I N T E R N AT I O N A L C O N F E R E N C E

PROTECTION AND RESTORATIONOF THE ENVIRONMENT XI

P R O C E E D I N G S

E D I T O R S:K. L. KatsifarakisN. Theodossiou

C. ChristodoulatosA. Koutsospyros

Z. Mallios

THESSALONIKI, JULY 2012

PROTECTIONAND RESTORATIONOF THE ENVIRONMENTXI

ON THE SPECIATION AND THE SOURCES OF CHROMIUM IN GROUNDWATER IN EASTERN STEREA HELLAS, GREECE:

NATURAL VERSUS ANTHROPOGENIC ORIGIN.

I. Megremi, Ch. Vasilatos, M. Economou-Eliopoulos & I. Mitsis Dept. of Geology & Geoenvironment, Section of Economic Geology & Geochemistry, University

of Athens, Panepistimiopolis, 15784 Athens

ABSTRACT Investigation of the water composition in Eastern Sterea Hellas, central Greece, has revealed high concentrations of Cr(total) in groundwater systems exceeding, sometimes, the Greek and the EU drinking water maximum acceptable level. Chemical analyses of the water samples were performed by using the GFAAS and ICP-MS for total chromium, diphenylcarbazide-Cr(VI) complex colorimetric method for hexavalent chromium, and flame-AAS and ICP-MS for other elements. The concentrations of Cr(VI) detected in several groundwater samples, range from < 1 (below detection limit) to 360�g.L-1 in central Euboea and from < 1 to 153�g.L-1 in Thiva–Tanagra–Malakasa basin, Eastern Sterea Hellas, Greece. The excellent correlation between Cr(VI) and Cr(total), indicates that hexavalent chromium is the predominant form of dissolved chromium in groundwater, with a pH near to neutral, regardless of its natural or industrial origin. Water samples from the Thiva–Tanagra–Malakasa basin are characterized by lower Si contents compared to those from central Euboea. Based on Na, Ca, Mg, Si and Cr(VI) content of the water samples, several discrimination diagrams have been proposed for the identification of their origin. According to their Na, Ca, Mg, Si and Cr contents, the water samples from central Euboea can be distinguished to a) those influenced by the sea water, having high Na and B concnetrations, b) those from the inner part of the island with lower Na and an average of 25�g.L-1 Cr(total) and c) those with very high Cr(total) values, up to 360 �g.L-1. The hydrochemical differences of the water samples from Euboea, suggest that in a) and b) cases the ultramafic rocks of the area may be the source of the chromium, whilst in case c) the chromium content of the samples is probably associated with human activities. In Thiva–Tanagra–Malakasa basin the hexavalent chromium content of the water is associated with anthropogenic activities as well (industrial wastes). Keywords water contamination; Cr(VI); chromium speciation; toxic metals; central Euboea; ophiolites

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1. INTRODUCTION The higher mobility and toxicity of Cr(VI) compared to Cr(III) for biological systems has been extensively documented, due to its strong oxidizing potential (Kotas and Stasicka, 2000, Bielicka et. al., 2005, Wise S. and Wise J., 2012). The speciation and the transport of chromium within the terrestrial and water systems is governed by pH and redox transformations. Three subsystems had been distinguished, considering chromium transport in natural waters: river, lake and ocean water (Bielicka et. al., 2005). In the neutral pH conditions the Cr(III) present in water has a low solubility and readily precipitate as Cr(OH)3(s) or mixed Cr-Fe hydroxides colloids in pH values greater than 4 (Schlautman and Ihnsup, 2001). The trivalent chromium ions have a tendency to bind with the suspended solids and thus are detectable in the sediment (Kotas and Stasicka, 2000). Cr(III) is the most stable oxidation state of chromium. In the pH range of water Cr(VI) exists as CrO42

-, HCrO4-

and Cr2O72- ions. These form many Cr(VI) compounds, which are relatively soluble and thus

mobile in the environment. The Cr(VI) in groundwater can be reduced to Cr(III) in low pH, under reducing conditions. In environmental systems, Cr(VI) exists as oxyanions such as chromate (CrO4

