Adsorption of mutagens by humic acid.

Humic acid inhibited the mutagenicity of various mutagens. The inhibitory effect was desmutagenic, heat-resistant and increased with an increase of the humic acid molecular weight. Typical monomeric components of humic acids had no desmutagenic effect. The desmutagenic effect of humic acid was caused by adsorption of mutagen, not by decomposition of mutagen. The adsorption activity was largest at its critical micelle concentration and the adsorbed mutagen was released by ultrasonication. Humic acids exist in natural environment in large amounts and may play an important role for natural purification by adsorption of mutagens.