SPECIATION AND MOBILITY OF ARSENIC AND ANTIMONY IN GROUNDWATER AT MELIVOIA, EAST THESSALY AND KERAMOS AREA NW CHIOS, GREECE

E. CHATZIDIAKOS, M. FANOURAKI, A. KELEPERTSIS, A. ARGYRAKI, AND D. ALEXAKIS

Department of Economic Geology and Geochemistry, Faculty of Geology and Geoenvironment, University of Athens, Panepistimioupoli Zographou, 15784 Athens, email:

shatzidiakos@yahoo.com

Key words: Speciation, Arsenic, Antimony, Saturation Index, Bourboulithra, Keramos

Abstract Groundwater and rock samples were collected from two areas in Greece, Bourboulithra area, East Thessaly and Keramos area, NW Chios Island. The water samples were analysed for main elements and toxic trace elements and the minerology of rock samples was studied by Scanning Electron Microscop (SEM). The geology of Melivoia area includes sedimentary and metamorphic rocks while the geology of NW Chios comprises a mixture of Paleozoic sedimentary and volcanic rocks. Minor occurrences of sulphide minerals containing Sb and As are present in both areas. The chemical speciation of As and Sb in groundwater and the saturation indexes of relevant minerals were assessed by using the code inverse model of the PHREEQC computer program. In Bourboulithra area of Melivoia, East Thessaly the groundwater is enriched in As and Sb because of the continuous dissolution of arsenopyrite (FeAsS) and stibnite (Sb2S3). The trivalent oxidant state of As is the predicted dominant speciess in groundwater during both the wet and dry period. The pentavalent oxidant state of Sb is the dominant species in springwater during the wet period but in the dry period the trivavalent Sb is the species that dominates. In the Keramos area of NW Chios heavy influence of Sb mineralization in the groundwater is observed. The continuous dissolution of stibnite (Sb2S3) results in polluted groundwaters with Sb. Trivalent oxidation state of Sb is predicted by PHREEQC in two of the three springs and pentavalent oxidation state in the third spring. 1.Introduction Arsenic (As) and antimony (Sb) are two metalloids which occur in the surface environment (soil, water, air and biota) in trace quantities and are characterized by similar chemical properties (Onishi 1969). Their presence in the natural environment is closely linked to sulfide ore occurrences and hydrothermal systems. Both elements can form toxic chemical speciess for human, their main intake pathway being drinking water. Toxicity, reactivity and bioavailability of the elements depend on their chemical forms. Arsenic can occur in the environment in several oxidation states (-3, 0, +3 and +5) but in natural waters is mostly found in inorganic form as oxyanions of trivalent arsenite or pentavalent arsenate (Cox 1997, Smedley and Kinniburgh 2002). The most common oxidation states of Sb are -3, +3, +5. The trivalent oxidation state of both elements is more toxic than the pentavalent one. PHREEQC program (Parkhurst and Appelo 1999) is based on an ion-association aqueous model and has capabilities for speciation and saturation-index calculations and inverse modeling, which uses available chemical analyses that are assumed to be representative of the chemical evolution of groundwater along a given flow path and attemps both to identify and quantify the heterogeneous reactions that may have been responsible for that chemical evolution (Konikow and Glynn 2005). In this study the speciation and mobility of As and Sb in groundwater is assessed by the modeling software of PHREEQC. The groundwater quality characterististics of the two studied areas have been previously assessed based on the collection of 100 samples in Melivoia area and 151 in Keramos area. These results

have been presented in previous publications (Kelepertsis et al. 2006, Chatzidiakos et al. 2006, Fanouraki et al. 2006). The objectives of this paper are: (a) To assess the speciation of As and Sb in groundwater samples from 3 springs at Melivoia area of Larisa and Keramos area of NW Chios. (b) To define the reactions which control the changes of groundwater’s chemistry between the wet and the dry seasons and calculate the saturation indexes of the minerals which take part in these reactions. 2. Study areas 2.1 Location and land use

