Water selenium in natural

In contrast to arsenic, the reduced form of selenium, Se(IV), is very strongly adsorbed by HFO. This may account, in part, for the very low selenium concentration in many strongly reducing environments. Furthermore, also in contrast with arsenic, the oxidized form of selenium, Se(VI), is less strongly adsorbed to HFO than the reduced species. These differences, also reflected by other oxide-based sorbents including clays, account for the markedly different behavior of arsenic and selenium in natural waters. 

Adkins R., Walsh N., Edmunds W., and Trafford J. M. (1995) Inductively coupled plasma atomic emission spectrometric analysis of low levels of selenium in natural waters. Analyst 120, 1433-1436. 

Bueno M. and Potin-Gautier M. (2002) Solid-phase extraction for the simultaneous preconcentration of organic (selenocys-tine) and inorganic Se(IV), Se(VI) selenium in natural waters. J. Chromatogr. A 963, 185-193. 

Haraldsson C, Poliak M, Oehman P. 1992. Simultaneous determination of antimony, arsenic and selenium in natural waters by means of hydride generation coupled to plasma source mass spectrometry. 

The method is suitable for the determination of selenium in natural waters with concentrations between 0.001 and 0.25 mg of Se/1. 

Howard, J.H. Control of geochemical behavior of selenium in natural waters by absorption on hydrous ferric oxides, p.485-496, in [D.D. Hemphill (ed.)] Trace Substances in Environmental Health-V., Proc. Univers. Missouri s 7 th Ann. Conf., Trace Substances in Environm. Health, Columbia, Univers. Missouri, 1973 Johnson, H. Environ. Sci. Technol. 4, 850 (1970)... 

Olivas, R.M., Donard, OXF., Gilon, N. and PotinGautier, M. (1996) Speciation of organic selenium compounds by high-performance liquid chromatography inductively coupled plasma mass spectrometry in natural waters./. Anal. At. Spectrom., 11, 1171-1176. 

Hydride generation AAS is a well-established technique for the determination of selenium because of its selectivity and sensitivity. The detection limits are improved by concentrating the hydride prior to the transfer to the spectrometer. Cryogenic condensation in a U-tube at liquid nitrogen temperature is a preferred method of pre-concentration. However, selenium hydride is formed essentially only from Se. The selectivity for Se has been combined with various chemical preparation steps to determine the sum of SeIV and Se and the total selenium content of samples. Se concentrations are measured by the difference between the (Se + Se ) and Se contents. The difference between total selenium and (Se + Se ) contents represents the concentrations of Se° and Se2- species. These methods have been used for determinations of selenium species in natural waters. Soluble organic matter in some groundwater samples interferes with the hydride generation determination of selenium. Isolation of humic substances by their adsorption on resins has overcome this problem. 

Campanella, L. 1996. Problems of speciation of elements in natural water The case of chromium and selenium. In S. Caroli (ed.), Element Speciation in Bioinorganic Chemistry, pp. 419 444. New York Wiley-Interscience. 

Vien and Fry [762] have reported a gas chromatographic determination of arsenic, selenium, tin and antimony in natural waters. The gaseous hydrides are generated, concentrated on a cold trap, and then injected into the gas chromatograph with the use of drying agents or carbon dioxide scrubbing. A specially conditioned Tenax column suppresses unwanted byproduct elution and separates the volatile hydrides at room temperature. A photoionisation detector was used and the authors reported a detection limit as low as 0.001 pg L ... 

Shimoishi and Toei [766] have described a gas chromatographic determination of selenium in non saline waters based on l,2-diamino-3,5-dibromobenzene with an extraction procedure that is specific for selenium (IV). Total selenium is determined by treatment of non saline water with titanium trichloride and with a bromine-bromide redox buffer to convert selenide, elemental selenium and selenate to selenious acid. After reaction, the 4,6-dibromopiazselenol formed from as little as lng of selenium can be extracted quantitatively into 1 ml of toluene from 500ml of natural water up to 2ng L 1 of selenium(IV) and total selenium can be determined. The percentage of selenium(IV) in the total selenium in river water varies from 35 to 70%. 

Selenium occurs in natural waters principally in two oxidation states, Se(IV) (selenite) and Se(VI) (selenate). Elemental selenium, Se(0) (red and black forms), and selenide, Se(—II), are essentially insoluble in water Se(VI)04 occurs mainly in oxidizing waters while HSe(IV)03 and Se(IV)Oi dominate under reducing conditions (Figure 9). The concentration ratio of Se(IV) to Se(VI) species in natural waters does not necessarily follow that of other redox couples (e.g., Fe /Fe ). This reflects the slow kinetics involved (White and Dubrovsky, 1994). 

Crecehus, E. A., Bloom, N. S., Cowan, C. E., and Jenne, E. A., 1986, Speciation of selenium and arsenic in natural water and sediments, volume 2 Arsenic speciation Palo Alto, California, BatteUe, Pacific Northwest Laboratories, p. variously paginated. 

The dithizone method has been used in determination of mercury in natural waters [80], coal and its products [81], sulphide minerals [82], silver [12], tin [10], cadmium [83], uranium compounds [84] selenium [85], Hg-Cd-Te thin films [86], foodstuffs [87,88], and water... 

Pratt, LK. and Elrick, K.A. (1987) Interference effects of selenium on the determination of mercury in natural waters using cold vapor/atomic absorption spectrometry. Atom. Spectrosc., 8, 170-171. 

Copper interacts with numerous compounds normally found in natural waters. The amounts of the various copper compounds and complexes present in solution depend on water pH, temperature, and alkalinity and on the concentrations of bicarbonate, sulfide, and organic ligands. In animals, copper interacts with essential trace elements such as iron, zinc, molybdenum, manganese, nickel, and selenium and also with nonessential elements including silver, cadmium, mercury, and lead interactions may be either beneficial or harmful to the organism. The patterns of copper accumulation, metabolism, and toxicity from these interactions frequently differ from those produced by copper alone. Acknowledgment of these interactions is essential for understanding copper toxicokinetics. 

In natural waters selenium occurs only in very low concentrations. Sea water contains an average of about 0.005 mg/1. Higher concentrations are rarely found in surface waters. Regionally limited ground waters form an exception if they occur in an area with rocks and soils containing large amounts of selenium, they may contain between 0.05 and 0.1 mg/1 or in exceptional cases even more. 

High selenium contents cannot be expected in natural waters and interference must be anticipated from other substances contained in the water. Consequently, it is advisable to concentrate the selenium and carry out distillation before photometric determination. Alkaline concentration of 1 - 2 litres of water in a vacuum rotation evaporator and subsequent distillation of the concentrate with hydrobromic acid containing bromine leads to... 

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