2-), bichromate (HCrO4-) and dichromate (Cr2O7

2-) and has a high solubility in water. In contrast, Cr(III), is an essential nutrient required for normal glucose and lipid metabolism in body, as it enhances the effect of insulin. Chromium enters the body through inhalation, ingestion and dermal absorption. The general population is exposed to chromium through ingestion of chromium in food and water while occupational exposure occurs predominantly through inhalation and dermal contact. In terms of toxicity of Cr(VI) although it is a known carcinogen through inhalation, the WHO, EU and US agencies have not yet classified Cr(VI) in terms of ingestion (USEPA, 2010). Due to the toxicity of hexavalent chromium, the California Office of Environmental Health Hazard Assessment (�����) developed a Public Health Goal (PHG) for hexavalent chromium of 0,02 �g.L-1 in drinking water (OEHHA, 2011). In all other states the Federal drinking water standard for total chromium is 100�g.L-1 (WHO, 2003). However, that situation may change as a result of recent research showing elevated levels of Cr(VI) in the drinking water supplies of 31 different cities across the United States. The U.S. Environmental Protection Agency could move to establish federal limits for Cr(VI) in drinking water as early as 2012, following the completion of its own risk (OEHHA, 2011). Italy has regulated a maximum permissible level of Cr(VI) in drinking water at 5 �g.L-1 (Fantoni et. al., 2002, Stepek, 2002). Most countries including the European Union have currently regulated the limit of 50�g.L-1 for total chromium in drinking water(EC, 1998) which assumes a mixture of hexavalant chromium and trivalent chromium. Greece has adopted the above limit. Cr(VI) and its compounds can originate in the aqueous environment from both anthropogenic (industry wastes and emissions, combustion processes e.t.c.) and natural sources (weathering of chromium bearing minerals). Numerous studies of naturally occurring aqueous Cr(VI) at concentrations up to 73�g.L-1 have been reported in ground and surface waters from New Caledonia, California, Italy and Mexico, associated mainly with serpentine soils and ultramafic rocks (Ball and Izbicki, 2004, Oze et al., 2007, Izbicki et al., 2008, Wise S. and Wise J., 2012). Given that chromium is a major trace element in both serpentinized ultramafic ophiolitic rocks and Ni-laterites and extended massive serpentinized ultramafic ophiolitic formations and large Ni-laterite deposits are located in the central part of Greece (Lokris and Euboea), (Katsikatsos et. al., 1986, Eliopoulos and Economou-Eliopoulos, 2000, Valeton et al., 1987), where previous analytical data had shown significant (some tens of �g.L-1) Cr(total) concentrations (Vardaki and Kelepertsis, 1999, Megremi 2010), the area of central Euboea had been selected as a case of chromium bearing natural water related to natural processes. The objective of this study is the presentation of geochemical data on the Cr species and its relations with other chemical elements in natural waters of central Euboea and the comparison to those from the neighbouring Thiva – Tanagra – Malakasa

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basin, characterized by widespread industrial activity (Vasilatos et al, 2008b) in order to define the sources of the Cr(VI) contamination.

2. HYDRO-GEOLOGICAL SETTING

In the central Euboea (sampling area 2 in Figure 1), the sampled springs have being issued from the upper Cretaceous limestones and are located near to the contact with the underlying upper Jurassic-lower Cretaceous ophiolitic complex. The ophiolitic complex is consisted by serpentinites, diabases and peridotites. The main aquifer of the wells is hosted into the same ophiolitic complex and it is assumed as a fissured rock aquifer. The wells have a depth between 4-180m. In the Thiva – Tanagra – Malakasa basin (central and north part of the sampling area 1, in Figure 1), the wells are sited on a thick Neogene formation(up to over 600 m thick), consisted by intercalations of marles, sands, clays and limestones. The aquifer is porous and is consisted of several sub-aquifers, as the clay intercalations are impermeable by the water. The wells have a depth between 200-220m and those which are used for the agriculture in that area, have a depth between 15-300m. At the southeast of this basin there are the Mavrosouvala wells (at the edge of the sampling area 1, towards Malakasa town, see Figure 1). Those are sited in middle Triassic to middle Lias, limestone formation (up to over 500 m thick) which is the north extension of the thick Parnis Mountain limestone formation.

