Study of the distribution of copper in an acid sandy vineyard soil by three different methods

Copper sulphate (Bordeaux mixture) has been used as a fungicide against mildew in vineyards for more than a hundred pears. This treatment has resulted in significant Cu accumulation in soils (from 100 to 1500 mg kg(-1)). It is desirable to determine the distribution of Cu in these soils to predict if this element is potentially toxic. Several speciation methods have been compared: sequential and single-step extractions, analytical transmission electron microscopy (ATEM, ASEM) and physical fractionation to study a profile of a vineyard acid soil in Beaujolais (France). Physical fractionation showed that copper is concentrated in the coarse organic fractions associated with plant residues and in the fine clay fraction. Analytical electron microscopy showed a great diversity of fixation sites (bacteria, amorphous organic and mineral compounds). Chemical sequential extractions showed that after the sequential extraction treatments, 60% of Cu was not extracted. Extraction data showed that in the case of an acid sandy soil, sequential chemical extraction did not seem to be sufficiently selective to speciate copper. In the single-step extractions study, the hydroxylamine treatment was the most selective. In the nonselective cases several phenomena may be responsible for the failure, the analytical electron microscopy study showed copper redistribution after certain single-step extractions were carried out. After comparing three different distribution methods we conclude that the distribution of this element in acid soils should be investigated by several analytical methods to establish the true speciation.