The trace heavy metals existing in freshwaters are present in various physico-chemical forms, which include simple hydrated ions, hydroxo complexes, inorganic and organic complexes, and colloidal particles. 1 These physico-chemical forms can effectively change their bioavailabilities and toxicities. For example, chromium(III) is an essential element, whereas chromium(VI) is highly toxic and even carcinogenic. Arsenic(III) is much more toxic than arsenic(V).2,3 The heavy metal speciation, therefore, arouses substantial interest in water analysis because the geochemical behavior and biological effects of heavy metals depend greatly on their physicochemical forms. The chemical speciation has been a topic of increasing research interest in geochemical, biological and environmental sciences, and waste water treatment processes.Humic and fulvic acids are also known to interact with various metal ions, hydrated metal oxides, clay minerals and organic compounds. 1 Humic substances, major organic constituents of natural waters, interact strongly with various heavy metals to form humic complexes and affect adsorption-desorption behavior of metals. Physico-chemical forms of metal humic-complexes, however, are complicated because they may exist alone or be adsorbed on other colloidal particles. 4 Up to now, methods such as coprecipitation, 5,6 sorption on adsorbent resins 7-10 and separation by ion exchange resins 4,11,12 have been used in determining metal ions both free and bound to humic substances present in natural and waste waters. Among these techniques used in trace element determination, adsorption is one of the most widely used. For this purpose, commercially available Amberlite XAD copolymers [13][14][15][16] have been widely used as adsorbents suitable for multielement preconcentration from different matrices, because of their purity and good adsorption properties. Amberlite XAD-16 resin is an adsorbent based on polystyrene divinylbenzene-copolymer. It is used in continuous filtration for adsorption of water-soluble substances. XAD-16 has excellent physical resistance, hydraulic characteristics and thermal stability. In addition, it has high porosity, low polarity and the largest surface area (825 m 2 g -1 ) among the XAD series of Amberlite resins. Therefore, it was selected as an adsorbent resin, owing to these high performance characteristics. But it can show little swelling/shrinking upon changing between organic solvent and aqueous media (Rohm and Haas Co.).In the present work, determinations were carried out of metals bound to humic substances and to suspended particles, and of the free metal ions in water samples taken from different regions of Sultansazlıg ı, a wetland and wildlife refuge. Due to very low metal contents of natural water samples to be analyzed, enrichment procedures are often required. A column filled with Amberlite XAD-16 resin as a preconcentration means was used to determine the metals bound to humic substances and free metal ions. The measurements of the metal concentrations were pe...
