The organic portion of soil that remains after prolonged microbial decomposition, and that is formed by the decay of leaves, wood, and other vegetable matter. Humic substances can impart a yellowish-brown to brownish-black color to water; dectectable to 0.1 ppm in water.
Humic substances are commonly classified on the basis of solubility.
If a material containing humic substances or humus is extracted with a strong base and the resulting solution is then acidified, the products are a) a nonextractable plant residue called humin, b) a material called humic acid that precipitates from the acidified (pH < 2) solution, and c) an organic material called fulvic acid that remains dissolved in the acidified solution.
The high molecular weight and polyelectrolytic humic substance macromolecules range from a molecular weight of a few hundred for fulvic acid to tens of thousands for the humic acid and humin fractions.
Humic substances form suspected-carcinogenic trihalomethanes (THMs, such as chloroform, dibromochloromethane, bromodichloromethane, and bromoform) by reaction with chlorine. Humic substances are excellent chelating agents that bind with and hold metal ions in water, and they also effectively exchange cations with water.
See Also: Chelation Chelating Agent Organic Iron Chelation Chelating Agent Organic Iron Free Acid Form Weak Acid Cation Exchangers Total Acidity Strong Acid Cation Exchanger Chelation Chelating Agent Organic Iron Trihalomethanes (THMs) Humic Acid Humin Fulvic Acid Tannin Chelation Chelating Agent Organic Iron Free Acid Form Weak Acid Cation Exchangers Total Acidity Strong Acid Cation Exchanger Fulvic Acid