1.

2.

Figure 1: Map of the studied areas. 1. Thiva-Tanagra-Malakasa basin, 2. Central Euboea

3. MATERIALS AND METHODS

3.1 SamplingThe water sampling areas, located at central Euboea, are shown on Figure 2. A total of 41 groundwater samples were collected from wells and springs in the extended area of the municipality of Messapia and N. Artaki (areas of N.Artaki – Kastella – Psachna – Makrymalli – Kondodespoti – Dafni - Lefkanti).

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3.2 Field work Some physical and chemical parameters (pH, redox, total dissolved solids, conductivity and temperature) of the water samples were measured in the field using a portable Consort 561 Multiparameter Analyzer. The samples were collected, divided in two portions and each one was stored in polyethylene containers at 40C in a portable refrigerator. The second portion of each sample was acidified by addition of concentrated HNO3 acid and stored at 40C as well.

Figure 2. Sketch map showing the location of the studied area,(central Euboea), along with a simplified map showing the sampling sites of groundwater samples.

3.3 Analytical Methods Knowing that pH reduction could reduce the solubility of hexavalent chromium and any biotic activity could change the valence state of chromium in the samples, the chemical analyses of total and of hexavalent chromium have been performed in the non nitrified portion of the samples, within 24 hours after collection. The analyses of total chromium were performed by GFAAS (Perkin Elmer 1100B). The estimated detection limit of the method was determined at 2 �g.L-1. The chemical analyses for Cr(VI) were performed by the 1,5-diphenylcarbohydrazide colorimetric method, within 24 hours after sampling, using a HACH DR/4000 spectrophotometer. The estimated detection limit of the method was determined at 4 �g.L-1. The analyses of calcium and magnesium were performed by flame AAS (Perkin Elmer 603). The estimated detection limit of the method was determined at 50 �g.L-1 and 20 �g.L-1 respectively. All the above analyses were performed at the Laboratory of Economic Geology and Geochemistry in the Faculty of Geology and Geoenvironment of University of Athens. The other elements (Ni, Mn, Si, Na, K, B, Li, Ba, As, Cd, Co, Cu, P, Pb, S, Se, V and Zn), were analysed, in the acidified portion of the samples, by Inductively Coupled Plasma Mass Spectroscopy (ICP/MS) at the ACME Analytical Laboratories in Canada.

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4. RESULTS The analytical results showing the concentrations of chemical constituents of the water samples are given in Table 1. Concentrations over the maximum acceptable level for Cr(total) in drinking water (50 �g.L-1, according to the EU Directive), (EC, 1998) were found in thirteen groundwater samples from central Euboea. Relatively high Cr(VI) concentrations have been detected in the same groundwater samples, rising up to 359 �g.L-1. The very good correlation (r=0,99) between Cr(total) and Cr(VI) indicate that Cr(VI) is the predominant form of dissolved Cr in the area studied. This conclusion does not support the implication of OEHHA according to which Cr(VI) comprises only the 7% of total chromium in groundwater (OEHHA, 2001). With the exception of Cr(total), Cr(VI) and in some cases of Zn, which in a few drilling wells exhibited extremely high values, all the other elements in groundwater samples, were found to be in concentrations below the maximum permeable limits for human usage (EC, 1998). The range of pH (7,1-7,9) and Eh (-62 to 16mV) measurements of the groundwater indicate alkaline and almost neutral redox conditions, suitable for the stability of Cr(VI) in solution. Table 1. Concentrations of chemical constituents of water samples from central Euboea (the cells in shadow contain the Cr(total) concentrations over the maximum acceptable level in drinking water) .

