Can Cone Scales and Bark of Aleppo Pine Be Used in the Biomonitoring of Some Heavy Metals?

Abstract

The highest levels of Pb in soils and needles were detected in the Lisbon Botanical Garden, reflecting the intense car circulation since the end of the late nineteenth century, and the presence of tetraethyl lead in petrol. Levels of Pb in Aleppo bark were at or above the threshold values for plant tissues as defined by the UN-ECE/EC (>4–30 μg/g). Nickel was easily washed by distilled water from the bark, indicating a predominant adsorption due to atmospheric deposition, while only Pb was water-extracted from cone scales, but no more than 0.88 μg/g (4.3% of the total). If we take into account the dry weight of each cone, we can assess the amount of extractable lead present in a given time (ranges between 3.0 and 15.5 μg), although its eventual transfer to the ground through rainfall will be hampered by the cone architecture. The average levels of total Pb in the cones (12.7–35.4 μg/g) fall within the range defined by the UN-ECE/EC, generally; only the reference value is below 4 μg/g. Due to the high capabilities of allocating Pb inside the structure and through adsorption, Aleppo bark and cones can be very interesting tools in the monitoring of Pb.

Keywords:

• Heavy metals
• Pinus halepensis
• bark
• cone scales
• highway

Acknowledgements

The authors are very grateful to both reviewers for useful comments and suggestions and to Dr. Alan Phillips (FCT/UNL) for the rapid and the accurate revision of the manuscript.