Pedosphere 22(4): 544–553, 2012 ISSN 1002-0160/CN 32-1315/P c  2012 Soil Science Society of China Published by Elsevier B.V. and Science Press Attenuation of Metal Bioavailability in Acidic Multi-Metal Contaminated Soil Treated with Fly Ash and Steel Slag *1 QIU Hao 1 , GU Hai-Hong 1 , HE Er-Kai 1 , WANG Shi-Zhong 1,∗2 and QIU Rong-Liang 1,2 1 School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275 (China) 2 Guangdong Provincial Key Lab of Environmental Pollution Control and Remediation Technology, Guangzhou 510275 (China) (Received March 14, 2012; revised May 22, 2012) ABSTRACT A pot experiment was conducted with multi-metal (Pb, Cd, Cu, and Zn) contaminated acidic soil to investigate changes in available metal burden resulting from the application of industrial wastes (fly ash and steel slag). The efficiency of amendments- induced metal stabilization was evaluated by diffusive gradients in thin films (DGT), sequential extraction, and plant uptake. The stability of remediation was assessed by an acidification test and by chemical equilibrium modeling. Addition of fly ash (20 g kg -1 ) and steel slag (3 g kg -1 ) resulted in similar increase in soil pH. Both amendments significantly decreased the concentrations of metals measured with DGT (C DGT ) and the metal uptake by Oryza sativa L. Significant correlations were found between C DGT and the concentration of a combination of metal fractions (exchangeable, bound to carbonates, and bound to Fe/Mn oxides), unraveling the labile species that participate in the flux of metal resupply. The capability of metal resupply, as reflected by the R (ratio of C DGT to pore water metal concentration) values, significantly decreased in the amended soils. The C DGT correlated well with the plant uptake, suggesting that DGT is a good indicator for bioavailability. Acidification raised the extractable metal concentration in amended soil but the concentration did not return to the pre-amendment level. Equilibrium modeling indicated that the soil amendments induced the precipitation of several Fe, Al and Ca minerals, which may play a positive role in metal stabilization. Chemical stabilization with alkaline amendments could be an effective and stable soil remediation strategy for attenuating metal bioavailability and reducing plant metal uptake. Key Words: acidification, chemical stabilization, diffusive gradients in thin films (DGT), heavy metal, remediation Citation: Qiu, H., Gu, H. H., He, E. K., Wang, S. Z. and Qiu, R. L. 2012. Attenuation of metal bioavailability in acidic multi-metal contaminated soil treated with fly ash and steel slag. Pedosphere. 22(4): 544–553. Industrial mining and smelting activities have pro- duced a large amount of metal-rich wastes such as tai- lings and acid mine drainage (Pruvot et al., 2006; Gu et al., 2011). The metals in mining wastes are spread through surface run-off, leaching and crop irrigation, resulting in serious contamination of agricultural soils around mining areas (Kumpiene et al., 2007; Gu et al., 2011). Significant efforts have been made to es- tablish a widely usable approach for soil remediation (Lombi et al., 2002; Guo et al., 2006). Among them, chemical stabilization with amendments for decreas- ing metal bioavailability and toxicity has emerged as a promising technology (Kumpiene et al., 2008; Lee et al., 2011; Lopareva-Pohu et al., 2011). Chemical stabilization relies heavily on decreasing metal bioavailability, because it is designed to reme- diate soils not by removing metals from soil, but by fixing them in more stable forms (Hamon et al., 2002). Therefore, the identification of a form or com- bination of forms of a metal as the bioavailable frac- tion is a fundamental task in improving remedia- tion and risk assessment. In many studies where re- searchers tried to couple metal speciation to metal uptake by plants, good correlations were found be- tween the amount of metal bioaccumulation and free ion concentrations (Slaveykova and Wilkinson, 2002; Kalis et al., 2006). On the other hand, Knight et al. (1997) found that the amount of Zn depletion in soil solution caused by uptake by the hyperaccumulator Thlaspi caerulescens was only about 1% of total Zn accumulated, indicating that a considerable part of Zn accumulated by T. caerulescens originated from labile, solid-phase binding Zn. A better understanding of the fate of soil solid-associated metals is needed, because when dissolved metal concentrations alone are used to predict bioavailability, then environmental risks could be underestimated if there is bioavailable metal asso- ciated with soil particles. *1 Supported by the NSFC-Guangdong Joint Foundation of China (No.U0833004), the National Natural Science Foundation of China (No.41101483) and the Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme (2011), China. *2 Corresponding author. E-mail: wshizh2@mail.sysu.edu.cn.