ppm

Cr(total) Cr(VI) Ca Mg Ni Mn Si Na K B Li Ba As Cd Co Cu P Pb S Se V ZnE1 33 32 30235 50228 1,6 <0,05 12757 22307 1227 30 2,7 13 0,9 <0,05 0,11 0,4 <20 0,05 15 0,9 1,9 0,25E2 130 128 17685 81239 4,2 <0,05 19838 72683 12434 146 6,8 8 0,7 <0,05 0,16 1,1 <20 0,05 41 1,5 3,1 2,2E3 53 51 31957 76331 5,1 0,11 16908 37641 1665 38 4,1 10 0,8 <0,05 0,12 0,5 <20 0,05 29 1,2 2,5 110E4 60 59 33134 74522 4,4 0,11 16261 37990 1594 35 4 15 0,8 <0,05 0,09 1,0 <20 0,05 28 1,2 2,5 10E5 114 110 63671 103068 3,6 <0,05 17439 40245 4821 61 5,8 45 0,9 <0,05 0,22 0,6 <20 0,05 68 2,1 2,7 0,5E6 70 68 16479 113559 1,8 0,13 24490 52708 3883 68 6,8 2 1,4 <0,05 0,2 0,8 <20 0,05 27 3,5 4 0,9E7 360 360 63996 124808 4,8 <0,05 27740 31678 1951 42 7,3 9 0,7 <0,05 0,29 1,3 <20 <0,01 44 1,6 2,1 0,7E8 70 64 63979 154598 5,8 <0,05 20315 97906 1061 79 16,4 25 2 <0,05 0,15 1,1 <20 <0,01 58 5,4 5,8 3,9E9 86 83 59146 88952 3 0,07 19327 44314 1784 47 11,1 23 1,3 <0,05 0,07 0,8 <20 <0,01 32 2,2 4,3 2,6E10 105 104 64455 114602 4,6 <0,05 15410 37594 914 35 4,6 10 0,6 <0,05 0,21 0,8 <20 <0,01 52 1,1 2,2 5,7E11 68 63 112831 86920 3,6 0,26 13279 38825 2470 36 6,3 30 1,6 <0,05 0,05 1 <20 <0,01 57 2,1 2,2 89E12 75 62 75354 56128 0,5 0,93 12889 25155 2751 28 5,6 38 1,7 0,09 <0,02 0,5 <20 1,1 13 1,4 1,8 527E13 56 56 141554 133648 5,4 <0,05 12988 79452 4531 88 9,1 59 1,4 <0,05 0,19 1,9 <20 <0,01 110 3,5 2,1 1,2E14 16 16 15302 59021 8,9 <0,05 24094 15750 598 25 2,4 1 0,5 <0,05 0,04 0,4 <20 0,05 7 0,7 3 1,9E15 25 25 19905 52310 2,1 <0,05 24310 19559 537 21 3,8 9 0,7 <0,05 0,02 0,3 <20 0,05 6 0,25 6,1 0,25E16 18 18 35283 28411 0,3 <0,05 10018 12446 453 10 0,2 4 0,25 <0,05 0,04 0,3 <20 0,05 3 0,5 1 0,25E17 37 36 7442 66797 0,8 <0,05 32983 20987 316 19 4,3 2 0,5 <0,05 <0,02 0,3 <20 0,05 1 0,8 8,4 0,25E18 33 32 94009 44922 5,2 1,18 19770 19422 666 19 2 15 0,25 <0,05 0,12 25 30 1,5 19 1,4 1 55E19 32 32 95186 45392 5,8 0,80 18793 19316 652 19 2 15 0,25 <0,05 0,13 3 32 0,6 17 1,3 1 48E20 16 12 98618 51604 11 1,56 23215 22313 455 25 2,7 20 0,25 0,08 0,24 5,9 37 10,6 29 1,7 