GROUNDWATER QUALITY DEGRADATION DUE TO

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common form (PbCrO4) (Mitrakas et al. 2013). Gaseous emissions of chromium are mainly Cr3+ in the form of particles or aerosols. The most important industrial ...

GROUNDWATER QUALITY DEGRADATION DUE TO Cr6+ PRESENCE IN SCHINOS AREA, PREFECTURE OF CORINTH, CENTRAL GREECE PAPADOPOULOS K.* and LAPPAS I. National Centre of Sustainable Development – Institute of Geology and Mineral Exploration, Directorate of Water Resources and Geothermy, Department of Hydrogeology, 13677 Acharnai, Athens, Greece, [email protected], [email protected] Keywords: Groundwater pollution, Human intervention, Physical appearance, Hydrochemical analysis, Groundwater sampling, Monitoring network. Abstract The present essay deals with the assessment of Cr6+ presence in Schinos groundwater and the identification of natural or/and anthropogenic processes which have led to groundwater quality degradation. Groundwater sampling and chemical analysis (major ions and trace elements) from several sampling sites took place during two periods (wet and dry). Both sampling campaigns confirmed the existence of groundwater pollution across the research area due to Cr6+ contamination. The hexavalent chromium values were found highly above the threshold value of 50 ȝg/L (upper limit of total Cr) rising concerns about the origin of the groundwater quality deterioration and the health impact. Hydrochemical analysis and linear plots confirm the groundwater enrichment in Cr6+ which exceeds 90% of total chromium verifying that chromium presence within fresh water is contributed to Cr6+. High chromium concentration is found in regions where groundwaters are hosted in alluvial deposits derived from weathering and erosion of adjacent ophiolitic rocks (serpentinites, peridotites etc.). In the contrary, fresh waters hosted in ophiolitic formations show chromium content significantly lower than the threshold value. The present study outlines the need to establish a monitoring network of wells and boreholes so as to effectively monitor the area’s groundwater quality and to act immediately, if needed, to any further Cr6+ increase. 1.

Introduction

The study presents the procedure required for detailed monitoring of the qualitative and quantitative Schinos aquifers status and its evolution within a hydrological cycle. It also aims at improving the water balance between supply and demand making, if possible, reversible the qualitative and quantitative degradation tend when the groundwater deterioration is due to natural causes and proposing scientifically accepted solutions when water worsening is caused by human intervention. Generally, a sustainable groundwater management is achieved through certain measures and actions resulting from the research study evaluation. The sustainable water resources management, i.e. the conservation and protection through continuous monitoring of the quantitative and qualitative characteristics of the groundwater as well as of the surface water bodies, taking measures in case of groundwater deterioration and ensuring the continuous water renewal, are of utmost priority to preserve the good status of an aquifer, according to EU directive 2000/60. Nowadays, the contamination of an aquatic environment, even from natural causes, is one of the major issues, that is why the groundwater quality preservation and upgrade is of the same importance as the new water resources searching. Due to anthropogenic activities, the groundwater quality in the region may be significantly deteriorated when the contaminants concentrations exceed the threshold values. For that reason, an integrated monitoring network of groundwater quality and quantity parameters should be developed thus contributing to protection, preservation and groundwater quality improvement as well as to rational and sustainable exploitation. In the frame of water resources management, suggestions such as i) the thorough study of aquifers combining the wells yields and recharge from surface waters, ii) the establishment of a groundwater quality monitoring network ensuring the

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continuous data acquisition and iii) the protection zones delineation of wells, springs and aquifers, should be promoted. 2.

Materials and Methodology

2.1.

Study Area

The area of Schinos is located at the western side of Attica prefecture nearby the city of Megara and lies between the latitude 22055’ and 23005’N and the longitude 38005’ and 38015’E. It belongs to the Water District of North Peloponissos (01) covering a drainage area of approximately 16.7 Km2 and a perimeter of 19.4 Km including mostly rural developing areas. Elevation varies between the sea level and approximately 780 m a.s.l., while the mean elevation reaches 135 m a.s.l. Schinos relief is mainly hilly to valley while the catchment is bounded from Gerania Mountains at the south and seawater at the north. ȉhe valley shows a sparse drainage network, developed due to the presence of permeable alluvial deposits and the significant amount of infiltrated surface water (Figure 1).

Figure 1. (left) Geomorphological relief of Schinos area with contributing drainage area and (right) regional tectonic map of Gulf of Corinth (the study area is within the red square). 2.2.

