Environmental Geochemistry and Health 26: 51–57, 2004. © 2004 Kluwer Academic Publishers. Printed in the Netherlands. An operationally defined method to determine the speciation of mercury Sirima Panyametheekul Department of Environmental Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand. (tels.: +66 2218-6667/6669; fax: +66 2218-6666; e-mail: Sirima.P@Chula.ac.th) Received 4 December 2002 Accepted 3 October 2003 Key words: combustion, mercury, soil, speciation, sulphur Abstract This paper presents a modified method of an operationally determined speciation of mercury in soil. The analytical work was mainly concerned to suit properly with inductively coupled plasma-atomic emission spectrometry (ICP-AES). Soil samples analysed in this study were selected from open areas around a crematorium, a waste incinerator, and two power plants. Results show that both topsoil and subsoil samples were dominated by elemental mercury Hg(0) and mercuric sulphide (HgS). The significant correlation between sulphur concentration and HgS was found in topsoil samples. Introduction A major proportion of mercury species in air is ele- mental mercury Hg(0) that normally has a residence time up to 1 year (e.g., Suzuki et al. 1991). This may result in long-range transport of Hg(0) and remote de- position. However, oxidation and transformation of Hg(0) to Hg(II) species followed by deposition (wet and/or dry) probably occur. This reaction, therefore, leads to a local deposition of Hg surrounding the point sources (e.g., Mason et al. 1994). In order to estimate how much of any species of mercury deposited on to soils, a sequential extraction procedure was carried out in this work. The method based on a determ- ination of operationally defined mercury fractions in soil samples is a modification of those reported by Di Giulio and Ryan (1987), Biester and Scholz (1997), and Lechler (1999). The samples higher in Hg were se- lected and shown in Table 1. Both topsoil and subsoil samples were collected from the same point. Materials and methods Samples The study sites were focused to four combustion plants in the UK (i.e., a crematorium, a waste incinerator, and two coal-fired power plants). Both power plants are in rural areas; one is equipped with flue gas desulphurisa- tion (FGD) system whereas another is non-FGD plant. In each sampling point, five samples in 1 m 2 area were comprised to be a representative sample for both top- soil (0–15 cm) and subsoil (15–30 cm) samples. Those samples were kept in the Kraft bags with sealed poly- ethylene bags to avoid both absorption of mercury from air and revolatilisation back to the atmosphere from soil samples (Davies 1976; Jones et al. 1995). The samples are then kept in a cooler box to preserve their chemical integrity until analysis. Eight samples selected from the combustion sys- tems and four reference materials were analysed un- der the operationally determined speciation described later. Table 1 presents a key of those investigated samples. Reference materials of National Institute of Standard & Technology, NIST (NBS) and House of Reference Materials were investigated in the same conditions. Two NBS samples are NBS2709 and NBS2711, and two House of Reference Materials are HRM1 and HRM2. HRM2 are soil samples taken from various parts in the UK whilst HRM1 contains soil in one specific area. Procedure The operationally defined speciation of mercury are elemental Hg, water soluble Hg, exchangeable Hg,