Humic acids (03C, 04C, 05C, 06C, 07C, 08C, 09C, 10C, 11C, 12C, 13C, 14C, 15C, 16C)
The brown polymeric product from the decomposition of organic matter, particularly dead plants.  This combination of polymers may contain aromatic and heterocyclic structures, carboxy groups, and nitrogen.