Regional Geological, Tectonics and Hydrogeological Settings

The main geological formations of the study area are the carbonate formations (limestones) heavily fractured and fissured due to alpine and post-alpine tectonic movements, the flysch consisted of sandstones, clastic limestones and radiolarites, intensely tectonized, the ophiolitic formations mainly serpentinites and peridotites (ultra mafic and mafic rocks), the schists at the base of ophiolitic melange with radiolarites and limestones interbeds as well as the post-alpine sediments consisted of marls, talus and debris, alluvial deposits (sands, clays, conglomerates), coastal formations of Quaternary age The alpine rocks cover the hilly and mountainous areas while the post-alpine formations the rest of the plain. The wider region of Pissia – Schinos is tectonically active resulting in an intense topographic relief. The abrupt slope change and the extensive altitude fluctuations are due to geodynamic processes. The whole area is controlled by the active normal faults of NW-SE and E-W directions interrupting both Mesozoic rocks and post-alpine deposits. Furthermore, the successive overthrusts and upthrusts are a typical characteristic of regional tectonics in the study area (Pavlidis et al. 2006). The drainage network is developed on alpine and post-alpine formations and generally is characterized asymmetric mainly due to active tectonics. Between the valley and hilly areas, where Neogene and Quaternary formations prevail, the river network becomes parallel with smooth topographic slopes inadequately developed. On the areas where carbonate formations prevail, the river network becomes dendritic with steep slopes (sparse drainage network).The area occupied by ophiolitic rocks shows and echelon type drainage due to rocks

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Figure 2. Geological (left) and topographical (right) map with study area’s sampling points (boreholes are shown with red colour and wells with green). faulting zones (well developed network).In general, the river network is considered dense and the surface runoff is often lacking. As far as the formations hydrolithological behaviour is concerned, the area’s formations can be divided into permeable, semi-permeable and impermeable ones. The coastal and fluvial deposits occupy a limited area and their small thickness cannot host significant groundwater quantity. However, they allow groundwater to infiltrate to the underlying stratigraphically alluvial deposits. The alluvial sediments, formed by sands, gravels and conglomerates of ophiolitic and carbonate origin, are highly permeable due to their relatively high effective porosity and host the shallow porous aquifer. The aforementioned aquifer is open to the sea where it discharges through the coastal permeable formations. Moreover, the marls are regarded as semi-permeable to impermeable formations and constitute the basic impermeable basement of the porous aquifer. Gerania Mountains are occupied by the high permeability karstic limestones which host aquifers directly controlled by fault tectonics. Nevertheless, schists interventions within the limestone sequence create hydrolithological inhomogeneities which enables the appearance of springs of local hydrogeological interest as well as of drenched aquifers of limited hydrocapacity. Much of the groundwater moving through the carbonate formations flows into the sea. Unlike flysch which is practically an impermeable formation, utramafic rocks are considered semi-permeable due to their secondary porosity caused by fault tectonics and weathering which allows groundwater to flow in a preferential way. 2.3.

Groundwater Sampling

The groundwater sampling sites are spatially allocated within the investigation area and the methods employed for this study are field measurements, sampling and laboratory analysis. During the years 2012 – 2013, groundwater samples from wells, boreholes and springs were collected, filtered and kept in different polyethylene bottles for analyses of cations, anions and trace elements (especially total and hexavalent Cr). After the sampling, the bottle was capped immediately to minimize oxygen contamination and avoid the escape of dissolved gases. All samples have been subjected to in-situ physico-chemical measurements (air and water temperature, pH, electrical conductivity, dissolved oxygen) using portable instruments (WTW instrumentation) in order to acquire representative values of ambient aquifer conditions. All major ions and trace elements were analyzed shortly after sampling in the Water Analysis laboratory of the National Center of Sustainable Development (former Institute of Geology and Mineral Exploration – I.G.M.E.).

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3.

Results and Discussion

3.1.

