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

Javier Pérez-Esteban, Consuelo Escolástico, Inés Sanchis, Alberto Masaguer and Ana Moliner
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Javier Pérez-Esteban: Department of Organic and Bio-Organic Chemistry, Sciences Faculty, Universidad Nacional de Educación a Distancia, Paseo de Senda del Rey 9, 28040 Madrid, Spain
Consuelo Escolástico: Department of Organic and Bio-Organic Chemistry, Sciences Faculty, Universidad Nacional de Educación a Distancia, Paseo de Senda del Rey 9, 28040 Madrid, Spain
Inés Sanchis: Soil Science Unit, Department of Agrarian Production, Agricultural Engineering School, Universidad Politécnica de Madrid, Avenida Puerta de Hierro 2, 28040 Madrid, Spain
Alberto Masaguer: Soil Science Unit, Department of Agrarian Production, Agricultural Engineering School, Universidad Politécnica de Madrid, Avenida Puerta de Hierro 2, 28040 Madrid, Spain
Ana Moliner: Soil Science Unit, Department of Agrarian Production, Agricultural Engineering School, Universidad Politécnica de Madrid, Avenida Puerta de Hierro 2, 28040 Madrid, Spain

Sustainability, 2019, vol. 11, issue 18, 1-13

Abstract: 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.

Keywords: copper; fulvic acid; humic acid; leonardite; metal mobility; soluble organic carbon; zinc (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2019
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