Heavy Metals, Major Metals, Trace Elements

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Feb 23, 2013 - concentration (RC), and amount of resin on the column (AR) [147]. ...... g−1 for cadmium and 105 µg g−1 for copper on functionalized SBA-15.
15 Heavy Metals, Major Metals, Trace Elements Jorge E. Marcovecchio, Sandra E. Botté, Claudia E. Domini, and Rubén H. Freije Contents Sampling................................................................................................................................................. 380 Storage and Preservation......................................................................................................................... 383 Pretreatment of Samples......................................................................................................................... 384 Digestion of Samples.............................................................................................................................. 385 Analytical Methods................................................................................................................................. 386 Classical Methods.............................................................................................................................. 386 Spectrophotometric Method.............................................................................................................. 386 FAAS Techniques.............................................................................................................................. 390 Electrothermal Atomic Absorption Spectroscopy.............................................................................. 395 Inductively Coupled Plasma Methods............................................................................................... 397 Electrochemical Methods.................................................................................................................. 401 Voltammetric Techniques.............................................................................................................. 401 Potentiometric Techniques............................................................................................................ 403 Ion Chromatography.......................................................................................................................... 404 Other Chromatographic Techniques............................................................................................. 404 Other Techniques............................................................................................................................... 405 Luminescence............................................................................................................................... 405 X-Ray Fluorescence Spectrometry............................................................................................... 406 Neutron Activation Analysis......................................................................................................... 407 The Particular Case of Mercury......................................................................................................... 407 Summary................................................................................................................................................. 408 References............................................................................................................................................... 408 The contamination of natural waters is a worldwide distributed problem which deserves large attention not only due to its environmental hazardous effects but also for the risks involved to human health as well as economic 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 (i.e., eroded minerals within sediments, leaching of ore deposits, and vulcanism extruded products) or anthropogenic in nature (i.e., solid waste disposal, industrial or domestic effluents, harbor channels dredging). The term heavy metal includes both essential and nonessential 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 oxide-reduction potential of the system. Also these parameters regulate the chemical speciation of heavy metals within the system. 379

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Handbook of Water Analysis

It has been largely recognized that heavy metal concentrations are much higher in urban or industrial areas than in natural environments [1–3]. Consequently the possibility of incorporation of heavy metals in drinking water or trophic webs exists, and so the potential generation of deleterious effects on human populations [4–6]. 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 (Table 15.1) 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 allows to detect and quantify extremely low levels of heavy metals in natural waters (which could be quite dangerous for both aquatic biota and human health) that is strongly remarked. By the way, those considered as trace elements (Li, Be, B, Al, Co, V, Se, Sb, Sr, Sn, Ti) occur at trace or ultratrace 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 −1) or at parts-per-trillion (ppt = ng L −1) levels. However, much higher environmental concentra­tions may occur due to mining and industrial activities, hightemperature waters, or weathering of mineralized and metal-rich rocks [7–10]. 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 (USEPA, WHO, European Union Commission) [11]. The usefulness of the determination of aque­ous elements at trace and ultratrace levels has been highlighted to distinguish the natural background from anthropogenic inputs, as well as to recognize significant variations in long-term monitoring programs [12,13]. Finally, when major metals are considered, it is referred to those metal ions whose concentrations are considerably higher than those of other cations in natural waters. The most important major metals are Na, K, Ca, Mg, Mn, or Fe. Usually the essential nutrients and their deficiencies can produce different diseases for humans, animals, or plants. In addition, several of the metals can produce severe toxicity effects when there is an excess in certain levels in water. The main goal of this chapter is to summarize the significant items of these analytical protocols, including the steps corresponding to sampling, storage and preser­vation, laboratory pretreatments and instrumental techniques to determine heavy metals, trace elements, and major metals in natural waters.

Sampling Sampling is the first step, and probably the most important one in the analysis of a natural water sample. Any mistake which could occur during this step will mean the whole analysis useless. In this sense it must be pointed out that different sampling methods can be applied considering the heavy metals range of concentrations, sample characteristics, and purposes of the analysis. Nürberg and Mart [14] and Kremling [15] have opportunely outlined the main aspects of accurate sample collection for different water types. The collected sample must be a representative of the real water composition, and usually a large volume of water is collected to get it. Then, it must be homogenized for subsampling and consequent analysis of the corresponding aliquots. It can be sustained that a shorter time between the collection of a sample and its analysis strongly correlates with more reliable analytical results. The occurrence of turbidity or suspended matter within the sample as well as the method used for their elimination is an important factor to be considered [16–18]. The composition of water within the studied system is another important point to consider in deciding the sampling strategy to use for. So, when this composition remains unchanged over time, usually a discrete sample may be used, keeping in mind that this sample represents the state of the system at that moment. Unlike this, if the aim of the study is to know the average concentration of a certain component over an established period the use of a composite sample (mix of different water samples obtained at different times) is fully recommended [19–21].

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NA

NA

NA

Se

Sn

NA

0.05

0.027

0.76

NA

NA

NA

Hg

2.6

NA

NA

Fe

0.069

Sb

0–2.0

Cu

NA

NA

NA

NA

0.2–0.7

NA

NA

NA

0.0028/0.0029 0.224/1.228

1.0

NA