Sr Isotope Composition of Bottled British Mineral Waters for Environmental and Forensic Purposes

Durham Research Online Deposited in DRO: 17 December 2013 Version of attached le: Accepted Version Peer-review status of attached le: Peer-reviewed Citation for published item: Montgomery, J. and Evans, J.A. and Wildman, G. (2006) 'Sr-87/Sr-86 isotope composition of bottled British mineral waters for environmental and forensic purposes.', Applied geochemistry., 21 (10). pp. 1626-1634. Further information on publisher's website: http://dx.doi.org/10.1016/j.apgeochem.2006.07.002 Publisher's copyright statement: NOTICE: this is the author's version of a work that was accepted for publication in Applied geochemistry. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reected in this document. Changes may have been made to this work since it was submitted for publication. A denitive version was subsequently published in Applied geochemistry, 21 (10), 2006, 10.1016/j.apgeochem.2006.07.002 Additional information: Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full DRO policy for further details. Durham University Library, Stockton Road, Durham DH1 3LY, United Kingdom Tel : +44 (0)191 334 3042 | Fax : +44 (0)191 334 2971 https://dro.dur.ac.uk 87Sr/86Sr isotope composition of bottled British mineral waters for environmental and forensic purposes J. Montgomery+, J. A. Evans‡* and G. Wildman‡. + Department of Archaeological Sciences, University of Bradford, Bradford, BD7 1DP, UK. ‡BGS, Keyworth, NOTTS NG12 5GG, UK *Corresponding author: J.A. Evans, NIGL, BGS, Keyworth, NOTTS, NG12 5GG, 0115 936 9396, Fax, 0115 9363302, e-mail: [email protected] Abstract Mineral waters in Britain show a wide range of 87Sr/86Sr isotope compositions ranging between 87Sr/86Sr = 0.7059 from Carboniferous volcanic rock sources in Perthshire, to 87Sr/86Sr = 0.7207 in the Dalradian aquifer of Aberdeenshire. The 87Sr/86Sr composition of the waters shows a general correlation with the aquifer rocks, resulting in the waters from older rocks having a more radiogenic signature than those from younger rocks. This wide range of values means that the Sr isotope composition of mineral water has applications in a number of types of studies. In the modern commercial context, it provides a way of fingerprinting the various mineral waters and hence provides a method for recognising and reducing fraud. From an environmental perspective, it provides the first spatial distribution of bio-available 87Sr/86Sr in Britain that can be used in modern, historical and archaeological studies. Keywords Sr-isotopes; mineral water; Britain; environment; provenance; forensic; archaeology. Introduction Sr as an environmental tracer Sr isotopes are well established as a method of fingerprinting biosphere signatures and are increasingly used as a tool for human migration studies in archaeology; recent examples include Price et al. (2004), Montgomery et al. (2005), Hodell et al. ( 2004) but so far little has been published on their use as a forensic tool. Barbaste et al. (2002) demonstrated the use of the technique in provenancing and finger printing wine; ivory was traced using 87Sr/86Sr isotopes (van der Merwe et al., 1990) and Negrel et al. (2004) used them to trace river catchments and monitor the effect of agricultural pollutants. More recently, Sr was one of the key isotope tools used in tracing modern humans (Beard et al., 2000) and the origins of a murder victim (Pye, 2004). The rapid expansion of bottled mineral water over the last decade has lead to bottled water being produced and available all over Britain. Such waters are purchased primarily for the perceived “ purity” of the product but, because of the ready availability of water, the potential for fraud is considerable. Isotope fingerprinting should be able to provide a clear and precise Sr isotope ratio to mineral springs that can be used to help define the product. Sr has four naturally occurring isotopes, three of which (84Sr, 86Sr, 88Sr) are stable but 87Sr is derived from the decay of 87Rb. This means that the 87Sr/86Sr ratio of a rock is dependent upon the Rb content and age of the rock. As a result, younger, low-Rb rocks such as basalt will have whole rock 87Sr/86Sr values around 0.706 whereas older and more Rb rich rocks such as granites tend to have much higher values. The Sr isotope composition of water has been used in many studies of water rock interaction including aquifer sources, groundwater pathways and pollution studies (Wickman and Aberg, 1987; Aberg, 1995; Negrel et al., 2004). Water equilibrates