Catena 122 (2014) 216–228

Contents lists available at ScienceDirect

Catena

j ourna l homepage: www.e lsev ie r .com/ locate /catena

Application of chromium stable isotopes to the evaluation of Cr(VI)contamination in groundwater and rock leachates from central Euboeaand the Assopos basin (Greece)

Maria Economou-Eliopoulos a,⁎, Robert Frei b,c, Cathy Atsarou a

a Department of Geology and Geoenvironment, University of Athens, Athens 15784, Greeceb Department of Geoscience and Natural Resource Management, University of Copenhagen, NordCEE, University of Copenhagen, Denmarkc Department of Geoscience and Natural Resource Management, Nordic Center for Earth Evolution, NordCEE, University of Copenhagen, Denmark

⁎ Corresponding author. Tel./fax: +30 210 7274214.E-mail address: econom@geol.uoa.gr (M. Economou-E

http://dx.doi.org/10.1016/j.catena.2014.06.0130341-8162/© 2014 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 5 December 2013Received in revised form 13 May 2014Accepted 24 June 2014Available online xxxx

Keywords:Chromium isotopesGroundwaterLeachatesCr(VI)EuboeaAssopos

Major and trace elements (a) in groundwater, ultramafic rocks from natural outcrops and soil samples from cul-tivated sites of Central Euboea and Assopos basin, and (b) in experimentally produced laboratorywater leachatesof rocks and soils were investigated by SEM/EDS, XRD and ICP/MS. In addition, stable chromium isotopes(expressed as δ53Cr values) were measured in groundwater and leachates in order to identify potential sourcesfor Cr-contamination.The higher Cr(VI) concentrations in soil leachates compared to those in the rock pulp leachates potentially can beexplained by the presence of larger amounts of Fe (Fe(II)) and Mn (Mn-oxides acting as oxidizing catalysts).Assuming that redox processes produce significant Cr isotope fractionation (groundwater δ53Cr values range be-tween 0.8 and 1.98‰), the compilation of the obtained analytical data suggests that the dominant cause of Cr iso-tope fractionation is post-mobilization reduction of Cr(VI). However, the lack of a very good negative relationshipbetween Cr(VI) concentrations and δ53Cr values may reflect that sorption, precipitation and biological processes(fractionation during uptake by plants) complicate the interpretation of the Cr isotope signatures.The variation in δ53Cr values (0.84 to 1.98‰ in groundwater from Euboea, and from 0.98 to 1.03‰ in samplesfrom the Assopos basin) imply initial oxidative mobilization of Cr(VI) from the ultramafic host rocks, followedby reductive processes that lead to immobilization of portions of Cr(III). Using a Rayleigh distillation modeland different fractionation factors of Cr(VI) reduction valid for aqueous Fe(II) and Fe(II)-bearingminerals, we cal-culate that more than ~53%, but maximum ~94%, of the originally mobile Cr(VI) pool was reduced to immobileCr(III) in the waters investigated. This indicates that efficient processes in the aquifers may facilitate natural at-tenuation of the toxic Cr(VI) to less harmful Cr(III).

© 2014 Elsevier B.V. All rights reserved.

1. Introduction

Chromium contamination of soil and groundwater is a significantproblem worldwide and is becoming a serious threat to our environ-ments. In nature, chromium occurs as trivalent [Cr(III)] and hexavalent[Cr(VI)] species, with respective compounds (Hem, 1970). Health prob-lems, such as lung cancer and dermatitis are caused by the highly toxicand very soluble oxidized Cr(VI), in chromate oxyanions such as CrO42−,HCrO4− and Cr2O72− (ATSDR, 2000; Losi et al., 1994). In contrast, the re-duced Cr(III) is an essential nutrient, required for normal glucose andlipid metabolism in human bodies, adsorbs strongly on solid surfacesand co-precipitates with Fe(III) hydroxides (Kotas and Stasicka, 2000).Due to the toxicity of Cr(VI), most countries of the European Union

liopoulos).

have currently regulated the limit to 50 μg·L−1 for total chromium[EC, 1998 Council Directive (98/83/EC)].

A number of studies have shown that chromium stable isotopes areeffective in monitoring Cr in natural conditions to determine naturaland/or anthropogenic sources (Basu and Johnson, 2012; Berna et al.,2010; Døssing et al., 2011; Ellis et al., 2002, 2004; Han et al., 2012;Izbicki et al., 2008; Jamieson-Hanes et al., 2012; Johnson, 2011; Kitchenet al., 2012; Novak et al., 2014). Recently, Cr stable isotopes have seengrowing use in environmental applications that range formmonitoringCr at a contaminated site to paleo-environmental applications thatexamine oxygenation of our environment in the Precambrian (BIFs,paleosols) etc. (Crowe et al., 2013; Frei and Polat, 2013; Frei et al.,2009). The monitoring of Cr-contaminated groundwater using Cr stableisotope tracing has been demonstrated by Berna et al. (2010), Ellis et al.(2002), Halicz et al. (2008); Izbicki et al. (2008), Novak et al. (2014);Schoenberg et al. (2008), Sikora et al. (2008), Zink et al. (2010) andothers.

http://crossmark.crossref.org/dialog/?doi=10.1016/j.catena.2014.06.013&domain=pdfhttp://dx.doi.org/10.1016/j.catena.2014.06.013mailto:econom@geol.uoa.grUnlabelled imagehttp://dx.doi.org/10.1016/j.catena.2014.06.013Unlabelled imagehttp://www.sciencedirect.com/science/journal/03418162

217M. Economou-Eliopoulos et al. / Catena 122 (2014) 216–228

Chromiumhas four stable isotopes; 54Cr, 53Cr, 52Cr, and 50Cr, with nat-ural abundances of 2.37%, 9.5%, 83.8%, and 4.35%, respectively (Moynier etal., 2011; Rotaru et al., 1992). Redox processes have been shown to pro-duce significant Cr isotope fractionation during the transition fromCr(VI) to Cr(III) (Schauble et al., 2004). During reduction, the lighter iso-topes are preferentially reduced, resulting in an enrichment of 53Cr rela-tive to 52Cr values in the remaining Cr(VI) pools. This enrichment ismeasured as the change in the ratio of 53Cr/52Cr, and is expressed asδ53Cr values in units per mil (‰) relative to a standard (Ellis et al.,2002). The enrichment or depletion of 53Cr relative to 52Cr can be quanti-fied by measuring the 53Cr/52Cr values in aqueous solutions (Basu andJohnson, 2012; Berger and Frei, 2013; Berna et al., 2010; Farkas et al.,2013; Halicz et al., 2008; Han et al., 2012; Izbicki et al., 2008;Jamieson-Hanes et al., 2012; Kitchen et al., 2012; Schoenberg et al.,2008; Sikora et al., 2008; Zink et al., 2010; Wanner and Sonnenthal,2013). The reduction of Cr(VI) species to Cr(III) species in aqueous sys-tems, by abiotic (e.g. Fe(II)-minerals) and/or biological (microorganisms,organic acids) reduced species is accompanied by an isotope fractionationpreferring the light isotopes in the reductant (Basu and Johnson, 2012;Sander and Koschinsky, 2000). The reduction of toxic and mobile Cr(VI)to Cr(III) is a remediation technology commonly proposed, and can natu-rally be enhanced by organic matter, Fe(II)-minerals and reduced speciesof sulfur (Kozuh et al., 1994). Thus, measurement of the 53Cr/52Cr valuesin groundwater has been proposed as amethod to track Cr(VI) migrationprocesses and evaluate the performance of remediation activities(Blowes, 2002; Ellis et al., 2002; Jamieson-Hanes et al., 2012).

Since the fractionation of Cr isotopes is considered to be little affect-ed bydilutionor adsorption processes (Ellis et al., 2004), local anomaliesin the isotope signature of natural water can be used as a tracer for thereduction of Cr(VI). Thus, they can potentially give clues to the efficien-cy of natural attenuation processes transforming the dissolved and toxichexavalent Cr(VI) to less harmful Cr(III) at specific sites (Berna et al.,2010; Ellis et al., 2002; Izbicki et al., 2008; Johnson, 2011; Raddatzet al., 2011).

The research interest has focused on the Assopos basin because it isan industrial zone (hundreds of industrial plants, such as using chromi-um plating, leather tanning, and applying wood staining) and the run-ning Assopos river was proclaimed as a “processed industrial wastereceiver” since 1969. Besides, untreated or poorly treated industrialwaste may have been dumped illegally in now covered fills. The Assopos(Avlona) and Central Euboea basins (Messapia), dominated geologicallyby thewidespread occurrence of ophiolites,were selected for the presentstudy, because there is no clear-cut answer to the question regarding theinfluence of industry versus natural processes to the soil and groundwa-ter contamination (Economou-Eliopoulos et al., 2011, 2012). The hereinpresented integrated approach is based on a compilation of geochemi-cal/hydrochemical data of (a) ultramafic rocks, soils and groundwatersamples, (b) experimentally produced laboratory water leachates ofthese rocks and soils and (c) stable chromium isotope data (expressedas δ53Cr values) of selected natural and experimentally produced leach-ate water samples, originally aimed at identifying potential sources forCr-contamination in these basins.

2. Geological and hydrological outline

2.1. Central Euboea

The area of central Euboea is covered by alluvial and Neogene sedi-ments. It is characterized by strong geomorphological contrast and isbuilt up mainly of Pleistocene to Holocene sediments hosting the mostproductive aquifers in this area (Fig. 1, sampling area). In addition,two different types of aquifers are hosted by strongly tectonized ultra-mafic rocks, which are widespread in central Euboea, and by the deeperkarstified Triassic–Jurassic limestones.

The ophiolitic masses consist mainly of serpentinised peridotites(harzburgites and lherzolites) with some minor mafic rocks. The

ophiolitic rocks are overthrusted onto Upper Cretaceous limestonesand flysch sediments. The main aquifer which is probed by the wellsis hosted by ophiolitic rocks and is categorized as a fissured rock aquifer.Alluvial deposits are the host rocks to the aquifer which is probed bymany shallow wells for agricultural activities. These wells reach depthsbetween 11 and 180 m (Megremi, 2010).

2.2. Assopos basin (Avlona)

The Neogene Assopos basin (Fig. 1, sampling area 2) is mainly com-posed by Tertiary and Quaternary sediments of more than 400 m thick-ness, and expands over approximately 700 km2. Alternations of marlsand marly limestones occur in the lowest parts of the basin sequences,and continental sediments consisting of conglomerates with small in-tercalations of marls, marly limestones, schists, sandstones, clays andflysch are dominant in the upper parts. A sharp tectonic contact be-tween the sediment types, due to the intense neotectonic deformation,is a characteristic feature of the entire area (Chatoupis and Fountoulis,2004). Peridotites and a Ni-laterite occurrence, overthrusted on theTriassic–Jurassic carbonates, have been described from the Aynolaarea by (Valeton et al., 1987). The morphotectonic structure and evolu-tion of this basin are the result of E–W to WNW–ESE trending faultsystems (Chatoupis and Fountoulis, 2004; Papanikolaou et al., 1988).Quaternary sediments cover large parts of the Assopos valley and hosttwo types of aquifers: a) aquifers within Neogene conglomerates, sand-stones and marly limestone to a depth approximately 150 m, andb) karst type aquifers within the Triassic–Jurassic limestones at deeperlevels of the basin fill (Giannoulopoulos, 2008).

