Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2006
Publication Date: 7/15/2006
Citation: He, Z., Honeycutt, C.W., Zhang, T., Bertsch, P.M. 2006. Preparation and initial characterization of metal phytate compounds. Journal of Environmental Quality. 35:1319-1328.
Interpretive Summary: The availability of both applied and native soil phosphorus (P) is influenced by a number of soil characteristics. For example, both inorganic and organic P in soil can interact with metal ions like iron (Fe) and aluminum (Al) to form different P-metal complexes which affect the bioavailability and runoff of P in different time scales. Various advanced spectroscopic techniques have been applied to investigate the metal-P species in animal manure and soil. However, it is not possible to interpret these data on specific metal-organic P compounds due to the lack of reference metal-organic P compounds. In this work, we synthesized eight metal-organic P compounds. These compounds were characterized by several different methods. Results indicate that metal speciation is an important factor influencing P behavior in the environment. Our long-term goal is to establish reference data from these model metal-organic P compounds for characterizing manure and soil P species using advanced technologies.
Technical Abstract: Phytic acid (inositol hexaphosphoric acid, IP6) has long been recognized as the predominant organic P form in soil and animal manure. Whereas many studies have investigated the wet chemistry of IP6, there is little information on the characterization of solid metal IP6 compounds. This information is essential for further understanding and assessing the chemical behavior of IP6 in diverse soil-plant-water ecosystems. As the first step in full characterization, we synthesized eight metal phytate compounds and investigated their structural features using Fourier transform infrared spectroscopy (FT-IR) and their bioavailability using enzymatic dephosphorylation. The absorption features from 900 to 1200 cm-1 in FT-IR could be used to identify these phytates as: (1) light divalent metal (Ca and Mg) compounds with a sharp band and a broad band, (2) heavy divalent metal (Cu and Mn) compounds with splitting broad bands, and (3) trivalent metal (Al and Fe) compounds with a broad band and a shoulder band. Although both reagents have been reported to effectively remove the inhibitory effects of Fe and/or Al ions on enzymatic dephosphorylation of soluble IP6, EDTA and dithionite were not as efficient in facilitating the enzymatic release of P from Fe and Al IP6 compounds. The different structural and chemical properties of these metal compounds indicate that metal speciation is an important factor controlling phytate behavior in the environment.