Abstract
The aim of this study was to establish the fractionation of copper and zinc in a small apple orchard using the revised (four-step) Bureau Communautaire de Référence (BCR) sequential extraction procedure and assess their potential mobility in soil. Soil samples were collected at the depth of 10 cm to 25 cm, sixteen from the orchard and five control samples from a meadow located some 200 m away from the orchard. As the distribution of trace-element concentrations in the control samples was normal, they were used for comparison as background levels. We also determined soil mineralogical composition, carbonate content, soil pH, cation exchange capacity, and soil organic matter. The extraction yields of Cu and Zn from the control soil were lower than from the orchard soil (25% vs. 34% and 47% vs. 52%, respectively), which pointed to natural processes behind metal bonding in the control soil and greater influence of man-made activities in the orchard soil. Compared to control, the orchard soil had significantly higher concentrations of total Cu (P=0.0009), possibly due to the application of Cu-based fungicides. This assumption was further supported by greater speciation variability of Cu than of zinc, which points to different origins of the two, Cu from pesticides and Zn from the parent bedrock. Copper levels significantly better (P=0.01) correlated with the oxidisable fraction of the orchard soil than of control soil. Residual and organically bound copper and zinc constituted the most important fractions in the studied soils. However, the use of Cu-based fungicides in the apple orchard did not impose environmental and health risk from Cu exposure.
Highlights
Minor chlorite-smectite occurrences were observed only in one orchard sample and in the control soil while kaolinite was found in the orchard samples but not in control
This mineral composition largely supports low Cation exchange capacity (CEC), whose range between 50 μEq g-1 and 250 μEq g-1 strongly correlates with these phyllosilicate minerals [22]
To understand Cu and Zn findings in our apple orchard we first need to discuss the characteristics of control soil
Summary
In order to harmonise methodology throughout the European Union so that the analytical results could be comparable, the Community Bureau of Référence (BCR) invented a simple, three-stage sequential extraction protocol for speciation or fractionation of trace elements in sediment and soil samples [17]. We used Kendall’s tau correlation coefficient to evaluate the relationships between variables for every group of samples (apple row, between rows, combined orchard, and control).
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