Study of the copper distribution in contaminated soils of hop fields by single and sequential extraction procedures

Hop growing in Bavaria requires the use of copper containing fungicides aga inst mildew, which results in an accumulation of copper in the upper soils to concentrations of up to approximately 450 mg kg(-1). The naturally occur ring concentration of copper is approximately 10-15 times lower. Several si ngle and sequential extractions were performed in parallel to the determina tion of total copper content after aqua regia digestion. By these means cop per mobility and retention, its availability to plants as well as its distr ibution in soils was assessed. Three agricultural soils and two soils from fallow land have been analysed to elucidate whether the copper distribution changes in relation to agricultural activities and to predict environmenta l risks due to the high copper concentrations. This work also focuses on th e difficulties arising from different results when using single and sequent ial extraction procedures. EDTA, acetic acid, deionised water, ammonium nit rate and calcium chloride were used as single extractants for the functiona lly defined speciation. EDTA and acetic acid can be regarded as extractants for the plant-available species, while deionised water, NH4NO3 and CaCl2 o nly release electrostatically weakly bound metals to estimate the mobile sp ecies. The extraction behaviour of copper in these procedures is discussed with respect to the quantities extracted from the contaminated and non-cont aminated soils. The studies indicate that no vertical copper translocation is observed in the ground, but the main amounts are highly available to pla nts. Sequential extraction procedures were used for operationally defined s peciation, quantifying copper in specific soil phases. The 'five-step extra ction scheme' first applied, suggested by the Standard Measurement and Test ing Programme of the European Community, overestimated the amounts of coppe r bound to the residual phase. This was mainly due to the non-specific natu re of the reagents for the organic/sulfidic and crystalline iron oxide frac tion. A second reason could be the fact that this scheme was developed for sediment and not for soil analysis. Therefore, the sequential extraction ha s been applied using an adapted method of Zeien and Bruemmer, using differe nt extractants for the two phases. The copper distribution was different, s howing that approximately 40-50% of the total copper was bound to the organ ic fraction and approximately 15-30% could be extracted with the iron oxide s. The amounts in the residual fraction were much lower. After comparing th e results of the different extraction procedures the environmental behaviou r of copper and its risks for plants, micro-organisms and groundwater is di scussed in brief. (C) 2000 Elsevier Science B.V. All rights reserved.