Can isotopes be used as lead tracers in shooting-range soils?

Lead isotopes have been widely used to assess the sources of Pb in the soil environment since lead isotopes ratios have a specific signature that allows us to use them as environmental tracers. However, some lead sources are difficult to be identified. This article contains the lead isotope data from soils and shot pellets collected in an abandoned shooting range (NW Spain). Twelve soil and three-shot pellet samples were randomly collected and analyzed using MC-ICP-MS. The isotope ratios are shown, and analyses proved that Pb originated predominantly from the used shot pellets. Contaminated soils exhibited an isotopic composition (206Pb/207Pb, 208Pb/204Pb, 206Pb/204Pb and 208Pb/206Pb) close to some shot pellets from different manufacturers. These results offer new, valuable data for other researchers working on lead contamination research and the identification sources of Pb for adjacent areas to shooting-range facilities and for wildlife ecotoxicology. Still, the use of several ammunitions derived from different sources, such as recycled Pb, showed that it is hard to identify the lead source and these kinds of facilities.Ministerio de Economía y Competitividad | Ref. CGL2013-45494-RFundação para a Ciência e Tecnologia | Ref. UIDB/04423/2020Fundação para a Ciência e Tecnologia | Ref. UIDP/04423/2020Fundação para a Ciência e Tecnologia | Ref. CEECIND/03794/2017Ministerio de Ciencia e Innovación | Ref. IJC2020-044197-

Molybdenum-isotope signals and cerium anomalies in Palaeoproterozoic manganese ore survive high-grade metamorphism

Abstract Molybdenum (Mo) and its isotopes have been used to retrieve palaeoenvironmental information on the ocean–atmosphere system through geological time. Their application has so far been restricted to rocks least affected by severe metamorphism and deformation, which may erase or alter palaeoenvironmental signals. Environmental Mo-isotope signatures can be retrieved if the more manganese (Mn)-enriched rocks are isotopically depleted and the maximum range of δ98Mo values is close to the ~2.7‰ Mo-isotope fractionation known from Mo sorption onto Mn oxides at low temperature. Here, we show that the Morro da Mina Mn-ore deposit in Minas Gerais, Brazil, contains Mn-silicate–carbonate ore and associated graphitic schist that likely preserve δ98Mo of Palaeoproterozoic seawater, despite a metamorphic overprint of at least 600 °C. The extent of Mo-isotope fractionation between the Mn-silicate–carbonate ore and the graphitic schist is similar to modern Mn-oxide precipitates and seawater. Differences in δ98Mo signals are broadly reflected in cerium (Ce) anomalies, which suggest an oxic–anoxic-stratified Palaeoproterozoic ocean

Redox-driven geochemical partitioning of metal(loid)s in the iron-rich anoxic sediments of a recently flooded lignite mine pit: Lake Medard, NW Czechia

We evaluated the geochemical partitioning of Fe, Mn, As, V, and REE in sediments of a recently flooded open-cast lignite mine to interpret their response to recently established anoxia, and minor variations in the redox potential of its ferruginous bottom water column. Results from a sequential extraction scheme targeting reactive Fe mineral phases are combined with an assessment of sediment enrichment factors and REE systematics. Across the sediment pile metal(loid)s are being released from pre-existing authigenic phases as minor shifts in redox potential induce elemental immobilisation throughout co-precipitation with Fe into mineral phases of diverse reactivity. REE systematics confirms that minor oscillations in the water column's redox state can trigger swift changes in the speciation of the redox-sensitive elements. The observed metal(loid)s enrichment in the sediments can either be considered an ecological risk, if a management scenario involving solely recreational purposes is conceived; but it can also be seen as a feasible source of critical metals (e.g., REE and V) that are amenable to sustainable, secondary metal recovery endeavours. By anticipating the fate of redox-sensitive metal(loid)s in our study site, we provide parameters useful to delineate management programmes of this and similar post-mining lakes