3. Samples and methods of investigation

For the purpose of the present study, 10 groundwater samples, 15soil samples and 21 rock samples were collected from the extendedarea of the municipality of Messapia in central Euboea and from theneighboring area of Avlona located in the Assopos basin (Fig. 1).

Soil and rock samples were collected from cultivated sites and fromnatural outcrops of ultramafic rocks on Central Euboea. Soils were airdried, crumbled mechanically and those containing large stones orclods were first sieved through a 10 mm mesh and then through a5 mm mesh. Subsequently, after passing the samples through a2 mm mesh, the fraction b2 mm was pulverized and used for analysis.Rock sampleswere crushed by jaw crusher, then pulverized using a trit-urator and an agatemortar and pestle, and subsequently sieved througha b2 mm mesh. This fraction was used for the leaching experiments.Major and trace elements were analyzed by inductively coupled plasmamass spectroscopy (ICP-MS) after multi-acid digestion (HNO3–HClO4–HF–HCl) at the ACME Analytical Laboratories in Canada. The detectionlimits for those elements are presented alongwith the analytical resultsin Table 1.

Groundwater samples were collected from domestic and irrigationwells spread over the study area in October 2012. Physical and chemicalparameters (pH, redox, total dissolved solids, conductivity and total dis-solved solids) of the water samples were measured in the field using aportable Consort 561 Multiparameter Analyzer. The collected sampleswere divided into two aliquots and each onewas stored in polyethylenecontainers at 4 °C in a portable refrigerator. One of the sample aliquotswas acidified by addition of concentrated HNO3 and stored at 4 °C aswell. Because acidification potentially can affect the solubility of Cr(VI)and because biotic activity could change the valence state of chromiumin the samples, concentrations of total Cr and Cr(VI)were determined inthe non-acidified aliquot of the water samples, within 24 h aftercollection. The analyses of total chromium were performed by GFAAS(Perkin Elmer 1100B system), with an estimated detection limit of~2 μg/L. The chemical analyses for Cr(VI) were performed by the 1,5-diphenylcarbohydrazide colorimetric method, using a HACH DR/4000spectrophotometer. The estimated detection limit of the method was

Fig. 1. Location map showing the localities of sampling. 1. Central Euboea, 2. Assopos Basin.

218 M. Economou-Eliopoulos et al. / Catena 122 (2014) 216–228

determined at ~4 μg·L−1. All the above described analyses were per-formed at the Laboratory of Economic Geology and Geochemistry,Faculty of Geology and Geoenvironment, University of Athens. Otherelements were analyzed in the acidified portion of the samples byInductively Coupled PlasmaMass Spectroscopy (ICP/MS) at ACME Ana-lytical Laboratories in Canada. The detection limits for those elementsare presented along with the analytical results in Table 2.

The mineralogical composition of soil and rocks was investigated byoptical microscopy, X-ray diffraction and mineral phase analysis. XRDdata were obtained using a Siemens Model 5005 X-ray diffractometer,applying Cu Ka radiation at 40 kV and 40 nA, in 0.020° steps at 1.0 sstep intervals. TheXRDpatternswere interpreted using the EVA2.2 pro-gram included in the D5005 software package. Polished sections pre-pared from soil and rocks, after carbon coating, were examined byreflected light microscopy and with a scanning electron microscope(SEM) and its energy dispersive spectroscopy (EDS) tool. Microprobeanalyses and SEM imaging were carried out at the Department of Geol-ogy and Geoenvironment, University of Athens, using a JEOL JSM 5600scanning electronmicroscope, equippedwith automated energy disper-sive analysis system ISIS 300 OXFORD, with the following operatingconditions: accelerating voltage of 20 kV, beam current of 0.5 nA, timeof measurement of 50 s and beam diameter of 1–2 μm.

A series of batch leaching experiments were carried out in order tostudy the long-term leaching responses of Cr under atmospheric condi-tions. For these experiments, 10 g of a crushed soil and/or rock samplewas suspended in 100 mL of deionized water in a 200 mL Erlenmeyerflask at room temperature. The reaction flask was shaken at approxi-mately 120 rpm by a reciprocal shaker for seven days. After the periodof shaking, the slurrieswere filtered through a 0.45 μmpolyamidemem-brane filter. The filtered leachates were first analyzed for Cr(VI) concen-trations, using a HACH DR/4000 spectrophotometer (estimateddetection limit ~4 μg·L−1), and then for total Cr by GFAAS (PerkinElmer 1100B system) (estimated detection limit of themethod ~2 μg/L).

Water samples in the amount which would yield about 1 μg of totalchromiumwere pipetted into 25mLErlenmeyerflasks togetherwith an

amount of a 50Cr–54Cr double spike so that a sample to spike ratio of~3:1 (total chromium concentrations) was achieved. The addition of a50Cr–54Cr double spike of a known isotope composition to a sample be-fore chemical purification allows accurate correction of both the chem-ical and the instrumental shifts in Cr isotope abundances (Ellis et al.,2002; Schoenberg et al., 2008). The mixture was totally evaporatedand 3 mL of concentrated aqua regia was subsequently added. After 3h during which the sample was exposed to aqua regia on a hotplate at100 °C, the sample was again dried down. Finally, the sample wasthen taken up in 20 mL of Milli Q water and 1 mL of 1 N HCl, to which0.5mL of a 1M ammoniumperoxydisulfate solution (puratronic® qual-ity) was added. The samples were then boiled for 30min in a sand bath,during which an hour glass prevented evaporation of the sample in theErlenmeyer flask. This enabled the total oxidation of the chromium toCr(VI). After cooling to room temperature, the solutionwas then passedover an extraction column (BioRad) charged with 2 mL of intensivelypre-cleaned 200–400 mesh AG1 × 8 (BioRAD) anion resin. Cr(VI) isretained by the resin while cations such as Ca2+, Na+, and K+ are effi-ciently washed out. After rinsing with 5 mL of 0.1 N HCl, Cr(VI) was re-duced, during 30 min on the columns, with 1 mL of 2 N HNO3 to whichthree drops of hydrogen peroxide were added. Cr(III) was then extract-ed with another 5 mL of the same 2 N HNO3–hydrogen peroxide mix-ture into a 17 mL Savillex™ beaker and subsequently dried down. Thisextraction procedure usually has a chromium yield of N90%. The so pro-duced chromium fractionwas then purified by passing the sample in 0.5N HCl over a miniaturized disposable pipette-tip extraction column(fitted with a bottom and a top disposable PVC frit) charged with300 μL of a 200–400 mesh cation resin (AGW-X12; BioRad) employinga slightly modified extraction recipe published by Trinquier et al.(2009) and Bonnand et al. (2011). The yield of this mini-column extrac-tion and purification step is usually ~70%.

Samples were loaded onto Re filaments with a mixture of 3 μL silicagel, 0.5 μL 0.5 mol L−1 of H3BO3 and 0.5 μL 0.5 mol L−1 of H3PO4. Thesampleswere staticallymeasured on a IsotopX “Phoenix”multicollectorthermal ionization mass spectrometer (TIMS) at the Department of

image of Fig.�1

Table 1Major and trace elemnt contents in ultramafic rock and soils from central Euboea (Messapia).

mg·kg−1 wt.%

Rocks Cr Ni Co Mn Cu Pb Zn Cd Sb As Zr Y Sr Ba V La Ce Th Nb U Li Te Fe Al Mg Ca P Ti Na K

M1R1 1180 940 82 1900 24 2.8 39 b0.1 0.4 4 6.4 3.9 13 11 45 3.7 9 0.8 1.2 0.1 15 3.0 4.0 1.3 11.3 10.6 0.004 0.052 0.047 0.09M1R2A 840 940 44 1180 30 7.7 48 0.2 0.2 3 31 8.8 19 8 53 11.9 27 3.9 5.9 0.7 55 3.4 3.8 3.1 9.8 10.4 0.027 0.190 0.017 0.04M1R2B 2100 1340 110 1120 28 1.9 39 b0.1 0.4 6 4.2 3.5 16 12 57 2.3 6 0.5 0.7 0.1 20 0.8 6.2 1.3 6.7 12.2 0.003 0.056 0.016 0.05M1R3 1340 1730 85 1040 16 0.5 28 b0.1 0.2 b1 0.4 1.1 17 9 22 0.6 b1 b0.1 0.2 b0.1 30 9.7 4.4 0.6 3.8 20.9 b0.001 0.022 0.005 b0.01M1R4 1620 1510 74 900 17 0.1 43 b0.1 0.1 b1 0.5 1.6 59 14 37 0.1 b1 b0.1 0.2 b0.1 19 2.5 4.0 0.8 11.4 12.2 b0.001 0.028 0.007 b0.01M1R5 1660 1730 87 740 14 0.2 39 b0.1 0.1 1 0.5 1.0 13 11 41 0.1 b1 b0.1 0.3 0.1 4.5 1.2 5.0 0.7 18.2 4.6 0.001 0.023 0.003 b0.01M1R6 1660 2000 90 680 29 1.7 50 b0.1 b0.1 b1 0.2 0.9 4 6 57 b0.1 b1 b0.1 0.1 0.1 3.3 4.6 5.8 0.8 21.2 0.7 b0.001 0.024 0.004 b0.01M1R7 1050 1650 84 610 7.4 0.3 25 b0.1 b0.1 1 0.4 0.7 5 5 53 b0.1 b1 b0.1 0.2 0.4 1.8 2.8 5.2 0.5 19.1 2.6 b0.001 0.015 0.003 b0.01M1R8 1020 1520 77 640 21 0.2 29 b0.1 b0.1 1 0.5 0.9 105 7 45 b0.1 b1 b0.1 b0.1 0.2 3.0 3.0 4.3 0.9 18.7 3.6 b0.001 0.021 0.007 b0.01M1R9 1320 2120 100 790 8.7 0.3 53 b0.1 0.1 2 0.3 1.0 5 11 41 b0.1 b1 b0.1 0.1 b0.1 2.2 6.6 5.5 0.7 22.2 0.2 b0.001 0.021 0.002 b0.01M1R10 1250 1770 80 680 17 0.1 38 b0.1 b0.1 b1 0.2 0.5 6 3 38 0.1 b1 b0.1 0.2 b0.1 1.4 1.4 5.5 0.5 21.3 1.6 b0.001 0.014 0.002 b0.01M2R1 160 1810 66 340 2.5 b0.1 17 b0.1 b0.1 b1 0.1 b0.1 67 3 2 0.2 b1 b0.1 0.1 b0.1 0.4 5.6 2.7 0.0 12.6 11.7 0.002 b0.001 0.004 b0.01M2R2 860 2300 93 540 2.7 0.1 23 b0.1 b0.1 b1 0.1 b0.1 65 3 4 b0.1 b1 b0.1 0.1 b0.1 0.7 4.8 3.9 0.0 17.8 5.7 0.002 b0.001 0.004 b0.01M2R3 520 2030 95 600 2.8 0.2 22 b0.1 b0.1 b1 0.1 0.1 21 4 9 b0.1 b1 b0.1 0.2 b0.1 0.5 3.5 4.2 0.1 19.3 5.4 0.001 0.002 0.004 b0.01M2R4 320 1640 76 520 2.9 0.4 18 0.1 b0.1 1 0.2 b0.1 70 4 7 0.1 b1 b0.1 0.2 b0.1 0.5 4.9 3.3 0.1 12.3 15.3 0.004 0.001 0.005 b0.01M2R5 1170 2140 100 980 2.8 b0.1 35 b0.1 b0.1 b1 b0.1 0.3 23 6 36 b0.1 b1 b0.1 0.2 b0.1 2.9 4.4 6.0 0.6 18.9 1.3 0.001 0.006 0.004 b0.01M2R6 1000 2090 100 650 5.2 0.1 30 b0.1 b0.1 b1 0.1 b0.1 7 4 30 b0.1 b1 b0.1 0.1 b0.1 0.8 5.1 5.7 0.3 20.2 1.7 0.003 0.003 0.003 b0.01M3R1 1630 2200 100 530 10 b0.1 43 b0.1 b0.1 b1 b0.1 b0.1 2 2 43 b0.1 b1 b0.1 0.1 0.9 3.9 13 5.8 0.5 21.9 0.3 b0.001 0.005 0.003 b0.01M3R2 1140 1490 74 530 8.3 1.0 26 b0.1 b0.1 3 1.7 0.9 20 11 25 0.7 1 0.3 0.4 1.1 6.3 1.7 3.7 0.5 9.8 15.4 0.003 0.010 0.008 0.03M3R3 1720 1850 95 660 9.7 0.2 37 b0.1 b0.1 b1 0.2 0.3 6 4 33 b0.1 b1 b0.1 0.2 0.7 1.5 1.6 5.2 0.4 17.0 7.0 0.001 0.005 0.003 b0.01M3R4 1100 1630 70 520 6.8 b0.1 22 b0.1 b0.1 b1 0.2 0.2 23 7 13 0.1 b1 b0.1 0.1 0.4 1.8 5.4 3.5 0.3 10.1 18.5 0.002 0.002 0.008 b0.01