Melivoia is situated about 50 km east of Larisa town in central Greece. The study area lies between latitudes 39ο 36΄ – 39ο 50΄ and longtitudes 22ο 46΄ - 22ο 54΄ (Fig.1). The relief of the area varies, and is characterised as smooth to intense . Most of the area is covered by forest. Agricultural activity is intense with cultivated apple and chestnut trees. Chios is the fifth bigest island of Greece and is located in eastern Aegean Sea. The study area in NW Chios lies between latitudes 38ο28΄ and 38ο35΄ and longitudes 25ο50΄ and 25ο59΄΄ (Fig.1). The topographic pattern of NW Chios is uneven with steep slopes and cliffs. The area’s vegetation consists of bushes, olive and walnut trees, as well as pine tree forest.

Figure 1. Sketch map of Greece, showing the Melivoia and Chios island study areas. Legend: Study areas.

N

2.2 Geology, hydrogeology and mineralization Melivoia area belongs to the Pelagonian tectonic zone. The geology of the area comprises the following rock types in order of increasing age (IGME 1984): a) Quaternary sediments, b) Neogene sediments, c) Marbles of Agia (Upper Cretaceous), d) Pre–Upper Cretaceous tectonic cover (metamorphic ophiolitic rocks and metasediments), e) Middle Upper Triassic – Upper Jurassic marbles. f) Neopaleozoic – Lower Middle Triasic metamorphic formations, g) Paleozoic crystalline basement. According to Migiros (1998) the area is characterized by many occurrences of Fe oxides-hydroxides and Sb and As mineralization of hydrothermal origin (Fig. 2). The geological structure of NW Chios is characterized by the Paleozoic autochthonous system consisting of greywackes with conglomerate intercalations, shales and cherts, limestone lenses and volcanic rocks (IGME 1971). Two types of sulphide mineralization occur within this system: (a) stibnite (Sb2S3) mineralization, extending on a north-south direction from Agiasmata to Volissos (Fig. 3). The highest deposits of antimony are located at the village Keramos, East and West of the Albanos river (b) mixed sulphide mineralization (PBG) extending in a parallel direction to Sb mineralization on the eastern edge of the study area. Both types of mineralization are of hydrothermal origin (Dimou et al. 1986).

Figure 2. Geological map and locations of sampled spring water and rocks in area of Bourboulithra (Melivoia – East Thessaly).

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#

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#

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KERAMOS

AGIASMATA

R9R8

R5

R3

R4

R12

S7S8

S10

LEGEND

!( springs S7, S8, S10

# Rocks

Ore occurrence³ Sb

´ PBG

« Cu-pyrite (Fe,Cu)

FaultFault observed

Fault propable

Stream

") Village of NW Chios

GeologyGreywakes,conglomerates,shales and cherts (Silurian - Carboniferous)

Alluvial deposits (Quaternary)

Figure 3. Geological map of the research area and sampling location of spring water and rocks in the area of Keramos (NW Chios).

