Investigations on the time-series partitioning of 210Pb, 207Bi and 210Po between marine particles and solution under different salinity and pH conditions

The long-lived progeny of radon-222, lead-210 (Pb-210), polonium-210 (Po-210) and bismuth-210 (Bi-2(10)), serve as a tool in the study of marine biogeochemical processes. Here, we report our investigations on the partitioning of Pb-210, Po-210 and Bi-210 (Bi-207) between seawater and solids (twelve commonly-occurring mineral particles) under different values of pH, salinity and contact time. The K-d values of Pb-210 and Bi-207 for MnO2 varied widely between the synthetic and natural minerals, and thus the suitability of using synthetic material for their partitioning studies in marine system needs to be re-assessed. The K-d values of Pb-210 in clay minerals were found to be in the order: smectite > illite > kaolinite. The sorption efficiencies ( = the particulate activity divided by the sum of particulate and dissolved activity) of Pb-210, Bi-207 and Po-210 on illite were above 81% when the contact time was > 2 h. These radionuclides were more soluble when pH was <= 5, but show more particle-reactive nature for pH of 6 to 8. The fractionation factor between Po-210 and Pb-210 (F-Po/Pb) varied with salinity for different mineral components while the FB,/pb was less affected by mineral components, salinity and pH. The insitu experimental results showed that the F-B(i/Pb) increased with increase in Chl-a concentration. Considering the much shorter half-life of Bi-210 (5.0 d) and the high K-d values established in this study, we propose that Bi-210/Pb-210 activity ratio could potentially be used to estimate the particle export from phytoplankton bloom on time scale much shorter than Th-234 or Po-210.