SoilsMSS1 670 610 42 760 28 15 61 0.2 6.8 11 32 13 80 180 61 20 40 6.3 6.6 1.2 27 2.6 3.7 3.9 2.8 6.2 0.06 0.20 0.44 0.96MSS2 930 930 60 1050 36 18 83 0.2 0.7 14 39 15 64 220 77 23 47 7.1 7.5 1.4 31 1.1 5.3 4.7 4.3 3.2 0.09 0.24 0.52 1.19MSS3 2100 2260 120 1180 24 15 83 0.2 0.4 7 22 8 20 120 55 10 22 3.5 4.0 0.8 12 1.7 7.7 2.3 13.8 0.6 0.05 0.11 0.15 0.56MSS4 1050 1190 72 1080 37 17 99 0.3 0.7 12 36 14 58 190 76 20 41 6.1 7.0 1.4 29 5.3 5.9 4.1 6.2 3.1 0.14 0.23 0.45 1.11MSS5 880 780 52 780 30 17 73 0.2 0.7 14 30 13 76 200 67 21 42 6.5 6.2 1.3 30 b0.5 4.3 4.1 3.7 6.1 0.05 0.21 0.49 1.05MSS6 2100 2200 120 1200 30 16 96 0.4 0.4 6 31 10 40 140 61 14 30 4.5 5.2 1.1 12 2.9 8.5 2.7 10.8 1.8 0.09 0.14 0.23 0.75MSS7 1340 1460 80 790 28 16 79 0.4 0.4 6 35 11 49 140 56 16 32 5.4 6.5 1.0 16 5.1 6.0 3.2 7.8 3.2 0.10 0.17 0.28 0.81MSS8 1760 2220 120 1130 25 12 84 0.2 0.3 6 34 9.3 28 120 59 14 28 4.7 5.8 1.2 12 2.9 8.6 2.9 10.8 0.9 0.04 0.13 0.16 0.68MSS9 1790 2300 110 690 22 12 71 0.3 0.2 5 19 6.8 21 80 46 9 17 2.8 3.5 0.7 14 4.7 8.1 2.0 14.8 0.6 0.04 0.09 0.11 0.40MSS10 3350 3050 160 1360 27 12 96 b0.1 0.3 6 23 7.1 22 98 74 10 22 3.3 4.0 0.8 15 2.2 11.6 2.4 10.8 0.8 0.04 0.11 0.11 0.54MSS11 2200 2220 140 1630 57 22 110 0.5 0.7 14 50 16 43 210 100 23 48 7.9 8.8 1.4 27 b0.5 10.0 4.9 3.9 3.1 0.07 0.24 0.23 1.01MKR1S 2000 2560 130 1130 19 9.1 70 0.1 0.3 2 12 3.6 19 47 44 6.1 11 1.4 2.0 1.0 6.7 3.2 8.2 1.3 14.8 0.3 0.05 0.05 0.05 0.29MKR2S 1380 1830 97 990 23 15 69 0.3 0.4 8 33 9.7 28 120 74 14 27 4.9 5.7 0.8 24 2.7 6.8 3.6 6.2 7.9 0.04 0.16 0.10 0.66PS1 2750 2280 100 1070 34 12.4 99 0.4 0.3 3 20 5.7 23 91 54 8.4 17 2.6 3.2 0.9 7.2 3.5 7.5 1.9 14.4 0.8 0.09 0.09 0.12 0.54PS2 2300 2100 97 980 22 9 70 0.2 0.2 3 19 5.2 28 73 51 7.8 17 2.6 3 0.6 9.4 1.1 7.3 1.8 13.4 1.9 0.04 0.08 0.1 0.49Det. limit 1 0.1 0.2 1 0.1 0.1 1 0.1 0.1 1 0.1 0.1 1 1 1 0.1 1 0.1 0.1 0.1 0.1 0.5 0.01 0.01 0.01 0.01 0.001 0.001 0.001 0.01

Reference materialsSTD OREAS24P 200 144 43 1061 49 3.2 111 b0.1 b0.1 2 128 22.7 380 267 155 19.8 36 3.0 19.1 0.7 8.1 b0.1 7.37 7.67 3.97 5.65 0.137 1.035 2.252 0.65STD OREAS45C 811 304 95 1086 586 25.3 75 0.2 0.8 11 157 12.7 35 259 251 27.7 47 11.1 21.5 2.4 15.6 b0.1 16.49 6.90 0.25 0.47 0.052 1.069 0.098 0.32STD OREAS45C 879 312 95 1005 579 21.8 73 0.2 1.7 10 157 12.6 32 261 228 24.0 47 10.1 22.7 2.1 13.0 b0.1 19.26 6.71 0.21 0.45 0.048 1.044 0.086 0.32STD OREAS24P 183 131 41 949 45.0 2.8 100 b0.1 b0.1 1 123 20.8 321 258 136 16.5 32 2.7 17.0 0.7 7.1 b0.1 7.60 6.79 3.72 5.11 0.123 0.914 2.084 0.60BLK 2 0.2 b0.2 3 0.7 0.3 b1 b0.1 b0.1 b0.01 0.1 b0.1 b1 b1 b1 b0.1 b1 b0.1 b0.1 b0.1 b0.1 b0.1 b0.01 b0.01 b0.01 b0.01 b0.001 b0.001 b0.001 0.01

219M.Econom

ou-Eliopoulosetal./Catena

122(2014)

216–228

Table 2Trace element concentrations in groundwater and water after leaching peridotites and soils from C. Euboea (Messapia) and the Assopos basin (Avlona).

μg·L−1 mg·kg−1

Wells Crtotal Cr(VI) Al As B Ba Br Co Cu Li Mn Ni P Pb S Sb Sc Se Sr Ti U V Zn Ca Mg Na K Si Cl

E2 77 77 3 b0.5 105 42 120 0.1 4.0 4.6 0.5 2.3 b10 0.7 20 b0.05 4 0.7 291 b10 1.19 1.6 102 90 69 47.6 1.6 18 37E5 102 102 2 0.9 88 74 210 0.2 2.7 7.5 0.2 10 b10 b0.1 43 b0.05 5 1.8 332 b10 3.28 2.1 1.3 102 94 40.0 5.4 25 51E7 230 230 1 b0.5 57 27 290 0.3 2.6 8.9 1.2 6.5 b10 b0.1 30 b0.05 7 2.2 260 b10 0.20 2.1 1.2 92 124 32.2 1.9 38 57E10 48 48 2 0.8 46 18 150 0.1 2.4 4.8 5.6 5.6 b10 b0.1 16 b0.05 5 1.2 155 b10 0.11 1.5 6.5 76 72 35.0 2.0 24 46E13 65 62 3 0.7 136 21 140 0.1 1.8 5.5 0.4 6.8 b10 b0.1 15 b0.05 5 0.6 174 b10 b0.02 2.0 b0.5 79 66 39.5 2.3 25 47E18 41 40 1 b0.5 29 17 160 0.1 1.7 3.1 b0.05 5.0 b10 b0.1 18 b0.05 5 0.9 154 b10 2.74 1.0 b0.5 83 49 22.3 1.0 26 30MSW8 65 63 3 1.5 54 4 240 0.1 2.6 8.4 0.3 5.1 10 b0.1 15 b0.05 10 1.7 61 13 0.23 3.7 1.6 38 114 25.9 1.9 49 46M3W8 45 43 1 b0.5 35 16 130 0.0 0.9 3.3 b0.05 15 b10 b0.1 11 b0.05 5 0.6 161 b10 1.84 1.2 b0.5 81 48 22.7 1.7 25 30AVLO13W 50 48 2 1.0 35 37 150 0.3 1.1 5.9 0.7 3.0 b10 b0.1 8 b0.05 4 0.9 151 b10 0.15 2.8 1.5 80 74 25.9 0.9 22 40AVLO14W 93 85 1 3.5 37 64 300 b0.02 0.6 12 0.1 0.8 b10 b0.1 3 b0.05 6 2.2 203 b10 0.34 9.6 b0.5 47 70 29.8 0.8 29 97

