Surface properties of humic acids from peat and sapropel of increasing transformation

Humic substances are complex, organic substances occurring in natural media such as water, soils and sediments. Humic substances represent the highest pool of recent carbon on earth, and they influence climate, soil fertility and depollution. In spite of such importance, the structure and properties of humic substances are largely unknown. We studied the surfactant activity of humic acids from peat of increasing degrees of humification and sapropel, sampled in the Upa River of the Tula region. We measured critical micelle concentration (CMC) of humic acids of different ages. Our results show that CMC decreases from 1.5 g/100 ml for the less transformed sapropel, to 1.0 g/100 ml for the medium-transformed mesotrophic sphagnum peat, to 0.25 g/100 ml for the most transformed eutrophic alder peat. We also found that the limiting adsorption of humic acids from the younger sapropel, of 7.1 x 10(-6) mol/m(2), and from sphagnum peat, of 7.6 x 10(-6) mol/m(2), are higher than the limiting adsorption of humic acids from the older eutrophic alder peat, of 3.3 x 10(-6) mol/m(2).