Andrea Bazzano

Lead isotopic analysis of Antarctic snow using multi-collector ICP-mass spectrometry

Reliable determination of Pb isotope ratios in Antarctic snow is challenging because of the low analyte concentration and the low volume of sample typically available. In this work, a combination of a total sample consumption introduction system (the torch-integrated sample introduction system, TISIS) with multi-collector ICP-mass spectrometry (MC-ICP-MS) was used for this purpose. With this instrumental setup, accurate and precise determination of Pb isotope ratios was possible at concentrations as low as 0.5 ng mL−1, while using 0.2 mL of solution only (total amount of Pb: 100 pg). At 10 ng mL−1, the repeatability for the 207Pb/206Pb ratio was 0.16‰ RSD. The concentration range was further extended downwards by using 100-fold analyte element preconcentration via freeze-drying of 20 g of snow. The Pb concentration in procedural blanks was 0.5 ± 0.3 pg g−1, enabling the determination of Pb isotope ratios in snow samples containing down to 5 pg g−1 of Pb. After development and validation, the procedure was applied to snow samples collected at Dome C (East Antarctic Plateau) on a monthly basis during the 2006 and 2010 campaigns. The method developed was able to reveal a seasonal variation in the Pb isotope ratios occurring during 2006 and strong inter-annual variation between the two campaigns.

An integrated study of the chemical composition of Antarctic aerosol to investigate natural and anthropogenic sources

Environmental context Owing to its remoteness, Antarctica is an excellent natural laboratory for conducting studies on the behavior of marine aerosols and for monitoring the impact of global human activities. The aim of this study is to provide an extensive chemical characterization of Antarctic aerosol and to investigate its sources. A distinction among anthropogenic, crustal, and biogenic sources was defined using several chemical markers. Abstract During the 2010–11 austral summer, an aerosol sampling campaign was carried out at a coastal Antarctic site (Terra Nova Bay, Victoria Land). In this work, previously published data about water-soluble organic compounds and major and trace elements were merged with novel measurements of major ions, carboxylic acids and persistent organic pollutants (polychlorobiphenyls, polycyclic aromatic hydrocarbons, polychlorinated naphthalenes, polybrominated diphenylethers and organochlorine pesticides) in order to provide a chemical characterisation of Antarctic aerosol and to investigate its sources. The persistent organic pollutants were determined using a high-volume sampler, able to collect both particulate and gaseous fractions, whereas remaining compounds were determined by performing an aerosol size fractionation with a PM10 cascade impactor. Ionic species represented 58% (350ng m–3) of the sum of concentrations of all detected compounds (596ng m–3) in our Antarctic PM10 aerosol samples due to natural emission. Trace concentrations of persistent organic pollutants highlighted that the occurrence of these species can be due to long-range atmospheric transport or due to the research base. Factor analysis was applied to the dataset obtained from the samples collected with the PM10 sampler in order to make a distinction between anthropogenic, crustal and biogenic sources using specific chemical markers.

Source identification of atmospheric particle-bound metals at Terra Nova Bay, Antarctica

Environmental context The atmosphere above Antarctica, the cleanest part of the Earth’s troposphere, serves as a valuable laboratory for studying natural atmospheric processes and for monitoring the impact of human activities on the global environment. Central to these studies is an understanding of long-range transport of pollutants to Antarctica, and distinguishing the relative contribution of natural and anthropogenic sources. We use chemical tracers and isotopic analysis to assess the origin of metals associated with atmospheric particulates in Antarctica. Abstract During the 2010–2011 austral summer, size-segregated aerosol samples were collected at a coastal Antarctic site (Terra Nova Bay, Victoria Land) and analysed for major and trace elements and lead isotopic composition, in order to provide a better understanding of the sources of metals and their transportation pathways towards Antarctica. Aerosol size fractionation was performed by a cascade impactor, able to collect aerosol particles of aerodynamic diameter 10–7.2, 7.2–3.0, 3.0–1.5, 1.5–0.95 and 0.95–0.49µm. It was found that Al, Co, Fe, Li, Mn, Rb, Y and V were mainly related to crustal inputs, whereas the marine contribution was significant for Li, Mg, Na and Rb. An additional anthropogenic source influencing the concentration of Cr, Cu, Mo and Pb was clearly demonstrated. The concentration of the elements associated to the crustal and marine inputs showed high values in the coarse mode (7.2–3.0µm), whereas the anthropogenic elements were also characterised by a high concentration in the finer (1.5–0.95µm) particles. The study of the temporal trends of the measured chemical markers along with the meteorological variables revealed that both the crustal and anthropogenic elements were related to the air masses carried by the katabatic wind from the inland, whereas the marine input appeared to be higher in January when the sea-ice extent was reduced. Finally, lead isotope ratios pointed out that the anthropogenic input was likely related to the polluted aerosols from South America and Australia, representing the predominant fraction (50–70%) of the lead measured in the samples.

