Arsenic, Copper, and Zinc Leaching through Preferential Flow in Mining‐Impacted Soils

Abstract

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Arsenic, Copper, and Zinc Leaching through Preferential Flow in Mining-Impacted Soils Soil Chemistry T he fate and mobility of As and other hazardous metals in soils impacted by mining wastes are infl uenced by coupled biogeochemical processes that control the element oxidation state, mineral surface sorption and desorption, and solid-phase precipitation and dissolution. Knowledge of the mechanisms that control contaminant release, mobility, and natural attenuation is crucial to minimize the risk and consequences associated with mine wastes (Cheng et al., 2009; Johnson and Hallberg, 2005). Th e role that inhomogeneous infi ltration and wetting front instabilities leading to preferential fl ow (PF) phenomena play on the distribution and solid speciation and transport of As and other metals in soils aff ected by acid mine drainage (AMD) is less well studied, however. Preferential fl ow is the rapid movement of water and solutes through soils that bypasses large portions of the soil matrix and thus aff ects a small fraction of the soil volume (Hagedorn and Bundt, 2002). Flow through structural macropores such as soil fi ssures, cracks, root channels, or earthworm burrows are the main causes for PF (Jarvis, 2007). In sandy soils, fi ngering can occur (Lennartz et al., 2008) due to

Characteristics of preferential flow paths and their effects on soil properties

“…Rajesh and Bhagat (1999) found that the flow of silicon through porous carbon was greatest at the macro level. In the subsoil, preferential flow domains act as conduits for the transport of Cu and Zn into the soil matrix but retain heterogeneously by adsorption on amorphous iron oxides that may dissolve and precipitate within macropores (Helmhart et al 2012). In this study, the lower soil metal content in the stained areas was caused by preferential flow, which can transport metal quickly (Subramanian and Cathles 2013) and reduce the adsorption of metal to soil particles (Anaya et al 2013).…”

“…The results shown by Novak et al (2001) indicate that losses of metolachlor (an organic compound widely used as a herbicide) in drain water are primarily caused by preferential flow, which is greater in clay soils than in silt loam and occurs mainly in spring and summer. The effect of preferential flow on the spatial distribution of arsenic, copper and zinc was studied within the surface riverbed layer of a small stream that collects surface runoff from an arsenic-bearing waste pile of an abandoned mine, showing that in the subsoil, preferential flow paths were associated with lower copper and zinc concentrations and higher concentrations of arsenic (Helmhart et al 2012). Anaya et al (2013) found that preferential flow paths can increase soil organic matter content.…”

Spread and partitioning of arsenic in soils from a mine waste site in Madrid province (Spain)

“…The site includes an abandoned smelting factory at which arsenopyrite that was encapsulated in quartz was processed for the extraction of wolfram during the Second World War. The mining wastes, which contain up to 19 g kg −1 of As and currently remain where they were dumped on the soil surface (Recio-Vazquez et al, 2011;Helmhart et al, 2012), are subject to erosion and weathering processes (Fig. 1).…”

“…As the surface runoff from the waste pile converges into the small creek, a fraction of the transported As and companion elements is retained in the uppermost layer of the riverbed (section B 1 ), which corresponds to the riverbed hyporheic layer as described by Helmhart et al (2012); another fraction infiltrates into the subsurface soil layer, and the remainder flows downward within the course of the creek. However, the volume-averaged pseudo-total As concentrations in the subsurface sections of cores B and C do not capture the extreme spatial variability in element concentrations associated with preferential flow paths, as previously described (Helmhart et al, 2012). The XANES spectra results and SEM observations (Figs.…”

“…Helmhart et al (2012) studied in the same area, the effect of preferential flow on the spatial distribution and chemical speciation of As, Cu and Zn at a pedon-scale. They found that As was leaching into the subsoil from the surface of a small, dry riverbed that seasonally collects acidic surface runoff from a waste pile mainly composed of scorodite [FeAsO 4 ·2H 2 O].…”