Application of field-portable-XRF for the determination of trace elements in deciduous leaves from a mine-impacted region

摘要

Deciduous leaves (n = 87) from beech (Fagus sylvatica), birch (Betulaspp.) and oak (Quercusspp.) trees have been collected from three metal mine-impacted sites in southwest England and tested for concentrations of trace elements (As, Cu, Pb and Zn) using a field-portable-x-ray fluorescence (FP-XRF) spectrometer configured in a low density mode and housed in a stand. When intact leaves were analysed directly, mean detection limits ranged from about 10 (As) to 70 μg g−1(Cu) on a fresh weight basis; after freeze-drying, respective limits increased to about 20 and 120 μg g−1on a dry weight basis. Within these constraints, As and Zn were detected in samples from all genera, with concentration differences between fresh and dry states attributed to the mass of water present and its propensity to attenuate x-rays. A comparison with As and Zn concentrations in local soils and determined by XRF in a higher density mode revealed different accumulation and exclusion characteristics among the three genera of tree. In contrast, and despite soil concentrations that were similar to those of Zn, Cu was detected in only two dried leaves and Pb evaded detection throughout. Pooled results from the study showed good agreement with independent results derived from ICP following acid digestion, with a slope defining the overall relationship that was close to unit value. Accordingly, the XRF approach is able to provide a rapid assessment of the levels of certain trace elements in leaves from contaminated sites, with the configuration deployed on site having potential to deliver immediate results.