Influence of organic matter on the adsorption of 210Pb, 210Po, 7Be and their fractionation on nanoparticles in seawater

Improved applications of Po-210, Pb-210 and Be-7 as geochemical proxies require more detailed understanding of their interactions with particles. Here, laboratory sorption experiments were carried out to examine the adsorption of Po-210, Pb-210 and Be-7 and their fractionation on inorganic nanoparticles, including SiO2, CaCO3, Al2O3, TiO2 and Fe2O3, in the presence or absence of macromolecular organic compounds (MOCs) that include humic acids (HA), acid polysaccharides (APS) and proteins (BSA), in natural seawater. Results showed that nanoparticle sorption was not greatly enhanced over that of microparticles as would be expected from their much higher specific surface areas, likely indicating their aggregation in seawater. It was found that synergistic interactions between inorganic nanoparticles, MOCs, and radionuclides determined the sorption, although their adsorption was particle composition-dependent. MOCs enhanced the sorption of selected nuclides on most nanoparticles. On average, in the presence of MOCs, partition coefficients (K-c) of Po-210, Pb-210 and Be-7 on nanoparticles increased 2.9-, 5.0- and 5.9-fold, respectively. The effect of MOCs could be explained for Po-210 and Pb-210 from their different log K-c values on inorganic nanoparticles. In addition, fractionation effects between Po-210 and Pb-210 (or between Pb-210 and Be-7) could be quantified from their relative log K-c values on end-member sorbent components. Applications of both Po-210-Pb-210 and Be-7-Pb-210 pairs as particle dynamics tracers could be more quantitative when the nature of the organic coatings is taken into account. (C) 2015 Elsevier B.V. All rights reserved.