1,7 2637E21 13 12 121734 28617 33 0,52 14341 18789 480 22 2,1 16 0,25 <0,05 0,11 1,4 35 0,2 13 1,1 0,7 48E22 52 51 77791 83110 3,8 1,11 27856 29876 321 29 3,5 20 0,25 <0,05 0,25 1,1 43 0,05 35 2,5 2,3 2,2E23 15 15 9482 79568 1 0,5 34096 14701 381 15 1,6 0 2,6 <0,05 0,03 0,3 <20 0,05 8 0,8 3,4 0,6E24 14 14 17822 81488 4,5 <0,05 34071 35108 1223 16 2,3 3 1,5 <0,05 0,02 0,5 <20 0,05 13 1,4 6,8 0,25E25 37 36 8939 67548 0,9 <0,05 32050 21587 353 21 4,5 2 0,5 <0,05 <0,02 0,3 <20 0,05 1 1 9,3 0,25E26 31 30 48557 74139 1,9 0,08 30719 21727 353 23 3,7 19 0,25 <0,05 0,03 0,5 35 0,05 5 1,2 6,1 0,9E27 33 32 47628 74201 2,3 0,13 29935 21652 346 23 3,4 19 0,25 <0,05 0,05 0,6 33 0,05 4 1,3 6,2 0,7E28 27 26 94422 43404 4,1 <0,05 20699 19146 668 17 1,9 15 0,25 <0,05 0,1 0,4 34 0,05 19 1,4 1,1 0,25E29 26 25 65403 69857 2,4 0,43 26503 22651 579 17 2,7 21 0,25 <0,05 0,06 0,4 33 0,05 5 1,1 0,8 0,6E30 18 18 36575 26933 6,8 <0,05 15371 15295 2299 19 1,6 6 0,5 <0,05 0,06 0,2 <20 0,05 6 0,25 1 0,25E31 17 12 113181 26442 11 0,06 14137 16032 1765 24 1,6 8 0,25 <0,05 0,08 0,4 75 0,05 5 0,8 0,7 0,25E32 15 15 68168 55767 7,2 0,8 23667 15523 463 26 2,1 11 0,25 0,07 0,04 2,5 34 2,1 7 1,5 1,9 6086E33 <2 <4 97979 5167 1,5 0,18 4092 12030 448 10 1,4 24 0,25 <0,05 0,03 7,1 34 0,2 5 0,5 0,4 32E34 <2 <4 46161 7726 1,4 <0,05 5586 14215 1065 13 0,7 13 0,6 <0,05 0,07 0,2 <20 0,05 6 0,5 1,2 0,25E35 2 <4 53424 11063 0,1 <0,05 6764 15359 684 11 2,2 11 0,7 <0,05 0,02 0,2 <20 0,05 5 0,7 1,3 0,25E36 3 <4 43605 9744 0,7 <0,05 6355 13984 471 11 0,9 8 0,25 <0,05 0,06 0,3 <20 0,05 5 0,7 0,5 1,10E37 <2 <4 51112 4384 0,1 <0,05 3896 11944 410 8 1 7 0,5 <0,05 0,02 0,3 <20 0,05 4 0,5 0,7 0,25E38 5 <4 117858 12917 1,9 0,23 6891 10758 356 10 0,7 6 0,25 <0,05 0,03 1,1 34 0,05 4 0,5 0,4 0,8E39 22 20 84847 42096 0,9 0,35 7583 65542 2037 24 3,7 30 1,8 <0,05 0,06 3,5 <20 0,05 13 2,2 2,5 25E40 23 20 85373 43022 0,6 0,19 7553 66542 2009 23 3,5 22 2 <0,05 0,05 2 <20 0,05 11 2,3 2,3 16E41 23 19 86244 43642 0,7 <0,05 7501 65576 1986 23 3,7 26 2 <0,05 0,06 1,5 <20 0,05 12 2,4 2,1 0,5

