Retention of copper originating from different fungicides in contrasting soil types

Abstract

This work described the retention of Cu from two different commonly used pesticides, the Bordeaux mixture (CuSO 4 + Ca(OH) 2) and Cu-oxychloride (3Cu(OH) 2·CuCl 2), and from Cu(NO 3) 2 in contrasting soil types (Leptosol, Chernozem, Cambisol). Thermodynamic modeling showed that Cu speciation was similar in all fungicide solutions. However, the retention of Cu differed with the fungicide used (maximum retention from the Bordeaux mixture) which indicates that different retention processes occurred in the studied soils. The suggested mechanisms include: specific and non-specific adsorption (especially on soil organic matter), precipitation of newly formed phases, such as CuO, Cu(OH) 2, Cu 2(OH) 3NO 3, CuCO 3/Cu 2(OH) 2CO 3 and in the case of the Bordeaux mixture, precipitation of various Cu-hydroxysulfates. These phases were identified by the speciation model. The retention of fungicide-derived Cu in the studied soil types followed well the Freundlich isotherm and was directly controlled by the chemical form of Cu. This fact should be taken into account for both environmental and practical applications.