ABSTRACT

Hydrogeochemical study of ground water samples from tube/bore-wells in the pre- and post-monsoon periods, in five-blocks of the Chhindwara district, Madhya Pradesh points to noticeable health problems in peoples due to higher/lower fluoride values than the desirable World Health Organization (WHO) limits. The geological reasons for high fluoride release in the ground water in the deep tube wells in granites and basalts in pre- and post-monsoon periods has been discussed.

Keywords: Fluoride, Ground water, Dental fluorosis, Dental carries, Central India.

INTRODUCTION

Fluorine is widely dispersed in nature as the 13th most abundant element in the earth crust. As per the WHO, the Indian Council of Medical Research (ICMR, 1975) and Vishwanathan, (2009) standards the drinking preferred values of fluoride should range from 0.6-1.5 ppm for the development of strong-bones and teeth; values lower than this may cause dental caries, while above it may causes dental/skeletal fluorosis (Agrawal, 1997 and Duraiswami, 2011).

The rural population in many parts of India is suffering from fluoride-contaminated ground water, especially where people totally, depend on ground water rich in fluoride. Madhya Pradesh is one of the states in India where fluorosis is emerging as a health-problem in different districts (Chatterjee, 1998 and Susheela, 1999).

Granites/granitoids and basalts are thought to be the main sources of F- in the ground water in many parts of the world. As these rocks occur most of the parts of Chhindwara district, therefore qualitative study of ground water in this area without a noticeable industry can has been found mainly due to geological reasons discussed in the paper.

Chhindwara district is situated in the southern part of Madhya Pradesh. The study area, approximately located between latitude 21^˚52’ N to 22^˚17’ N and longitude 78^˚45’ E to 79^˚20’E (Fig.1) is traversed by Pench and Kulbehra rivers.

GEOLOGY OF THE AREA

Geologically, the main formations are: (a) Archaeans- mainly granites, granitic-gneisses (granitoids) intruded by pegmatites and qurtzo-feldspathic veins; (b) Gondwanas- mainly shales and sandstones; (c) Deccan basaltic lava flows; and (d) Quaternaries- black cotton soil and river-alluvium (silty and clayey-loam, Fig.2).

In general, the main source of F- in ground water is fluoride minerals {fluorspar (CaF2), fluorapatite [Ca5 (PO4)3F], cryolite (Na3AlF6) and hydroxyl-apatite} in granites (Rafique, 2008 and Carrillo-Rivera, 2002). Such minerals occur in basalts in ‘lattice-locked’ state of other minerals (Wedepohl, 1972). In Gondwana sediments, however, only dugwell (not exceeding 30 feet depth) have been developed in the area that did not give abnormal values of F-sampling. While the deep tube wells, whether in granitoids or basalts show values above/below the desirable limits (0.6 to 1.5 ppm).

METHODOLOGY

Water-sample from the tube-wells (in pre- and post monsoon periods) were collected in one-liter plastic-bottle each from 53 bore-wells in the five blocks namely- Parasia, Amarwara, Chourai, Mohkhed and Chhindwara blocks of the Chhindwara district in pre-monsoon (June, 2010) and post-monsoon (January, 2011) months. Since the ground water samples from dug wells in Gondwanas (in pre-monsoon) show normal values of F- they were not sampled in the post monsoon period.

The concentrations of major ions (Table 1, 2 & 4) in the ground water samples were determined as per the American Public Health Association (APHA), 1975. The values of pH and EC were measured by pH/ion meter, concentration of Ca²⁺, Mg²⁺, HCO₃^- and Cl^2- were determined by titrimetric method. Flame photometer was used todetermine Na⁺ and K⁺. Ion, F^- was determined using ion selective electrodes, UV Spectrophotometer for SO4 2²⁺, NO₃^- and Fe.

DISCUSSION

Groundwater occurs under phreatic conditions in the weathered zone, fractured, vesicular basalts and under semiconfined to confined conditions in the fractured zone (deep aquifer). The depth of water level varies from 54 to 150 ft below ground level (bgl) in the granitoids and from 45 to 180 ft bgl in the basalts in deeper aquifers. Rainfall is the main source of ground water recharge.

