Importance of acid polysaccharides for 234Th complexation to marine organic matter

In order to study the role of polysaccharides (PS) in the colloidal organic matter (COM) pool for complexing 234 Th, controlled laboratory experiments were carried out to determine the chemical nature of the strong Th(IV) binding to macromolecular organic ligands (.1 kDa). The partition coefficient of 234 Th between marine COM and solution, Kc, is higher than that for any known marine mineral sorbent. PS-enriched fractions of COM had the highest partition coefficient (Kc) of any sorbent for 234 Th. Kc of 234 Th and other metals, including Fe, Mn, Zn, Pb, and Pu, were up to an order of magnitude higher than that for bulk COM. Most importantly, log Kc values correlated linearly with the fraction of PS-enriched carbon ( f PS) of marine COM, as Kc 5 Kc(0) 3 The log Kc value 2.2 f PS 10 . of ;7.9 of the pure PS end-member fraction was very similar to the highest values obtained for model acid PS (log Kc ; 8). A value for the conditional stability constant for Th binding to the pure PS end member of 10 7.8 could be determined from a concentration of strong acid binding sites (with a pKa #3) of 1.3 mmol g 21 COM. Through the novel use of gradient gel electrophoresis (including two-dimensional polyacrylamide gel electrophoresis), the strong Th(IV) binding ligand was shown to be ;13 kDa in size and to have strong acidic functional groups. We propose that the observed variability of OC : 234 Th ratios in suspended, and sinking matter in the ocean might be caused by the variability of PS content.

[1]  M. P. Crosby,et al.  A convenient procedure for radiolabeling detritus with [14C]dimethylsulfate , 1983 .

[2]  O. Trubetskoj,et al.  Isolation, purification and some physico-chemical properties of soil humic substances fractions obtained by polyacrylamide gel electrophoresis , 1992 .

[3]  G. Wasserburg,et al.  Precise Timing of the Last Interglacial Period from Mass Spectrometric Determination of Thorium-230 in Corals , 1987, Science.

[4]  P. Santschi,et al.  A Brownian-pumping model for oceanic trace metal scavenging : Evidence from Th isotopes , 1989 .

[5]  R. Benner,et al.  Chemical composition of dissolved organic nitrogen in the ocean , 1997, Nature.

[6]  M. Baskaran,et al.  Boundary exchange and scavenging of radionuclides in continental margin waters of the Middle Atlantic Bight: implications for organic carbon fluxes , 1999 .

[7]  K. Buesseler.  The decoupling of production and particulate export in the surface ocean , 1998 .

[8]  C. Hung,et al.  Distributions of carbohydrates, including uronic acids, in estuarine waters of Galveston Bay , 2001 .

[9]  D. S. Smith,et al.  Characterizing Heterogeneous Bacterial Surface Functional Groups Using Discrete Affinity Spectra for Proton Binding , 1999 .

[10]  E. Morris,et al.  Biological interactions between polysaccharides and divalent cations: The egg‐box model , 1973 .

[11]  Robert F. Chen,et al.  A major biopolymeric component to dissolved organic carbon in surface sea water , 1997, Nature.

[12]  P. Santschi,et al.  A critical evaluation of the cross-flow ultrafiltration technique for sampling colloidal organic carbon in seawater , 1996 .

[13]  W. Burnett,et al.  Polonium in Florida groundwater and its possible relationship to the sulfur cycle and bacteria , 1989 .

[14]  E. Tanoue,et al.  Strong ligands for thorium complexation in marine bacteria. , 2001, Marine environmental research.

[15]  C. H. Coleman,et al.  The distribution of colloidal and dissolved organic carbon in the Gulf of Mexico , 1994 .

[16]  W. Burnett,et al.  Bacterial mobilization of polonium , 1996 .

[17]  A. Engel.  The role of transparent exopolymer particles (TEP) in the increase in apparent particle stickiness (α) during the decline of a diatom bloom , 2000 .

