Immobilization of Chlorobenzenes in Soil Using Wheat Straw Biochar Yang Song, †,‡ Fang Wang, †,‡ Fredrick Orori Kengara, †,§ Xinglun Yang, † Chenggang Gu, † and Xin Jiang* ,† † State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, P. R. China § Department of Chemistry, Maseno University, Maseno 40105, Kenya * S Supporting Information ABSTRACT: Biochar has shown great potential for immobilizing organic contaminants in soil. In this study, pentachlorobenzene (PeCB), 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB), and 1,2,4-trichlorobenzene (1,2,4-TCB) artificially spiked soil was amended with wheat straw biochar at 0.1%, 0.5%, 1%, and 2% application rates, respectively. The sorption, dissipation, and bioavailability of chlorobenzenes (CBs) in soil were investigated. The sorption of PeCB by biochar was significantly higher than that of its sorption by both biochar-amended and unamended soil (p < 0.05). The dissipation and volatilization of CBs from biochar-amended soil significantly decreased relative to unamended soil (p < 0.05). Bioavailability of CBs, expressed as butanol extraction efficiency and earthworm (Eisenia fetida) bioaccumulation factor, significantly decreased with increasing aging time and biochar application rate. The effect of biochar content in soil on the bioavailability of CBs was more pronounced for 1,2,4-TCB relative to other CBs. This study suggested that wheat straw biochar, even at low application rates, could effectively immobilize the semivolatile CBs in soil and thus reduce their volatilization and bioavailability. KEYWORDS: biochar, bioavailability, butanol extraction, earthworm, POPs, volatilization ■ INTRODUCTION Biochar, a form of charred organic matter, is an increasingly utilized cost-effective soil amendment in agricultural and environmental applications. 1-3 Crop-residue-derived biochar, which has variously been described as a “soil conditioner”, can sequester C, reduce the emission of greenhouse gases, and improve soil fertility and thus plant growth. 4-6 Besides these characteristics, biochar has a large surface area and high microporosity, which results in a very high affinity and capacity for sorbing and immobilizing organic contaminants. 7,8 There- fore, biochar lends itself as a good material for contaminant immobilization, a kind of soil remediation strategy. 8 It is increasingly recognized that the bioavailable concen- tration, rather than total concentration, of contaminants in soil dominates their potential risks, degradation, uptake by biota, leaching, and other environmental fates. 9,10 Therefore, immobilization, which seeks to reduce the bioavailability and mobility of contaminants in soil by applying different organic/ inorganic amendments, has become an increasingly popular in situ soil remediation strategy. 11-13 Meanwhile, a series of chemical extraction methods, such as mild solvent extraction and solid-phase extraction, have been developed to assess the bioavailability of organic contaminants in soil. 10,14,15 Applica- tion of crop straw or hardwood-derived biochar, especially the ones pyrolyzed at high temperature, to contaminated soil could reduce the bioavailability of organic contaminants to soil biota. 16,17 For example, plant uptake of chlorpyrifos decreased with increasing biochar addition in soil. 16 The microbial degradation of benzonitrile, 18,19 atrazine, 20 and simazine, 21 etc., decreased in biochar-amended soil. Reduced earthworm accumulations of polycyclic aromatic hydrocarbons (PAHs) 22 and atrazine 11 in biochar-amended soils have also been reported. Most of the above studies were based on immobilizing polar or less volatile organic contaminants with biochar. 16-21 However, reports on whether or not biochar could immobilize semivolatile or volatile compounds are limited. 23 China is an important producer of chlorobenzenes (CBs) in the world and accounts for more than 50% of the worldwide production. 24 A lot of vegetable fields are close to the CB factories in the suburban areas of China. CBs can be released into air from factories and then enter into soil through dry/wet deposition and wastewater irrigation. 25 It has been reported that all the CB congeners, especially trichlorobenzenes (TCBs) and tetrachlorobenzenes (TeCB), have been detected in the soil of vegetable fields within 1 km from a CB factory. 25 Therefore, it is of great importance to immobilize the detected CBs in soil for safe vegetable production and to reduce their revolatilization from soil into air. Our previous study demonstrated that the bioavailability of hexachlorobenzene (HCB) was significantly decreased by wheat straw biochar addition into soil and established a mild solvent extraction method, butanol extraction, to assess the bioavailability of CBs. 26 However, among CBs congeners, the lower chlorinated CBs are more easily volatilized 27 and less persistent 28 than HCB. The objective of the present study was therefore to investigate whether wheat straw biochar could immobilize the semivolatile CBs in soil thereby reducing their volatilization losses and whether the immobilization efficiency of contami- nants by biochar is dependent on the volatility of the chemicals. CBs of different volatilities, pentachlorobenzene (PeCB), Received: January 28, 2013 Revised: April 6, 2013 Accepted: April 11, 2013 Published: April 11, 2013 Article pubs.acs.org/JAFC © 2013 American Chemical Society 4210 dx.doi.org/10.1021/jf400412p | J. Agric. Food Chem. 2013, 61, 4210-4217