(393bj) Aggregation of Humic Substances: Effects of Filtration

Humic acids are complex polyelectrolytes which exhibit various conformations and aggregation states depending on the solution chemistry. In the current research, dynamic light scattering and fluorescence spectroscopy were used to investigate the size distributions and fluorescence quenching behavior for the dissolved organic fractions of commercial humic acid (Sigma Aldrich grade). The size distribution results suggested that the HA molecules re-aggregate after filtration through 0.45 mm nylon fiber filters, and form significantly large micron sized aggregates even at low concentrations around 8 ppm dissolved organic carbon (DOC).  The size distributions for the total organic carbon (TOC) were compared with the filtered samples as a function of carbon concentration. These results suggest that humic substances are dynamic in nature and their size is constantly changing due to interactions with other HA molecules. The fluorescence of DOC at different carbon concentrations was examined to detect potential fluorescence quenching behavior due to re-aggregation of HA molecules after filtration.