INVESTIGADORES
BOTTE Sandra Elizabeth
capítulos de libros
Título:
Ch 11: Heavy Metals, Major Metals, Trace Elements
Autor/es:
MARCOVECCHIO, J.E.; BOTTÉ, S.E.; FREIJE, R.H.
Libro:
Handbook of Water Analysis, 2nd. Edition
Editorial:
CRC Press, Taylor & Francis Group
Referencias:
Lugar: Boca Raton, Florida; Año: 2007; p. 275 - 311
Resumen:
Natural waters contamination is a worldwide distributed problem which deserves large attention not only due to its environmental hazardous effects but also for the risks to the human health as well as the economical damages it produces. Between the wide diversity of pollutants affecting water resources heavy metals receive particular concern considering their strong toxicity even at low concentrations. The occurrence of heavy metals in water bodies can be of natural origin, eroded minerals within sediments, leaching of ore deposits, vulcanism extruded products) or for anthropogenic one (solid waste disposal, industrial or domestic effluents, harbour channels dredging. The term heavy metal includes both essential and non-essential trace metals, which may be toxic to the organisms depending on their own properties, availability (chemical speciation) and concentration levels. Heavy metals (Ag, As, Cd, Cu, Cr, Hg, Ni, Pb, Zn) can be present in the aquatic system in both dissolved forms (which can cause toxic effects on a wide diversity of organisms, including vertebrates) and particulated ones (including adsorbed on sediments, suspended particulate matter or colloids, in transitional complexes and Fe / Mn hydroxides nets, linked to organic matter and carbonates, etc). The dynamics which regulates the transference of heavy metals between the dissolved and the particulated phases (in both senses) depends on the pH and oxyde-reduction potential of the system. Also these parameters regulate the chemical speciation of heavy metals within the system. It has been largely recognized that heavy metals concentrations are much higher in urban or industrial areas than in wild ones. Consequently the possibility of incorporation of heavy metals into drinking water or trophic webs exits, and so the potentially generation of deletereous effects on Human Populations. Moreover the toxicity of heavy metals can be significantly increased due to synergistic effects within natural systems. In addition, and considering the average long-life of these elements, their persistence and potential transformation to more toxic compounds must be addressed. Even though the natural levels of heavy metals are well known those from aquatic ecosystems have significantly increased in the last decades simultaneously with the high development of industrial activities and urban developments. So, the necessity to develop analytical methods which allow to detect and quantify extremely low levels of heavy metals in natural waters (which could be quiet dangerous for both aquatic biota and Human Health) is strongly remarked. By the way, those considered as (Li, Be, B, Al, Co, V, Se, Sb, Sr, Sn, Ti) occur at trace or ultra-trace level in the crust (with the exception of aluminum which is a major component). They are usually included at parts-per-billion (ppb = µg/L) or at parts-per trillion (ppt = ng.L-1) levels. However, much higher environmental concentrations may occur due to mining and industrial activities, high-temperature waters, or weathering of mineralized and metal-rich rocks. Even though the effects of most trace elements on the Biosphere are still not well known, many of them are considered dangerous or potentially harmful. In this sense, guidelines for the protection of aquatic life and human health have been settled by different international organizations (US EPA, WHO, European Union Commission). The usefulness of the determination of aqueous elements at trace and ultra-trace levels has been highlighted to distinguish the natural background from anthropogenic inputs, as well as to recognize significant variations in long-term monitoring programs. Finally, when major metals are considered, it is refered to those metal ions which concentrations are considerably higher than those of other cations in natural waters. The most important major metals are Na, K, Ca, Mg, Mn, Fe. They usually are essential nutrients, and deficiencies of them can produce different diseases for humans, animals or plants. In addition, several of them can produce severe toxicity effects when exceed certain levels in water. The main goal of the present chapter is to summarize the significant items of these analytical protocols, including the steps corresponding to sampling, storage and preservation, laboratory pre-treatments and instrumental techniques to determine heavy metals, trace elements and major metals in natural waters.