Aquatic colloids: Provenance, characterization and significance to environmental monitoring

Aquatic colloids are ubiquitous in all kinds of natural water and in general found to be small in size (< 100nm) and low in number density (< 10(14) particles per liter). Colloids of such properties may play a significant role for the aquifer migration of environmentally hazardous contaminants: radioactive elements as well as other trace chemical composites. Insightful knowledge on aquatic colloids is therefore perceived as indispensable for monitoring the environmental behavior of hazardous trace constituents. This chapter describes the chemical process of generating aquatic colloids, e.g. their kernels like hydroxy aluminosilicate (HAS) colloids, as well as the incorporation of radionuclides into such colloid formation. Likely processes are characterized in particular by a combination of different nanoscopic approaches. The colloid formation is monitored radiochemically in conjunction with the highly sensitive spectroscopic speciation, e.g. time-resolved laser fluorescence spectroscopy (TRLFS), which facilitates the chemical characterization of trace actinides in particular. Colloids thus generated are quantified for their average size and number density by laser-induced breakdown detection (LIBD) upon optical plasma monitoring. Exemplary illustrations are summarized for the fori-nation of colloid-borne trivalent actinides (Am, Cm), which become incorporated into HAS-colloids. Discussion is extended to the migration behavior of radionuclides as colloid-borne species in natural aquifer systems, for which a field experiment is chosen as a case in point.