Chapter Two: Fate and transport of molybdenum in soils: Kinetic modeling.

Molybdenum (Mo) is an essential trace element for human, animal and plant health. Mo deficiency in soils has frequently been reported, especially under P-deficient conditions. However, Mo is also a potentially toxic contaminant to soils and aquifers that may pose significant threat to ecological and human health. This review article illustrates briefly about Mo, its production and use, its natural occurrence, its fate and behavior in the soil-water system, and its retention mechanisms in soils. Furthermore, a range of transport models (multi-reaction model, second order model, stir-flow model, and competitive model) for describing and predicting Mo fate and transport behavior in the environment have been reviewed. It was shown that equilibrium Langmuir and Freundlich equations can be extended to simulate the pH dependent and time-dependent sorption and transport in soils. An advantage of modified Freundlich and Langmuir approaches is that they are relatively less complex and require fewer parameters. On the other hand, geochemical models, which are based on surface complexation concepts, were incorporated into kinetic models to accurately describe the reactive transport of Mo in soil components under a wide range of environmental conditions. [ABSTRACT FROM AUTHOR]