Ground water from tube-wells is alkaline (pH 6.5 to 8 in pre and 6.4 to 9.3 in post-monsoon) from the granitoids, while that from neutral to highly alkaline (pH 7 to 9 in pre- and 6.6 to 9.7 in post-monsoon) from the basalts. The samples have electrical conductivity (EC μS/cm) values in the range of 201 to 1031 in pre- and 348 to 1236 in postmonsoon periods from granitoids, while 252 to 1173 and 311 to 1583 in pre- and post-monsoon periodsrespectively from basalts. The average calcium (Ca²⁺) concentration from granitoids is in the range 19 to 98.8 ppm and 6.1 to 91.2 ppm; and from basalts 15 to 95 ppm and 4 to 95.76 ppm in the pre- and post-monsoon periods respectively. Similarly, sodium (Na⁺) concentration ranges from 8.1 to 116.6 ppm and 11.8 to 112 ppm in the preand post-monsoon periods respectively from the granitoids; and from basalts range from 14 to 119 ppm and 14 to 98.5 ppm in the pre- and post-monsoon periods, respectively (Table 1 & 2). The concentration of chloride (Cl^-) in granitoids and basalts from deep aquifers is within the permissible limit in both the periods.

The F^- concentration ranges from 0.11-7.9 ppm and 0.27-17 ppm in pre- and post-monsoon periods, respectively from granitoids; while in the basalts it ranges from 0.2-7.4 ppm and 0.3-10 ppm in the pre- and post-monsoon periods, respectively. Ground waters of the study area are of bicarbonate-type.

The analysis shows high-concentration of F^- in pre- and post-monsoon periods in Bangaon and Seonimegha villages in Chhindwara; Mandla and Urdhan villages in Parasia; Rajola village in Amarwara; and Jhilmili and Khutpipariya villages in Chourai blocks of Chhindwara district (Table 3).

The F^--concentrations above permissible limits (>1.5 ppm) occur in 25% samples from 4 villages in Parasia; 7 in Chhindwara; 1 in Chourai; and 1 in Amarwara blocks in the pre-monsoon and in 43% samples from 11 villages in Parasia; 7 in Chhindwara; and 2 Amarwara; and 2 in Chourai blocks in the post-monsoon periods, causing dentalfluorosisin villagers (Table 3, 5 & Fig. 3a-3d,). The highest-concentration of F^- occurs in the Bangaon village, Chhindwara block (7.9 ppm) in pre-monsoon and in the Seonimegha village, Chhindwara block (17 ppm) in the post-monsoon periods. Figure 4 a, and b show that a high F^- belt trending NNE-SSW occurs along the Pench valley in the north-eastern part of the area, in both the periods. About 51% of all the samples from 27 villages (15 in Chhindwara; 8 in Parasia; 2 in Chourai and 2 in Mohkhed blocks) in pre-monsoon and 27 % samples from 13 villages (10 in Chhindwara; 2 in Parasia and 1 in Mohkhed blocks) in post-monsoon are below the desirable limits of F^- (0.6 ppm), causing dental-carries in villagers (Table 5 & Fig. 3 e).

At higher pH (alkaline medium) such minerals release F^- gradually into the ground waters because of increased anion-exchange of OH- with F^-.

In general, the varying concentration of F^- in ground water depends on the geological formations due to pH and solubility of F^- bearing minerals and the presence or absence of other precipitating or complexing ions. However, in this study F^- shows negative correlation with Ca²⁺ and positive with Na⁺+K⁺ in the granitoids and basalts in the preandpost-monsoon periods (Fig. 5 & 6). The high Na⁺+K⁺ from basalts in a sample (No. 49) in the pre-monsoon period and two samples (Nos. 40 and 42) of the post-monsoon period seem to be anomalous due to presence of calcareous Intertrappeans within basalts (Fig 6).

The main source of F^- in natural water are the F^- bearing minerals (fluorspar, fluorapatite, cryolite and hydroxylapatite) as well as F^- replacing OH^- in the ferromagniseum silicates (amphiboles and micas) and soils consisting of clay minerals (Madhnure et al, 2007). Besides the basalts with calcareous veins and clays like can also release F^- to some extent (Khatik, 2012).

