Study of soils in St. John’s, Canada showed elevated Pb levels representing a potential ex-posure risk for young children. Old trees growing in the city present a potential annually-resolved record of Pb levels over past centuries that provides important temporal and spatial dimensions to Pb exposure risk assessment. This paper reports the results of our analytical tests to develop a fast, reliable and cost-efficient method using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for measuring Pb concentration in annual tree rings from available tree species. Our tests focused on approaches to sample preparation as they affect the laser ablation process, the relative merits of the ablation sampling method, and the response of our available tree species, which have contrasting wood structures, to laser ablation. The range of annual Pb concentrations (ppm) measured for each of the study species were as follows: spruce (0.18–6.42); elm (0.12–7.91); and horse chestnut (0.40–14.09). Our results demonstrate that the cutting procedure for preparing tree cores produced the most consistent Pb concentrations of the three methods, although they each displayed problematic anomalies. The selection of the best laser ablation technique appears to be highly dependent on study species and goals. In general, spot analysis permits detailed and targeted studies of tree-ring structures, but requires careful sampling attention for species with complex wood anatomy. The line scan method is ideal for reconstructing annually resolved element concentrations from trees and to some degree mitigates the complicating issue of intra-ring variability. Horse chestnut was determined to be the best of the available tree species because it exhibited a good response to laser ablation and produced the lowest intra-ring variations in Pb concentration.
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The study presents the results of investigations aimed at construction of a site chronology for oak wood from the surroundings of Żary (SW Poland). The 366-year chronology ZY_2006, covering the period 948-1314 AD was determined on the basis of 189 individual ring patterns representing samples of archaeological wooden objects lifted at the excavation works led in the Old Town of Żary in the years 2004-2005. The chronology produced exhibits high similarity to the standards for the neighbouring regions: Wielkopolska and Lower Silesia. The statistical parameters of the chronology are very high and, thanks to the signature years determined, it should be an excellent tool for dating samples of mediaeval timbers from the whole region of Ziemia Lubuska, including some with relatively short dendrochronological sequences.
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