Cadmium, lead, and zinc mobility and plant uptake in a mine soil amended with sugarcane straw biochar A. P. Puga, C. A. Abreu, L. C. A. Melo, J. Paz-Ferreiro & L. Beesley
Environmental Science and Pollution Research ISSN 0944-1344 Environ Sci Pollut Res DOI 10.1007/s11356-015-4977-6
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Author's personal copy Environ Sci Pollut Res DOI 10.1007/s11356-015-4977-6
RESEARCH ARTICLE
Cadmium, lead, and zinc mobility and plant uptake in a mine soil amended with sugarcane straw biochar A. P. Puga 1 & C. A. Abreu 1 & L. C. A. Melo 2 & J. Paz-Ferreiro 3 & L. Beesley 4
Received: 23 March 2015 / Accepted: 29 June 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract Accumulation of heavy metals in unconsolidated soils can prove toxic to proximal environments, if measures are not taken to stabilize soils. One way to minimize the toxicity of metals in soils is the use of materials capable of immobilizing these contaminants by sorption. Biochar (BC) can retain large amounts of heavy metals due to, among other characteristics, its large surface area. In the current experiment, sugarcane-straw-derived biochar, produced at 700 °C, was applied to a heavy-metal-contaminated mine soil at 1.5, 3.0, and 5.0 % (w/w). Jack bean and Mucuna aterrima were grown in pots containing a mine contaminated soil and soil mixed with BC. Pore water was sampled to assess the effects of biochar on zinc solubility, while soils were analyzed by DTPA extraction to confirm available metal concentrations. The application of BC decreased the available concentrations of Cd, Pb, and Zn in the mine contaminated soil leading to a consistent reduction in the concentration of Zn in the pore water. Amendment with BC reduced plant uptake of Cd, Pb, and Zn with the jack bean uptaking higher amounts of Cd and Pb than M. aterrima. This study indicates that biochar application during mine soil remediation could reduce plant concentrations of heavy metals. Coupled with this, symptoms of Responsible editor: Elena Maestri * A. P. Puga
[email protected] 1
Instituto Agronômico de Campinas, Campinas, SP 13020-902, Brazil
2
Universidade Federal de Lavras, Campus Universitário, Lavras, MG 37200-000, Brazil
3
School of Civil, Environmental and Chemical Engineering, RMIT University, GPO Box 2476, Melbourne, VIC 3001, Australia
4
The James Hutton Institute, Craigiebuckler, Aberdeen AB158QH, UK
heavy metal toxicity were absent only in plants growing in pots amended with biochar. The reduction in metal bioavailability and other modifications to the substrate induced by the application of biochar may be beneficial to the establishment of a green cover on top of mine soil to aid remediation and reduce risks. Keywords Soil contamination . Biochar . Metals . Remediation . Immobilization . Pollution
Introduction Soils and waters are frequently subject to contamination by inorganic elements including As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, and Zn, mainly due to anthropogenic activities (Ahmad et al. 2014), such as mining, incineration of wastes, and agricultural practices (i.e., pesticides and sewage sludge application). Phytotoxic concentrations of contaminants, imbalanced ratios of key nutrients, the poor physical condition of contaminated soils, and low cation exchange capacity limit the establishment of vegetation preventing or restricting the ability of soil to perform its normal functions (Lu et al. 2015a). Remediation strategies that provide in situ immobilization of contaminants rather than ex situ removal and dumping elsewhere of soils are generally more cost-effective and environmentally friendly. In addition, as well as dilution of pollutants, these materials can reduce the mobility of heavy metals due to various mechanisms, such as adsorption, precipitation, or complexation, which decrease the (bio)availability of pollutants in soils (Venegas et al. 2015). Due to their positive effect on soil remediation, the use of such amendments also represents a satisfactory alternative for the beneficial reuse of wastes (Venegas et al. 2015).