Trace elements in surface sediments from Kongsfjorden, Svalbard: occurrence, sources and bioavailability

ABSTRACT Concentration levels, potential sources and bioavailability of trace elements in marine sediments from Kongsfjorden (Svalbard Islands, Norwegian Arctic) were assessed and discussed. Surface sediments were collected by a Ponar grab and characterised in terms of mineralogical composition, grain-size distribution, total organic carbon and nitrogen percentage contents, and major and trace elements concentrations. Anthropogenic and natural sources of trace elements were inferred from lead isotope ratios, while the potential metal bioavailability was evaluated by size-fractionation and solid-phase speciation studies and by the analysis of acid-volatile sulphides (AVS) and simultaneously extracted metals (SEM). Concentrations of metals, their enrichment factors and solid speciation patterns collectively indicated that the anthropogenic impact of trace elements in the fjord is generally low, with a minor enrichment with respect to crustal values (by a factor of 2–11) for As, Cr, Ni and V. The lead isotope ratios (208Pb/207Pb: 2.474–2.498 and 206Pb/207Pb: 1.206–1.212) were close to the natural signature except in the outer fjord, due to the influence of the Atlantic marine circulation. Many elements of toxicological concern (e.g. Pb, V, Zn) were enriched in the finest sediment fraction, which was by far the preponderant one, especially in the inner fjord. However, less than 15% of most trace elements (exceptions Cd and Mn) in the finest fraction was actually associated with easily leachable sediment phases. Finally, the high SEM/AVS ratios determined on samples from sites close to the glacier fronts (11–15), due to low AVS content, highlighted that the sediment in that zone cannot remove additional inputs of heavy metals by sulphide precipitation.

Determination of the isotopic composition of sub-ng amounts of Sr in Antarctic snow by multi-collector ICP-mass spectrometry

Determination of the 87Sr/86Sr isotope ratio in Antarctic snow can provide useful information on the sources of the atmospheric particulates in present and ancient times. However, precise and accurate determination of the 87Sr/86Sr ratio is challenging because of the low analyte concentration and the limited amount of sample typically available. In this work, Sr was first pre-concentrated 30-fold via evaporation, after which Sr was chromatographically isolated from the matrix (and thus separated from Rb, avoiding isobaric overlap of 87Sr and 87Rb). Subsequently, the sensitivity of the multi-collector ICP-mass spectrometer was maximized by using an Aridus II membrane desolvating system, a high-transmission interface and 1012 Ω amplifiers instead of the standard 1011 Ω ones. With this instrumental setup, the repeatability for 87Sr/86Sr ratio measurements was 0.3 and 0.5‰ RSD at 0.8 ng mL−1 (or for 320 pg in the 0.4 mL of sample solution consumed) and at 0.4 ng mL−1 (or for 160 pg) of Sr, respectively. The procedural blank was 2.5 ± 0.5 pg and did not significantly affect the 87Sr/86Sr ratio measured using 160 pg of analyte (at 0.4 ng mL−1). The accuracy of the procedure was evaluated via replicate analysis of NIST SRM 987 SrCO3 isotopic reference material. The experimental data agreed with the accepted value within the experimental uncertainty both at 0.8 ng mL−1 (for 320 pg) and at 0.4 ng mL−1 (for 160 pg) of Sr. The method was applied to the analysis of Antarctic snow samples (30 g) containing 0.5–2.1 ng of Sr. The precision was fit for the purpose of discriminating between potential source areas (PSAs). The entire procedure required ∼30 g of snow per sample, potentially enabling the contributions of PSAs to be unravelled with high temporal resolution.

Lead isotopic analysis of Antarctic snow by quadrupole ICP-MS using a total-consumption sample introduction system

Measurement of lead isotope ratios in snow samples using inductively coupled plasma-dynamic reaction cell-mass spectrometry (ICP-DRC-MS) at a low sample consumption rate was thoroughly studied. Sample volumes were reduced from 20.0 to 0.200 mL by freeze-drying, and the pre-concentrates were efficiently introduced into the plasma source at 20 μL min−1 by using the heated torch-integrated sample introduction system (hTISIS). In addition, the DRC was pressurised with neon to improve the precision by collisional damping. Sensitivity was maximised by optimising the operating parameters of the sample introduction system (nebulizer/sheathing gas flow rate ratio), the reaction cell (rod offset and damping gas flow rate) and the signal measurement conditions. The developed method was then characterised in terms of the analytical working range, accuracy and uncertainty estimation. Under the optimal conditions, isotope ratios did not differ in the 0.1–20 μg L−1 range. Internal precision, expressed as relative standard deviation, varied from 0.12 to 0.18% (c = 10 μg L−1; n = 12), while the external precision was <0.1%. The potential influence of the pre-concentration procedure on the analytical data was carefully investigated in terms of blank contribution, recovery and isotopic fractionation. The lowest Pb concentration needed in the samples to limit the influence of the blanks within an experimental precision of 0.5% was 4.4 pg g−1, and the recovery of five standard reference solutions with a Pb concentration of 100 ng L−1 was 90 ± 5%, with no significant isotopic fractionation. The developed ICP-DRC-MS method was finally applied to a number of representative Antarctic snow samples previously characterised by multi-collector ICP-MS, obtaining a satisfactory agreement between the data provided by the two techniques and analytical results consistent with literature data on the glaciochemistry of Antarctic ice cores.