Since early in 18th century, humates have been categorized as humic acid, fulvic acid, and humin. These fractions are defined by their solubility in either acid or alkali solutions and fail to provide any chemical information concerning their functional activity.
Humic acid is defined as a dark brown humic substance that is soluble in water only at pH values greater than 2.
Fulvic acid is defined as a yellow to yellow-brown humic substance that is soluble in water under all pH conditions.
Humin is defined as a brownish amorphous substance that is produced from acidic reactions on certain sugars, carbohydrates or simply, the remaining residue of humic acid extraction.
Humates’ primary acids are Humic Acid and Fulvic Acid. Both compounds are unique, possessing complex structures with active side groups yielding different physiochemical properties
Humic substances are the final product from the degradation of non-living plant tissues created by different cells. In living tissues, cellular function requires various biochemical components to function. These include carbohydrates, lipids, proteins, lignin (plants), minerals and phytochemicals. The resulting humic substances is actually biomolecules because of the previous intimate association with various biochemical components.
Humic compounds are all part of an extremely heterogeneous ‘supramolecular structure’ (Piccolo, 2002; Fiorentino et al., 2006) which are relatively small bio-organic molecules associated by dispersive weak forces (e.g. van der Waals bonds) into a larger molecule. The differences between the subdivisions are due to variations in chemical composition, acidity, degree of hydrophobicity and self-associations of molecules. In order to observe the functionality of these compounds requires separation into a large number of different bioorganic molecules into homogenous fractions.
Humic substances possess both aromatic and aliphatic structural characteristics. The dominant functional groups are phenolic & carboxyl groups that contribute to the surface charge and reactivity of humic substances (Stevenson, 1994).
Humic substances may bind or chelate multivalent cations such as magnesium (Mg2+), calcium (Ca2+) & iron (Fe2+). Chelating the elements in ionic forms increases the availability of these cations to animal and human tissues, including plants and microorganisms.
A substantial fraction of humic acids mass is in carboxylic acid functional groups. This enables the humic compound to chelate (bind or precipitate in some media, make solution in other media) positively charged multivalent ions. These include Mg2+, Ca 2+, Fe 2+, Fe3+, most trace elements of value to plants, as well as other ions that have no positive biological role (i.e. cadmium Cd2+ and lead Pb2+).
Chelation of ions plays a major role of humic acids with respect to interacting within living biological systems. By chelating the elements ions, they facilitate the uptake of these ions by several mechanisms. Chelation prevents their precipitation and also seems to be a direct and positive influence on their bioavailability.
Humic acids' ability to chelate substances makes them powerful substances for detoxifying tissues of heavy metals, toxins, pesticides and herbicides. In the environemtnt (soils), humic acid bind tightly to heavy metals and prevent them from be absorbed into plants, thereby keeping those plants clean.