of the periodic table, and is corrosion-resistant to many media. Tin occurs in nature mostly as the oxide mineral cassiterite and is ubiquitous in the earth crust in an abundance of 2.5 x 10-4% (Clarke s number, 4 x 10 3). It is one of the earliest metals known to mankind, and evidence of its use dates back over 4000 years. The ancients... 

Trivalent chromium (Cr+3) is an essential trace element in humans and some species of laboratory animals, but the database is incomplete for other groups of organisms... 

Devineau, J. and C. Amiard Triquet 1985. Patterns of bioaccumulation of an essential trace element (zinc) and a pollutant metal (cadmium) in larvae of the prawn Palaemon serratus. Mar. Biol. 86 139-143. Dib, A., J.P Clavel, and J.P. Carreau. 1989. Effects of gamma-linolenic acid supplementation on lipid composition of liver microsomal membranes. I. Pregnant rats fed a zinc-deficient diet and those fed a balanced one. Jour. Clin. Biochem. Nutr. 6 95-102. 

Sub-systems 211. foodstuffs of terrestrial origin (XIV) + foodstuffs of aquatic origin (XV) drinking water (39) balanced essential trace element daily intake for... 

System 23. balanced intake of various essential elements (XVI) atmosphere air (33) domestic animals—their productivity and biological reactions, endemic diseases (XVII) human, biological reactions (XVIII). The recommendations for balanced essential trace element daily intake for humans are under development in various countries. 

System 241. feeding of domestic animals, forage (XIV, XV) balanced essential trace element daily intake (XVI) domestic animals (XVII). The additions of requirement trace elements should be applied for forage in various biogeochemical provinces. 

System 242. human nutrition, foodstuffs (XIV) balanced essential trace element daily intake for humans (XVI) human health (XVIII). Research should be carried out on the endemic diseases induced by deficient or excessive content in the biogeochemical food webs of different essential elements, like N, Cu, Se, I, F, Mo, Sr, Zn, etc. 

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