A critical review of selenium analysis in natural water samples

This paper critically reviews the current understanding of the analysis of selenium in the natural environment. Several inorganic species of Se (−2, 0, +4, and +6) and organic species (monomethylated and dimethylated) have been reported in aquatic systems. Inorganic speciation of Se varies with pH and Eh. Many different analytical methods including UV–visible spectrophotometry, spectrofluorimetry, atomic fluorescence spectroscopy (AFS), chromatography, flameless atomic absorption spectroscopy (FAAS), electrochemistry, and inductively coupled plasma with atomic emission (ICP-AES) or mass spectrometry (ICP-MS) are available for quantification of selenium levels in different matrices. In recent years, analytical speciation techniques made a great leap in separating and detecting low levels of Se, but analyzing reduced species such as Se(0), polyselenides, and sulfur–selenium mixed species in the environment need further development. A number of selenium compounds has been identified in biota, but positive identification of such compounds in environmental samples is needed to understand the speciation of selenium in natural waters, sediments, and soils.