[18]  K. Buesseler,et al.  Carbon and nitrogen export during the JGOFS North Atlantic Bloom experiment estimated from 234Th: 238U disequilibria , 1992 .

[19]  G. G. Leppard.  Colloidal organic fibrils of acid polysaccharides in surface waters : electron-optical characteristics, activities and chemical estimates of abundance , 1997 .

[20]  D. Kushner,et al.  Strategies of response to copper, cadmium, and lead by a blue-green and a green alga. , 1980, Canadian journal of microbiology.

[21]  R. Philippis,et al.  Exocellular polysaccharides from cyanobacteria and their possible applications , 1998 .

[22]  G. G. Leppard,et al.  Ethanol Fraction of Lacustrine Colloidal Fibrils , 1984 .

[23]  P. Santschi,et al.  Thorium sorption in the marine environment: Equilibrium partitioning at the hematite/water interface, sorption/desorption kinetics and particle tracing , 1995 .

[24]  Alice L. Alldredge,et al.  Aggregation of a diatom bloom in a mesocosm: The role of transparent exopolymer particles (TEP) , 1995 .

[25]  S. Arad,et al.  Chelating Properties of Extracellular Polysaccharides from Chlorella spp , 1987, Applied and environmental microbiology.

[26]  J. Marinsky.  Ion binding in charged polymers , 1976 .

[27]  J. Newton,et al.  Export flux of particulate organic carbon from the central equatorial Pacific determined using a combined drifting trap-234Th approach , 1996 .

[28]  J. Cochran,et al.  Export flux of carbon at the equator during the EqPac time-series cruises estimated from 234Th measurements , 1996 .

[29]  C. Duarte,et al.  Strong seasonality in phytoplankton cell lysis in the NW Mediterranean littoral , 2000 .

[30]  P. Santschi,et al.  Interactions of thorium isotopes with colloidal organic matter in oceanic environments , 1997 .

[31]  J. Southon,et al.  Isotopic evidence for the contemporary origin of high-molecular weight organic matter in oceanic environments , 1995 .

[32]  M. Bender,et al.  Tracers in the Sea , 1984 .

[33]  Bruce E. Logan,et al.  The abundance and significance of a class of large, transparent organic particles in the ocean , 1993 .

[34]  C. Hung,et al.  Spectrophotometric determination of total uronic acids in seawater using cation-exchange separation and pre-concentration by lyophilization , 2001 .

[35]  G. Benoit,et al.  Scavenging of thorium isotopes by colloids in seawater of the Gulf of Mexico , 1992 .

[36]  K. Hunter,et al.  Equilibrium adsorption of thorium by metal oxides in marine electrolytes , 1988 .

[37]  M. Rinaudo,et al.  On the physicochemical properties of gellan gum , 1990, Biopolymers.

[38]  M. Baskaran,et al.  Plant pigments as biomarkers of high‐molecular‐weight dissolved organic carbon , 1995 .

[39]  S. B. Moran,et al.  Size-fractionated 234 Th in continental shelf waters off New England: Implications for the role of colloids in oceanic trace metal scavenging , 1993 .

[40]  A. Boraie,et al.  Colloidal organic carbon and colloidal 234Th dynamics during a coastal phytoplankton bloom , 1995 .

[41]  E. Balnois,et al.  Fibrillar polysaccharides in marine macromolecular organic matter as imaged by atomic force microscopy and transmission electron microscopy , 1998 .

[42]  P. Santschi,et al.  Sorption irreversibility and coagulation behavior of 234Th with marine organic matter , 2001 .

[43]  H. Dam,et al.  The role of surface-active carbohydrates in the flocculation of a diatom bloom in a mesocosm , 1995 .

[44]  P. Hatcher,et al.  Bulk Chemical Characteristics of Dissolved Organic Matter in the Ocean , 1992, Science.

[45]  Erik Östhols.  Thorium sorption on amorphous silica , 1995 .