186 Khan et al.: Journal of aoaC InternatIonal Vol. 96, no. 1, 2013 Speciation of Vanadium in Coal Mining, Industrial, and Agricultural Soil Samples Using Different Extractants and Heating Systems Sumaira Khan, TaSneem Gul Kazi, 1 haSSan imran afridi, nida faTima Kolachi, naeem ullah, and Kapil dev University of Sindh, Center of Excellence in Analytical Chemistry, Jamshoro, Pakistan, 76080 Received November 18, 2011. Accepted by AK February 9, 2012. 1 Corresponding author’s e-mail: tgkazi@yahoo.com DOI: 10.5740/jaoacint.11-499 RESIDUES AND TRACE ELEMENTS A fast microwave-assisted extraction procedure was developed for the speciation of vanadium (V) species in soil samples collected from the vicinity of the Lakhra coal power plant (situated near a coal mining area) and industrial and agricultural areas. Soil samples were treated with two extracting reagents, (NH 4 ) 2 HPO 4 (0.2–1 M) and Na 2 CO 3 (0.1– 0.5 M), and heated by conventional and microwave methods for different time intervals to extract V +5 species. The V +4 and total V were extracted from filtration residue and the same subsamples of soil by treating with the acid mixture of HNO 3 –HCl–HClO 4 – H 2 SO 4 (1:1:1:1, v/v/v/v). No significant difference between V +5 contents obtained by conventional heating and microwave-assisted extraction was observed (P = 0.485). The extraction efficiency of 0.6 M (NH 4 ) 2 HPO 4 for V +5 was lower (4–7%) than that obtained by 0.2 M Na 2 CO 3 solution. The levels of V +5 were higher in soil samples collected from the vicinity of the Lakhra coal power plant and industrial areas, compared to those obtained from agricultural soil. V anadium (V) is a natural constituent of the earth that is distributed extensively in nature (1). Major sources are oil and fossil fuels; hence, the combustion of fossil fuel has been described as one of the largest sources of environmental pollution by V (2). Through human activities, such as the disposal of V-containing waste and oil leakage (3), industrial activities, and anthropogenic emissions, the concentrations of V in soil have increased significantly in recent years (4), and the number of people affected by V pollution has increased (5). Though V can exist in different oxidation states in the environment, V +4 and V +5 are usually found in minerals (6). V at trace levels is an essential element for normal cell growth and has been found to possess properties that reduce the effects of cancer (7), diabetes (8), and human immunodeficiency virus (HIV; 9). At higher concentrations, V is toxic to both plants and animals (10–12). V +5 compounds are more toxic than V +3 and V +4 compounds (13). It is important to separate and quantify V +5 species in order to assess their potential risk to the environment and biological systems, rather than determining total V content (14). Many investigations that have been dedicated to the determination of V in soils were mainly concentrated on the determination of total V contents (15, 16). The U.S. Environmental Protection Agency has not listed V as a pollutant requiring urgent research and legislation, because there is no evidence that the general population is at risk either through deficiency of or overexposure to V (17). Consequently, there are few countries where standards and regulations for environmental pollution in soil with V are accepted, e.g., Russia, where the maximum content of V is 150 µg/g allowed in agricultural soil (16, 17). Several analytical techniques have been used to determine V and its species at trace levels in various samples (18–20). Graphite furnace atomic absorption spectrometry (AAS) is usually the technique of choice for trace element analysis due to its high sensitivity, low sample consumption, simplicity of operation, and reduced matrix effects (21). Most of the publications concerning the speciation of V in environmental samples deal with liquid samples such as water (22, 23), while selective determination of V species in solids, until now, requires additional effort (12). Finally, there is no official method for V +5 speciation in solid samples. (NH 4 ) 2 HPO 4 and Na 2 CO 3 have been used as effective reagents to extract all V +5 species from plants (24) and soils of contaminated areas in the vicinity of a V mine (25, 26). Microwave power is an extremely useful auxiliary factor, which has lately been exploited for increasing the rate of different chemical processes (27, 28). A rapid solvent chemical extraction (29) and metals fractionation in different solid samples are some of the most known applications. The aim of this work was to assess the potential pollution impact of a coal power plant situated near a coal mining area in southern Sindh, Pakistan, on the surrounding areas by monitoring V species in soil samples. For comparison, soil samples from industrial and agricultural areas were also collected. The V +5 and V +4 content was determined in soil samples using two extracting reagents and heating conventionally, as well as by microwave. The microwave and conventional heating times were optimized for extraction of V +5 from soil samples. For comparison purposes, soil samples from an agricultural field, devoid of any industrial activity, were also analyzed. The concentration of V was determined by graphite furnace AAS using different modifiers. Experimental Sample Collection The surface layer of soil samples (0–25 cm) were collected during 2008 to 2009 from different areas of Sindh, Pakistan, six sites of the Lakhra coal power plant, and an industrial area (n = 24 each). For comparative purposes, agricultural soil samples from an area devoid of any industries were also collected. The collected samples were air dried at room temperature for 4 days, screened through a 2 mm sieve (Retsch GmbH, Haan, Germany), Downloaded from https://academic.oup.com/jaoac/article/96/1/186/5654937 by guest on 30 January 2023