Colloidal behavior of actinides in an oligotrophic lake

Abstract

Understanding the speciation of low levels of actinides from fallout and from local sources in freshwater systems is important if we are to predict their distributions in the environment. Since these materials make excellent tracers for determining sedimentation rates and other environmental parameters, it is important to determine their physical and chemical properties in relatively pristine systems. Reported here are the results of actinide analyses in an artificial, oligotrophic lake in northwest Wales, United Kingdom, which is used as a source of cooling water for a nuclear power plant. The concentrations of the actinide elements plutonium, americium, thorium, and curium, and their distributions among different colloidal sizes were determined. Actinide concentrations in the dissolved fraction (<0.45 /um) were as follows: 239-240Pu, 6.4-12.5 fCi/L;241 Am, 2.5-18.2 fCi/L; 232Th, 0.11-1.09 fCi/L; and 244Cm, 0.3-1.4 fCi/L. The majority of the actinides in the lake were retained by hollow-fiber ultrafilters of 5-nm (nominal 100000 MW) or 100-nm pore sizes; the actinides appeared to be bound reversibly to colloidal material of unknown composition. The two environmentally stable oxidation states of plutonium, IV and V, could be separated by ultrafiltration. These results indicate that submicron colloidal material can dominate the aqueous properties of actinides.

Plutonium isotopes as tracers for ocean processes: A review

“…Interaction with complexing agents and hydrolysis reactions are generally strongest for Pu(IV) and weakest for Pu(V), which leads to the preferential removal of reduced Pu species from solution by adsorption onto colloidal and suspended material (Nelson and Lovett, 1978;Orlandini et al, 1990;Mitchell et al, 1995). In contrast, oxidised Pu(V) has a high 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 13 affinity for adsorption onto carbonate particles, e.g.…”

Size fractionation and characterization of nanocolloidal particles in soils

“…Natural colloids are mixed complexes of silicates, inorganic oxides and humic substances (Doucet et al 2004(Doucet et al , 2005 with a broad particle size distribution and diversity of shapes (Baalousha et al 2006). Colloids in soil and water are involved in the adsorption, transport, and transformation of heavy metals, organic pollutants, and nutrients (Means and Wijayaratne 1982;McCarthy and Zachara 1989;Orlandini et al 1990; Ledin et al 1995;Lead et al 1997Lead et al , 1999Doucet et al 2001).…”

Molecular size distribution of Pu in the presence of humic substances in river and groundwaters

“…[2][3][4] Some parts of actinides and lanthanides in natural waters are associated with anionic organic materials, especially humic substances (humic and fulvic acids) in the different molecular size fractions. [5][6][7][8][9][10] The authors have reported the complexation properties of humic substances with actinides-lanthanides such as Eu, Am and Pu [11][12][13][14] . These molecular size effects of humic substances on the complexation affinity and the sorption ability may significantly affect the migration behavior of actinides.…”