Samples ppb ppb

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Based on the Na, B, Mg and Cr concentrations, the water samples from central Euboea can be distinguished to a) those influenced by the sea water, having high Na, K and B concentrations, b) those from the inner part of the island with lower B and Na and an average of 25�g.L-1 Cr(total) c) those with lower B and Na and Cr(total) below the detection limit(2�g/L) and d) those with very high Cr(total) values, up to 360 �g.L-1. Discrimination between water samples from the inner part of central Euboea and from near to the western coastline of the area studied, based on the differences of their chemical composition is presented by the bivariate plot of Mg versus B (Figure 3). A possible seawater intrusion to the aquifer near the coastline, may explain the high Na, K, and B concentrations in these samples in comparison to those from the inner part of central Euboea.

Figure 3: Bivariate plot of Mg versus B showing the differences in the chemical composition of the water samples from central Euboea

The enrichment of natural waters in central Euboea with a mean value in Cr(VI) of 25�g.L-1, may be linked, mainly, to the Cr-extraction and oxidation from Cr-bearing silicate minerals (serpentinite and chlorite) in ophiolitic rocks that host along with the limestone the aquifer and lesser to chromite and to Cr-bearing goethite [FeO(OH)] which is abundant in Fe-Ni laterite deposits. This suggestion for a natural origin of Cr(VI) in waters of central Euboea is enhanced by the strong correlation coefficients between Cr(total) versus Mg (0.75) and between Cr(total) versus Si (0.72) and Mg versus Si (0.98). These strongly correlated elements discriminated these water samples from those presenting high Cr(VI) concentrations, where no correlation between the above elements was observed [Cr(total) versus Mg (0.17), Cr(total) versus Si (0.35), Mg versus Si (0.47)]. The above assumption, concerning Cr(VI) origin from the ophiolitic rocks mainly, may also be enhanced, by the Mg/Si ratio in the groundwater samples with a mean value of Cr(total) 25�g.L-1, which seems to be rather constant and equal to 2,3(Figure 4), while the same ratio in the water samples exhibiting high Cr(VI) concentrations, is rather variable, ranging from 3,9 to 10,2.

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Figure 4: Bivariate plot of Mg/Si versus Cr show the trends and the variations of the chemical composition of the water samples from central Euboea (the dashed line corresponds to the value of

Mg/Si equal to 2,3).

5. DISCUSSION The case of central Euboea, could be compared with that of the Thiva – Tanagra – Malakasa basin (Eastern Greece) where the impact of anthropogenic activities on ground water quality is more intense(Vasilatos et al. 2008b). For this purpose the data of ground water values from the Thiva – Tanagra – Malakasa basin were projected in a bivariate plot of Ca/Si versus Mg/Si (Figure 5). The ground water samples from the Thiva – Tanagra – Malakasa basin that are characterized by high values of Cr(total) and Cr(VI) and are linked mainly to the industrial activities in the area, are projected in the field that comprise the ground water samples of elevated Cr(VI) concentrations, from Euboea and exhibit also a variability in Mg/Si ratio ranging from 2,9 to 10,3. Also the Mg/Si ratio is lower in central Euboea samples with a mean Cr(VI) value of 25�g.L-1 due to the elevated concentrations of Si as a result of water interaction with the Mg-rich ophiolitic rocks. Also, the Ca/Si ratio of the samples from the karstic limestone Mavrosouvala aquifer is higher than the ratio of the rest samples from the Thiva – Tanagra – Malakasa basin and the samples from central Euboea as well, as the host rocks consist mainly of CaCO3. Moreover, there is a negative trend between the Cr concentrations in water wells and their depth (Figure 6). Groundwater from wells of karst-type is characterized by Cr concentrations below detection limit. Although the majority of water samples show a wide variation, as far as the Cr concentrations, they fall into the field of shallow wells. Furthermore, on the basis of their spatial distribution two groups can be distinguished: one group covering the areas of Makrymallis and Dafni, located mostly in ultramafic rocks and a second group of wells located at the area of Psachna, which are strongly contaminated by Cr (Megremi, 2010). Regardless the source of the

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groundwater contamination by Cr(VI) it seems likely that deep wells of karst-type could be used to supply water instead of the Neogene aquifer.

