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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Institutional Research Information System University of Turin This Accepted Author Manuscript (AAM) is copyrighted and published by Elsevier. It is posted here by agreement between Elsevier and the University of Turin. Changes resulting from the publishing process - such as editing, corrections, structural formatting, and other quality control mechanisms - may not be reflected in this version of the text. The definitive version of the text was subsequently published in Chemosphere, Volume 85, issue 6, Oct 2011, doi: 10.1016/j.chemosphere.2011.06.061 You may download, copy and otherwise use the AAM for non-commercial purposes provided that your license is limited by the following restrictions: (1) You may use this AAM for non-commercial purposes only under the terms of the CC- BY-NC-ND license. (2) The integrity of the work and identification of the author, copyright owner, and publisher must be preserved in any copy. (3) You must attribute this AAM in the following format: Creative Commons BY-NC- ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/deed.en), doi 10.1016/j.chemosphere.2011.06.061 1 Fractionation and speciation of arsenic in three tea gardens soil profiles and distribution of As in different parts of tea plant (Camellia sinensis L.) Tanmoy Karak1,2, Ornella Abollino3*, Pradip Bhattacharyya4, Kishore K. Das5, Ranjit K. Paul6 1Pollution Control Board, Assam, Bamunimaidam, Guwahati-21, India 2 Present address: Department of Soil, Tocklai Experimental Station, Tea Research Association, Jorhat- 8, Assam, India 3 Department of Analytical Chemistry, University of Torino, Via Pietro Giuria 5, 10125 Torino, Italy 4 Department of Environmental Sciences, University of California, Riverside, CA 92521, USA 5Department of Statistics, Gauhati University, Guwahati-781014, Assam, India 6 Central Inland Fisheries Research Institute, Barrackpore, Kolkata-700120, West Bengal, India *Corresponding author. Tel.: +39 011 6707844; fax: +39 011 6707615 E-mail address: [email protected] (O. Abollino) 2 ABSTRACT The distribution pattern and fractionation of arsenic (As) in three soil profiles from tea (Camellia sinensis L.) gardens located in Karbi-Anglong (KA), Cachar (CA) and Karimganj (KG) districts in the state of Assam, India, were investigated depth-wise (0-10, 10-30, 30-60 and 60-100 cm). DTPA-extractable As was primarily restricted to surface horizons. Arsenic speciation study showed the presence of higher As(V) concentrations in the upper horizon and its gradual decrease with the increase in soil depths, following a decrease of Eh. As fractionation by sequential extraction in all the soil profiles showed that arsenic concentrations in the three most labile fractions (i.e., water-soluble, exchangeable and carbonate-bound fractions) were generally low. Most arsenic in soils was nominally associated with the organic and Fe-Mn oxide fractions, being extractable in oxidizing or reducing conditions. DTPA-extractable As (assumed to represent plant-available As) was found to be strongly correlated to the labile pool of As (i.e. the sum of the first three fractions). The statistical comparison of means (two-sample t-test) showed the presence of significant differences between the concentrations of As(III) and As(V) for different soil locations, depths and fractions. The risk assessment code (RAC) was found to be below the pollution level for all soils. The measurement of arsenic uptake by different parts of tea plants corroborated the hypothesis that roots act as a buffer and hold back contamination from the aerial parts. Keywords: Soil Arsenic Sequential extraction Speciation Risk Assessment Code Tea 3 1. Introduction Tea (Camellia sinensis L.) plant grows in moderately hot (13 to 32oC) humid climate and in well-drained fertile acidic soils (pH between 4.5 and 5.5). Tea is known as a part of nonalcoholic dietary habits in many countries around the world due to its medicinal values (Higdon and Frei, 2003; Crespy and Williamson, 2004; Cabrera et al., 2006 ; Zaveri, 2006), and therefore it undoubtedly acts as a fillip in the global market. The popularity of tea is also connected to its easy access, therapeutic efficacy, relatively low cost and also for the assumption of the absence of any toxic side effects, which is clear from the fact that about 18-20 billion tea cups are consumed daily in the world (Pedro et al., 2001; Ganguly, 2003). However, tea has effect in human body; a recent review and research publications discussed and reported cases of heavy metal (e.g. chromium, cobalt, copper, cadmium, zinc, manganese, nickel, lead and mercury) accumulation and contamination in tea (Han et al., 2005; Jin et al., 2005; El-Hadri et al., 2007; Han et al., 2007a; Jin et al., 2008; Ashraf and Mian, 2008; Seenivasan et al., 2008a; Seenivasan et al., 2008b; Karak and