1. Schnitzer, M., Kahn, S. U.: Humic Substances in the Environment. New York: Dekker 1972
2. Schnitzer, M., in: Soil Organic Matter, p. 1 (M. Schnitzer, S. U. Khan, eds.). Amsterdam: Elsevier 1978
3. Stevenson, F. J.: Humic Chemistry. Somerset, N J: Wiley 1982
4. Prakash, A., MacGregor, D. J., in: Aquatic and Terrestrial Humic Materials, p.481 (R. F. Christman, E. T. Gjessing, eds.). Woburn, MA: Ann Arbor Science 1983
5. Senesi, N., Miano, T. M. (eds.): Humic Substances in the Global Environment and Implications on Human Health. Amsterdam: Elsevier 1994