Trace element regulation

Chandra, R. K. (1985), Grace A. Goldsmith Award lecture. Trace element regulation of immunity and infection, J. Am. Coll. Nutr., 4, 5-16. 

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. 

Although Fe is required as a trace element, its uptake is critically regulated since excess leads to the generation of toxic hydroxyl radicals, and complex interactions involving Fe(II) and Fe(HI) exist within the cell (Touati et al. 1995). The role of Fe(III)-complexing siderophores in maintaining homeostasis has been noted in Chapter 3, Part 5. Details of the role of Fe and its relation to the... 

Soil solution is the aqueous phase of soil. It is in the pore space of soils and includes soil water and soluble constituents, such as dissolved inorganic ions and dissolved organic solutes. Soil solution accommodates and nourishes many surface and solution reactions and soil processes, such as soil formation and decomposition of organic matter. Soil solution provides the source and a channel for movement and transport of nutrients and trace elements and regulates their bioavailability in soils to plants. Trace element uptake by organisms and transport in natural systems typically occurs through the solution phase (Traina and Laperche, 1999). 

Johnson, C. A., 1986, The regulation of trace element concentrations in river and estuarine waters with acid mine drainage, the adsorption of Cu and Zn on amorphous Fe oxyhydroxides. Geochimica et Cosmochimica Acta 50, 2433-2438. 

Regulation of Trace Elements by the Solid-Water Interface in Surface Waters... 

The solid-water interface, mostly established by the particles in natural waters and soils, plays a commanding role in regulating the concentrations of most dissolved reactive trace elements in soil and natural water systems and in the coupling of various hydrogeochemical cycles (Fig. 1.1). Usually the concentrations of most trace elements (M or mol kg-1) are much larger in solid or surface phases than in the water phase. Thus, the capacity of particles to bind trace elements (ion exchange, adsorption) must be considered in addition to the effect of solute complex formers in influencing the speciation of the trace metals. 

This chapter is organized as follows We first attempt to discuss, in terms of simplified models, how particles carrying functional groups behave in solutions whose variables are known or controlled. This is followed by observations and interpretations on the concentration of trace elements in rivers and how these trace elements are distributed between particulate and dissolved phase. Then, we will consider the regulation of metal ions and of other reactive elements in lakes above all, it will be shown that the interaction of these trace elements with biotic and non-biotic particles and the subsequent settling of these particles will be of utmost importance for their removal from the water/column. Finally considerations will be given to inquire to what extent similar interpretations can be given to oceans. 

In Fig. 1.1 we already encountered a scheme of some of the chemical, biological, and physical processes which regulate the concentration of trace elements in the water column of lakes and oceans. When these trace elements are introduced into a lake by riverine and atmospheric input, they interact... 

Table 11.4 The Role of Settling Particles in Regulating Trace Elements in Lakes... 

Mn(UI,IV) oxides mostly formed within the lake - High affinity for heavy metals and high specific surface area. Redox cycling [MnOx(s) Mn2+(aq)] (Chapter 9.6) is usually important in regulating trace element concentrations and transformations in lower portion of lake and sediments. 

Sigg, L. (1992), "Regulation of Trace Elements in Lakes", in J. Buffle, Ed., Chemical and Biological Regulation of Aquatic Processes, in press. 

Many aquatic organisms exhibit an ability to concentrate a variety of trace elements and this ability has been identified as a function of the tendency of the elements to be complexed by ligands (159). The alkaline earth metals are poorly com-plexed in relation to the transition metals, copper, nickel, cobalt, zinc and manganese. The actinides should be regarded as members of an intermediate group. It has been suggested by Martin (160) that at least five mechanisms may regulate the uptake of metals by marine biota. These are... 

Determination of the roles of microelements and the human daily requirements can be very difficult due to their low concentrations in the human body and problems connected with the elimination of their constant inflow. Throughout the evolution process, the human body developed mechanisms to regulate the absorption of microelements and balance their levels within required ranges. Therefore, human bodies are adjusted to the natural levels at which those elements are present in the non-polluted environment and in non-contaminated foodstuffs. However, human industrial and economic activities are frequently and widely disturbing the environmental balance and leading to contamination of the environment, including foods, with trace elements. 

As the human body is able to store many minerals, deviations from the daily ration are balanced out over a given period of time. Minerals stored in the body include water, which is distributed throughout the whole body calcium, stored in the form of apatite in the bones (see p. 340) iodine, stored as thyroglobulin in the thyroid and iron, stored in the form of ferritin and hemosiderin in the bone marrow, spleen, and liver (see p. 286). The storage site for many trace elements is the liver. In many cases, the metabolism of minerals is regulated by hormones—for example, the uptake and excretion of H2O, Na, ... 

Table 5.3. Some typical and preferred heavy and trace element concentrations for soils and composts various local regulations specify different maximum levels.

Table 5. Trace element concentrations in distilled water after a lb day leach test compared with the limit rallies of the Italian regulation...

Specific recommendations on contaminants (e.g., maximum levels of lead, cadmium or mercury) in foodstuffs are summarized in the European Union Regulations.9 The specifications concerning trace elements in foods and food additives are As < 3mgkg 1, Pb < lOmgkg-1, and Hg and Cd < lmgkg-1. 

One very useful feature of the regulations is the inclusion of a detailed list of permitted feed ingredients (see Chapter 4, this volume). More countries should follow the New Zealand example. The minerals and trace elements used in animal feeding have to be of natural origin or, failing that, synthetic in the same form as natural products. Synthetic vitamins identical to natural vitamins are allowed. Roughage, fresh or dried, or silage must be added to the daily ration for poultry but the quantity is not specified. 

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