Catálogo de publicaciones - libros

The quality of human life depends on the chemical composition of food and of the surroundings. Recent improvements and new methods in analytical chemistry and increasing fields of environmental investigations have added substantially to our knowledge of the biogeochemistry of trace elements. In the last three decades there has been a real “explosion” of research data and various publications on occurrence and behavior of almost all trace elements including both elements of known and unknown physiological functions in organisms. In order to realize the vast significance of the biogeochemistry of trace elements, it is essential to gather the knowledge acquired over this period into one comprehensive compilation.

The biosphere, also called the ecosphere, is the natural environment of living organisms and is the complex biological epidermis of the Earth whose dimensions are not precisely defined. It consists of the surficial part of the lithosphere, a lower part of the atmosphere, and the hydrosphere. Several ecosystems have been developed within the biosphere. Each ecosystem is a fundamental division of the total environment consisting of living organisms in a given area and having a cycling of chemical elements and energy flow.

Soil is not only a part of the ecosystem but also occupies a basic role for humans, because the survival of man is tied to the maintenance of its productivity. Soil functions as a filtering, buffering, storage, and transformation system protect against the effects of trace element pollution. Soil is effective in these functions only as long as its capacity for cation exchange and its biological activity are preserved. The frequent association of trace element pollution with acid deposition (mainly S, NO, and HF) greatly complicates the overall effects in the environments.

. Water plays fundamental functions in processes both geochemical and biochemical. It is also a main carrier for all chemical elements; its amount and chemical composition control element cycling in water-air-soil systems. Thus, water is probably the most studied medium that governs the forms of trace elements of which investigated Cr, Se, Cu, As, Pb, Cd, and Hg have been studied the most frequently (Das et al. 2001).

Air pollution has arisen from both natural (meteoric, terrestrial, marine, volcanic, erosion and surface winds, forest fires, biogenic) and anthropogenic (coal and fuel combustion, industry, automobile, agriculture) sources. The steady global increase of trace element concentrations in the atmosphere has been observed and monitored in some countries for over 30 years. The majority of trace element emitters have been located in the northern hemisphere (mainly between 40–55† N). Buat-Ménard (1984) calculated that emissions of trace elements in the Northern Hemisphere are several times higher than in the Southern Hemisphere and are about 80% and 30%, respectively of anthropogenic origin. However, at the global scale, the natural emissions of trace elements cannot be neglected because large amounts of dusts containing trace elements come from natural sources. The estimated principal trace elements emissions for natural sources are as follow: 50% of Cr, Mn, and V, and >20% of Cu, Mo, Ni, Pb, Sb and Zn. Volcanic activities may contribute over 20% of the atmospheric Cd, Hg, As, Cr, Cu, Ni, Pb, and Sb. Sea salt aerosols may also contribute about 10% of total trace element emissions to the atmosphere (Allen et al. 2001). Differentiating natural and anthropogenic sources of metals is not easy and some methods for monitoring various sources of metal pollution have been discussed (Dias and Edwards 2003).

Trace element concentrations in plants reflect, in most cases, their abundance in growth media (soil, nutrient solution, water) and in ambient air. The metabolic fate and role of each element in plants can be characterized in relation to some basic processes such as: uptake (absorption), transport within plants, concentration, and speciation, metabolic processes, deficiency and toxicity, and ionic competition and interaction. Some trace elements, particularly trace metals such as Cu, Fe, Mn, Mo, and Zn play a key role in plant metabolisms and are constituents of several enzymes.

Organisms have developed their internal biochemistry in close connection to the composition of the natural environment. Humans, as well as all mammals, unlike prokaryotes and other lower organisms, are not able to adapt easily to any change in the chemical composition of their surroundings. Changes in trace element concentrations are of especially vital importance. The homeostatic balance of chemical elements in an organism is the basic requirement of good health. Ionic relationships within any organism are very fragile and governed by several factors. Their balance is controlled by factors such as bioavailability of an element, capability of tissues or organs to accumulate and excrete an element and by interactions among elements that might vary from antagonistic to synergistic depending mainly on their quantitative ratio.

The trace alkali elements of Group 1 are: lithium (Li), rubidium (Rb), and cesium (Cs). Their common characteristic is a single electron in the outermost energy level and highly reactive chemical behavior. These cations do not usually form complex ionic species but can be bound in some chelates and organometallic compounds. Although their properties differ (Table II-1.1), they are quite similar, especially Rb and Cs, in their behavior in crystallochemical and geochemical processes. Lithophilic elements, Li, Rb, and Cs, are closely associated with the major crustal components and are likely to enter silicate minerals.

The trace elements of Group 2, beryllium (Be), strontium (Sr), and barium (Ba), belong to the alkaline earths and behave similarly to Ca and Mg. Their physical properties, especially sizes of their ionic radii are fairly similar to those of Ca, and they may substitute for each other, however, the small ionic radius of Be prevents its replacement by other cations (Table II-2.1). All the alkaline earths are associated with the carbon cycle that strongly controls their behavior in the terrestrial environment. Radium (Ra), which occurs as several radionuclides, also belongs to this group, and is a product after the decay chain of U and Th.

Geochemical and biochemical properties of the elements of Group 3, as well as their abundance in the biosphere are highly divergent. Two elements, scandium (Sc) and yttrium (Y) are rather rare in the environment, and usually exhibit an affinity for oxygen and their oxidation state is mainly +3 (Table II-3.1). Together with two other elements of this group, lanthanum (La) and actinum (Ac), two subgroups of elements are distinguished as: lanthanides and actinides, of which many elements are either natural or artificial radionuclides.