The hydrogeology of the Melivoia area depends mainly on tectonics. Weathered metamorphic rocks create an upper aquifer of minor significance, while the underlying karstic carbonated rocks create a deeper aquifer of greater importance. A minor aquifer also exists into the Tertiary sediments (Stamatis and Migiros 2004). In NW Chios, contact and overflow springs occur within the Paleozoic rocks of the area. Aquifers of limited dimensions occur due to alternation of permeable and impermeable clastic deposits as well as due to localized occurrences of limestone lenses and layers. A hot spring occurs in the village of Agiasmata on the northern coast (Banos, Paraschoudis and Pipidis 1995). 3. Methodology 3.1 Water Sampling, Preparation, Chemical Analysis and SEM Groundwater samples were collected from springs over a course of one year. The sampled springs were S1, S2, S3 in Bourboulithra area and S7, S8, S10 in Keramos area. The water samples were collected in polyethylene bottles. Critical physicochemical water parameters, pH, Eh, TDS and temperature were determined immediately after collection by using a WTW 350i multimeter, then 100 ml of each sample was filtered on site using 0.45 µm filters, and was acidified to a final concentration of about 1% nitric acid. Sulphate, nitrate, nitrite, phosphate and chloride were measured photometrically using a Hach DR/4000 apparatus. Bicarbonate was measured using a Hach alkalinity titrator. Arsenic and Sb concentrations were determined by Hydride Generation Atomic Absorption Spectrometry with an AAS Perkin Elmer 1100B instrument, while B, Ba, Ca, Cr, Ni, Cu, Zn, Fe, K, Li, Mg, Mn, Na, Mo, Pb, Si, Sr were measured by Flame-AAS and Graphite Furnace-AAS. All chemical analyses were performed at the Laboratory of Economic Geology and Geochemistry of the Faculty of Geology and Geoenvironment, University of Athens. Rock samples were collected at the vincinity of springs in order to be representative of the solid phases in contact with groundwater. The rock samples R1, R2 (serpentinites), R16(schists) from the Bourboulithra area (Table 3) and the rock samples R3, R4, R5, (silificated zone around Sb mineralization), R8, R9 (exposed mining waste), R12 (sandstone exposure) from the Keramos area (Table 4) analyzed by scanning electron microscope (SEM), type GEOL JSM 5600, geared with micro analyzer OXFORD ISIS 300. The code inverse model of the computer program PHREEQC was used for each spring for the wet and dry period. The minteq.v5 thermodynamic database was used for Melivoia area and the minteq.v4 for Keramos area. The input for PHREEQC modelling was the elemental concentrations of As, Sb, K, Na, Ca, Mg, SO4

2-, NO3-, PO4

3-, HCO3-, Cl,, Fe, Zn, Cu, Cr and K, Na, Ca, Mg, SO4

2-, NO3

-, PO43-, HCO3

-, Cl, Sb, As, Fe for the Melivoia and NW Chios area respectively. The chemical parameters pH, pe (Eh), and T were used for both areas. The Eh of a solution is the redox potential measured in the field. It is directly related to pe by the relation: pe=Eh*(F/2.303RT), where F is the Faraday constant, R is the gas constant, and T is the temperature in Kelvin. 4. Results and discussion The chemical analyses of the three springs S1, S2, S3 (wet and dry period) of Melivoia are presented in Table 1 in comparison with parametric values of 98/83/E.C (E.E.C., 1998). These springs have As and Sb concentrations higher than the E.U. limit of 10 and 5 ppb respectively. The high As and Sb concentrations in water reflect the influence of arsenopyrite and pyrite mineralization. Concentrations of elements in groundwater from Chios (springs S7, S8, S10) are presented in Table 2. These springs show much higher Sb concentrations than the 5 ppb limit. The high Sb concentration of groundwater is attributed to the influence of the mineralization at Keramos area. The Sb concentration in sample S10 is below the detection limit for the wet season.

Identified minerals in the rocks of Bourboulithra area include (Fig. 4) crystals of arsenopyrite of diameter approximately 60 µm, pyrite with a length of 10 µm with As together with chromite, scorodite, hematite and crystals of hydroxylapatite of 40 µm. Chromite’s length is approximately 200 µm and pyrite is replaced mostly by hematite. We use the minerals mentioned above for displaying the reactions to code inverse model through the computer program PHREEQC. Other minerals observed by SEM are: quartz, calcite and barite. Identified minerals in the mineralysed rocks of Keramos area include (Fig. 5): Stibnite residuals in contact with antimony oxides, pyrite replaced mostly by goethite, crystals of calcite and hydroxylapatite. Other minerals identified in the samples include quartz, rutile, mica, feldspars and monazite. Table 1. Results of chemical analysis of spring water S1, S2, S3 at the area of Bourboulithra (East Thessaly).

