Humic acid

From Freepedia

Humic acid is a complex mixture of organic acids produced mostly by the decomposition of plant material, especially lignin. Humic acid is dark brown and is a major constituent of humus where it contributes to soil fertility and is a precursor of fossil fuels. It can also be found in peat, coal, and ocean water.

A substantial fraction of the mass of the humic acids is in carboxylic acid functional groups, which endow these molecules with the ability to chelate multivalent cations (Mg++, Ca++, Fe++,...). This chelation of ions is probably the most important role of humic acids with respect to living systems. By chelating the ions, they faciliate the uptake of these ions by several mechanisms, one of which is preventing their precipitation, another seems to be a direct and positive influence on their bioavailability.