ACID-BASE ADJUSTMENT AND CHEMICAL FRACTIONATION TO ASSESS COPPER AVAILABILITY IN SPANISH VINEYARD SOILS AND SEDIMENTS


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Abstract

Copper mobilization from vineyard soils and sediments to waterways can be potentially toxic to aquatic organisms and cause ecosystem degradation, depending on their behavior as a sink or source of Cu. To assess Cu mobilization to waterways, soil (n = 5) and sediment (n = 5) samples from vineyards at different pH levels were used to determine the equilibrium concentration of Cu (ECuC0). Relationships between ECuC0 and physicochemical properties and Cu fractions of soils and sediments were also determined. Sediments had total Cu content (256-947 mg kg−1) greater than did the soils (166-359 mg kg−1), with Cu bound to organic matter as the dominant fraction. The ECuC0 were similar in soils and sediments (<0.1-0.3 mg L−1) without acid or alkali addition, but lower than those obtained using natural river water (0.2-0.5 mg L−1). These results suggest that soils and sediments act as a source of Cu to waters rather than as a sink considering the Cu concentrations found in the river waters from a vineyard area. Equilibrium concentrations of Cu increased notably when the solutions were acidified (5-133 mg L−1) but to a lesser extent when solution pH was raised (4-20 mg L−1), indicating that pH changes control how soils and sediments behave as a source of Cu. Organic carbon and Al forms were significantly correlated with ECuC0 values obtained using natural river water, whereas cation exchange capacity, organic carbon, sand, and clay correlated with ECuC0 when the pH solution was modified. Percentage of exchangeable Cu with respect to total Cu was closely correlated with ECuC0 values in both more acidic and more alkaline samples, whereas percentage of Cu bound to organic matter was significantly correlated with ECuC0 in the more alkaline samples.

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