The inclusion of atmospheric particles into the bark suber of ash trees

A slow deposition of atmospheric components occurs on tree barks. One part of them can be incorporated into bark tissues. This work demonstrates that mineral particles are present inside the suber tissue in four-year-old ash tree stems. Most of these particles are smaller than 2 μm. Scanning electronic microscope studies – using energy dispersive X-ray spectroscopy (SEM–EDX) – on stem cuttings show that they are located either inside the dead suber cells or between these cells. Numerous particles are composed of clay, quartz, feldspar or mica. Others, clearly of anthropogenic origin, are metallic fragments composed of Fe, Ni, Cr, Pb, etc. Spherical fly ashes were found, composed of Si, Al or Fe, and demonstrating an anthropogenic formation. Such particles were isolated and purified from suber ashes obtained at 550 °C, after aqueous and acidic treatments, and their composition was established through SEM–EDX. These results reinforce the idea that the suber of tree barks alone can be considered as archives for atmospheric deposition.