Adsorption characteristics of Pb-210, Po-210 and Be-7 onto micro-particle surfaces and the effects of macromolecular organic compounds
Po-210, Pb-210 and Be isotopes (e. g. Be-7 and Be-10) have long been used as proxies of particle/sediment dynamics, carbon cycling, and oceanographic investigations of coupled processes. However, adsorption characteristics and interactions between these nuclides and particle surfaces remain poorly understood. Laboratory studies have been conducted to examine the adsorption of Po-210, Pb-210 and Be-7 onto micro-particles, including marine suspended particulate matter, kaolinite, Al2O3, SiO2, CaCO3, Fe2O3, MnO2, and chitin in natural seawater (<1 kDa), and the role of macromolecular organic compounds (MOCs), including humic acids (HA), acid polysaccharides (APS) and proteins (BSA) in regulating the adsorption process. In the absence of MOCs, the partition coefficients (K-d, reported in log K-d) range from 3.02 to 5.19 for Po-210, from 3.22 to 6.29 for Pb-210, and from 3.57 to 4.65 for Be-7. Ferric and manganese oxides are the strongest sorbents of Po-210 and Pb-210, comparing with SiO2 and CaCO3. In the presence of the protein BSA, both SiO2 and CaCO3 preferentially adsorb Po-210 over Pb-210, whereas the opposite effect was observed in the presence of acid polysaccharides, indicating that proteins could enhance the adsorption of Po-210 and acid polysaccharides enhance the adsorption of Pb-210. The logK(d) values of both Po-210 and Pb-210 in the presence of MOCs become similar (logKd at similar to 4.0) for all lithogenic and biogenic particles, suggesting that their adsorption is likely controlled by specific natural organic compounds associated with particle surfaces. For Be-7, the highest and lowest logKd value was measured, in general, on SiO2 and CaCO3, respectively, consistent with field observations. Nevertheless, the logKd values of Be-7 varied little between particle types regardless of the presence or absence of MOCs, suggesting that the adsorption of Be on particle surfaces is less affected by particle composition or MOCs. These results indicate that Be-7 and Be-10 could quantitatively track the bulk particles and their fluxes in marine environments while both Po-210 and Pb-210 could be quantitative proxies for the bulk organic carbon, although Po-210 and Pb-210 could be fractionated by specific organic compounds during their sorption or scavenging on particle surfaces. (C) 2013 Elsevier Ltd. All rights reserved.
GEOCHIMICA ET COSMOCHIMICA ACTA
(2013). Adsorption characteristics of Pb-210, Po-210 and Be-7 onto micro-particle surfaces and the effects of macromolecular organic compounds. GEOCHIMICA ET COSMOCHIMICA ACTA, 107, 47-64.
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