Rock leachatesM1R1 14 12 b1 0.5 268 11 7 b0.02 0.9 1.4 0.2 7.0 b10 b0.1 b1 0.37 3 0.5 20 b10 0.04 1.2 9.1 27 2.1 3.2 1.8 13 b1M1R2AB 18 16 4 1.6 154 3.3 13 0.04 1.5 2.7 0.1 4.2 11 b0.1 b1 0.19 2 b0.5 20 b10 0.03 3.2 3.5 26 1.9 4.2 1.1 12 1M1R2BA 35 35 b1 1.7 124 2.4 b5 b0.02 0.3 3.2 0.2 2.3 b10 b0.1 b1 0.11 3 b0.5 19 b10 b0.02 4.2 5.5 26 1.9 3.4 0.7 12 b1MIR2BB 64 63 b1 b0.5 98 1.3 b5 b0.02 0.5 0.2 b0.05 0.9 b10 b0.1 b1 b0.05 b1 b0.5 21 b10 b0.02 1.4 1.3 26 6.1 2.8 0.6 18 b1M1R3 30 29 1 0.8 78 5.1 b5 b0.02 0.6 14.8 0.5 0.7 b10 b0.1 b1 0.36 3 b0.5 15 b10 b0.02 2.1 6.1 25 2.9 2.4 0.6 13 b1M1R4 3.0 b4 2 0.6 46 1.6 b5 b0.02 0.5 3.4 0.1 0.7 b10 0.3 b1 0.15 3 b0.5 13 b10 b0.02 2.2 6.9 18 4.7 2.1 0.6 15 b1M1R5 3.2 b4 2 0.5 23 1.5 b5 b0.02 0.4 1.6 0.7 1.1 b10 b0.1 b1 0.24 4 b0.5 12 b10 b0.02 2.0 6.0 18 6.8 1.9 0.9 17 b1M1R6B 2.0 b4 1 b0.5 103 1.6 12 b0.02 0.3 1.0 0.1 0.7 b10 b0.1 b1 0.27 4 b0.5 15 b10 b0.02 4.3 3.5 12 11.4 3.3 0.7 18 3M1R7 2.3 b4 1 0.6 204 7.0 b5 b0.02 0.3 1.4 b0.05 0.9 b10 b0.1 b1 0.13 5 b0.5 13 b10 b0.02 5.8 3.7 13 11.8 1.9 0.8 23 b1M1R8 2.2 b4 2 0.7 106 3.6 b5 0.03 0.4 0.8 0.2 0.8 b10 b0.1 b1 0.16 1 b0.5 27 b10 b0.02 2.9 8.2 13 8.6 1.8 0.6 20 b1M1R9B 3.9 b4 2 0.6 55 9.0 13 0.06 0.7 0.5 b0.05 0.7 b10 b0.1 b1 0.56 b1 b0.5 56 b10 b0.02 2.1 2.2 15 20.0 1.6 0.6 19 4M1R10B 3.1 b4 1 b0.5 272 1.7 5 0.05 0.3 0.5 0.2 0.2 b10 b0.1 b1 b0.05 1 b0.5 17 b10 b0.02 1.3 4.7 15 11.6 1.7 0.6 26 b1M2R1 4.8 4.5 1 b0.5 46 1.9 11 0.04 0.3 0.5 0.5 0.4 b10 b0.1 b1 b0.05 1 b0.5 22 b10 b0.02 b0.2 29 25 8.1 1.5 0.8 33 b1M2R2 11 8 b1 b0.5 40 3.2 8 0.05 0.4 0.5 0.1 b0.2 b10 b0.1 b1 b0.05 b1 b0.5 22 b10 b0.02 b0.2 2.3 26 7.6 1.6 1.6 23 b1M2R3 3.4 b4 b1 b0.5 148 3.3 b5 0.03 0.2 0.4 b0.05 b0.2 b10 b0.1 b1 b0.05 b1 b0.5 11 b10 b0.02 0.2 b0.5 12 13.8 1.6 0.6 23 b1M2R4 5.0 4.8 1 b0.5 221 1.2 5 b0.02 0.4 0.4 0.1 0.7 b10 b0.1 b1 b0.05 b1 b0.5 16 b10 b0.02 0.9 1.9 17 7.0 1.7 0.7 22 b1M2R6 6.4 5.0 1 b0.5 143 1.0 13 0.04 b0.1 0.6 b0.05 0.7 b10 b0.1 b1 b0.05 b1 b0.5 11 b10 b0.02 0.7 1.8 16 11.3 2.3 0.6 22 5M3R1 5.5 4.0 1 b0.5 58 1.8 18 b0.02 0.2 0.9 b0.05 b0.2 b10 b0.1 b1 0.11 b1 b0.5 21 b10 b0.02 1.0 0.5 20 13.2 2.1 0.4 19 4M3R2 3.6 b4 1 b0.5 229 1.7 b5 0.08 0.3 1.6 b0.05 0.6 b10 b0.1 b1 0.10 b1 b0.5 17 b10 b0.02 1.9 1.9 18 6.3 2.1 1.0 17 b1M3R3 8.8 7.0 1 b0.5 48 1.7 b5 0.04 0.3 0.5 b0.05 0.4 b10 b0.1 b1 0.07 b1 b0.5 16 b10 b0.02 1.1 1.6 21 8.1 1.7 0.8 17 2M3R4 15 13 2 b0.5 292 1.7 27 0.05 0.4 0.9 0.1 0.7 b10 b0.1 b1 b0.05 b1 b0.5 16 b10 b0.02 0.5 5.8 20 6.8 4.0 1.5 20 b1

Soil leachatesMSS1 21 17 3 4.9 2811 8.5 52 0.2 6.0 5.5 0.2 10 38 b0.1 2 0.40 b1 1.1 45.8 b10 0.47 4.9 7.8 30 11.7 7.5 7.8 17 b1MSS2 27 21 7 11 5417 9.6 54 0.4 6.7 7.3 0.2 15 1040 0.4 1 0.67 b1 1.4 50.4 b10 0.50 8.8 5.0 26 15.9 10.1 9.5 20 b1MSS3B 94 87 3 5.2 930 8.5 24 0.4 3.4 2.9 0.2 32 874 0.2 b1 0.24 b1 b0.5 29.9 b10 0.20 4.0 9.8 13 17.4 4.1 12.6 22 b1MSS4B 38 34 4 10 1233 10 36 0.4 6.7 4.4 0.2 21 2124 0.5 1 0.41 b1 1.1 38.6 b10 0.31 7.4 1.3 20 18.7 5.9 16.3 14 b1MSS5B 37 28 7 4.6 1412 11 27 0.3 3.8 4.5 0.2 9 120 b0.1 1 0.55 b1 0.9 45.3 b10 0.56 4.1 3.8 34 6.8 4.1 8.6 13 b1MSS6B 76 68 2 5.6 767 12 31 0.9 3.7 2.3 0.3 28 1236 0.2 3 0.38 b1 0.8 49.9 b10 0.42 5.9 4.1 25 12.8 4.4 19.8 17 2MSS7B 35 35 2 12 254 11 45 0.5 6.5 3.1 0.1 25 747 b0.1 2 0.46 b1 1.1 47.7 b10 0.35 10.7 4.2 29 12.1 4.7 8.7 14 1MSS8B 64 43 6 3.4 253 11 26 0.8 7.4 2.7 0.5 39 746 0.2 3 0.13 b1 b0.5 41.0 b10 0.46 4.4 43.5 26 21.4 3.6 14.4 21 b1MSS9 57 43 3 4.6 248 6.8 43 0.1 3.5 4.0 0.1 22 972 b0.1 1 0.22 1 1.1 32.4 b10 0.13 6.9 1.8 20 15.7 4.6 6.4 21 b1MSS11 58 76 4 2.7 620 10 49 0.2 5.2 3.0 0.1 13 214 0.1 b1 0.12 b1 b0.5 26.2 b10 0.19 4.1 5.5 26 8.4 3.9 6.2 17 b1MSS10 84 81 4 2.9 1019 10 35 0.3 7.3 2.7 0.1 17 463 0.2 1 0.16 b1 0.5 32.5 b10 0.50 3.7 7.6 32 6.1 3.4 5.7 12 b1MKR1S 70 48 2 1.6 286 7.2 24 0.63 4.5 3.7 0.4 54 756 b0.1 2 0.27 b1 b0.5 46 b10 0.07 3.1 19 16 14.2 3.9 18 18 3MKR2S 22 18 5 2.1 511 6.0 34 0.46 2.8 1.8 0.2 24 38 0.2 1 0.13 b1 1.1 22 b10 0.29 2.4 9.6 44 4.6 2.3 11 11 b1PS1 54 51 4 5.7 620 9.1 18 0.8 12.0 2.2 0.2 51 1910 0.2 2 0.24 1 0.8 36 b10 0.42 4.3 33.0 17 16.0 3.3 31 21 1PS2 58 55 4 2.3 740 6.7 18 0.4 2.0 2.4 0.1 13 360 b0.1 b1 0.28 1 0.5 31 b10 0.20 3.4 b0.5 29 14.0 3.4 19 18 1Detection limit 0.5 1 0.5 5 0.05 5 0.0 0.1 0.1 0.1 0 10 0.1 1 0.05 1 0.5 0.01 10 0.02 0.2 0.5 0 0 0.1 0.1 40.00 1

Reference materialsSTD TMDA-70 404.2 506 41.9 17 332.7 28 287.3 399.4 22.6 327 330 b10 468 7 22.30 b1 26.4 452.07 b10 59.30 332.6 497.3 22.41 5.78 8.8 1.00 428 13STD TMDA-70 413.5 543 43.0 18 348.2 25 292.8 415.2 21.1 340 324 b10 456 b1 23.40 b1 26.2 460.98 b10 61.95 322.8 504.0 23.70 6.05 8.7 1.00 469 13BLK b0.5 b1 b0.5 b5 b0.05 b5 b0.02 b0.1 b0.1 b0.05 b0.2 b10 b0.1 b1 b0.05 b1 b0.5 b0.01 b10 b0.02 b0.2 b0.5 b0.05 b0.05 b0.05 b0.05 b40 b1

220M.Econom

ou-Eliopoulosetal./Catena

122(2014)

216–228

221M. Economou-Eliopoulos et al. / Catena 122 (2014) 216–228

Geoscience and Natural Resource Management, University of Copenha-gen, at temperatures between 980 and 1100 °C, aiming for beam inten-sity at atomic mass unit (AMU) 52.9407 of 30–60 mV. Every load wasanalyzed two to four times (see Table 3). Titanium, vanadium andiron interferences with Cr isotopes were corrected by comparing with49Ti/50Ti, 50V/51V and 54Fe/56Fe ratios. The final isotope composition ofa sample was determined as the average of the repeated analyses andreported relative to the certified SRM 979 standard as

δ53Cr ‰ð Þ ¼ 53Cr=52Crsample=53Cr=52CrSRM979

� �−1

h i� 1000:

Repeated long-term analysis of 0.5 μg loads of unprocessed doublespiked NIST SRM 979 standard yield an average δ53Cr value of 0.08 ±0.05‰ (n = 245; 2σ; 52Cr signal intensity at 0.4 V) on the “Phoenix”TIMS which we consider as a minimum external reproducibility for asample reproducibility, including separation procedure, double spikecorrection error, and respective internal analytical errors.

