Miljøprojekt, 902 – The Influence of Sorption on the Degradation of Pesticides and other Chemicals in Soil

The Influence of Sorption on the Degradation of Pesticides and other Chemicals in Soil

2 The soil organic matter

Organic matter (humus) is a result of the biological and chemical degradation of dead plant residue or animal remains in the soil. After a number of transformations the matter no longer has any resemblance to plant residue or animal remains after which it is called organic matter, macromolecular matter or humus. The soil organic matter has a complex structure, and it can be classified into soluble organic matter (DOM, dissolved organic matter) and insoluble matter. A classification of the organic matter according to its chemical structure includes fulvic acids, humic acids, and humin, where fulvic acid is soluble in both acidic and alkaline solutions, humic acid is soluble only in alkaline solutions, and humin is not soluble. The soil organic matter is further composed of polysaccharides, lignin, simple carbohydrates, lipids, proteins, and organic acids (Lassen, 1995; Stevenson, 1992). The exact structure of the organic matter is not known, but most hypotheses agree that the organic matter is composed of amorphous polymers of a three-dimensional structure of which both aromatic and aliphatic hydrocarbons form part and where there are both hydrophobic and hydrophilic side chains. Thus, it is not possible to give a complete description of the binding of pesticides and other xenobiotic chemicals to the soil organic matter.