tailieunhanh - Geochemical and Hydrological Reactivity of Heavy Metals in Soils - Chapter 7

Hình thành các oxit hữu cơ Mangan và ảnh hưởng của họ về Nhặt phế liệu của các nguyên tố vi lượng độc hại Mn sinh học quá trình oxy hóa là một quá trình trong môi trường quan trọng bởi vì nó không chỉ điều khiển xe đạp và sinh khả dụng của Mn bản thân, nhưng cũng có khả năng tác điều khiển trên xe đạp và sinh khả dụng của kim loại vi lượng khác, hoặc là độc hại (Nelson và cộng sự, 1999a.) hoặc các chất dinh dưỡng (Bartlett, 1988), mạnh mẽ ràng buộc ít hòa tan. | 7 Formation of Biogenic Manganese Oxides and Their Influence on the Scavenging of Toxic Trace Elements Yarrow M. Nelson and Leonard W. Lion CONTENTS Introduction Kinetics of Biological Mn Oxidation Trace Metal Adsorption to Biogenic Mn Oxides Trace Metal Adsorption to Mixtures of Biogenic Mn Oxides and Fe Oxides Role of Mn Oxides in Controlling Trace Metal Adsorption to Natural Biofilms Conclusions Acknowledgments References INTRODUCTION Biological Mn oxidation is an important process in the environment because it not only controls the cycling and bioavailability of Mn itself but also is likely to exert controls on the cycling and bioavailability of other trace metals either toxic Nelson et al. 1999a or nutrients Bartlett 1988 that strongly bind to sparingly soluble biogenic Mn oxides. Biogenic Mn oxides may also play important roles in the abiotic oxidation of complex organic compounds Sunda and Kieber 1994 and as terminal electron acceptors in biologically mediated degradation reactions Nealson and Myers 1992 . Because of the importance of Mn cycling in the environment a significant amount of research has been devoted to determining the enzymatic pathways responsible for biological oxidation of Mn II Tebo et al. 1997 . Also a 2003 by CRC Press LLC kinetic model for biological Mn oxidation has recently been developed Zhang et al. 2002 and the implications of strong trace metal binding by biogenic Mn oxides have been explored through sampling and analysis in aquatic environments Nelson et al. 1999a Dong et al. 2000 Wilson et al. 2001 . The abiotic oxidation of Mn II is kinetically inhibited below pH 9 Morgan and Stumm 1964 Langen et al. 1997 and therefore Mn oxidation in natural aquatic environments is expected to be predominantly driven by biological processes either by direct enzymatically catalyzed oxidation Ghiorse 1984 or indirectly by biologically induced microenvironment changes such as a localized pH increase caused by algae .