4. Geochemistry of rocks, soils and groundwater

4.1. Major and trace element contents in rocks and soils

The rock samples were collected from outcrops along the nationalroad from Makrymallis toward Kondodespoti, and from outcrops eastof the Psachna area (Fig. 1). The peridotite samples exhibit varying de-gree of serpentinization. Although they are generally highly tectonized,some less altered parts still remain.Major and trace element concentra-tions are presented in Table 1. As expected, the Cr, Ni, Co, Mn and Fecontents are elevated in the ultramafic rocks while the relatively highZr, Y, Li, K and Ca, and low Mg contents in some samples reflect thestrong serpentinization and alteration of the peridotites. The soil sam-ples, collected from the neighboring cultivated area of Messapia arecharacterized by significant Cr, Ni, Mn, Fe and Co contents, reflectingthe contribution of host ultramafic ophiolitic rocks (Table 1) and arecomparable to those given for the area of Avlona (Atsarou andEconomou-Eliopoulos, 2012). Also, a salient feature is the relativelyhigh B, P, K, Ba, U, Th, Nb, Li, Zr, and Y contents in soils compared to

Table 3Field paramenters, total chromium, Cr(VI) and δ53Cr values for groundwater from wells and le

Sample Χ xΥ Depth (m) Crtotal Cr(VI)

μg·L−1 μg·L−1

WellsEuboeaE7 38°34′13″N 23° 40′09″E 35 230 230E18 38° 36′28″N 23°40′03″E 20 41 40E2 38°34′13″N 23°37′48″E 22 77 77E5 38°34′11″N 23°37′35″E 11 102 102E10 38°34′13″N 23°37′32″E 20 48 48Ε13 38°33′49″N 23°37′02″E 18 65 62MSW8 38°35′21″N 23°41′15″E 27 65 63Μ3W8 38°35′21″N 23°41′15″E 30 45 43

AvlonaAVLO13W 38°16′12″N 23°41′10″E 120 50 48AVLO14W 38°16′01″N 23°42′7″E 80 93 85

Leachates EuboeaR.L.M1R2BA 38°37′47″N 23°39′0.5″E R. L. 35 35M1R2BB 38°37′47″N 23°390.5″E R. L. 64 63M1R3 38°37′47″N 23°39′0.5″E R. L. 30 29

S.L.MSS4B 38°34′52″N 23°39′42″E S. L. 38 34MSS6B 38°34′54″N 23°40′19″E S. L. 76 68MSS7B 38°34′52″N 23°40′49″E S. L. 35 35

Symbols: R.L. = ultramafic rock leachates; S.L. = soil leachates.

ultramafic rocks (Table 1), probably reflecting the contamination by ap-plied synthetic fertilizers (Kabata-Pendlas, 2000).

4.2. Cr-host minerals

The study by XRD and SEM/EDS revealed that the dominant min-erals in soil are quartz, calcite, silicates (serpentine, olivine and chlorite),chromite, ferrian-chromite, hematite, magnetite and Cr-bearing goe-thite while montmorillonite, Fe-sulfides and zircon occur in lesseramounts. A portion of the chromium in soils from both central EuboeaandAvlona is hosted in chromite grains or fragments, in Cr-bearing goe-thite and in silicates (Fig. 2) transported as detrital components origi-nally derived from the weathering of the ophiolitic parent rocks andNi-laterite deposits.

4.3. Trace element concentrations in groundwater

The majority of groundwater samples from domestic and irrigationwells throughout Central Euboea (Messapia) andAssopos basin (Avlona)exhibit concentrations exceeding the maximum acceptable level forCrtotal in drinking water (50 μg/L, according to the EU Directive; (EC,1998)). At the Avlona area (Assopos), the total chromiumconcentrationsrange from 50 μg·L−1 to 93 μg·L−1 and for waters from Messapia from41 to 230 μg·L−1 (Table 2). With the exception of total Cr all the otherelements in the groundwater samples were found to have concentra-tions below the maximum permissible limits for human usage (EC,1998). However, there is a significant variation in the concentrations ofseveral elements, such as As, ranging from b0.5 to 3.5 μg/L, U from 0.02to 3.3 μg/L, Ni from 0.2 to 15 μg/L, Mn from b0.05 to 5.6 μg/L, Cu from0.6 to 4 μg/L and in the Ca, Mg, Na, Si and B ones (Table 2). Since Ca,Mg, Na, Si and B are common components of water, rocks and sea-water, the plot of Mg/Si ratio versus Cr(VI) is given to discriminate po-tential sources (Fig. 3a). Values are compared to those from the entirecentral Euboea as well as from Mg-rich waters from Italy with a similargeological setting where they are affected by the interaction with ultra-mafic rocks (Fig. 3b; Fantoni et al., 2002; Megremi et al., 2013). Thiswas done to evaluate the importance of water–rock interaction vs. sea-water contribution into the aquifer. In addition, the plot of Mg/Si ratios

achates (R.L. and S.L.).

Crtotal D DS d53Cr (per mil) 2SE (abs) n pH Eh (mV)

249 0.98 0.08 2 7.3 −2842 1.42 0.05 3 7.47 −3573 0.84 0.01 3 7.2 −23

117 1.22 0.07 4 7.26 −2647 1.98 0.05 5 7.72 −5264 1.41 0.04 3 7.48 −3863 1.76 0.08 5 7.3 −1940 1.34 0.06 3 7.3 −19

53 0.98 0.03 3 7.36 −2686 1.03 0.01 3 7.54 −34

38 0.56 0.04 3 8.07 −9266 0.86 0.06 4 8.1 −8739 0.96 0.06 4 8.3 −102

40 0.59 0.05 4 7.96 −6576 0.51 0.08 5 8.14 −7240 0.33 0.06 4 7.86 −68

a b

c d

Fe-chr

goethchr chr

Fig. 2. Selected backscattered electron (BSE) images from central Euboea (Messapia) soils, showing Cr-hosts: fragments of chromite (panels a, d), serpentine (panels a, b) and goethite(panel d). Abbreviations chr = chromite; serpentine = srp; goeth = goethite.

222 M. Economou-Eliopoulos et al. / Catena 122 (2014) 216–228

vs. Na concentration (Fig. 3c) shows that elevated Mg/Si ratios are ac-companied by an increase of Na concentration. The range of pH (from7.2 to 7.5) and Eh (from −52 to −19 mV) values measured in thegroundwater (Table 3) indicate slightly alkaline and almost neutralredox conditions.

4.4. Trace element concentrations in rock and soil leachates

The results of leaching experiments of variously serpentinized peri-dotite samples and soils under atmospheric conditions are contained inTable 2. In general, the Cr(VI) concentration in leachates from perido-tites is much lower than those in soils (Table 2). Also, the highest con-centrations of Cr in rock leachates were measured in those sampleswhich exhibit a strong degree of serpentinization. The Cr(VI) concentra-tions in soil leachates, ranging from 17 to 87 μg·L−1, show a positivecorrelationwith concentrations of the total Cr, Fe, Mn and Co in the cor-responding soils (Fig. 4). The Mg/Si ratio in leachates from less alteredperidotites is higher than those from highly serpentinized ones whilethe Cr(VI) concentrations are much lower in the former than in the lat-ter (Fig. 3a). In addition, the soil leachates are characterized by both rel-atively high Mg/Si ratio and Cr(VI) concentrations, but the Mg/Si ratiosare lower than those in groundwater.

4.5. Chromium stable isotope values in groundwater

δ53Cr values in groundwater from central Euboea, which is an areadominated by Cr-bearing peridotites and Fe–Ni laterite deposits (poten-tial sources for chromium contamination by natural processes), andfrom the Assopos basin (Avlona area) with a strong industrial impactand natural contamination as well (Economou-Eliopoulos et al., 2013)are listed in Table 3. There are significant variations in δ53Cr values. Iso-topic signatures range from0.84 to 1.98‰ in groundwater samples from

Euboea, and from 0.98 to 1.03‰ in samples from the area of Avlona(Assopos basin). The highest Cr(VI) concentration in groundwater(230 μg·L−1), at the same time characterized by a relatively low δ53Crvalue (0.98‰), was measured in a sample from a shallow well in thePsachna area, which is dominated by alluvial sediments. The five sam-ples with the lowest Cr(VI) concentrations (average of 51.2 ±10.1 μg·L−1) are characterized by elevated δ53Cr values (average1.58 ± 0.28‰) instead.

4.6. Chromium stable isotope values in leachates

Highly serpentinized peridotites and soil samples which yieldedsignificant Cr(VI) concentrations in their leachates were also ana-lyzed for their Cr isotope composition. The measured δ53Cr valuesfor the highly serpentinized peridotite leachates range from 0.56 to0.96‰ and those for the soil leachates range from 0.51 to 0.59‰(Table 3). Although there is no clear-cut relationship betweenCr(VI) concentrations and δ53Cr values, there is a tendency, howeverthat rock leachates yield at average higher δ53Cr values (mean of~0.8‰, at lower 4.6 wt.% Fe) than soil leachates (mean ~0.5‰, at av-erage 7.3 wt.% Fe), while mean Cr(VI) concentrations in the leachatesremain similar (42 and 45 μg·L−1, respectively). Such a negativetrend is also suggested by the plot of δ53Cr values in the rock andsoil leachates versus Fe content in the corresponding rock and soilsamples (Fig. 6).

5. Discussion

The occurrence of Cr(VI) in ground and surfacewaters has been pre-viously reported (Fantoni et al., 2002; Megremi, 2009, Oze et al., 2004,2007; Raddatz et al., 2011; Villalobos-Aragón et al., 2012; Wanneret al., 2012). The ratio of Cr(VI) to Cr(total) ranges from 0.9 to 1 and

image of Fig.�2

0.10

1.00

10.00

1 10 100 1000

Cr(VI) (μg/L)

Mg/

Si

Groundwater

L rocks Cr(VI)< 5 μg/L

L rocks Cr(VI) 5 - 63 μg/L

L soil Cr(VI) 17 - 87 μg/LMg/Si ratio equal to 2.2

a

0,10

1,00

10,00

100,00

0,1 1 10 100 1000

Mg/

Si

Cr(total) (μg/L)

Selective data from Fantoni et al., 2002

Central Euboea Cr50μm/L

Mg/Si ratio equal to 2,3

b

Fig. 3. Plot of the Mg/Si ratio versus Cr showing trends and variations of the chemical components of the groundwater and rock, soil leachates from central Euboea, in comparison withpublished data (the dashed line corresponds to the value of Mg/Si ratio equal to 2.3–2.2). (Data: Table 3 (panel a) and Megremi et al., 2013; Fantoni et al., 2002; panel b).