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Figure 6 : Bivariate plot of wells depth from central Euboea versus their Cr (total) concentrations. 6. CONCLUSIONS The geological and geochemical data of water samples from central Euboea, combined with those from the Thiva-Tanagra-Malakasa basin lead to the following conclusions:

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- Significant concentrations over the maximum acceptable level of total Cr in drinking water and high Cr(VI) values have been detected in central Euboea.

- According to the Mg, Si and Cr(total) composition, water samples from central Euboea could be classified into two groups: (a) the water samples with a mean value of Cr(total) equal to 25�g/L and a constant ratio of Mg/Si up to 2,3, which suggests that the ultramafic rocks of the area may be the source of the chromium, and (b) the water samples exhibiting high Cr(VI) concentrations and a variability in the value of Mg/Si ratio.

- The contamination by Cr(VI) of the ground water in central Euboea may be mainly linked to the chromium extraction and oxidation from the Cr-bearing silicate minerals of serpentinites of the ophiolitic rocks and lesser to chromite (a mineral of very low solubility) and to Cr-bearing goethite which is abundant in Fe-Ni laterite deposits.

- According to their Na, B, Mg and Cr content, the water samples from central Euboea can be discriminated between those that come nearby the coastline which are influenced by the sea water, having high Na, K and B concentrations and to those from the inner part of the studied area with lower Na and higher Cr(total) and Cr(VI) values which have not been affected by the sea water.

- The bivariate plot of of Si-normalized Mg versus Si-normalized Ca has been successfully used for the discrimination and the identification of the origin of the water samples from central Euboea and Thiva-Tanagra-Malakasa basin.

- The chemical evolution and the speciation of the chromium of the groundwater in the study areas is governed by natural (geological) and anthropogenic factors.

Acknowledgments The University of Athens is greatly acknowledged for the financial support of this work, and two anonymous reviewers for their constructive criticism and suggestions regarding an earlier version of this paper. The authors would like to thank Mr Efstathios Vorris for his technical support at the field work. REFERENCES 1. Ball J. and Izbicki J., (2004) ‘Occurrence of hexavalent chromium in ground water in the

western Mojave Desert, California’ Applied Geochemistry 19, 1123–1135. 2. Bielicka A., Bojanowska, I., Wi�niewski, A., (2005) ‘Two Faces of Chromium - Pollutant and Bioelement’ Polish Journal of Environmental Studies Vol. 14, No. 1 (2005), 5-10. 3. EC, (1998) Council Directive (98/83/EC) of 3 November 1998 on the quality of water intended for human consumption. Offic J Eur Commun, L330. 4. Eliopoulos, D., Economou-Eliopoulos, M., (2000) ‘Geochemical and mineralogical characteristics of Fe–Ni and bauxitic-laterite deposits of Greece’Ore Geology Reviews 16, 41 - 58. 5. Fantoni, D., Brozzo, G., Canepa, M., Cipolli, F., (2002) ‘Natural hexavalent chromium in groundwaters interacting with ophiolitic rocks’ Environmental Geology, 42, 871-882. 6. Izbicki J., Ball J., Bullen T., Sutley S., (2008) ‘Chromium, chromium isotopes and selected trace

elements, western Mojave Desert, USA’ Applied Geochemistry 23, 1325–1352. 7. Katsikatsos, G.,Migiros, G., Triantaphyllis, M., Mettos, A., (1986) ‘Geological structure of internal Hellenides’ Geol. Geoph. Res., Special issue, 191-212. 8. Kotas, J., Stasicka, Z., (2000) ‘Chromium occurrence in environment and methods of its speciation’ Environmental Pollution, 107 (3), 263-283. 9. Megremi I. 2009 ‘Distribution and bioavailability of Cr in central Euboea, Greece’ Central European Journal of Geosciences 1 (2), 103-123.

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