title: Colloid-borne forms of tetravalent actinides: a brief review.
abstract: Tetravalent actinides, An(IV), are usually assumed to be little mobile in near-neutral environmental waters because of their low solubility. However, there are certain geochemical scenarios during which mobilization of An(IV) in a colloid-borne (waterborne) form cannot be ruled out. A compilation of colloid-borne forms of tetravalent actinides described so far for laboratory experiments together with several examples of An(IV) colloids observed in field experiments and real-world scenarios are given. They are intended to be a knowledge base and a tool for those who have to interpret actinide behavior under environmental conditions. Synthetic colloids containing structural An(IV) and synthetic colloids carrying adsorbed An(IV) are considered. Their behavior is compared with the behavior of An(IV) colloids observed after the intentional or unintentional release of actinides into the environment. A list of knowledge gaps as to the behavior of An(IV) colloids is provided and items which need further research are highlighted.
authors.affiliation: Institute of Resource Ecology, Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 51 01 19, D-01314 Dresden, Germany. Electronic address: h.zaenker@hzdr.de.
authors.forename: Harald
authors.initials: H
authors.lastname: Zänker
authors.affiliation: Institute of Resource Ecology, Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 51 01 19, D-01314 Dresden, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Hennig
mesh_terms: D008671:Actinoid Series Elements / Q000737:chemistry*; D000327:Adsorption; D003102:Colloids; D060587:Groundwater; D014872:Water Movements; D014875:Water Pollutants, Radioactive / Q000737:chemistry*
chemical_list: D008671:Actinoid Series Elements; D003102:Colloids; D014875:Water Pollutants, Radioactive
keywords: Colloids; Groundwater; Nanoparticles; Subsurface transport; Tetravalent actinides