Elsevier

Journal of Environmental Management

Volume 146, 15 December 2014, Pages 226-234
Journal of Environmental Management

Evaluating the potential of three Fe- and Mn-(nano)oxides for the stabilization of Cd, Cu and Pb in contaminated soils

https://doi.org/10.1016/j.jenvman.2014.08.004Get rights and content

Highlights

  • Efficiency of 3 (nano)oxides for stabilization of Cd, Cu and Pb was investigated.

  • Batch, column and adsorption tests coupled with bioassays were performed.

  • The amorphous Mn oxide proved to be an efficient amendment for Cd, Cu and Pb.

  • The ability of amorphous Mn oxide to oxidize soil organic matter was observed.

  • The ability of amorphous Mn oxide to increase soil pH was observed.

Abstract

The potential of three Fe- and Mn-(nano)oxides for stabilizing Cd, Cu and Pb in contaminated soils was investigated using batch and column experiments, adsorption tests and tests of soil microbial activity. A novel synthetic amorphous Mn oxide (AMO), which was recently proposed as a stabilizing amendment, proved to be the most efficient in decreasing the mobility of the studied metals compared to nano-maghemite and nano-magnetite. Its application resulted in significant decreases of exchangeable metal fractions (92%, 92% and 93% decreases of Cd, Cu and Pb concentrations, respectively). The adsorption capacity of the AMO was an order of magnitude higher than those recorded for the other amendments. It was also the most efficient treatment for reducing Cu concentrations in the soil solution. No negative effects on soil microorganisms were recorded. On the other hand, the AMO was able to dissolve soil organic matter to some extent.

Introduction

Commonly used methods of contaminated soil remediation, such as soil excavation, encapsulation, in situ and ex situ washing/flushing, vitrification etc., are not only costly and energy demanding, but also disruptive for the soil in the context of natural site conditions (Kumpiene et al., 2008, Tsang et al., 2007, Tsang and Yip, 2014). Due to the limited funding available for soil remediation and with the emphasis on environmental and landscape protection, research on the stabilization of metals in contaminated soils has become a high priority (Bolan et al., 2014, Geebelen et al., 2006, Komárek et al., 2013, Kumpiene et al., 2008, Mench et al., 2006a, Mench et al., 2006b, Renella et al., 2008). Stabilization of metals and metalloids by decreasing their mobility, bioavailability and bioaccessibility in soils can be achieved using living plants and associated microbial communities in the root zone (phytostabilization), application of various immobilizing amendments (chemical stabilization) or using a combination of both (aided phytostabilization) (Komárek et al., 2013, Kumpiene et al., 2008).

Nano-sized oxides (particle size of 1–100 nm) act as important scavengers for contaminants in soils, mainly due to their high reactivity and large specific surface area (Klaine et al., 2008). To date, research on the use of engineered nanoparticles for remediation purposes has focused mainly on the treatment of contaminated water (Hashim et al., 2011, Tang and Lo, 2013). For example, nano-sized particles of γ-Fe2O3 and Fe3O4 were successfully used for the removal of anionic metal/metalloid species (e.g., Cr(VI) and As(V)) from water (Hu et al., 2004, Hu et al., 2005). Although numerous studies have been published on the use of nanoparticles for water treatment, research on their application in soil remediation is still scarce. Komárek et al. (2013) reviewed recently the use of metal oxides in general for the stabilization of metals and As in contaminated soils and even though the remediation potential of some naturally occurring or synthetic metal oxides has been already tested, these data cannot be easily extrapolated as oxide particles have unique properties on the nano-scale (Mueller and Nowack, 2010, Tratnyek and Johnson, 2006). On the other hand, Mn-oxides were found to be more efficient for adsorbing Pb and Cd compared to Fe-oxides (Dong et al., 2000, O'Reilly and Hochella, 2003). A new amorphous Mn oxide (AMO) has been previously synthesized and tested as a promising amendment for chemical stabilization of metals in soils due to its good adsorption properties and simple preparation (Della Puppa et al., 2013, Ettler et al., 2014).

Environmental effects of engineered nanoparticles are still not much known, as the up-to-date research has been largely limited to their ecotoxicity (Nowack and Bucheli, 2007). Their bioavailability and potential ecotoxicity depends on many factors, such as speciation (dissolved, colloidal or particulate phase) (Klaine et al., 2008), size (Madden et al., 2006), shape (Pal et al., 2007) and surface properties (Yang and Watts, 2005) etc. Auffan et al. (2008) observed a strong impact of the Fe oxidation state on the oxidative stress (and associated cytotoxic effect) towards Escheria coli, as nano zerovalent Fe (nZVI) and magnetite (Fe3O4) generated reactive oxygen species. On the other hand, maghemite (γ-Fe2O3) particles did not cause any cytotoxicity. In vitro experiments are useful tools for elucidating toxicity interactions at the molecular level, yet the behavior and ecotoxicity in complex soil environments is difficult to predict. Nevertheless, simple toxicity tests are useful for a fast evaluation of potential toxicity of stabilizing amendments. The aim of this work was thus to evaluate the potential of two selected Fe nanooxides (maghemite and magnetite) and one amorphous Mn oxide (AMO, Della Puppa et al., 2013) to stabilize metals (Cd, Cu, Pb) in two contaminated soils and examine the interactions of these (nano)oxides in soil environments including their influence on soil microbiota.

Section snippets

Soil properties

Two soils from the vicinity of a Pb (Haplic Udept) and Cu smelter (Dystric Udept) were chosen for the experiment, mainly due to their increased content of Pb, Cd and Cu and varying characteristics. Soil samples were collected from the superficial layer (0−20 cm), air-dried, homogenized and sieved through a 2-mm stainless sieve. Particle size distribution was determined using the hydrometer method (Gee and Bauder, 1986). Soil pH was measured in suspension using a 1:2.5 (w/v) ratio of soil and

Soil properties

Basic physico-chemical properties and metal contents in the studied soils are summarized in Table 2. Dystric Udept has a coarse texture (62% sand, 30% silt and 8% clay), has a lower pH value and a higher SOM content compared to the Haplic Udept. Concentrations of trace elements exceeded their limit values for agricultural soils set by the Ministry of the Environment of the Czech Republic (1994) in the case of Pb and Cd in the Haplic Udept and Cu and Cd in the Dystric Udept. According to the

Conclusions

Results from batch and column experiments coupled with adsorption tests proved that the AMO was the most effective treatment for the stabilization of metals in the studied soil samples at the given w/w ratios (1 and 2%, w/w). Metal stabilization resulted from combined specific adsorption onto the AMO surface together with an increase in soil pH promoting the adsorption of metallic cations. On the other hand, no impact on soil pH was found for the Fe oxides. Furthermore, the AMO had a positive

Acknowledgement

This work was supported by the Czech Science Foundation (projects GAČR P503/11/0840 and GA14-01866S). Zuzana Michálková is thankful for the support from the Czech University of Life Sciences Prague (project CIGA 20134209) and Ondřej Vaněk for the support from Charles University in Prague (project UNCE 204025/2012). The authors thank two anonymous reviewers for their valuable suggestions and comments.

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