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 microm. 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 degrees 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.

A PIXE and ICP-MS analysis of metallic atmospheric contaminants in tree bark tissues, a basis for biomonitoring uses.

The qualitative and quantitative metallic content of tree barks of Argania spinosa (L.) Skeels were studied. Argania spinosa is an endemic species in Morocco. This tree is adapted to semi-arid climates and exposed to specific conditions of relative humidity, temperature, wind, and particle transport. Three sites were sampled in Morocco: the large town of Rabat, the harbor of Agadir, and Aït Baha, a countryside location exposed to continuous desert wind. The methodologies included (1) in situ microanalysis with proton-induced X-ray emission (PIXE) and (2) trace element determinations by mass spectrometry with inductively coupled plasma (ICP-MS) associated with extraction procedures. Both methods allowed detection of elements coming from different bark compartments. The profile of airborne contaminants in the barks was typical of the sampling sites. The level of lead in barks sampled in Rabat reached 100 ng cm(-2), or higher, while it varied between 3 and 35 ng cm(-2) in Aït Baha. The in situ study of the microscopic structure of the bark provided the location of major and minor elements at various depths inside the bark. A differential between free deposit on the bark surface and penetrated content was found for the major and trace elements. The free deposit on the bark surface was suspected to be mostly the result of recent contamination. Part of the contaminants spread out on the surface penetrated the superficial suber. This long-term accumulation affected mostly Pb. In deeper levels, airborne elements at low concentrations and elements resulting from root uptake were concurrently present and resulted in a complex situation, as noted for zinc.