Sizes and shapes of humic substances

This series of papers focuses on considerations of the sizes and shapes of humic macromolecules. The initiative arose because of the divergent views held by participants at a symposium/workshop held under the auspices of the Soil Science Society of America and the International Humic Substances Society in Anaheim, CA in October 1997, Three different viewpoints were expressed, and each satisfied its proponent. One suggested that humic substances (HS) are macromolecular and assume random coil conformations in solution; a second proposed that HS are molecular associations of relatively small molecules held together by weak interaction forces; a third considered that HS are in solution as micelle or "pseudomicellar" structures. Viewpoints two and three could be broadly considered to be under the same umbrella. We have considered the experimental procedures that led the proponents to their points of view, and we do not consider it to be our brief to side with one or another of the concepts. Much work remains to be done before a definitive answer is found. We understand that the various concepts arose from studies of different soils using different experimental techniques, and we share the view that the matter/controversy can best be resolved when data are available from applications of the same advanced techniques and procedures to a variety of HS from different sources. We are convinced that awareness of the sizes and shapes of humic molecules is of fundamental importance for an understanding of the many basic reactions and interactions that take place in the soil environment and that have considerable environmental significance. It is our hope that this series of papers will stimulate researchers to pool their views, skills, and instrumentation and set about finding a solution to this fundamental aspect of humic structures.