The Influence of Biochar and Black Carbon on Reduction and Bioavailability of Chromate in Soils

University of South Australia, Australia.
Journal of Environmental Quality (Impact Factor: 2.65). 07/2012; DOI: 10.2134/jeq2011.0145


The widespread use of chromium (Cr) has a deleterious impact on the environment. A number of pathways, both biotic and abiotic in character, determine the fate and speciation of Cr in soils. Chromium exists in two predominant species in the environment, trivalent [(Cr(III)] and hexavalent [Cr(VI)]. Of these two forms, Cr(III) is non-toxic and is strongly bound to soil particles, while Cr(VI) is more toxic, soluble and readily leaches into groundwater. The toxicity of Cr(VI) can be mitigated by reducing it to Cr(III) species. The objective of this study was to examine the effect of organic carbon sources on the reduction, microbial respiration and phytoavailability of Cr(VI) in soils. Organic carbon sources such as black carbon and biochar were tested for their potential in reducing Cr(VI) in acidic and alkaline contaminated soils. An alkaline soil was selected to monitor the phytotoxicity of Cr(VI) in sunflower plant. Our results showed that using black carbon resulted in greater reduction of Cr(VI) in soils compared to biochar. This is attributed to the differences in dissolved organic carbon (DOC) and functional groups that provide electrons for the reduction of Cr(VI). When increasing levels of Cr were added to soils, both microbial respiration and plant growth decreased. The application of black carbon was more effective than biochar in increasing the microbial population and in mitigating the phytotoxicity of Cr(VI). The net benefit of black carbon emerged as an increase in plant biomass and a decrease in Cr concentration in plant tissue. Consequently, it was concluded that black carbon is a potential reducing amendment in mitigating Cr(VI) toxicity in soil and plants.

Download full-text


Available from: Girish Choppala, Jul 18, 2015
  • Source
    • "Before we would gamble the future climate on these considerable uncertainties, biochar and C budgeting studies should consider these factors and address if the stability of biochar in soil does have the potential to ensure environmental safety. 4. Agronomic and environmental implications: associated values and risks Biochar is generally used to restore and reclaim infertile and degraded soils because it improves physico-chemical characteristics of soil, reduces greenhouse gas emissions, enhances nutrient use efficiency, increases crop productivity, and the sorption of organic contaminants (Bracmort, 2010; Choppala et al., 2012). However, not all soils demonstrate broader improvements, and not all crops behave in the same way with biochar amendment (Sparkes and Stoutjesdijk, 2011). "
    [Show abstract] [Hide abstract]
    ABSTRACT: 'Biochar' represents an emerging technology that is increasingly being recognized for its potential role in carbon sequestration, reducing greenhouse gas emissions, waste management, renewable energy, soil improvement, crop productivity enhancement and environmental remediation. Published reviews have so far focused mainly on the above listed agronomic and environmental benefits of applying biochar, yet paid little or no attention to its harmful effects on the ecological system. This review highlights a balanced overview of the advantages and disadvantages of the pyrolysis process of biochar production, end-product quality and the benefits versus drawbacks of biochar on: (a) soil geochemistry and albedo, (b) microflora and fauna, (c) agrochemicals, (d) greenhouse gas efflux, (e) nutrients, (f) crop yield, and (g) contaminants (organic and inorganic). Future research should focus more on the unintended long-term consequences of biochar on biological organisms and their processes in the soil.
    Full-text · Article · Feb 2016 · Environment International
  • Source
    • "Therefore, the restoration of such heavy metalrich soils using novel and economically feasible technologies is an urgent necessity before they are used in agriculture. Soil washing/flushing (Davis and Olsen 1995) chelate-enhanced phytoremediation/phytoextraction (Mahimaraja et al. 2011) and application of soil amendments are some of the more common soil treatment processes applied for the remediation of Cr polluted soils (Choppala et al. 2012). Chromium remediation in soils involves extraction from the soil matrix by washing with a chelating agent, and the major risk of applying this remediation approach is the increase in the oxidation potential of soil enhancing the conversion of trivalent Cr into the soluble and more toxic hexavalent form of Cr (Di Palma et al. 2012). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Purpose This study was aimed to investigate the potential of biochar (BC), a waste byproduct of a bioenegy industry, Sri Lanka, as a soil amendment to immobilize and reduce the phytotoxicity of Cr in tannery waste-polluted soil (TWS). Materials and methods The TWS and bioenergy waste BC were characterized for physio-chemical parameters. A pot experiment was conducted by adding three BC application rates, 1, 2.5, and 5 % (w/w) to investigate the immobilizing capacity and bioaccumulation of chromium (Cr) in tomato plants (Lycopersicon esculentum L.). Soils and plants were digested via microwave digestion and analyzed for total Cr. Further, sequential extraction was conducted to assess the fractionation of Cr before and after the application of bioenergy waste BC on TWS. Results and discussion The total Cr concentration in TWS was 12,285 mg/kg. The biomass of tomato plants grown in the 5 % BC amendment doubled compared to the biomass in BC-unamended soil. Bioaccumulation of Cr in plants grown in 5 % BC-amended TWS showed a decrease by 97 % compared to that of the BC-unamended soil. The CaCl2 extractability of Cr indicated that the bioavailability of Cr in the 5 % BC amendment has decreased by 68 % compared to the control. Sequentially extracted Cr in the exchangeable fraction decreased by 98 % in the 5 % BC amendment. Conclusions Pore diffusion, and adsorption via π-π electron donor-acceptor interactions were the primary mechanisms to be involved in the Cr retention in BC. Results suggested that the addition of BC to TWS reduces the mobility, bioavailability, and phytotoxicity of Cr in tomato plants.
    Full-text · Article · Dec 2015 · Journal of Soils and Sediments
    • "The addition of BC did increase the microbial activity of soil, as measured by increased respiration but we didn't examine reducers. Choppala et al. (2012) found addition of BC increased the microbial respiration by 2 times, which may be due to the greater abundance of carbon as an energy source for microbes. BC application to soil significantly increased CO 2 evolution through increases in soil microbial activity, which may be attributed to the addition of labile C and increase in soil pH (Farrell et al., 2013). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Heavy metals such as chromium (Cr) and arsenic (As) occur in ionic form in soil, with chromate [Cr(VI)] and arsenate As(V) being the most pre-dominant forms. The application of biochar to Cr(VI) and As(V) spiked and field contaminated soils was evaluated on the reduction processes [(Cr(VI) to Cr(III)] and [As(V) to As(III))], and subsequent mobility and bioavailability of both As(V) and Cr(VI). The assays used in this study included leaching, soil microbial activity and XPS techniques. The reduction rate of As(V) was lower than that of Cr(VI) with and without biochar addition, however, supplementation with biochar enhanced the reduction process of As(V). Leaching experiments indicated Cr(VI) was more mobile than As(V). Addition of biochar reversed the effect by reducing the mobility of Cr and increasing that of As. The presence of Cr and As in both spiked and contaminated soils reduced microbial activity, but with the addition of biochar to these soils, the microbial activity increased in the Cr(VI) contaminated soils, while it was further decreased with As(V) contaminated soils. The addition of biochar was effective in mitigating Cr toxicity by reducing Cr(VI) to Cr(III). In contrast, the conversion process of As(V) to As(III) hastened by biochar was not favourable, as As(III) is more toxic in soils. Overall, the presence of functional groups on biochar promotes reduction by providing the electrons required for reduction processes to occur as determined by XPS data.
    No preview · Article · Sep 2015 · Chemosphere
Show more