Lead isotope ratios of Fitzroy Basin river sediment, preliminary values

Freshwater river sediments were sampled from eight sites within the Comet, Nogoa and Mackenzie Rivers, Fitzroy Basin, Central Queensland, an area broadly associated with grazing, cropping and coal mining. Following ICP-MS measurement of total recoverable metal content (in the <60 μm size fraction), stable Pb isotope ratios (Pb207/Pb206 = 0.838-0.886 and Pb208/Pb206 = 2.08-2.18) were opportunistically determined and may help to better understand natural and anthropogenic inputs within this river system. The intra-assay (n = 10) relative standard deviation of ratios determined from CRM-016, a freshwater sediment from a stream in the Western United States, were 1.4 % and 1.2 % for Pb207/Pb206 and Pb208/Pb206, respectively. Inter-assay (3 x n = 5) relative standard deviation for the same ratios were 0.78 % and 1.1 %, respectively. Various data visualisation techniques (e.g. two-ratio scatter plots) were used to investigate how the samples and CRM ratios compared with literature values including, the NIST SRM981 common Pb isotopic standard, sediment results from a coal mining area in India, and the Pb composition of various terrestrial materials compiled in a recent IUPAC Technical Report. Aspects of a review of Pb isotopes in environmental sciences and an estimate of Pb isotope composition of the Upper Continental Crust were among the various other literature considered when speculating on the potential sources of Pb in Fitzroy Basin sediments and when further evaluating the suitability of the sample preparation and analytical methods for retrospective stable Pb isotope analysis.