Functions of minerals

Until 1950, 13 mineral elements were classified as essential these comprised the major elements (calcium, phosphorus, potassium, sodium, chlorine, sulphur, magnesium) and the micro or trace elements (iron, iodine, copper, manganese, zinc and cobalt). By 1970, molybdenum, selenium, chromium and fluorine had been added to the list subsequently, arsenic, boron, lead, lithium, nickel, silicon, tin, vanadium, rubidium and aluminium have also been included, the list varying slightly according to the different authorities. Plant and animal tissues contain a further 30 mineral elements, in small quantities, for which no essential function has been found. They may be acquired from the environment, but it has been suggested that as many as 40 or more elements may have metabolic roles in mammalian tissues. Fortunately, many of these trace elements, especially those of more recent discovery, are required in such minute quantities, or are so widely distributed in foods for animals, that deficiencies are likely to be extremely rare under normal practical conditions. 

The classification of the essential minerals into major elements and trace elements depends upon their concentration in the animal or amoimts required in the diet. Normally trace elements are present in the animal body in a concentration not greater than 50 mg/kg and are required at less than 100 mg/kg diet. Those essential mineral elements that are of particular nutritional importance together with their approximate concentrations in the animal body are shown in Table 6.1. 

The minerals are held in different forms in the body, which can be considered as compartments. There is a central reserve or interchange compartment, which is usually blood plasma, and one or more compartments that interchange the mineral with the central compartment at various rates, e.g. compartments easy or difficult to mobilise. Metabolic processes take place via the central reserve (plasma), which receives minerals from other compartments, the digestive tract and the difficult to mobilise compartment. The central reserve secretes mineral into the readily mobilised compartments, the difficult to mobilise compartment, the gastrointestinal tract, the kidneys and milk. The flux between the compartments can be measured by a combination of balance trials and injection of radioactive marker followed by sampling the tissues over time. An example of the body compartments of copper is shown in Fig. 6.1. 

Adapted from Symonds H W and Forbes J M 1993 Mineral metabolism. In Forbes J M and France J (eds) Quantitative Aspects of Ruminant Digestion and Metabolism, Wallingford. CABI. 

Elements such as sodium, potassium and chlorine have primarily an electrochemical or physiological function and are concerned with the maintenance of acid-base balance, membrane permeability and the osmotic control of water distribution within the body. Some elements have a structural role, for example calcium and phosphorus are essential components of the skeleton and sulphur is necessary for the synthesis of structural proteins. Finally, certain elements have a regulatory function in controlling cell replication and differentiation zinc acts in this way by influencing the transcription process, in which genetic information in the nucleotide sequence of DNA is transferred to that of an RNA molecule. It is not uncommon for an element to have a number of different roles for example, magnesium functions catalytically, electrochemically and structurally. 

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The last column in the table lists some of the functions of minerals. It should be noted that almost all of the macroelements in the body function either as nutrients or electrolytes. Iodine (as a result of its incorporation into iodothyronines) and calcium act as signaling substances. Most trace elements are cofactors for proteins, especially for enzymes. Particularly important in quantitative terms are the iron proteins hemoglobin, myoglobin, and the cytochromes (see p. 286), as well as more than 300 different zinc proteins. 

Fig. 156. Explosive properties of ammonium nitrate-mineral oil mixtures as a function of mineral oil content [71],...

The amount of organic matter in skeletal material can be as low as 0.01 percent in some mollusc shells, and as high as 20 to 30 percent in vertebrate bones or teeth in a few isolated instances concentrations may go up to 90 percent. The origin, nature and function of mineralized tissues in calcification is only tentatively known. 

A recent contribution to mass-balance modeling of weathering (Bowser and Jones, 2002) utilizes a spreadsheet graphical method to interpret mass balance in watershed systems in place of the strictly numerical solution methods. Key to the approach is to solve the mass-balance equation for a 10 X 10 matrix as a function of mineral composition (specifically in terms of plagioclase feldspar and smectite compositions). Exploration by means of models that cover mineral compositional space limited the range of possible compositions and restricted the range of possible mass-balance solutions. Figure 1 (after Bowser and Jones, 2002) is an example of the spreadsheet approach applied to the Sierra Nevada ephemeral... 

General functions of mineral elements in animal nutrition (Pfost and Swinehart, 1970) are as follows ... 

The functions of minerals in the body involve building tissue and regulating numerous body processes. Their role in the human body is summarized in Table 4.3. 

Figure 11. Mineral He and Ar retention is shown as a function of grain size and accumulation time. The time required for a grain to lose 90% of its He or Ar is contoured as a function of mineral diffusivity and grain size, using Equation (30) assuming spherical grains after Mussett (1969) the diffusivities of He at 100°C and for Ar at 300°C are shown for a few representative minerals (data from Lippolt and Weigel 1988 McDougal and Harrison 1988 Wolf et al. 1996). For example. He in a muscovite grain with an effective radius of 100 pm (10 cm) at 100°C will lose 90% of its He in a few hundred thousand years, while Ar in the same grain is still effectively retained at 300°C over >10 Ma.

The cations Sr and Ba concentrate in the vertebrate skeleton, and the amounts of these elements vary as a function of mineral stmcture. In vivo, strontium has been found to accumulate in bone by exchange onto crystal surfaces, and is rapidly washed out after exogenous strontium is withdrawn (Dahl et al. 2001). Incorporation of strontium into the crystal lattice as a substitute of calcium occurs at a low level in vivo, in contrast to the extensive lattice substitution of strontium for calcium in fossil bone. Strontium is not easily washed out of subfossil bone (Tuross et al. 1989), and the uptake of strontium into biological apatite was once proposed as a potentially useful chronometer analogous to fluorine uptake (Turekian and Kulp 1956). The combined uptake of strontium and fluorine into vertebrate calcified tissue may in no small part account for the existence of a fossil record. Both of these elements stabilize biological apatite, and add substantially to the crystal stability of apatite under acidic conditions (Curzon 1988). 

Figure 4,1-6 Solubility data as a function of mineralizer concentration in hydrothermal systems [17].

Fig. 2.40. Variations of physical-chemical and structural characteristics of fiim materials based on PE as a function of mineral oil content (1) elasticity moduius (E), (II and III) crystallinity degree (D731 and Diaes - optical density of absorption bands at 731 and 1368 cm frequencies in IR spectra of the materials S - melting peak areas on thermograms)...

Fig. 3.39. Delamination force of the polymer coating from Cu foil as a function of mineral oil content in the coating...

As shown in I Table 12.4, the functions of minerals are consistent with their classification as major or trace and with the amount required daily in the diet. For example, compounds of some major minerals (Ca and P) are the primary inorganic structural components of bones and teeth. Other major minerals (Na, K, Cl, and Mg) form principal ions that are distributed throughout the body s various fluids. Some trace minerals are components of vitamins (Co), enzymes (Zn and Se), hormones (I), or specialized proteins (Fe and Cu). Thus, we see that even though trace minerals are required in small quantities, their involvement in critical enzymes, hormones, and the like makes them equally as important for good health as the major minerals. 

The breakthroughs in our understanding of the functions of minerals in the body did not come for many centuries because laboratories for research were not developed until the Renaissance although the medieval alchemists appear to have invented some of the techniques and tools of chemistry in their futile efforts to change base metals into gold. 

Figure 14.16 Material and fibre rebound as a function of mineral admixture particle size ...

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