Humic substances (HS)
In terms of quantity, humic substances are the most common class of organic substances on earth, including in natural waters.
Their formation is still not completely understood, both aggradative pathways (polymerisation), as well as degradative degradative pathways (hydrolysis, oxidation) are possible. In the aquatic environment, it is considered likely that the formation of humic substances is linked to the death of bacteria. Humic substances are operationally divided into humins, humic acids, fulvic acids and humic hydrolysates - in reality the transitions are fluid.