Rapid determination of Pb-210 and Po-210 in water and application to marine samples

Abstract

Measurement of radionuclides in marine samples, specifically radioactive pairs disequilibrium, has gained interest lately due to their ability to trace cutting edge biogeochemical processes. In this context, we developed a fast, direct method for determining 210Pb and 210Po water through the use of ultra low-level liquid scintillation counting and alpha-particle spectrometry respectively and through Eichrom Sr resins for the Po-Pb separation. For 210Pb analysis, the method uses stable lead as a yield tracer measured by a robust ICP-MS technique, and 210Po is determined through self-deposition using the conventional 209Po yield tracer. The improvements of the method over other techniques are: a) the analysis can be completed within 6 days, simplifying other methods, b) very low limits of detection have been achieved −0.12 and 0.005 mBq L−1 for 210Pb and 210Po, respectively – and c) most of the method could be carried out in on-board analysis. We applied the method to different aqueous samples and specifically to marine samples. We determined 210Pb and 210Po in the dissolved fraction of Mediterranean Sea water and an estuary at the South-West of Spain. We found that it can be successfully employed to marine samples but we recommend to i) use a minimum of 20 L water to measure the 210Pb in the dissolved phase by LSC and lower volumes to measure total concentrations; ii) wait for 210Pb and 210Bi in secular equilibrium and measure the total spectrum to minimise the limit of detection and improve accuracy.