Origin and Forms of Chromium in Nature

Chromium is a chemical element occurring in rocks (mainly in mafic and ultra-mafic ones), animals, plants, soil as well as in volcanic ashes and gases with oxidation numbers from -1 to +6. The most common chemical form is of divalent chromium (Cr2+) which is reductive and unstable when oxygen is present. On the contrary, trivalent (Cr3+) and hexavalent (Cr6+) chromium are very stable and their salts are strong oxidizers (Giannoulopoulos et al. 2008; Rai et al. 1989; Richard et al. 1991). In nature, chromium appears in the form of trivalent and specifically of mineral chromite (Fe(Mg)Cr2O4). In case of hexavalent chromium, lead chromate is the most common form (PbCrO4) (Mitrakas et al. 2013). Gaseous emissions of chromium are mainly Cr3+ in the form of particles or aerosols. The most important industrial chromium sources in the atmosphere are those related to ferro-chromium alloy production (Sanders 1986; Saputro et al. 2014). The ore enrichment, the chemical and pottery (ceramics) processing, the cement production facilities, the bushing brakes, the auto catalytic converters, the tanneries as well as the chromium pigments contribute to air-pollution with chromium (Beedy 1991). Hexavalent chromium, as dichromate ion, is relatively strong oxidant in acidic solutions providing redox reactions with inorganic reductive substances like Fe, SO2 as with organic compounds in which Cr6+ is reduced to Cr3+. Chromates salts are insoluble in water except for alkali ones of sodium (Na+), potassium (K+), ammonium (ȃǾ4+), magnesium (Ȃg2+) and calcium (Ca2+). Chromium concentration in surface waters is directly influenced by industrial pollution. The population is exposed to Cr3+ by consuming foods, drinking water and inhaling air (Oze et al. 2007). The mean daily intake from air, water and food is estimated at 0.2-0.4 µg, 2 µg and 60 µg respectively while the food contributes approximately to 93 – 98% of total daily perception. Food may contain from 94%).

Figure 6. Linear regression analysis charts showing the relationship between NO3- and Cr6+ among all sampling points (up) and two separate groups (down-left, down-right). Moreover, there is quite strong correlation between Ca2+ and Cr6+ reaching 79% if taking into account all sampling points. Separating, however, the dataset into two smaller groups the correlation coefficient exceeds 95%. It should also be noted that calcium and hexavalent chromium may generate the calcium chromate salt (CaCrO4). The trace elements’ concentrations (Cd, Cu, Ni and Zn) are found far below the threshold values, with the exception of total and hexavalent chromium.

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Figure 7. Linear regression analysis charts showing the relationship between Ca2+ and Cr6+ among all sampling points (up) and two separate groups (down-left, down-right). As far as the sampling points is concerned, it is worth mentioning that in borehole G7, manganese (Mn2+) is often above the threshold value of 50 ȝg/L (173 ȝg/L). Manganese and its compounds are usually used in industrial catalysts, batteries, glasses, paints and fireworks (Oikonomou et al. 2010). At the same borehole the chemical analyses showed high concentration in Zn, Ba and B. The relationship between chromium and other ions and elements was adequately studied since the main area’s problem is the high hexavalent chromium concentration in many sampling points within Schinos aquifer. Of the 22 groundwater samples, 17 contain detectable amounts of chromium. Of these 17 samples, 8 have chromium concentration above threshold value of drinking water (50 ȝg/L), while 3 of them are quite near the upper limit for potable water (between 44 and 50 ȝg/L). In Figure 8, Cr6+ distribution curves are drawn through ordinary kriging geostatistical analysis reaching the following conclusions: x There is a limited area of high hexavalent chromium concentration (even 460 ȝg/L in a well). x The concentrations are smoothly and radially decreased from the center to outskirts based on the groundwater flow status. In Schinos area, the natural dissolution processes inducing the aquifer's enrichment in chromium are the following: x Based on the region’s geological-mineralogical study (Oikonomou et al. 2010) the prevailing petrographic formations belong to the ophiolitic complex of Gerania Mountains. These rocks are mainly serpentinites derived from peridotites weathering and erosion (ultra-mafic formations). The minerals containing Cr3+ are chromites, pyroxenes, chlorites and olivines. Especially, chromites contain Mg-Al with Cr2O3 concentration ranging from 15 to 30% possibly converted into ferro-chromites and magnetites. Moreover, MnO2 concentration often ranges from 0.12 to 0.20%. According to Eary and Rai (1987), Fendorf

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and Zasoski (1992) and Oze et al. (2007), MnO2 presence may cause the physical Cr3+ oxidation to Cr6+, according to the reaction Cr3+ + 1.5MnO2(s) + H2O ļ HCrO4- + 1.5Mn2+ + H+ x The presence of Fe-ore minerals that may enrich the groundwater in combination with MnO2 occurrence can justify the Cr3+ converting into Cr6+. Finally, in Schinos area, the human induced causes may be pollution from industrial waste disposal.

Figure 8. Cr6+ distribution curves of Schinos groundwater. 4.