with the host rock and reflects the isotope composition of the minerals able to exchange with water. In the case of carbonates, this is likely to reflect the bulk rock isotope composition as these rocks are essentially homogenous with respect to Sr but, in silicates, the Sr released during weathering is dominated by mineral-specific isotopic compositions which means that the composition of the water may be very different from the whole-rock value of the silicate host rock (Aberg, 1995; Blum et al., 1993; Jacobson and Blum, 2002; Bau et al., 2004). Derry et al. (2006) looked at the isotope variation between minerals within a quartz diorite from Puerto Rico and found the following variations in 87Sr/86Sr between minerals: biotite 87Sr/86Sr = 0.7827, feldspar 87Sr/86Sr = 0.7036 and amphibole 87Sr/86Sr 0.7058. This resulted in the pore fluid of the overlying soil varying between c. 0.711 and c. 0.705 depending upon the proportion of biotite to feldspar and amphibole within certain soil horizons. Britain has a very varied geological structure and might be expected to yield a wide range of Sr isotope compositions within its mineral waters. However very little data are presently available from British aquifers and groundwaters (Shand et al., 2001; Spiro et al., 2001; Bain and Bacon, 1994). The waters in this study Only mineral waters with clear details of provenance were included in this study. The labels on the bottles clearly stated that the content was bottled at source and an address was given. The locality of the sample is based on the post-code of the bottling address. Many of these samples are recognised “Natural Mineral Waters” as defined by The Food Standards Agency. The requirements of a “Natural Mineral Water” are that: 1) it must come from a specified groundwater source, protected from all kinds of pollution; 2) it must be officially recognised after a qualifying period of two years; 3) it must be untreated and bottled at source; 4) the label must carry the proper description “Natural Mineral Water”, which cannot be used for any other types of bottled water; and finally, 5) the label must show the name of the recognised source and mineral content values. At the time of writing, ninety-nine waters from Britain were certified as “Natural Mineral Waters” by the Food Standards Agency. Many wells that are now exploited on a commercial basis, such as St Anne’s Well in Buxton, Derbyshire, have a long documented history of use and it is highly likely they were also a source of drinking water in prehistoric times. Some were believed to be endowed with healing properties (e.g. Burnett 1925; Whelan and Taylor 1989) while others would have simply been a source of clean water. This means that the analysis of water from these wells not only gives us a useful forensic tool but it is also of use in environmental studies as it provides a direct measurement of a dietary component of ancient people that is free of modern contaminants. Method The seal on the bottled water was broken in the clean laboratory and 20 mls of each sample was measured into pre-cleaned Teflon beakers. Each sample was mixed with 84Sr tracer solution, acidified using 1ml of 6M Teflon distilled HCl, and evaporated to dryness. Sr was collected using conventional Dowex© resin ion exchange methods. Sr isotope composition and concentrations were determined using a 262 Finnigan MAT multi-collector mass spectrometer using TaF activator on single rhenium filaments (after the method of Birck, 1986). All samples were run to an internal precision of ± 0.000007 (1SE) or better. The international standard for 87Sr/86Sr, NBS987, gave values of 0.710207 ± 0.000030 (n=8, 2). All Sr ratios have been corrected to an accepted value for the standard of 0.710250. Sr blanks are c. 40 pg. The data and sample information are presented in Table 1. Results The results are presented on Figure 1 and the locations of the samples are given superimposed on the surface geology of Britain on Figure 2. The majority of the boreholes and wells from which these waters are drawn are between 50 and 200 m depth so that the water is drawn from aquifer rocks at or near the surface. From Figure 1 it can be seen that, in general, there is a trend for increasing 87Sr/86Sr signatures in the waters, with increasing stratigraphic age of the aquifer host rock. The results are discussed below in relation to the geology of their host aquifer. The absolute times given for each system are rounded to the nearest whole number and taken from Gradstein et al.

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