Speciation and fractionation of nickel in airborne particulate matter: comparison between selective leaching and XAS spectroscopy Kristof Tirez, * a Geert Silversmit, b Laszlo Vincze, b Kelly Servaes, a Chris Vanhoof, a Myriam Mertens, a Nico Bleux a and Patrick Berghmans a Received 16th June 2010, Accepted 24th November 2010 DOI: 10.1039/c0ja00049c Nickel speciation and fractionation using a multidisciplinary approach are discussed for different particulate matter samples collected in industrial and rural atmospheres. The technologies utilized in this research span from X-ray Absorption Near Edge Structure (XANES) and X-Ray Diffraction (XRD) to a wet chemistry sequential leaching assay (including determination by inductively coupled plasma atomic emission spectroscopy, ICP-AES). The Zatka sequential leaching method provides an inexpensive assay to differentiate among ‘soluble’, ‘sulfidic’, ‘metallic’, and ‘oxidic’ chemical forms of Ni. The XANES technique is especially well suited for Ni speciation between and to a lesser extent within the 4 defined Ni species groups of the Zatka sequential leaching procedure. Limitations for interpretation in the present study with respect to XANES are the availability of pure phase Ni species for uptake as reference spectra and the collinearity between the spectra of Ni compounds within a Ni species group (e.g. NiSO 4 $6H 2 O and Ni(NO 3 ) 2 $6H 2 O). The Ni speciation and fractionation results on the particulate matter samples reflect in general a good agreement between the modified Zatka sequential leaching procedure and the XANES data. For the particulate matter collected in and close to a stainless steel factory, Ni included in a spinel structure (NiFe 2 O 4 ) was identified as the principal Ni species. The particulate matter collected in rural atmosphere showed a 50/50 distribution between soluble and oxidic Ni species. Introduction The number of toxicity studies on the particulate matter in ambient air has increased in recent years and those studies have raised concerns about the role of metallic compounds. 1,2 For this reason total metal contents have been currently fixed as regula- tory target levels in ambient air. 3 The interpretation of health risks associated with ambient air exposure of metallic compounds is, however, somewhat limited by the lack of knowledge regarding the chemical speciation of metals in ambient air. It is known that different chemical forms of the same metal can have widely different biological and toxicological effects. It is therefore a necessity to have accurate knowledge about the chemical speciation in order to make an accurate assessment of the risks associated with respiratory exposure to fine particulates containing metals. 4 For example, nickel subsulfide (Ni 3 S 2 ) is considered the most carcinogenic Ni species on the basis of available human epidemiology and animal studies. 5,6 The carci- nogenicity of water-soluble Ni salts such as NiSO 4 $xH 2 O as well as insoluble Ni oxide compounds, and Ni spinels (e.g. NiFe 2 O 4 ), however, is controversial. Therefore, understanding the specia- tion of Ni—and metals in general—in ambient air is of the utmost importance for the assessment of respiratory health risks. This study was designed to provide new information on Ni speciation in particulate matter sampled from rural and indus- trial atmospheres. The technologies utilized in this research span from X-ray Absorption Fine Structure Spectroscopy (XAFS), Energy Dispersive X-ray Fluorescence (EDXRF), and X-Ray Diffraction (XRD) to a wet chemistry sequential leaching assay (including determination by inductively coupled plasma atomic emission spectroscopy, ICP-AES). The latter is a well established standard laboratory procedure for Ni speciation. 7,8 A wet chemical speciation method which exploits the differ- ence in chemical properties of the various Ni phases lacks the specificity of an instrumental method as it can only differentiate among groups of similarly reacting Ni compounds rather than individual species. However, the chemical speciation has an advantage in that it can be utilized in less sophisticated chemical laboratories. Furthermore chemical methods use larger (bulk) portions of particulate matter or dust samples, so intraparticle phase variability is not a problem. Wet chemical speciation a Flemish Institute of Technological Research—VITO, Environmental analysis and technology, Boeretang 200, 2400 Mol, Belgium. E-mail: Kristof.tirez@vito.be; Fax: +32 14339472; Tel: +32 14335036 b Ghent University, X-ray Microspectroscopy and Imaging Research Group (XMI), Department of Analytical Chemistry, Ghent University, Krijgslaan 281 S12, B-9000 Gent, Belgium This journal is ª The Royal Society of Chemistry 2011 J. Anal. At. Spectrom. Dynamic Article Links C < JAAS Cite this: DOI: 10.1039/c0ja00049c www.rsc.org/jaas PAPER Downloaded by VITO on 22 December 2010 Published on 22 December 2010 on http://pubs.rsc.org | doi:10.1039/C0JA00049C View Online