Conclusions – Remarks

Based on the available data and taking into account the pointed and relatively limited nature of study area’s groundwater contamination, uncontrolled and irrational industrial waste disposal should be considered the most likely cause of elevated levels of hexavalent chromium concentration in the area. Moreover, Cr6+ concentration seems to be over 90% of total chromium confirming its contribution to the fresh water. For that reason, an integrated study including soil sampling as well as an inventory map of all mining-metallurgical and industrial activities around the area should be performed in order to detect the possible industrial waste disposal areas and propose decontamination measures. Finally, more sampling points should be added so as to thoroughly examine the aquifer’s chemical status. 5.

Acknowledgements

The authors would like to thank the director Mr. Anastasios Mastrantonakis and the technical services of the Municipal Enterprise for Water and Sewage of Loutraki – Agioi Theodoroi for the unconditional help offered to all phases of the groundwater field sampling work as well as

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the accredited and certified Water Analysis laboratory of National Center of Sustainable Development (former Institute of Geology and Mineral Exploration – I.G.M.E.) for the groundwater samples’ chemical analysis. 6.

References

Beedy, A., (1991). Toxic Metal Upatake and Essential Metal Regulation Inter Invertebrates: A Review in Metal Ecotoxicology: Concepts & Applications, Michigan. Eary, E., Rai, D. (1987). Kinetics of Chromium (III). Oxidation to Chromium (VI) by Reaction with Manganese Dioxide. Environ. Sci. Technol., v.21, pp.1187-1190. Fendorf, E., Zasoski, J. (1992). Chromium (III) Oxidation by Manganese Dioxide. Environ. Sci. Technol., v.26, pp.79-85. Giannoulopoulos, P., Gintoni, H. (2008). Hydrogeological – Hydrochemical research of Groundwater Quality Degradation in Asopos region. Institute of Geology and Mineral Exploration, Athens. Luoma, S., Carter, L. (1991). Effects of Trace Metals on Aquatic Benthos in Metal Ecotoxicology: Concepts & Applications, Michigan. Mitrakas, M., Kaprara, E., Simeonidis, K., Kazakis, N., Zouboulis, A., Samaras, P. (2013). Hexavalent Chromium Presence in Potable Water of Greece. Assessment of its Origin. 9th Panhellenic Congress of Chemical Engineers. Contribution of Chemical Engineering in Sustainable Development, Athens. Oikonomou, G., Vekios, P., Tarenidis, D., Gkintoni, H., Filippou, S. (2010). A study of mineralogical – petrographic examination of rocks and soils in Loutraki aquifer. Institute of Geology and Mineral Exploration, Athens. Oze, C., Bird, D., Fendorf, S. (2007). Genesis of hexavalent chromium from natural sources in soil and groundwater. Proc. Natl. Acad. Sci. 104, pp.6544–6549. Pavlidis, S., Chatzipetros, A., Valkaniotis, S. (2006). Active and Possible Active Faults of Greece. Department of Geology, Aristotle University, Greece. Rai, D., Eary, L., Zachara, J. (1989). Environmental chemistry of chromium. Science of the Total Environment 86(1-2), pp.15-23. Richard, F., Bourg, A. (1991). Aqueous geochemistry of chromium: A review. Water Research 25, pp.807–816. Sanders, L. (1986). Toxicology Aspects of Energy Production, New York, pp.149-175. Saputro, S., Yoshimura, K., Matsuoka, S., Takehara, K., Narsito-Aizawa J., Tennichi, Y. (2014). Speciation of dissolved chromium and the mechanisms controlling its concentration in natural water. Chemical Geology 364, pp.33-41. U.S. Environmental Protection Agency (1998). Toxicological Review of Trivalent Chromium. National Center for Environmental Assessment, Office of Research and Development, Washington, DC. U.S. Environmental Protection Agency (1998). Toxicological Review of Hexavalent Chromium. National Center for Environmental Assessment, Office of Research and Development, Washington, DC. U.S. Environmental Protection Agency (1999). Integrated Risk Information System (IRIS) on Chromium III. National Center for Environmental Assessment, Office of Research and Development, Washington, DC. U.S. Environmental Protection Agency (1999). Integrated Risk Information System (IRIS) on Chromium VI. National Center for Environmental Assessment, Office of Research and Development, Washington, DC. U.S. Public Health Service (1998). Toxicological Profile for Chromium. U.S. Department of Health and Human Services, Agency for Toxic Substances and Disease Registry (ATSDR), Atlanta.

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