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

• Adsorption of radionuclides (Po, Pb and Be) onto nanoparticles in seawater were examined.
• Different organics/nanoparticles had distinct effects on the adsorption of Po, Pb and Be.
• Organic and inorganic carriers had synergistic effects on adsorption of Po, Pb and Be.
• Fractionation between Pb and Po or Be during their scavenging could be assessed.

Improved applications of 210Po, 210Pb and 7Be as geochemical proxies require more detailed understanding of their interactions with particles. Here, laboratory sorption experiments were carried out to examine the adsorption of 210Po, 210Pb and 7Be 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 (KcKc) of 210Po, 210Pb, and 7Be on nanoparticles increased 2.9-, 5.0- and 5.9-fold, respectively. The effect of MOCs could be explained for 210Po and 210Pb from their different log⁡Kclog⁡Kc values on inorganic nanoparticles. In addition, fractionation effects between 210Po and 210Pb (or between 210Pb and 7Be) could be quantified from their relative log⁡Kclog⁡Kc values on end-member sorbent components. Applications of both 210Po–210Pb and 7Be–210Pb pairs as particle dynamics tracers could be more quantitative when the nature of the organic coatings is taken into account.