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Effects of pH Conditions and Application Rates of Commercial Humic Substances on Cu and Zn Mobility in Anthropogenic Mine Soils

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Department of Organic and Bio-Organic Chemistry, Sciences Faculty, Universidad Nacional de Educación a Distancia, Paseo de Senda del Rey 9, 28040 Madrid, Spain
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Soil Science Unit, Department of Agrarian Production, Agricultural Engineering School, Universidad Politécnica de Madrid, Avenida Puerta de Hierro 2, 28040 Madrid, Spain
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Author to whom correspondence should be addressed.
Sustainability 2019, 11(18), 4844; https://doi.org/10.3390/su11184844
Received: 18 July 2019 / Revised: 26 August 2019 / Accepted: 30 August 2019 / Published: 5 September 2019
We studied the effects of commercial humic substances derived from leonardite at different rates (0, 0.25, 2, 10 g kg−1) and pH (4.5, 6.0, 8.0) on Cu and Zn mobility, to evaluate their use for remediation of metal contaminated mine soils and to optimize their application conditions. We conducted a single-step extraction experiment and analyzed extracts for metal concentrations, soluble organic carbon and their E4/E6 ratio (ratio of absorption at 465 to 665 nm). Metal speciation in a soil solution was simulated by the non-ideal competitive adsorption-Donnan (NICA-Donnan) model. Increasing the amount of humic substances and the pH caused higher release rates of soluble organic carbon with a lower humic/fulvic acids ratio. This led to a higher mobility of metals (up to 110 times Cu concentration in control and 12 times for Zn) due to the formation of soluble metal-humic complexes. Speciation modeling predicted that increasing rates of humic substances would result in a higher proportion of Cu and Zn associated with fulvic acids, more mobile than the humic acids fraction. Application of commercial leonardite humic substances at 2–10 g kg−1 and with pH levels similar to or below natural soil could be useful for assisted-phytoextraction of contaminated anthropogenic soils. High rates of humic substances in more alkaline conditions could entail a considerable risk of metal leaching to groundwater, toxicity and transfer to the trophic chain. View Full-Text
Keywords: copper; fulvic acid; humic acid; leonardite; metal mobility; soluble organic carbon; zinc copper; fulvic acid; humic acid; leonardite; metal mobility; soluble organic carbon; zinc
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MDPI and ACS Style

Pérez-Esteban, J.; Escolástico, C.; Sanchis, I.; Masaguer, A.; Moliner, A. Effects of pH Conditions and Application Rates of Commercial Humic Substances on Cu and Zn Mobility in Anthropogenic Mine Soils. Sustainability 2019, 11, 4844.

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