Polar snow

Over the next 30 years, Patterson used mass spectroscopy and clean laboratory techniques to demonstrate the pervasiveness of lead pollution. He traced the relationships between America s gas pump and its tuna sandwiches, between Roman slaves and silver dimes, and between Native American Indians and polar snows. He forged as close a connection between science and public policy as any physical scientist outside of medical research. He made the study of global pollution a quantitative science. And marrying his stubborn determination to his passionate conviction that science ought to serve society, Patterson never budged an inch. 

Clair C. Patterson, T. J. Chow, and M. Murozumi. The Possibility of Measuring Variations in the Intensity of Worldwide Lead Smelting during Medieval and Ancient Times Using Lead Aerosol Deposits in Polar Snow Strata. In Scientific Methods in Medieval Archaeology. Rainer Berger, ed. Berkeley University of California Press, 1970, pp. 339-350. 

The application of glaciochemical horizons to ice core dating is a recent and rapidly evolving development. A concerted search is under way to determine the impact of known events on the chemical composition of polar snow. So far, two types of universally applicable horizons have been detected in polar ice cores volcanic eruptions and Late Wisconsin dust. 

In summary, a number of chemical constituents in polar snow and ice have seasonal concentration variations that make them suitable for dating ice cores by counting annual layers. In... 

M. A. Bolshov, C. F. Boutron, Determination of heavy metals in polar snow and ice by laser-excited atomic fluorescence spectrometry, Analusis Magazine, 22 (1994), M44-M46. 

Trace element determination in polar snow and ice. An overview of the analytical process and application in environmental and paleoclimatic studies... 

This chapter will present an overview of the main aspects of the investigation of heavy metals in polar snow and ice, especially as regards sample collection and preparation and laboratory analysis. Some examples of the results obtained will also be given. 

As mentioned at the beginning of this chapter, most of the chemical compounds in polar snow and ice are present at extremely low concentrations (below the pg/g level). It took many years to realize that it was necessary to develop new analytical methodologies to study these very peculiar samples. Surface or shallow sampling can usually be well controlled, as we have seen in the previous sections, provided... 

Other chemicals used throughout the analysis of heavy metals in polar snow and ice by different analytical techniques have to fulfil strict specifications for ultraclean procedures as described in specific papers (6, 39-45). 

The ideal analytical technique to be used in the challenging task of reconstructing past changes and recent variations in the concentration of trace substances in polar snow and ice should present several important features. Of these, extremely low detection limits, multi-element capability, low sample consumption and the possibility to avoid, as far as possible, any preconcentration step which could be a source of contamination are the most appreciated. Nevertheless, there is currently no technique with all the special features listed above several instrumental methods have been used in the past for trace element determination in polar snow and ice (see Table 3.4). 

Table 3.4. Analytical techniques used for the determination of trace elements in polar snow and ice...

Atomic Fluorescence Spectrometry (AFS) (5, 58), quadrupole and double-focusing magnetic sector ICP-MS (59-63) have all been used in the past for the determination of trace element in polar snow and ice. Of those techniques only LEAFS, double-focusing magnetic sector ICP-MS and DPASV have proved capable of direct determination on the analytes in the samples at the required levels. 

However, it must be kept clear in mind that direct instrumental detection methods for trace substances are physically relative methods which require calibration, during which systematic errors, caused for instance by spectral and nonspectral interferences, may occur. Relative methods are in fact matrix-dependent and would require the analysis of Certified Reference Materials (CRMs) in order to guarantee the good quality of the analytical data. Unfortunately, CRMs are not available for polar snow and ice and hence the only way to assure the quality of the data is, whenever possible, to make careful intercomparisons of the techniques able to measure the same analytes with different approaches. 

TIMS has been used in the past few decades for the analysis of heavy metals in polar snow and ice of Antarctica and Greenland (11, 49-53, 66, 67). It is in fact an absolute technique, whose results can give not only the total concentration of the metal with unrivalled accuracy and precision, but also quantify the isotopic composition of the analyte. This last feature constitutes a precious tool for probing the sources of emission of heavy metals (e.g., Pb) to the global atmosphere throughout the centuries. 

Elements other than Pb have been measured by TIMS in polar snow (43, 49, 50, 53), showing the high potential of the technique. Bismuth determination (43) is characterized an accuracy comparable to that of LEAFS and takes advantage of the simultaneous ionisation of Bi and Pb during the Pb isotopic abundance measurements. Determination of Ba was also carried out on some Antarctic samples (53) showing its possible use as a reference element in monitoring the contribution of terrestrial dust level. 

A considerable advance in trace element determination in polar snow and ice was made during the 1980s by the use of ETA-AAS. The limitation of this technique... 

Although the detection power of ETA-AAS could also be improved by about one order of magnitude through electronic signal addition processing, there are a series of different possibilities based on on-line and off-line chemical and physical preconcentration methods which can greatly improve the detection power of the entire methodology in the analysis of polar snow and ice (39, 44, 45, 65). 

The ultra-sensitive technique of LEAFS was developed and exploited for the analysis of snow and ice to be carried out at the Institute of Spectroscopy of the Russian Academy of Science (ISAN) (46). This technique allows the direct determination of toxic metals in polar snow and ice to be carried out at and below the pg/g level in sample volumes of less than 100 pi. This is an important issue considering that very often the volume of sample obtained after the decontamination procedures amounts to just a few tens of milliliters in the best case and that this must be subdivided into different aliquots for a complete chemical characterisation. 

Over the past decade Inductively Coupled Plasma (ICP) sources, in particular coupled with Mass Spectrometry (MS) instruments, have shown an immense potential for multielement analysis in environmental samples (88). These capabilities have been obtained thanks to the combination of the great ionization energy of a plasma source with the high sensitivity and selectivity of the mass spectrometric detector. Since polar snow and ice are considered as the purest material on the earth surface, these environmental matrices constitute the ideal samples for ICP-MS since potential interferences formed in the plasma are kept at a minimum level. 

Coupled techniques for the analysis of polar snow and ice were used a few years ago in order to achieve good evidence of the influence of human activities and in particular of the use of gasoline additives, in the Pb pollution of the Arctic region... 

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