Application of Leaching Tests for Toxicity Evaluation of Coal Fly Ash V. Tsiridis, 1,2 P. Samaras, 3 A. Kungolos, 4 G. P. Sakellaropoulos 1,2 1 Chemical Process Engineering Laboratory, Department of Chemical Engineering, Aristotle University of Thessaloniki, 54006 Thessaloniki, Greece 2 Chemical Process Engineering Research Institute, 6th km Harilaou Thermi Road, 57001 Thessaloniki, Greece 3 Department of Pollution Control Technologies, Technological Educational Institute of West Macedonia, 50100 Kozani, Greece 4 Department of Planning and Regional Development, University of Thessaly, 38334 Volos, Greece Received 17 June 2005; accepted 21 March 2006 ABSTRACT: The toxic properties of coal ﬂy ash samples obtained from various coal combustion power plants were evaluated in this work using physicochemical analyses and bioassays. Physicochemical anal- yses showed that heavy metals present in solid samples included Cr, Cu, Mn, Ni, Pb, and Zn. The results of the chemical analysis of eluates deduced by the application of standard leaching tests according to EN 12457-2 and Toxicity Characteristic Leaching Procedure (TCLP) methods indicated that the compounds contained in ﬂy ashes could potentially be transferred to the liquid phase depending upon the leaching method used. Heavy metal concentrations were higher in TCLP eluates, indicating that the initial pH value of the leaching medium signiﬁcantly affected the transfer of these elements to the liquid phase. Tests con- ducted with the photobacterium Vibrio ﬁscheri (Microtox test), the crustacean Daphnia magna, and the rotifer Brachionus calyciﬂorus were used to assess toxicity of eluates obtained by both leaching tests. Daphnia magna was the most sensitive test organism. The EN 12457-2 method proved to be more reliable for toxicity evaluation of eluates. In contrast, the TCLP method showed some interference owing to acetic acid toxicity, and precipitation occurred after pH adjustment of eluates from acid to neutral range. The toxicity of both ﬂy ashes and the corresponding solid leaching residues of EN 12457-2 and TCLP leaching tests was also measured using the Microtox Basic Solid phase Test. The results generated with this bio- assay indicated that toxicity was greatly inﬂuenced by the pH status of the solid samples. # 2006 Wiley Periodicals, Inc. Environ Toxicol 21: 409–416, 2006. Keywords: ﬂy ash; leaching; eluates; heavy metals; Vibrio ﬁscheri; Brachionus calyciﬂorus; Daphnia magna INTRODUCTION The disposal of ﬂy ash solid residues from coal power plants is a signiﬁcant environmental problem, as ﬂy ash is currently produced in huge amounts. The amount of trace elements contained in ﬂy ash mainly depends on the quality of the coal used as well as on the combustion process and pollution control facilities applied to coal power plants (Vassilev and Vassileva, 1997). Several trace elements, such as Cd, Cr, Mn, Ni, Pb, Zn, present in the feed coal may appear in the bottom and ﬂy ash, depending upon their partial or total vaporization during combustion (Querol et al., 1996; Vassilev and Vassileva, 1997). The detection of all trace elements and the evaluation of their environ- mental impact represent a difﬁcult and complicated issue, Correspondence to: P. Samaras; e-mail: psamaras@kozani.teikoz.gr Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.20187  C 2006 Wiley Periodicals, Inc. 409