Humic substances components/heterogeneous

Humic acids (HA) and fulvic acids (FA) are the main components of humic substances (HS), which are the most chemically and biochemically active and widely spread fractions of nonliving natural organic matter in all terrestrial and aquatic environments. They comprise a chemically and physically heterogeneous group of substances with colloidal, polydis-persed, polyelectrolyte characteristics and mixed aliphatic and aromatic nature (Senesi and Loffredo 1999). 

Abstract The objective of this chapter is to present some recent developments on nonaque-ous phase liquid (NAPL) pool dissolution in water saturated subsurface formations. Closed form analytical solutions for transient contaminant transport resulting from the dissolution of a single component NAPL pool in three-dimensional, homogeneous porous media are presented for various shapes of source geometries. The effect of aquifer anisotropy and heterogeneity as well as the presence of dissolved humic substances on mass transfer from a NAPL pool is discussed. Furthermore, correlations,based on numerical simulations as well as available experimental data, describing the rate of interface mass transfer from single component NAPL pools in saturated subsurface formations are presented. 

Soil DOM comprises a wide variety of organic substances. Specific microbial or plant exudates are released as a consequence of metabolic activity of soil biota. Transformations of biogenic compounds, through partial degradation and polymerization, result in the formation of a structurally ill-defined mixture of humic substances, a term used to include both humic and fulvic acids (20, 21). Nonuniform effects of DOM components on metal mobilization may be anticipated because of the heterogeneity of their chemical structures and properties. 

Humic substances are typical products of the humification process. They are the basic component of the humus, occurring in the humus material to the extent of 80 to 90%. They consist of a group of acid, yellow to dark brown polymeric substances of a heterogeneous aromatic and polydisperse character. Their acid nature allows them to react with mineral substances to form stable organomineral complexes sometimes referred to as humines. They differ from the remaining organic material in the soil by various typical features as follows ... 

This book is devoted to the subject of soil colloidal components and their interaction with ionic species. The fundamental problem of ion binding to natural colloids (both inorganic, such as clays and oxides, and organic, mainly humic substances) is a multidisciplinary research field that raises special challenges. These come mainly from the heterogeneous and (sometimes) ill-defined nature of natural colloids, especially humic substances. Soil scientists, on one side, and colloid chanists, on the other, tend to have different views of the problem. This book is intended as a contribution to fill the gap and also to bring the latest advances in this active research field. 

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