Development of a method for determination of lead isotope ratios in marine suspended particles

The relative abundance of stable lead isotope in the global environment is not constant. It depends on the age of mineral formation and the geochemical properties of parent nuclides. Because of this characteristic, stable lead isotope ratios have been used as a useful tracer in the geochemical study. Lead is supplied to the ocean by human activities in addition to natural cycles, and the isotope ratios are important for understanding the circulation of lead. Since lead exists in seawater as dissolved and particulate forms, studying these isotope compositions is useful in elucidating inter-conversion process between the two phases. The particulate lead concentration is much lower than the dissolved one, requiring preconcentration of Pb from large volumes of seawater for precise isotopic analysis. In addition, marine particulate matter may contain heavy elements (W, Hg, Tl) and major crustal components that potentially interfere with lead isotope analysis. These components need to be removed prior to the analysis. Further, clean protocols are necessary for this contamination prone trace metal. In this study, we have investigated cleaning of filters for minimizing the filter blank value, separation of lead and interfering elements by anion exchange resin column (Reuer et al., 2003), and leaching process of Pb from particles using seawater samples in order to establishing a method for measuring particulate lead isotope ratios.