HR: 1340h
AN: B33C-1430    [Abstracts]
TI: Role of Natural Organic Matter in Regulating the Partitioning of Th(IV) and Pa(IV, V) on Aquatic Colloids and Nanoparticles
AU: * Guo, L
EM: Laodong.Guo@usm.edu
AF: University of Southern Mississippi, Department of Marine Science, 1020 Balch Blvd., Stennis Space Center, MS 39529, United States
AU: Roberts, K A
EM: robertsk@tamug.edu
AF: Texas A&M University, 5007 Avenue U, Galveston, TX 77551, United States
AU: Santschi, P H
EM: santschi@tamug.edu
AF: Texas A&M University, 5007 Avenue U, Galveston, TX 77551, United States
AB: Nanoparticles and colloids are important intermediaries in the fate, transport and bioavailability of particle reactive trace metals and radionuclides in aquatic environments. However, the interaction between nanoparticles and natural organic matter (NOM) and how the quality and quantity of NOM affect the mobility and environmental behavior of trace elements remain poorly understood. Controlled laboratory experiments have been conducted to examine the role of NOM in governing the partitioning of Th(IV) and Pa(IV, V) between truly dissolved and different sized colloidal phases. Radiotracers, model NOM, including humic substances (HS) and exopolymeric acid polysaccharides (EPS), and ultrafiltration were used in the partitioning experiments of Th and Pa between the <1 kDa, 1-10 kDa, 10-100 kDa, 100 kDa-0.4μm and >0.4 μm fractions, thus allowing the calculation of distribution coefficients between particle (Kd) or colloid (Kc) and solution phases. Our results show that in both seawater and 0.7 M NaClO₄ solution, Th(IV) has a higher distribution coefficient (Kd) between dissolved and particulate phases (with a logKd of 7.03) compared to Pa(IV, V) with a logKd of 6.05. Within the <0.4 μm dissolved phase, Th(IV) and Pa(IV, V) were mostly partitioned in the >1 kDa colloidal phase resulting in a logKc value of 6.08 and 5.70, respectively, for Th(IV) and Pa(IV,V). On average, about 4% of Th(IV) was measured in the <1 kDa fraction, but this fraction was up to 42% for Pa(IV, V). In the presence of HS and EPS (0.6 and 0.9 mg C/L) , however, the fraction partitioned in the <1 kDa become virtually the same (2-3%) for both Th(IV) and Pa(IV, V). The logKc value for Th(IV) and Pa(IV, V) was 7.05 and 7.06, respectively, in the presence of HS, and was 6.81 and 7.02 in the presence of EPS. While the partitioning of Th(IV) remained similar regardless of treatments, the change in the partitioning of Pa(IV, V) between dissolved and nanoparticles or macromolecules in the >1 kDa fraction resulted likely from the reduction of Pa(V), a more soluble form, to Pa(IV), a more particle-reactive form, by NOM. This experimental result has important implications for biogeochemical and environmental cycling of Pa(V,IV), which is being used as a tracer for ocean mixing and scavenging, and other redox sensitive trace elements in aquatic environments.
DE: 4807 Chemical speciation and complexation
DE: 4809 Colloids
DE: 4850 Marine organic chemistry (0470, 1050)
DE: 4860 Radioactivity and radioisotopes
DE: 4875 Trace elements (0489)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting