Copper accumulation, distribution and fractionation in vineyard soils of Victoria, Australia

The use of copper-based fungicides by Victorian vinegrowers has increased the total copper concentration in some vineyard soils to 250 mg/kg compared to background levels of approximately 10 mg/kg. The Australian and New Zealand guidelines for the assessment of contaminated sites recommend that total copper concentrations in soil exceeding 60 mg/kg require environmental investigation, and this level is exceeded in 8 of the 14 vineyards investigated. The focus of this paper is to measure the accumulation, distribution and fractionation of copper in contaminated and uncontaminated soils as a step towards understanding copper existence in soils and its potential for availability to flora and fauna. Physical and chemical properties and total copper concentrations were measured in soil samples from four selected wine-producing regions of Victoria, including vineyard soils and adjacent background soils. Copper fractionation in soils with high total copper concentrations was measured using a selective extraction procedure. Copper in surface soils (0-1 cm) and throughout soil profiles (maximum depth of 50 cm) was separated in the following fractions: water soluble (WS), exchangeable (E), sorbed (S), easily reducible Mn (ERMn), bound to carbonates (CA), organically bound (OM), bound to Fe and Al oxides (FeOx) and residual (RES). The results show that the source (anthropogenic or natural) of copper in soils and the content of organic matter has influenced the copper distribution among various soil fractions, and in turn its potential mobility and risk to biota. In vineyard soils, potentially available copper (defined as fractions WS+E+S) constitutes more than 60 wt.% of total copper in the upper part of soil profiles and the percentage decreases with increasing depth. However, copper associated with the less mobile fractions (FeOx+RES) is less than 10 wt.% in the top part of soil profiles and increases with increasing depth. Copper in uncontaminated soils exists mainly in less mobile fractions (FeOx+RES; 70-90 wt.%), whereas potentially available copper constitutes approximately 10 wt.% of total copper content throughout soil profiles. The study shows that the conversion between copper fractions is slow, indicating that copper can stay active in soils for long periods of time, greater than tens of years, and may result in leaching and transport to deeper soil layers.