223M. Economou-Eliopoulos et al. / Catena 122 (2014) 216–228

the very good correlation (r2 = 0.99) between Cr(total) and Cr(VI) im-plies that Cr(VI) is the predominant Cr species in the waters from theareas studied (Megremi, 2009). The issue of contamination by heavymetals, including Cr(VI), is a complex and politically delicate one,because there is often no clear-cut answer to the question regardingthe ultimate sources responsible for a contamination. Strongly positive-ly fractionated Cr(VI) is indicative of mass-transfer processes involvingreductive processes, and therefore stable Cr isotopes (δ53Cr values)have beenproposed as a tool for trackingCr(VI)migration in groundwa-ter (Berna et al., 2010; Blowes, 2002; Ellis et al., 2002; Halicz et al., 2008;Izbicki et al., 2008; Jamieson-Hanes et al., 2012; Schoenberg et al., 2008;Sikora et al., 2008; Zink et al., 2010). Sources of Cr used for industrialpurposes have δ53Cr values close to 0‰ relative to NIST 979 (Elliset al., 2002; Schoenberg et al., 2008), while naturally occurring Crin groundwater displays a range of δ53Cr: values from +1.0 to +5.8‰(Ellis et al., 2002; Izbicki et al., 2008; Novak et al., 2014). Such strongly

positively fractionated values reflect reduction of Cr(VI) (after initial ox-idative mobilization) during transportation in the aquifer.

The chromium isotope tracing technique has been applied inHinkley California (USA), at the Pacific Gas & Electric (PG&E) Compres-sor Facility, where a groundwater was contaminated by anthropogenicchromium. The δ53Cr values identified in groundwater samples from apilot study carried out at Hinkley (CH2MHill 2007) have been used toassess the Cr contamination source and to delineate redox processes(Izbicki et al., 2008) within the aquifer. On the basis of preliminary lab-oratory experiments these authors determined the variability of kineticisotope effects and Cr(VI) reduction, and concluded that industrialCr(VI) supplies probably have Cr isotope compositions close to thoseof the Earth's mantle. However, δ53Cr values of industrially contaminat-ed waters in the Czech Republic and Poland are positively fractionatedrelative to the pollution source, as a result of Cr(VI) reduction in thewater sheds (Novak et al., 2014).

image of Fig.�3

0

10

20

30

40

50

60

70

80

90

100

0 1000 2000 3000 4000

Cr (mg/kg)

L rocksL soils

0

10

20

30

40

50

60

70

80

90

100

0 500 1000 1500 2000

Mn (mg/Kg)

0

10

20

30

40

50

60

70

80

90

100

0.0 5.0 10.0 15.0Fe (wt%)

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200

Co (mg/Kg)

a b

c d

Cr(

VI)

(μg/

L)

Cr(

VI)

(μg

/L)

Cr(

VI)

(μg/

L)

Cr(

VI)

(μg

/L)

Fig. 4. Plots of Cr(VI) in rock (L rocks) and soil (L soils) leachates versus Cr, Mn, Fe and Co contents in ultramafic rocks and soils, respectively (data from Tables 1 and 2).

224 M. Economou-Eliopoulos et al. / Catena 122 (2014) 216–228

5.1. Use of δ53Cr values as a tracer for the reduction of Cr(VI) in naturalwaters

In order to evaluate the efficiency of natural attenuation of the dis-solved and toxic hexavalent Cr(VI) to less harmful Cr(III) in the ground-water of the studied basin on Euboea area, in our calculation we used aRayleigh distillationmodel, assuming the geogenic background compo-sition to be represented by the average δ53Cr value of 0.64‰ defined bythe soil and rock powder leachates presented herein. This value ishigher than the δ53Cr value of 0.37‰ reported by Ellis et al. (2002) forCr(VI) solutions from plating baths (industrial contaminant) and poten-tially implies that, if the Cr(VI) signatureswere purely produced bymix-tures of geogenic and industrial Cr(VI), the anthropogenic Cr(VI)contaminant would have to have δ53Cr values drastically exceedingthose reported by Ellis et al. (2002). We therefore prefer a scenario bywhich the measured δ53Cr values of aquifers studied herein reflect a re-sidual, partially reduced geogenic Cr(VI) pool.

Under this assumption,we computed the expected changes in the Crisotope composition of dissolved Cr(VI) species in the affected waters,as a function of the progressive reduction of Cr(VI) to Cr(III). In our cal-culation, we used the average δ53Cr signature of the soil and rock pulpleachates as the local geogenic Cr composition. The δ53Cr signature ofthe dissolved Cr(VI) species that remain in waters (the reactant pool)at any given time as back-reduction to Cr(III) proceeds was calculatedbased on the following Rayleigh relation (cf. Ellis et al., 2002; Johnson,2011):

δ53Cr ¼ δ53Cr0 þ 1000� �

� f α−1ð Þh i

−1000

where δ53Cr and δ53Cr0 represent the isotope compositions of theunreacted dissolved Cr(VI) in the run-off at the site of the Cr source atthe given time (i.e., sampling time) and at the initial stage when the re-action started (t= 0), respectively. The parameter f is the fraction (in %)of the unreacted Cr(VI) remaining in the groundwaters, and α repre-sents an isotope fractionation factor associated with the Cr(VI) reduc-tion, defined as:

α ¼ RPROD=RREACT

where RPROD and RREACT are the 53Cr/52Cr isotope ratios of the reactionproduct, Cr(III), and the reactant (the Cr(VI)), respectively. The relativeisotope difference Δ53/52Cr between these two, i.e. oxidized and re-duced, water soluble chromium pools can be calculated according tothe equation:

Δ53Cr PROD–REACTð Þ ¼ δ53CrPROD−δ53CrREACT

and/or approximated through the isotope fractionation factor α usingthe following relation:

1000 � lnα � Δ53Cr PROD−REACTð Þ:

We used a range of isotope fractionation values (α) associated withthe abiotic Cr(VI) reduction bymagnetite (α= 0.9965; Ellis et al., 2002;Zink et al., 2010), other Fe(II)-bearing phases (α = 0.9979–0.9961;Basu and Johnson, 2012) and aqueous Fe (II) (α = 0.9970–0.9958:Døssing et al., 2011), Kitchen et al., 2012), which corresponds to about2.1 to 4.2‰ lighter 53Cr/52Cr ratio in the reaction product, i.e. Cr(III),

image of Fig.�4

225M. Economou-Eliopoulos et al. / Catena 122 (2014) 216–228

compared to that of the reactant Cr(VI) pool. This is a simplistic assump-tion since it neither does take potentially biotic (microbial) reductionmechanisms into consideration, nor does account for the potential pres-ence of a heterogeneous aquiver with multiple reductants. However,under basic pH such as characterizing the rock leachates (average 8.2)and aquifers (7.37 ± 0.16) studied herein (Table 3), the reduction ofCr(VI) by organic reductants is considered minimal, and the reductionof Cr(VI) by Fe(II) most likely was the predominant reduction mecha-nisms. For our calculation, we also assume that adsorption/desorptionof Cr(VI) was insignificant (Ellis et al., 2004), and that, consequently,the dissolved Cr(VI) we measured was representative of the total dis-solved Cr(VI) pool, in terms of both isotopic composition and extent ofreduction.

The results of our numericalmodeling, assuming theCr isotope com-position of the local geogenic Cr source to be represented by the averageof δ53Cr = 0.64 +/0.47 (2σ; Table 3) (i.e., reflected in δ53Cr of an initialunreacted Cr(VI) pool, i.e. f=1), suggest thatmore than ~53%, butmax-imum 96%, of the original Cr(VI) pool was reduced to Cr(III) in the wa-ters investigated (Fig. 5 a and b). This implies that there is an ongoingand relatively efficient process in the basin aquifers studied that

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

δ53 C

r (pe

rmil)

53%

a

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0.3 0.4 0.5 0.6

0.3 0.4 0.5 0.6

δ53 C

r (pe

rmil)

b

Fig. 5. Results of a theoretical Rayleighmodeling for the quantitative estimates of the amount oassuming the geogenic background composition to be represented by the average 53Cr value of 0with the percentage numbers illustrate theminimum calculated amounts of Cr(VI) that was redreduced to Cr(III) in the waters investigated (panels a, b). We used a range of isotope fractionbearing minerals (Ellis et al., 2004).

facilitates natural attenuation of the dissolved and toxic hexavalentCr(VI) to less harmful Cr(III).

5.2. The use of δ53Cr values in rock and soil leachates for identifyingreduction of Cr(VI)

The combination of trace element data with δ53Cr values of rock andsoil leachates from central Euboea (Tables 1–3) and their comparison toδ53Cr values for geogenic and anthropogenic waters from centralEurope recently published by Novak et al. (2014) may contribute tothe identification of contaminant Cr sources. The measured higherCr(VI) concentrations in rock leachates from rocks with higher Mncontents compared to less altered peridotites, and the higher Cr(VI)concentrations in soil leachates compared to rock leachates (Tables 1and 2) in general seem to be consistent with the common occurrenceof ferrian chromite (FeCr2O4) and manganese oxides in the soils(Figs. 2b and 3b). These phases have a catalytic control over Cr(III) oxi-dation. In addition, the oxidation of Cr(III) to Cr(VI) in the cultivatedsoils of central Euboea may be facilitated by atmospheric oxygen(which in turn oxidize the Mn2+ to produce Mn4+ catalysts), as a

f

91%

α = 0.9979

0.7 0.8 0.9 1.0

0.7 0.8 0.9 1.0

f

96%74%

α = 0.9956

f hexavalent chromium Cr(VI) reduction to trivalent Cr(III) in groundwaters from Euboea,.64‰defined by the soil and rock powder leachates presentedherein. Dashed vertical linesuced, and suggest thatmore than ~53%, butmaximum96%, of the original Cr(VI) pool wasation values (δ) associated with the abiotic Cr(VI) reduction by aqueous Fe(II) and Fe(II)-

image of Fig.�5

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8

Fe (mg/Kg)

δ53 C

r (p

er m

il)

10

L rocksL soilsmean values

Fig. 6. Diagram of δ53Cr values in rock (L rocks) and soil (L soils) leachates versus Fe con-tents in ultramafic rocks and soils, respectively (data from Tables 1–3).

226 M. Economou-Eliopoulos et al. / Catena 122 (2014) 216–228

consequence of often applied soil mixing and soil turnovers during agri-cultural plowing, in contrast to in situ outcrops of peridotites. Lastly,Cr(VI) can be readily reduced in situ again to Cr(III) by aqueous Fe(II)or Fe(II)-bearing minerals (Ellis et al., 2002) and/or by bacteria (Sikoraet al., 2008).

