Risk assessment and copper geochemistry of an orchard irrigated with mine water: a case study in the semiarid region of Brazil.

Abstract

This study aimed to evaluate mine water reuse, elucidating the potential problems related to trace metal biogeochemistry focusing on Cu dynamics in water, soil, and plants. Water sampleswere collected from a Cu mine and a reservoir used to store mine water. Additional samples were taken from soils from an uncultivated area and a banana orchard (irrigated with mine water for at least 10years) and plant from the irrigated area. The following parameters were analyzed: pH, redox potential, dissolved ions in water samples (e.g., Ca2+, Mg2+, Na+, K+, Cu2+, SO 4 2- , and Cl-), bioavailable Cu and Cu solid-phase fractionation (in soils and reservoir sediments samples), as well as Cu content in banana plants. Mine water presents high dissolved Cu concentration (mean 2.3 ± 0.0mgL-1), limiting its use for irrigation. Water storage at the reservoir increased water quality, reducing dissolved Cu concentration (mean 0.2 ± 0.0mgL-1), due to adsorption/precipitation as carbonates (mean 131.8 ± 24.6mgkg-1), organic matter (mean 1526.2 ± 4.7mgkg-1) and sulfides (mean 158.4 ± 56.9mgkg-1). Despite higher water quality at the reservoir, the use of mine water increased the amount of bioavailable Cu in soils, which wasprimarily associated with organic matter. Increased bioavailable Cu in the soil did not increase the Cu content of banana leaves but resulted in high Cu content of roots and fruit, increasing the risk of toxicity for the population.