Availabilities of the Elements

No stable isotopes of any of these elements exist, the last element in the Periodic Table with a stable isotope being Bi (Bi-209). However, some of the An elements have isotopes with very long half lives, which means that they are found in nature in relative abundance, most notably as Th-232 (lO years). 

Element Most used isotope Log Half life(year) Source or production Avail amt (g) Electronic structure Oxidation states Origin of name 

U-235 (10 years), and U-238 (10 - years). Others are products of the decay of the above isotopes, so even though they are shorter lived, they persist in nature since they are continually being produced. The most important nuclides of this type are Ac-227 (21.8 years) and Pa-231 (10 years), both coming from U-235 decay. In U ores, very small amounts of Np-237 (10 years), Np-239 (2.4 days), and Pu-239(10 years) arise from the interaction of neutrons with U isotopes. 

Isotopes of the elements beyond U are produced artificially, Np and Pu by neutron capture by U, Am and Cm by multiple neutron capture by Pu, and elements beyond Cm by further neutron captures or bombardment of lower atomic number actinoids with ions of He, B, C, N, or O. As the atomic number increases, the elements become more unstable and thus tend to have shorter half lives. Np-237 and Pu-239 are available in multikilogram amounts Am-241 (430 years), Am-243 (7650 years), and Cm-244 (18.1 years) in 100-g amounts Bk-249 (320 days), Cf-252 (2.6 years), and Es-253 (20 days), in milligram amounts Fm-257 in microgram quantities and Md-258 (55 days), No-259 (1.0 h), and Lr (3.0 min) in trace amounts. 

As the half lives of isotopes become shorter, they get more difficult to study. This is because short-lived isotopes are highly radioactive, which causes the emitted radiations to produce redox reactions, even in dilute solutions. Special apparatus is needed to study them, because of their intense radioactivity and the need to work rapidly. Further, due to limited quantities of the heavier elements, they can be studied only in very dilute solutions which sometimes behave strangely. 

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We see that the total element abundance on the continental crust of Earth today (see Figures 1.4 and 1.5), is poorly reflected in the availability of the elements in the sea. Two major reactions affected the availability of the non-metals and the metals apart from abundances both concern solubility of salts ... 

An important point to note here and elsewhere in the description of cell activity is that the particular nature of calcium biochemistry, including the availability of the element and its necessary rejection from the prokaryote cell, when linked to stimulated input and interaction with specific internal proteins of selected properties, made it uniquely suitable for the function as an elementary ionic fast in/out messenger. It was then capable of signalling to cell changes once cell size and organisation increased beyond the elementary level of a cell with one small, rapidly... 

More importantly, the availability of the element descriptor, e, allows for the expression of the vdWs interactions as segment interactions ... 

Chemical elements that are either present naturally in the soil or introduced by pollution are more usefully estimated in terms of availability of the element, because this property can be related to mobility and uptake by plants. A good estimation of availability can be achieved by measuring the concentration of the element in soil pore water. Recent achievements in analytical techniques allowed to expand the range of interest to trace elements, which play a crucial role both in contaminated and uncontaminated soils and include those defined as potentially toxic elements (PTE) in environmental studies. A complete chemical analysis of soil pore water represents a powerful diagnostic tool for the interpretation of many soil chemical phenomena relating to soil fertility, mineralogy and environmental fate. This chapter describes some of the current methodologies... 

Virtually all microorganisms—with the exception of certain lactobacilli— require iron as cofactor of many metabolic enzymes and regulatory proteins because of its ability to exist in two stable oxidation states. Although iron is one of the most abundant elements in the environment, it is often a limiting factor for bacterial growth. This is so because of the formation of insoluble ferric hydroxide complexes under aerobic conditions at neutral pH, which impose severe restrictions on the availability of the element. Consequently, bacteria have evolved specialized high-affinity transport systems in order to acquire sufficient amounts of this essential element. 

The number of elements that are known to be biologically important comprises a relatively small fraction of the 109 known elements. Natural abundance limits the availability of the elements for such use. Molybdenum (Z = 42) is the heaviest metal, and iodine (Z = 53) is the heaviest nonmetal of known biological importance. The metals of importance in enzymes are principally those of the first transition series, and the other elements of importance are relatively light sodium, potassium, magnesium, calcium, carbon, nitrogen, phosphorus, oxygen, chlorine, and, of course, hydrogen. 

In a reconnaissance survey of the minerals in soil and plant samples in relation to adequate concentrations of the same elements in blood samples from animals in Lake Nakura National Park, Kenya, Maskall and Thornton (1989) showed that Mo concentrations in all plants were relatively high, and the availability of the element appeared to be increased... 

Nevertheless, the total nitrogen value is a meaningless indicator of the N turnover in the soil, incapable of supplying information about the availability of the element for crops in the short-term period and to evduate potential pollution risks inherent to losses of mineral N to the waters and to Ihe atmosphere. 

Acid soils favour the absorption of H2PO4 by plants and this ion is absorbed much faster than HPOy. At soil pH 5.0-7.2, H2PO4 dominates whereas at pH 7.2-9.0, HPOy is mostly present. Maximum uptake of P from the soil usually occurs at about pH 5.5-6.5 and a minimum uptake at pH 7.5-8.0. A high uptake of N from fertilisers occurs over a wider range of pH 5.5-8.0. Much of the absorbed phosphate is converted by enzyme processes to the many organophosphate esters which are present in plant cells. A large part of the organic phosphorus content of soils is provided by bacteria and their dead residues. The total amount of P in soils does not necessarily relate directly to the availability of the element to plants. 

Spraying the pasture with soluble salts of trace elements can increase the element content of the pasture. Alternatively, trace elements can be included in fertihsers in order to increase the herbage content via the soil. However, if the deficiency is due to poor availability of the element, then this type of application will not be successful. 

How and in what order these elements should be integrated rather depends mosdy on organizational interfaces or availability of the elements than the technical aspects. Integration should be accompanied by continues verifications and adequate tests to confirm the fulfilment of the given requirements for the relevant horizontal level of abstraction. 

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