The F^- contamination in the basalts is mainly due to presence of Intertrappeans (calcareous sandstones) along with locally concentrated calcareous veins (Gupta, et al., 2006) and secondary matter like montmorillonite (Khatik, 2012) and long ground water residence time. Fluoride has a unique chemical behavior towards most of the anionsand it can be easily replaced by them even under normal pressure and temperature conditions (Wenzel and Blum, 1992) causing concentration/pollution in ground waters.

The geochemical type of fluoride-bearing waters (Table 1, 2 and Fig. 7 & 8), based on the trilinear/Piper-diagram (Piper, 1944) show high F^- values besides changes in ‘ground water-chemistry’ in different rocks in different periods. It reveals that most of the samples (belonging to granitoids and basalts in both the periods) fall in ‘Ca-Mg-HCO₃’ field, with an exception of two ‘low F^- values samples’ (pre-monsoon) one each from granitoids (No. 15) falls in ‘Cl-Mg-K-HCO₃’ and other from basalts (No. 36) falls in ‘Na-HCO₃’ fields.

However, in ground water granitic areas soils being the end product of weathering of the parent granitoids become progressively rich in sheet-silicates (micas) that host F^- in fairly high concentration (Khatik, 2012).

Clay-bands in fracture-zones, responsible for controlling the local ground water regime, prolong soil/rock water interaction in weathered granitoids. Also, as shown in the Fig. 9 (a-d) and Table 3 high alkalinity of water is responsible for higher concentration of F^- in ground water in both granitoids and basalts in the pre- as well as postmonsoon periods that attest to the earlier views. Due to strong electro-negativity, F^-is attracted by positivelycharged Ca²⁺ in teeth and bones and cause dental-fluorosis, teeth-mottling, skeletal-fluorosis and deformation of bones (Figure 3.a-e).

CONCLUSION

Generally most ground water-samples from tube/bore-wells have higher F^- contamination/pollution. However, in the studied area the prevalence of F^- is found to be directly related to the distribution of F- bearing minerals mainly in granitoids and partly in the basalts. The most stable F^--bearing component is apatite apart from hornblende and biotite in the granites/granitoids in the area (Fig. 10 a & b). Besides, leaching of fluorine from micas in granitoids during weathering has also contributed F^- in aquifers to some extent. The degree of weathering and the leachableF^- in a terrain is more important in deciding F^- content in the water rather than the mere presence of F^--bearing minerals in the bulk rock/soils. The samples from granitoids show F^- as high as 7.9 ppm in pre-monsoon and 17ppm in post-monsoon periods.

Basalts are releasing F^- in small quantities are another dominating lithology in the area and no mineral-bearing high F^- could be traced, excepting amphibole, biotite and fluorapatite. The source of F^- in the ground water of this areaappears to be these OH^- minerals. Its shows F^- values raging from 7-10 ppm, in both the periods. Figure 4 a, and b show the F^- concentration extends in the post-monsoon period owing to a long span of contact-time of F^- minerals with fluids.

The study finds that high-alkalinity of water is responsible for higher concentration of F^- in ground water in granitoids and basalts.

The study also shows that the ‘high concentration belt’ of F^- extends in NNW-SSE and calls for more studies in adjoining north-west and south-east areas when the high-fluoride belt seems to extend (Fig. 4 a, and b).

The tube-wells with high/low F^- may be marked and prohibiting for drinking purposes. The study also shows that there is a need of a proper health-survey in the tribal belts of Chhindwara and surrounding districts located in the granitoids/basalts.

ACKNOWLEDGEMENT

The author thanks to the Head of the Department, Applied Geology Dr. Harisingh Gour University, Sagar, M. P. for providing the necessary research facilities and P. O. Alexander for useful discussion.

JK is thankful to the University Grants Commission (UGC) New Delhi for JRF and SRF under Rajiv Gandhi National Fellowship for completion of the work; R. K. Baronia for his profound help during the collection of water-samples and useful suggestions; T. K. Biswal, Head, Earth Sciences and D. Chandrasekharan, Indian Institute of Technology,Powai, Bombay; and Jakir Hussain, Central Water Commission, New Delhi for providing analytical facilities.

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Jemini Khatik, P. K. Kathal and R. K. Trivedi
Department of Applied Geology, Dr. H. S. Gour, central University, Sagar (M. P.)