S1 wet period

S1 dry period

S2 wet period

S2 dry period

S3 wet period

S3 dry period

98/83/E.C.

Κ (mg l-) 2 2 2 2 1 1 12 Na(mg l-) 19 16 17 12 18 9 200 Ca(mg l-) 83 64 83 95 98 65 Mg(mg l-) 25 16 25 15 27 15 SO4 (mg l-) 20 19 19 20 18 17 250 PO4 (mg l-) 0.074 0.108 0.260 0.150 0.054 0.198 6.66 ΝΟ3 (mg l-) 8 6 6 4 8 3 50 ΝO2 (µg l-) 8.25 82.5 9.9 18.5 11.55 10.2

HCO3 (mg l-) 203 162 189 184 203 172 Cl(mg l-) 12 29 12 12 9 9.5 250

NH3(µg l-) 61 122 134 26.8 61 47.8 500 Mn(µg l-) 0.7 0.5 1.8 0.7 1.3 1.9 50 Fe(µg l-) 12.5 11 46 7 21 3.4 200 Zn(µg l-) 12 10.4 26 53.6 27.8 8.5 Cu(µg l-) 1 2 3.2 4.4 3.6 3.9 2000 As(µg l-) 29.3 33 28.8 19.2 13.4 10.6 10 Sb(µg l-) 23.7 17.5 23 14.5 23.3 15 5 Cr(µg l-) 1.4 1.55 1 1 1.3 1 50 Ni(µg l-) 4.9 <2.5 <2.5 <2.5 <2.5 <2.5 20

pH 7.8 7.3 7.8 7.5 7.9 7.7 6.5 – 8.5 Τ0C 15.1 17.0 15 17.4 13.8 15.6

Eh (mV) -45.5 -41.6 -43.7 -39.7 -58.3 -52.5

Table 2. Results of chemical analysis of spring water S7, S8, S10 at the area of Keramos ( NW Chios).

S7 wet period

S8 wet period

S10 wet period

S7 dry period

S8 dry period

S10 dry period 98/83/E.C

Κ(mg l-) 1 1 1 1 1 1 12 Na(mg l-) 21 22 36 31 33 37 200 Ca(mg l-) 34 36 61 37 40 63 Mg(mg l-) 20 20 39 27 29 43 SO4 (mg l-) 81 81 166 112 111 167 250 PO4 (mg l-) 0.05 0.04 0.56 0.060 0.040 0.576 6.66 NO3 (mg l-) 4.84 4.4 3.96 5.72 7.48 4.84 50

HCO3 (mg l-) 108 120 148 125 140 155 Cl(mg l-) 22 23 45 34 38 54 250 Fe(µg l-) 3 36 28 5 44 30 200 As(µg l-) 6 5.78 0.93 6.13 5.82 1.60 10 Sb(µg l-) 146.85 141.06 <0.2 444.44 478.63 115.94 5

pH 7.4 7.3 7.0 7.0 7.1 8.1 6.5 – 8.5 T0C 12.0 11.7 15.5 16.4 16.8 16.6

Eh(mV) -27.0 -21.7 -10.3 -10.3 -14.6 -70.6

Table 3:Identified minerals (x) in rock samples from Bourboulithra area (Melivoia-East Thessaly).

Sample Arsenopyrite FeAsS

Scorodite FeAsO42H2O

Chromite FeCr2O4

Hematite Fe2O3

Hydroxylapatite Ca5(PO4)3OH

Pyrite FeS2

R1 - x x x - x R2 x x x x x x R16 - - - x - -

FeAsO4:2H2O

qtz

py

chr

qtz

qtz

asp

ap hm py

qtz

Figure 4: SEM images (BSE mode) of rock samples from Bourboulithra area:arsenopyrite(asp), pyrite(py), chromite(chr), scorodite(FeAsO4:2H2O), hematite(hm), hydroxylapatite(ap).

