Faculté de l'environnement naturel, architectural et construit ENAC, Département de génie rural, Institut de l'aménagement des terres et des eaux IATE

Translocation of copper in an alpine chronosequence by phenolic-type vectors

Oess, Andrea ; Védy, Jean-Claude (Dir.)

Thèse sciences Ecole polytechnique fédérale de Lausanne EPFL : 1999 ; no 1997.

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    Repeated applications of Cu for phytosanitary treatments of vineyards and orchards have contributed to a considerable increase of Cu levels in soils over the last decades. Therefore the risk of migration and Cu contamination of the groundwater and the drinking water supply has also increased. In order to contribute to a better understanding of these parameters, which control either the retention of Cu to soil or its mobilisation, a study has been carried out on the translocation of Cu in low polluted soils of an alpine chronosequence characterised by extremely low pH values. In particular the role of natural phenols released by plants and the organic fractions of soils was investigated by a two scale approach. On one hand field measurements were performed at the Arpette valley site and on the other hand mechanistic studies were carried out in the laboratory about the role of complexation reactions and polymerisation dynamics on these processes. The use of Electron Spin Resonance Spectroscopy (ESR), potentiometry, dynamic simulations and UV absorption revealed that ortho-dihydroxyphenols (ODP's) were the main complexing agents of Cu(II). They were even able to form complexes at very low pH values such as pH 4. The potential of ODP's released by the different plant species from the vegetation cover was determined for the different soils. Catechol, caffeic acid and protocatechuic acid were the dominant species present. Parameters responsible for the migration of Cu were determined through sampling of the soil solution with a tension free lysimeter device. Seasonal factors such as air and soil temperature amplitude, rainfall, solar radiation as well as physico-chemical parameters of the soil solution (pH, T°, DOC, phenols, Cu) were measured. Parameters responsible for the retention of Cu were studied by performing sorption isotherms of Cu in the presence of different horizons of a PODZOSOL OCHRIQUE. Despite the strong affinity of Cu for the insoluble organic fraction of the A-horizons, vertical migration of Cu was observed. These migrations were always higher between the O- and the A-horizon than between the A- and the under-laying horizons. The quantity of migration was always proportional to the levels of Cu present in the horizons of origin. The strong correlation observed between phenol concentration and Cu migration events suggested that phenols were the favourite translocation vectors of Cu in these soils at the cost of the DOC (dissolved organic carbon) fraction. Mechanistic studies also permitted to identify two types of functional reactivities around the phenol molecules: while ortho-dihydroxyphenols had strong chelating properties and were responsible for the complexation of Cu, carboxylic groups (COOH) which were not directly involved in the complexation reaction, played a key role by maintaining these complexes in a hydrosoluble form.