Author's personal copy Environ Sci Pollut Res
The reduction in bioavailability of metals and other modifications to the substrate induced by the application of biochar may be beneficial to the establishment of a green cover on top of the wastes to acquire long-term phytostabilization (Fellet et al. 2014; Paz-Ferreiro et al. 2014). The lower bioavailability of the toxic elements, higher water retention, and higher cation exchange capacity (CEC) provided by biochar promote plant growth in the polluted substrate (Fellet et al. 2014; Paz-Ferreiro et al. 2014). Because of its high aromaticity and high surface area, biochar is considered as a strong and effective sorbent for organic and inorganic pollutants (Tong et al. 2014). Metal sorption occurs primarily due to an electrostatic interaction between the positively charged metal ions and negative charge associated with delocalized π-electrons on aromatic structures (Harvey et al. 2011). In fact, research performed in the last few years has demonstrated that phytoremediation combined with biochar addition to soil can offer additional benefits, including the enhancement of soil biological activity (Lu et al. 2015a), promotion of root proliferation (Brennan et al. 2014), and associated improvements in plant growth (Lu et al. 2014). The functional groups on the surface of the biochar control the heavy metals by forming specific metal-ligand complexes in the soil; when operating continuously, these mechanisms might cause mineral precipitation on the surface of soil particles through a monolayer adsorption process (Han et al. 2013). With the incorporation of biochar, there are more negative charge on soil surface due to the decreasing zeta potential and increasing CEC (Peng et al. 2011). Such effects also depend on soil type and origin of biochar feedstock and the production temperature. Several feedstocks have been explored in relation to their potential to remediate heavy-metal-contaminated areas, including poultry manure and eucalyptus (Lu et al. 2014) and pruning residues (Fellet et al. 2014), but there are no studies considering the use of sugarcane straw biochar. This residue is abundant in many areas producing large amount of sugarcane in South America and Asia. In Brazil, sugarcane plantation currently represents ≈8.8 million hectares, spread all over the country with São Paulo state concentrating around 51 % of this amount (CONAB 2013), which generate more than 220 million tons of sugarcane straw (Ferreira-Leitão et al. 2010). The amount of sugarcane straw left after harvesting tends to increase due to traditional sugarcane plantations’ management in Brazil including pre-harvest fire, in order to facilitate manual harvest. However, a recent agreement between the ethanol industry and the government of São Paulo state established that sugarcane harvest change from manual to mechanical by 2014, resulting in the total suspension of pre-harvest burning (Costa et al. 2013). This surplus material could generate electricity and co-generate biochar via slow pyrolysis process (Quirk et al. 2012).
Recent studies also suggest that high-temperature biochars could be more effective than those produced at lower temperatures at immobilizing a variety of heavy metals, including Ni (Mendez et al. 2014), Cd (Kim et al. 2013; Melo et al. 2013), and Zn (Melo et al. 2013). Besides, biochar produced at higher pyrolysis temperature have higher C stability in soils than those produced at lower pyrolysis temperatures (Fang et al. 2015). In this paper, we present and discuss the results of a pot experiment to examine the remedial effects of biochar produced from sugarcane straw at a high temperature, in a Cd-, Pb-, and Zn-contaminated soil from a mining area. The results are discussed in the context of environmental chemistry.
Material and methods Soil sampling and characterization A soil, which was classified as a Technosol (IUSS-WRB, 2014), was sampled in a former zinc mining area in Vazante (Minas Gerais; 17° 55′ 43″ S, 46° 49′ 15″ W), in an opencast mine whose operation discontinued for more than 15 years. According to Köppen classification, the climate is “Aw,” characterized by a long period with low rainfall. About 250 kg of surface soil (0–20 cm) was collected from the site and homogenized using spades. The collection area had outcrops of phyllite with the presence of hematite, intercalations of shale, and red phyllite (strong oxidation). The samples were mixed, air-dried, and sieved (