Speciation of As and Sb and computation of saturation indexes for the mineral phases was subsequently calculated by PHREEQC. This was achieved by reactions (Table 5) involving mineral phases identified by SEM. These reactions are responsible for the change in chemistry of groundwater between the two periods. In all three springs (S1, S2, S3) of Bourboulithra the trivalent oxidant state of As is the predicted dominant species both in wet and in dry period. In the wet period the pentavalent oxidant state of Sb is the dominant species in spring water but in dry period the trivavalent Sb dominates (Table 6). Arsenic and Sb in spring water of Chios (samples S7, S8) are present with their trivalent forms for both wet and dry seasons. Differentiation of element speciess was observed only for spring S10 where Sb is only present during the dry season in pentavalent form (Table 7).

Table 4: Identified minerals (x) in rock samples from Keramos area.

Sample Calcite CaCO3

Goethite FeOOH

Hydroxylapatite Ca5(PO4)3OH

Pyrite FeS2

Stibnite Sb2S3

Valentinite Sb2O3

R3 - × - - - - R4 × × - × - - R5 - × × - - - R8 - - - - × - R9 - - - - × ×

R12 × × - × - -

Sb2O3

qtz py

qtz

stb

cal

qtzap

goe

Figure 5: SEM images (BSE mode) of rock samples from Keramos area: stibnite(sbtn), valentinite(Sb2O3), pyrite(py), goethite(goe), hydroxylapatite(ap), calcite(ca).

Table 5: Chemical reactions used for inverse modeling by PHREEQC.

FeS2 + 2H+ + 2e- = Fe2+ + 2HS-

Sb2S3 + 6H2O = 2Sb(OH)3 + 3H+ + 3HS-

FeOOH + 3H+ = Fe3+ + 2H2O Sb2O3 + 3H2O = 2Sb(OH)3

Sb2O4 + 2H2O + 2H+ + 2e- = 2Sb(OH)3CaCO3 = Ca2+ + CO3

2-

Fe(OH)3 + 3H+ = Fe3+ + 3H2O Ca5(PO4)3OH + H+ = 5Ca2+ + 3PO4

3- + H2O FeAsS +1.5000 H2O +0.5000 H+ = + 0.5000 AsH3 + 0.5000 H2AsO3

- + 1.0000 Fe++ + 1.0000 HS-

Cr2O3 + H2O + 2H+ = 2Cr(OH)2+

FeAsO4:2H2O + 3H+ = Fe3+ + H3AsO4 + 2H2O FeCr2O4 + 4H+ = 2Cr(OH)2

+ + Fe+2

Table 6: Speciation of As and Sb in spring water of Bourboulithra springs (S1, S2, S3). (Dominant species in shaded cell).

Samples As(3) molality

As(5) molality

Sb(3) molality

Sb(5) molality

S1 wet period 3.767 10-7 1.456 10-8 7.821 10-8 1.165 10-7

S1 dry period 4.394 10-7 1.154 10-9 1.351 10-7 8.687 10-9

S2 wet period 3.687 10-7 1.151 10-8 6.776 10-8 1.212 10-7

S2 dry period 2.502 10-7 6.196 10-9 9.093 10-8 2.821 10-8

S3 wet period 1.766 10-7 2.305 10-9 9.187 10-8 9.958 10-8

S3 dry period 1.397 10-7 1.838 10-9 8.5840 10-8 3.784 10-8

Table 7: Speciation of As and Sb in spring water of Keramos springs (S7, S8, S10) (Dominant species in shaded cells).