Bhagat, 2010). The probable reason behind the accumulation of heavy metals in tea is that this plant is acidophilic, and acidic soils in tea gardens are affected by an increase in heavy metal dissolution, in comparison to neutral and alkaline soils, which increases the uptake of metals by tea leaves (Han et al., 2007a). Besides the above mentioned metals, indigenous soil arsenic might be soluble in tea garden soils and consequently it might be assimilated by tea plants (Karak and Bhagat, 2010). The consumption of arsenic even at low levels through the food chain may lead to carcinogenesis (Mandal and Suzuki, 2002). Among the different oxidation states of As, arsenite [As(III)] and arsenate [As(V)] are the main inorganic forms in most contaminated soils and sediments (Smith et al., 1999). In oxygen-rich environments and well-drained soils, As(V) species dominate, notably in - the form of H2AsO4 in acidic soils (Van Herreweghe et al., 2003). Under reducing conditions As (III) is the stable oxidation state. According to the literature, As(III) is ten times more soluble, mobile and toxic than As(V) (Van Herreweghe et al., 2003) and it can react with sulphydryl groups in enzymes (Faust and Aly, 1981). After a critical evaluation of the available literature, it was seen that most of the research outcomes were on total soil arsenic, as it reflects the geological origins of soils as well as the anthropogenic inputs. However, the use of arsenic total concentration as a criterion to assess the potential effects of soil contamination 4 implies that all forms of a given element have an equal impact on the environment; such an assumption is clearly untenable (Tessier et al., 1979). Therefore, fractionation of soil arsenic is an important tool of chemical characterization and can provide useful information on its bioavailability (McLaren et al., 1998). To the best of our knowledge, research on arsenic has mainly been focused on the transfer of As from soil to the major most common plants (or crops), considering highly As-contaminated soils (Ma et al., 2001; Ming et al., 2001; Flynn et al., 2002; Alam et al., 2003; Baroni et al., 2004; Bondada et al., 2004; Hartley et al 2004; Norra et al., 2005 ; Lee, 2006; Chen et al., 2007; Anawar et al., 2008; Ngoc et al., 2009; Lu et al., 2010 and the references therein). Nevertheless, most of the food consumption originates from crops grown in countryside agricultural fields that are not heavily contaminated with arsenic, but may contain meaningful concentrations of this element, which may be harmful if transferred to the food chain. Assam is the state in North-East India and is characterized by all the favourable conditions for tea plantation. The total tea cultivation area in this state is ~510492 hectares and the total levels of production and exportation of tea in January 2009 were 21.57 MKg and 12.70 MKg respectively (Tea statistics of India, 2009). In India this plant is one of the major cash crops and is one of the major sources of foreign currency from agricultural products. However, no data is available on arsenic in tea garden soils and its uptake by tea plants in Assam, India, although the results of a soil geochemical prospect have revealed arsenic contamination in tea garden soils (Ngoc et al., 2009). The transfer of arsenic from soils to plants might be a key step in the route of As entry into food stuffs. The typical soil-to-plant transfer factors of As, summarized by Kloke et al. (1984), varied from 0.01 to 0.1. The transfer factors of arsenic for various vegetables, according to Alam et al. (2003) and Warren et al. (2003), ranged from 0.001 to 0.038 and 0.0007 to 0.032 respectively. However, the studies on the dynamics of As in soil and its uptake, translocation and accumulation by tea plants are scanty. Moreover, to the best of our knowledge, the ability of soil extraction methods to distinguish between As(III) and As(V) in the soils of tea gardens has not been reported so far. In view of the above facts, our studies were aimed to evaluating the ability of previously reported chemical extractants to measure the bioavailable fraction of As(III) and As(V) in soils collected from three tea gardens at different depths in the 5 state of Assam, India and also the arsenic dynamic from soil to tea plants. In particular, we have applied a sequential extraction scheme mainly based on Tessier’s protocol. Arsenic is mainly present as neutral or anionic species in soils, whereas Tessier’s protocol was originally designed for cations, like most of the chemical fractionation schemes available in the literature. However, many of such schemes have been adopted by several authors (e.g. Hlavay and Polyák, 1998; Matera et al., 2003; Rodriguez et al., 2003; Anawar et al., 2008) for arsenic fractionation too, and in our opinion they can represent a useful tool for the characterization of the behaviour and mobility of this element.