Since oxidation and reduction of chromium occur simultaneously innature, it has been suggested that a potential limitation to theuse of nat-ural attenuation of Cr(VI) depends on the oxidation capacity of the soils(Stanin, 2005). Also, due to the high redox potential of the Cr(VI)/Cr(III)couple, the only oxidants present in natural systems that are capable ofoxidizing Cr(III) to Cr(VI) are considered to be manganese oxides[Mn(IV/III)] and dissolved oxygen (Eary and Rai, 1987, 1988, 1989;Oze et al., 2007). However, Palmer and Wittbrodt (1994), based on ex-perimental work, concluded that under slightly acidic to basic condi-tions, due to kinetic reactions, sorption and/or precipitation of Cr(III)is much faster than oxidation, and hence the oxidation of Cr(III) by dis-solved oxygen is an unlikely process. With respect to the redox reac-tions between chromium and iron species, which involve verycomplex processes (Palmer and Puls, 1994), it has been emphasizedthat the reduction of Cr(VI) by Fe(II) is 100 times faster than the reduc-tion rate by organic matter (Wielinga et al., 2001). In addition, a signif-icant amount of Cr(VI) can potentially be reduced, due to the rapidcycling of Fe(II) back to Fe(III) (Stanin, 2005). The negative trend be-tween δ53Cr values in the rock and soil leachates, and respective Fe con-centrations in peridotite and soil samples (Tables 1 and 2; Fig. 6), may

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

1 10 100Cr(V

δ53 C

r (p

er m

il)

Water-GrL rocks-GrL soil-GrGeo-water-C.E.Antro-water-C.E.

Fig. 7. Diagram of δ53Cr values in water, rock (L rocks) and soil (L soils) leachates from Greece,Central Europe (C. E.) versus Cr(VI) concentrations. Data from Table 3 and from Novak et al. (2

point to the fact that oxidation of chromium has been facilitated consid-erably by Fe. In addition, in a plot of δ53Cr values vs Cr(VI) concentra-tions for studied waters (Table 3), supplemented with average valuesfor geogenicwaters from central Europe (Novak et al., 2014), it is appar-ent that geogenically contaminated waters define separate data arrayswhich are different from that defined by anthropogenically contaminat-ed waters by exhibiting generally lower Cr(VI) and somewhat less pos-itively fractionated δ53Cr values, while still showing the significantnegative trend to be expected by reduction processes (Fig. 7).

6. Conclusions

The compilation of trace element data on groundwater, ultramaficrocks and soil samples from Central Euboea, and δ53Cr values in repre-sentative groundwater, rock and soil water leachates, led to the follow-ing conclusions:

• The higher Cr(VI) concentrations in soil water leachates compared tothose of rock powder leachates can be explained by increased oxida-tion capacities in the presence of Fe(II) hydroxides and Mn oxides.

• Although the dominant cause for Cr isotope fractionation (δ53Crvalues ranging from 0.56 to 0.96‰ in rock leachates and from 0.51to 0.59‰ in the soil leachates) is reduction, processes other than re-duction, such as sorption, precipitation and uptake by plants maycomplicate the interpretation of the observed δ53Cr values.

• There is a significant variation in δ53Cr values, ranging from 0.84 to1.98‰ in groundwater samples from Euboea and from 0.98 to1.03‰ in samples from the area of Avlona (Assopos basin). Assumingthe geogenic background composition to be represented by our ex-perimental leachates of soils and rock powders, the elevated δ53Crvalues potentially imply reductive processes during transport of themobilized Cr(VI) in the different aquifers investigated.

• Using a range of different fractionation factors valid for aqueous Fe(II)and Fe(II)-bearing mineral reduction, and a geogenic δ53Cr value of~0.64‰ for an initial geogenic aquifer composition deduced fromthe leaching experiments, we calculate, using a Rayleigh distillationmodel, that is between 53% and 96% of the original Cr(VI) poolwas re-duced to Cr(III) in the waters investigated.

• This implies that there is an ongoing and relatively efficient process inthe groundwater studied that facilitates natural attenuation of the dis-solved and toxic Cr(VI).

1000 10000 100000I) (μg/L)

Reduction

(Gr), and water contaminated by geogenic (geo-water)/anthropogenic (anthro-water) in014).

image of Fig.�6image of Fig.�7

227M. Economou-Eliopoulos et al. / Catena 122 (2014) 216–228

Acknowledgments

TheMayor and theMunicipality ofMessapia–Dirfis is acknowledgedfor the financial support of this work (A.K. 70/3/11730). Mr. E.Michaelidis, University of Athens, is thanked for his assistance withthe SEM/electron probe analyses. We are thankful for the help of ToniLarsen with ion chromatographic separations and thank Toby Leeperfor always maintaining the mass spectrometers in perfect runningconditions. Financial support through The Danish Agency for Science,Technology and Innovation grant no. 11-103378 to RF and throughthe Danish National Research Foundation center of excellence NordCEE(DNRF grant number DNRF53) is highly appreciated. Constructive com-ments by Christopher Oze and an anonymous reviewer helped to im-prove the initially submitted manuscript.

References

Atsarou, C., Economou-Eliopoulos, M., 2012. Contamination by Cr(VI) and other heavymetals in groundwater, soil and crops at Avlona (Greece). Proc. Protection and Resto-ration of the environment XI, Water resources contamination control, Thessaloniki,pp. 471–480.

ATSDR (Agency for Toxic Substances, Disease Registry), 2000. Toxicological Profile forChromium. Agency for Toxic Substances and Disease Registry, Public Health Service,U.S. Department of Health and Human Services (http://www.atsdr.cdc.gov/toxprofiles/tp7.html).

Basu, A., Johnson, T.M., 2012. Determination of hexavalent chromium reduction using Crstable isotopes: isotopic fractionation factors for permeable reactive barrier materials.Environ. Sci. Technol. 46, 5353–5360.

Berger, A., Frei, R., 2013. The fate of chromium during tropical weathering: a laterite pro-file from Central Madagascar. Geoderma 213, 521–532.

Berna, E.C., Johnson, T.M., Makdisi, R.S., Basu, A., 2010. Cr stable isotopes as indicators ofCr(VI) reduction in groundwater: a detailed time-series study of a point-sourceplume. Environ. Sci. Technol. 44 (3), 1043–1048.

Blowes, D.W., 2002. Tracking hexavalent Cr in groundwater. Science 295, 2024–2025.Bonnand, P., Parkinson, I.J., James, R.H., Karjalainen, A.M., Fehr, M.A., 2011. Accurate and

precise determination of stable Cr isotope compositions in carbonates by doublespike MC-ICP-MS. J. Anal. At. Spectrom. 26 (3), 528–535.

Chatoupis, Th., Fountoulis, I., 2004. The neotectonic deformation of N. Parnis Mt, (Attica,Greece). Proceedings of 10th Congress of the Geological Society of Greece,Thessaloniki. Bull. Geol. Soc. Greece, 36(4). Bullettin of the Geological Society ofGreece, Thessaloniki, pp. 1588–1597.

Crowe, S.A., Døssing, L.N., Beukes, N.J., Bau, M., Kruger, S.J., Frei, R., Canfield, D.E., 2013.Atmospheric oxygenation 3 billion years ago. Nature 501, 535–538.

Døssing, L.N., Dideriksen, K., Stipp, S.L.S., Frei, R., 2011. Reduction of hexavalent chromiumby ferrous iron: a process of chromium isotope fractionation and its relevance to nat-ural environments. Chem. Geol. 285, 157–166.

Eary, L.E., Rai, D., 1987. Kinetics of chromium(III) oxidation to chromium(VI) by reactionwith manganese dioxide. Environ. Sci. Technol. 21, 1187–1193.

Eary, L.E., Rai, D., 1988. Chromate removal from aqueous wastes by reduction with ferrousion. Environ. Sci. 22, 972–977.

Eary, L.E., Rai, D., 1989. Kinetics of chromate reduction by ferrous ions derived from he-matite and biotite at 25 °C. Am. J. Sci. 289, 180–213.

EC, 1998. Council Directive (98/83/EC) of 3 November 1998 on the quality of waterintended for human consumption. Official Journal European Community L330.

Economou-Eliopoulos, M., Megremi, I., Vasilatos, Ch., 2011. Factors controlling the hetero-geneous distribution of Cr(VI) in soil, plants and groundwater: evidence from theAssopos basin, Greece. Chem. Erde 71, 39–52.

Economou-Eliopoulos, M., Antivach, D., Vasilatos, Ch., Megremi, I., 2012. Evaluation of theCr(VI) and other toxic element contamination and their potential sources: the case ofthe Thiva basin (Greece). Geosci. Front. 3 (4), 523–539.

Economou-Eliopoulos, M., Megremi, I., Atsarou, K., Theodoratou, Ch., Vasilatos, Ch., 2013.Spatial evolution of the chromium contamination in soils from the Assopos to Thivabasin and C. Evia (Greece) and potential source(s): anthropogenic versus natural pro-cesses. Geosciences 3, 140–158.

Ellis, A.S., Johnson, T.M., Bullen, T.D., 2002. Chromium isotopes and the fate of hexavalentchromium in the environment. Science 295, 2060–2062.

Ellis, A.S., Johnson, T.M., Bullen, T.D., 2004. Using chromium stable isotope ratios to quan-tify Cr(VI) reduction: lack of sorption effects. Environ. Sci. Technol. 38 (13),3604–3607.

Fantoni, D., Brozzo, G., Canepa, M., Cipolli, F., 2002. Natural hexavalent chro-mium in groundwaters interacting with ophiolitic rocks. Environ. Geol. 42,871–882.

Farkas, J., Chrastny, V., Novak, M., Cadkova, E., Pasava, J., Chakrabarti, R., Jacobsen, S.B.,Ackerman, L., Bullen, T.D., 2013. Chromium isotope variations (δ53/52Cr) in mantle-derived Cr sources and their weathering products: implications for environmentalstudies and the evolution of δ53/52Cr in the Earth's mantle over geologic time.Geochim. Cosmochim. Acta 123, 74–92.

Frei, R., Polat, A., 2013. Chromium isotope fractionation during oxidative weathering—implications from the study of a Paleoproterozoic (ca. 1.9 Ga) paleosol, SchreiberBeach, Ontario, Canada. Precambrian Res. 224, 434–453.

Frei, R., Gaucher, C., Poulton, S.W., Canfield, D.E., 2009. Fluctuations in Precambrianatmospheric oxygenation recorded by chromium isotopes. Nature 461,250–253.

Giannoulopoulos, P.A., 2008. Preliminary hydrological -— hydrochemical research.Contamination of Ground Water in the Assopos Basin, Boeotia Region. InternalReport. IGME, Athens, p. 74.

Halicz, L., Yang, L., Teplyakov, N., Burg, A., Sturgeon, R., Kolodny, Y., 2008. High precisiondetermination of chromium isotope ratios in geological samples by MC-ICP-MSJAAS 23, 1622–1627.

Han, R., Qin, L., Brown, S.T., Christensen, J.N., Beller, H.R., 2012. Differential isotopic frac-tionation during Cr(VI) reduction by an aquifer-derived bacterium under aerobic ver-sus denitrifying conditions. Appl. Environ. Microbiol. 78, 2462–2464.

Hem, J.D., 1970. Study and interpretation of the chemical characteristics of natural water,2nd ed. U.S. Geol. Surv. Water Supply Paper 1473.

