Fluorite Formation in Poplar Leaves (Populus balsamifera L.) in an HF-Polluted Area

Abstract

The article represents results of the study aimed on sensitivity of balsam poplar (Populus balsamifera L.) leaves to hydrogen fluoride airborne emissions in the vicinity of aluminum smelter. Widespread occurrence of poplar in urban land was one of the purposes to choose this plant as a research object. Reaction of poplar leaves on influence of hydrogen fluoride (HF) was investigated by ionometric technique, scanning electron microscopy-related method (SEM–EDS), X-ray diffraction analysis (XRD), and the thermodynamic modelling. The fluoride content in poplar leaves decreases with distance from the emission source. Leaves have signs of deterioration, e.g., chemical burns and necrosis, inside 2-km zone of the plant. In stomatal cells of poplar leaves, neogenic mineral fluorite (CaF2) was discovered. In sieve-tube elements of leaf phloem, a large quantity of secondary calcite (CaCO3) crystals was found. Ca2+ ions in enchylema react with F− that has released as part of airborne emissions from aluminum smelter. Result of their interaction is fluorite formation in stomatal cells of poplar leaves. Such fluorite is a mineral indicator of fluoride pollution in ground-level ambient air. Thermodynamic conditions of interaction of Ca2+ and F–, HCO3– and Ca2+ were estimated. The model of maintenance of phytochemical calcium barrier in the poplar leaves stomata in HF contamination was proposed and described.