Samples As(3) molality

As(5) molality

Sb(3) molality

Sb(5) molality

S7 wet period 8.007 10-8 3.531 10-11 8.596 10-7 3.469 10-7

S7 dry period 8.171 10-8 1.407 10-10 3.312 10-6 3.399 10-7

S8 wet period 7.715 10-8 1.815 10-11 8.773 10-7 2.816 10-7

S8 dry period 7.741 10-8 3.021 10-10 3.423 10-6 5.097 10-7

S10 wet period 1.241 10-8 1.145 10-11

S10 dry period 1.699 10-8 4.376 10-9 3.580 10-7 5.948 10-7

The calculated saturation index in wet and dry seasons were used as a criterion for the mobility of the elements between the solid and the aqueous phase. Bourboulithra area arsenopyrite (FeAsS), pyrite (FeS2), stibnite (Sb2S3), valentinite (Sb2O3), Cr(OH)2 and FeAsO4:2H2O have negative saturation indexes during the dry period reflecting the dissolution of these minerals (Fig. 6). On the other hand the saturation indexes of hematite (Fe2O3), hydroxylapatite (Ca5(PO4)3OH), chromium

oxide (Cr2O3) and chromite (FeCr2O4) are positive indicating the precipitation of these minerals. This is consistent with mineralogical data, since all 3 minerals were identified by SEM. At Keramos area and for both sampling periods, saturation index data indicate that stibnite is dissolved continuously releasing Sb in groundwater, while the oxides of Sb (Sb2O4 and Sb2O3) tend to precipitate (Fig. 7). As it appears from the reactions the dissolution of stibnite and Sb-oxides produce Sb(OH)3 which precipitates preventing the Sb release into water. Pyrite dissolves to a large extent while the mineral phases of calcite, goethite, hydroxylapatite and Fe(OH)3 dissolve very little and precipitate. This is consistent with mineralogical data of SEM.

-8

-6

-4

-2

0

2

4

6

8Cr2O3 FeCr2O4 Fe2O3 Ca5(PO4)3OH Sb(OH)3 Sb2O3

S1, S2, S3 (wet and dry period)

Sat

urat

ion

inde

x (in

vers

e m

odel

ing)

S1 wet periodS1 dry periodS2 wet periodS2 dry periodS3 wet periodS3 dry period

-100-90-80-70-60-50-40-30-20-10

0FeAsS Cr(OH)2 FeAsO4:2H2O FeS2 Sb2S3

S1, S2, S3 (wet and dry period)sa

tura

tion

inde

x (in

vers

e m

odel

ing)

S1 wet periodS1 dry periodS2 wet periodS2 dry periodS3 wet periodS3 dry period

Figure 6: Diagrams of Saturation Index and minerals using the code inverse modeling on spring water data of Bourboulithra area.

Figure 7: Diagrams of Saturation Index and minerals using the code inverse modeling on spring

. Conclusions ta of rock samples collected in the two study areas and water chemistry data were

ulithra area of Melivoia East Thessaly the groundwater is enriched in As and Sb

-6

-4

-2

0

2

4

6

8

10

CaCO3 Fe(OH)3 FeOOH Ca5(PO4)3OH Sb(OH)3 Sb2O4 Sb2O3

Springs S7, S8, S10 (wet and dry period)

Satu

ratio

n In

dex

(Inve

rse

mod

elin

g)

S7 w et period

S7 dry period

S8 w et period

S8 dry period

S10 w et period

S10 dry period

-90

-80

-70

-60

-50

-40

-30

-20

-10

0FeS2 Sb2S3

Springs S7, S8, S9 (wet and dry period)

Satu

ratio

n In

dex

(inve

rse

mod

elin

g)

