Mickaël Catinon

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.

Isolation of technogenic magnetic particles

Technogenic magnetic particles (TMPs) emitted by various industrial sources, such as smelting plants, end up after atmospheric transfer on the soil surface. In the present study, we characterised the origin and composition of such particles emitted by a large iron smelting plant and deposited on particular substrates, namely tombstones, which act as a very interesting and appropriate matrix when compared to soil, tree bark, lichens or attic dust. The isolation and subsequent description of TMPs require a critical step of separation between different components of the sample and the magnetic particles; here, we described an efficient protocol that fulfils such a requirement: it resorts to water suspension, sonication, repeated magnetic extraction, sedimentation, sieving and organic matter destruction at 550 °C in some instances. The isolated TMPs displayed a noticeable crystalline shape with variable compositions: a) pure iron oxides, b) iron+Cr, Ni or Zn, and c) a complex structure containing Ca, Si, Mg, and Mn. Using Scanning Electron Microscope Energy Dispersive X-ray (SEM-EDX), we obtained profiles of various and distinct magnetic particles, which allowed us to identify the source of the TMPs.

A comparative study of atmospheric deposits and lichen populations in a protected alpine area in the Grenoble region (France)

The atmospheric mixture deposited on ash tree stems was studied in Les Seiglieres, an alpine station located at an altitude of 1100 m in the Belledonne Mountains and in the town of Grenoble (300,000 inhabitants, altitude 200 m). The composition of the mixture of elements was fairly similar in the two stations, although the soil particles deposited on the stems had not the same geological origin. The deposit on the Seiglieres trees had a weight per area unit twice lower and a concentration of anthropic elements in this deposit three times lower than in Grenoble. Concurrently, the lichen flora of Seiglieres was studied from 1970 to 2007, showing a high biodiversity as well as important changes occurring in its composition, with a marked increase in the nitrophilous species, possibly due to higher amounts of NOx, P, Mg and S wafted over in the atmosphere.

Atmospheric elements deposition and evaluation of the anthropogenic part; the AAEF concept

The atmospheric deposition on tree trunks is commonly used for evaluating air contamination on a large time scale. However, the deposits are mostly composed of organic matter (generally more than 80 %) and of minerals of geogenic origin. From the elemental composition of the whole deposit, measured by ICP-MS, a calculation was conceived which allows to separate the amounts of elements corresponding to organic matter, to geogenic compounds and, finally, to anthropogenic minerals. For this purpose, the weight of organic matter was obtained through incineration at 550°C. The elements composition of organic matter was deduced from plant composition. The weight of geogenic compounds was evaluated from the Si, Al content. The formula of geogenic elemental composition took into account the composition of the local soil. This calculation was carried out on four different situations showing the contribution of the main anthropic atmospheric contaminants (Sb, Cd, Sn, Pb, Cu, V, Zn, W, Cr, Ni, Co, As).