Izbicki, J.A., Ball, J.W., Bullen, T.D., Sutley, S.J., 2008. Chromium, chromium isotopes and se-lected trace elements, western Mojave Desert, USA. Appl. Geochem. 23 (5),1325–1352.

Jamieson-Hanes, J.H., Amos, R.T., Blowes, D.W., 2012. Reactive transport modeling ofchromium isotope fractionation during Cr(VI) reduction. Environ. Sci. Technol. 46(24), 13311–13316.

Johnson, T.M., 2011. Stable isotopes of Cr and Se as tracers of redox processes in earthsurface environments. In: Baskaran, M. (Ed.), Handbook of Environmental IsotopeGeochemistry. Springer-Verlag, Berlin, Germany, pp. 155–175.

Kabata-Pendlas, A., 2000. Trace Elements in Soils and Plants. CRC Press, Inc., Boca Raton,Florida, p. 550.

Kitchen, J.W., Johnson, T.M., Bullen, T.D., Zhu, J., Raddatz, A., 2012. Chromium isotope frac-tionation factors for reduction of Cr(VI) by aqueous Fe(II) and organic molecules.Geochim. Cosmochim. Acta 89, 190–201.

Kotas, J., Stasicka, Z., 2000. Chromium occurrence in the environment and methods of itsspeciation. Environ. Pollut. 107, 263–283.

Kozuh, N., Stupar, J., Gorenc, B., 1994. Reduction and oxidation processes of chromium insoils. Environ. Sci. Technol. 34, 112–119.

Losi, M.E., Amrhein, C., Frankenberger, W.T., 1994. Environmental biochemistry of chro-mium. Rev. Environ. Contam. Toxicol. 136, 91–121.

Megremi, Ι., 2009. Distribution and bioavailability of Cr in Central Evia, Greece. Cent. Eur.J. Geosci. 2, 103–123.

Megremi, I., 2010. Controlling Factors of the Mobility and Bioavailability of Cr and OtherMetals at the Environment of Ni-Laterites(Ph.D thesis) Univ. of Athens, p. 316.

Megremi, I., Vasilatos, Ch., Atsarou, A., Theodoratou, Ch., Economou-Eliopoulos, M., Mitsis,I., 2013. Geochemical evidences for the sources of the Cr(VI) contamination ingroundwater in central Euboea and Assopos-Thiva basins, Greece. Natural versus An-thropogenic Origin, European Water (41), 23–34.

Moynier, F., Yin, Q.Z., Schauble, E., 2011. Isotopic evidence of Cr partitioning into theEarth's core. Science 331, 1417–1420.

Novak, M., Chrastny, V., Cadkova, E., Farkas, J., Bullen, Th.D., Tylcer, J., Szurmanova, Z.,Cron, M., Prechova, E., Curik, J., Stepanova, M., Pasava, J., Erbanova, L., Houskova, M.,Puncochar, K., Hellerich, L.A., 2014. Common occurrence of a positive δ53Cr shift inCentral European waters contaminated by geogenic/industrial chromium relative tosource values. Environ. Sci. Technol. 48 (11), 6089–6096.

Oze, C., Fendorf, S., Bird, K.D., Coleman, G.R., 2004. Chromium geochemistry of serpentinesoils. Int. Geol. Rev. 46, 97–126.

Oze, C., Bird, K.D., Fendorf, S., 2007. Genesis of hexavalent chromium from natural sourcesin soil and groundwater. PNAS 104, 6544–6549.

Palmer, C.D., Puls, R.W., 1994. Natural attenuation of hexavalent chromium in groundwa-ter and soils. Ground Water, EPA 540, S-94, 505.

Palmer, C.D., Wittbrodt, P.R., 1994. Processes affecting the remediation of chromium-contaminated sites. Environ. Health Perspect. 92, 25–40.

Papanikolaou, D., Mariolakos, I., Lekkas, E., Lozios, S., 1988. Morphotectonic observationsat the Assopos basin and the coastal zone of Oropos. Contribution to the neotectonicsof Northern Attiki. Bull. Geol. Soc. Greece 20, 251–267.

Raddatz, A.L., Johnson, T.M., McLing, T.L., 2011. Cr stable isotopes in Snake River Plainaquifer groundwater: evidence for natural reduction of dissolved Cr(VI). Environ.Sci. Technol. 45 (2), 502–507.

Rotaru,M., Birck, J.L., Allegre, C.J., 1992. Clues to early solar systemhistory from chromiumisotopes in carbonaceous chondrites. Nature 358 (6386), 465–470.

Sander, S., Koschinsky, A., 2000. Onboard-ship redox speciation of chromium in diffusehydrothermal fluids from North Fiji basin. Mar. Chem. 71, 85–102.

Schauble, E., Rossman, G.R., Taylor Jr., H.P., 2004. Theoretical estimates of equilibriumchromium-isotope fractionations. Chem. Geol. 205, 99–114.

Schoenberg, R., Zink, S., Staubwasser, M., von Blanckenburg, F., 2008. The stable Cr isotopeinventory of solid Earth reservoirs determined by double spike MC-ICP-MS. Chem.Geol. 249 (3-4), 294–306.

Sikora, E.R., Johnson, T.M., Bullen, T.D., 2008. Microbial mass-dependent fractionation ofchromium isotopes. Geochim. Cosmochim. Acta 72, 3631–3641.

Stanin, F.T., 2005. The transport and fate of chromium(VI) in the environment. In:Guertin, J., Jacobs, J.A., Avakian, C.P. (Eds.), Chromium (VI) Handbook. CRC Press,Boca Raton, FLA, pp. 165–214.

Trinquier, A., Elliott, T., Ulfbeck, D., Coath, C., Krot, A.N., Bizzarro, M., 2009. Origin of nucle-osynthetic isotope heterogeneity in the solar protoplanetary disk. Science 324,374–376.

Valeton, I., Biermann, M., Reche, R., Rosenberg, F., 1987. Genesis of Ni-laterites and baux-ites in Greece during the Jurassic and Cretaceous, and their relation to ultrabasic par-ent rocks. Ore Geol. Rev. 2, 359–404.

Villalobos-Aragón, A., Ellis, A.S., Armienta, M.A., Morton-Bermea, O., Johnson, T.M., 2012.Geochemistry and Cr stable isotopes of Cr-contaminated groundwater in León valley,Guanajuato, México. Appl. Geochem. 27, 1783–1794.

http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0225http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0225http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0225http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0225http://www.atsdr.cdc.gov/toxprofiles/tp7.htmlhttp://www.atsdr.cdc.gov/toxprofiles/tp7.htmlhttp://refhub.elsevier.com/S0341-8162(14)00183-0/rf0005http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0005http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0005http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0235http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0235http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0010http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0010http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0010http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0020http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0240http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0240http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0240http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0245http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0245http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0245http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0245http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0250http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0040http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0040http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0040http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0035http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0035http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0045http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0045http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0255http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0255http://refhub.elsevier.com/S0341-8162(14)00183-0/rf8950http://refhub.elsevier.com/S0341-8162(14)00183-0/rf8950http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0060http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0060http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0060http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0055http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0055http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0055http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0065http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0065http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0065http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0070http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0070http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0075http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0075http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0075http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0080http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0080http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0080http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0085http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0085http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0085http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0085http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0085http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0085http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0100http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0100http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0100http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0095http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0095http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0095http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0260http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0260http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0260http://refhub.elsevier.com/S0341-8162(14)00183-0/rf9010http://refhub.elsevier.com/S0341-8162(14)00183-0/rf9010http://refhub.elsevier.com/S0341-8162(14)00183-0/rf9010http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0265http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0265http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0265http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0270http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0270http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0115http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0115http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0115http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0275http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0275http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0275http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0280http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0280http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0280http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0285http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0285http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0290http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0290http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0290http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0130http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0130http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0135http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0135http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0140http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0140http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0145http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0145http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0295http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0295http://refhub.elsevier.com/S0341-8162(14)00183-0/rf9005http://refhub.elsevier.com/S0341-8162(14)00183-0/rf9005http://refhub.elsevier.com/S0341-8162(14)00183-0/rf9005http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0150http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0150http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0300http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0300http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0300http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0300http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0155http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0155http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0160http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0160http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0305http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0305http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0170http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0170http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0310http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0310http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0310http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0315http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0315http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0315http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0185http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0185http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0190http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0190http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0195http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0195http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0320http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0320http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0320http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0205http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0205http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0325http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0325http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0325http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0210http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0210http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0210http://refhub.elsevier.com/S0341-8162(14)00183-0/rf7000http://refhub.elsevier.com/S0341-8162(14)00183-0/rf7000http://refhub.elsevier.com/S0341-8162(14)00183-0/rf7000http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0215http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0215

228 M. Economou-Eliopoulos et al. / Catena 122 (2014) 216–228

Wanner, C., Eggenberger, U., Mäder, U., 2012. A chromate-contaminated site in southernSwitzerland — Part 2: reactive transport modeling to optimize remediation options.Appl. Geochem. 27, 655–662.

Wanner, C., Sonnenthal, E.L., 2013. Assessing the control on the effective kinetic Cr isotopefractionation factor: a reactive transport modeling approach. Chem. Geol. 337, 88–98.

Wielinga, B., Mizuba, M., Hansel, C., Fendorf, S., 2001. Iron promoted reduction of chro-mate by dissimilatory iron-reducing bacteria. Environ. Sci. Technol. 35, n. 3.

Zink, S., Schoenberg, R., Staubwasser, M., 2010. Isotopic fractionation and reaction kineticsbetween Cr(III) and Cr(VI) in aqueous media. Geochim. Cosmochim. Acta 74,5729–5745.

http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0220http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0220http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0220http://refhub.elsevier.com/S0341-8162(14)00183-0/rf5000http://refhub.elsevier.com/S0341-8162(14)00183-0/rf5000http://refhub.elsevier.com/S0341-8162(14)00183-0/rf8050http://refhub.elsevier.com/S0341-8162(14)00183-0/rf8050http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0330http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0330http://refhub.elsevier.com/S0341-8162(14)00183-0/rf0330

Application of chromium stable isotopes to the evaluation of Cr(VI) contamination in groundwater and rock leachates from ce...1. Introduction2. Geological and hydrological outline2.1. Central Euboea2.2. Assopos basin (Avlona)

3. Samples and methods of investigation4. Geochemistry of rocks, soils and groundwater4.1. Major and trace element contents in rocks and soils4.2. Cr-host minerals4.3. Trace element concentrations in groundwater4.4. Trace element concentrations in rock and soil leachates4.5. Chromium stable isotope values in groundwater4.6. Chromium stable isotope values in leachates

5. Discussion5.1. Use of δ53Cr values as a tracer for the reduction of Cr(VI) in natural waters5.2. The use of δ53Cr values in rock and soil leachates for identifying reduction of Cr(VI)

6. ConclusionsAcknowledgmentsReferences