S7 w et period

S7 dry period

S8 w et period

S8 dry period

S10 w et period

S10 dry period

water data of Keramos area (NW Chios). 5Mineralogical dasuccessfully combined within the PHRREQC modeling software to provide the following conclusions: 1. In Bourbobecause of the continuous dissolution of arsenopyrite (FeAsS) and stibnite (Sb2S3). In spring water samples the trivalent oxidant state of As is the predicted dominant species for both wet and dry

periods. During the wet period the pentavalent Sb is the dominant species in grounwater but during the dry period the trivalent Sb is the species that dominates. 2. In the Keramos area of NW Chios a heavy influence of Sb mineralization on the groundwater quality is observed. The continuous dissolution of stibnite (Sb2S3) results in Sb enrichement in water. Antimony (III) is the predicted dominant species in spring water from Keramos while Sb(V) is the dominant species in spring water downstream in the valley. The phase Sb(OH)3 has an important role in preventing dissolution of Sb. Acknowledgements This research is co-funded by the European Social Fund (75%) and National Resources (25%) – Research programme PENED2003. The authors would also like to thank people of local authorities in Melivoia and Amani, Chios for their help during fieldwork. References Banos C., Paraschoudis B. and Pipidis M., G. 1995. The readjustment of the hydrogeological

balance of the Chios island – Inregrated management of water resources. Reports of the 3th Hydrogeological Congress of Hellenic Comitee of Hydrogeology in Greece, Crete, 428-442.

Chatzidiakos E., Fanouraki M., Kelepertsis A., Argyraki A. and Alexakis D. 2006. Environmental research on groundwater pollution by toxic elements in two mineralised areas of Melivoia, East Thessaly and NW Chios Island, Greece. Proc of the 2nd International Conference Water Science and Technology – Intergated Management of Water Resources, Athens Greece, pp 85.

Cox, P.A. 1997. The elements on Earth. Inorganic chemistry in the environment, Oxford University Press, Oxford.

Dimou E., Papastaurou S. and Serment R. 1986. Antimony in Greece. (Second Part) – Research of antimony occurrence in Chios Island and in Pilio mountain. I.G.M.E., Athens.

E.E.C., 1998. Council Directive 98/83/EC on the quality of water intended for human consumption. Official journal of the European Communities, 330/32 – 330/54.

Fanouraki M., Chatzidiakos E., Argyraki A. and Kelepertsis A. 2006. Building a GIS database for spatial interpretation of arsenic and antimony concentrations in the soil – rock – groundwater system of NW Chios and East Thessaly. Proc of the 2nd International Conference Water Science and Technology – Intergated Management of Water Resources, Athens Greece, pp 113.

IGME, 1984. Ayia Panayia Sheet, Geological map 1:50000, Department of geological maps of IGME Athens, Greece.

IGME, 1971. Volissos Sheet, Geological map 1:50000. Department of geological maps of IGME, Athens, Greece.

Kelepertsis A., Alexakis D. and Skordas K. 2006. Arsenic, antimony and other toxic elements in the drinking water of Eastern Thessaly in Greece and its possible effects on human health. Environmental Geology 50: 76-84.

Konikow, L.F. and Glynn P. D. 2005. Modeling groundwater flow and quality, in o Selinus et al. (EDS) Essentials of Medical Geology, Elsevier Academic Press, London.

Migiros P., 1998. The mineral wealth of Thessaly, geotectonic setting – resource Development. Mineral Wealth, 108, 15 – 26.

Onishi, H. 1969. Geochemistry of Arsenic, In: Wedepohl K.H (Eds) Handbook of Geochemistry, vol II, Springer, Berlin.

Parkhurst D. and C.A.J. Appelo C.A.J. 1999. User’s guide to PHREEQC (version 2)—a computer program for speciation, batch-reaction, one-dimensional transport, Denver Colorado.

Smedley, P.L. and Kinniburgh, D.G. 2002. A review of the source, behaviour and distribution of arsenic in natural waters. Applied Geochemistry, 17, 517-568.

Stamatis, G. and Migiros, G. 2004. The relationship between fractured tectonics and groundwater reservoir of massive formations of Ossa mountain (East Thessaly, Greece. Proceedings of the 10th International Congress of Geological Society of Greece, Thessaloniki, 2077-2086 (in Greek with English abstract).