Some considerations in the reconstruction of lead levels using laser ablation: lessons from the design stage of dendrochemistry study, St.John's, Canada

Abstract

Study of soils in St. John's, Canada showed elevated Pb levels representing a potential exposure 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.

Chinook salmon exhibit long-term rearing and early marine growth in the Fraser River, British Columbia, a large urban estuary

“…One challenge with LA-ICPMS line scans is the lack of a standardized method for aligning the microchemistry results with post-ablation visual landmarks -such as otolith daily growth rings (Danek et al 2015). To address this, we used inflections in the calcium signatures to identify the otolith edges on the microchemistry scan and calculated the actual scan rate as the otolith scan time (using these edges) divided by the measured width of the otolith along the laser transect (Andrew Claiborne, Washington Department of Fisheries, Washington, personal communication, 2018).…”

Monitoring air pollution close to a cement plant and in a multi-source industrial area through tree-ring analysis

“…In April 2018 tree cores were cut using a microtome (Gärtner and Nievergelt 2010) for dendrochemical analysis. In details, tree cores were not sanded, as usually done in dendrochronology, to avoid the contamination effect due to wood dust (Danek et al 2015). The tree-ring width was measured using the LINTAB instrument (Rinntech, Heidelberg, Germany) and a Leica MS5 stereoscope (Leica Microsystems, Germany).…”

“…The analysis of chemical elements was performed on annual tree rings from 1990 to 2016 using the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) (Danek et al 2015;Perone et al 2018). Only one of the two cores collected from each tree was used in this analysis.…”

“…Wood samples were ablated orthogonally to the tree rings. Tree rings were ablated in the latewood where the presence of narrow-lumen and thick-walled cells defines conditions for a better combustion during the ablation (Danek et al 2015). A summary of the main standard operating conditions and parameters used in the laser ablation analysis is reported in Table 1 66 Zn, were measured.…”

Determination of Metal Concentration in Road-Side Trees from an Industrial Area Using Laser Ablation Inductively Coupled Plasma Mass Spectrometry

“…The actual wood sample was considered for data collection when the target value ( 208 Pb: 50,000 cps) was reached. Laser ablation was performed in line scan mode [23]. The ICP-MS set-up and other parameters are provided in Table 2.…”