Geochemical behavior of fluoride-rich groundwater in Markapur, Andhra Pradesh, South India

Excess fluoride in drinking water has been one of the leading problem faced by the arid and semi-arid regions of the world. Significantly in India the people suffer from fluorosis comparing to other toxic elements like Arsenic etc., in drinking water. Approximately, in India the excessive fluoride in groundwater is noticed in 177 districts covering 21 states, affecting 66 million people, including 6 million children and Moreover, the latest estimation gives nearly 200 million people, from among 25 nations the world over, are affected by the deadly disease of fluorosis [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14]. The fluoride of the groundwater varies from 0.4 to 5.8 mg/L with a mean of 1.98 mg/L (Table 1 & 2), which indicates that the concentration of fluoride is not uniform in the study area. In general intake of small quantities of fluoride in the permissible limit of 0.5 to 1 mg/L is known to be beneficial for human health in production and maintenance of proper health. However, in India safe limit of fluoride in potable water is considered to be between 0.6 to 1.2 mg/L, less than 0.6 mg/L can cause dental caries, while higher than 1.2 mg/L leads to fluorosis [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16].


Subject area
Earth Science More specific subject area Hydro-geochemistry Type of data Table, figure How data was acquired The fluoride concentration in water was determined electrochemically, using thermo Scientific Orion Star A214 Benchtop pH/ISE meter (9609BNWP fluoride ion-selective electrode) using the USEP ion selective electrode method [15]. This method is applicable to the measurement of fluoride in drinking water in the concentration range of 0.1-1000 mg/L. Standard fluoride solutions (0.1-10 mg/L) were prepared from a stock solution (100 mg/L) of sodium fluoride. As per experimental requirement, 2 ml of total ionic strength adjusting buffer grade III (TISAB III) was added in 20 ml of water sample. The ion meter was calibrated for a slope of −59.2 72. The composition of TISAB solution was as follows: 58 g NaCl, 4 g of CDTA (Cyclohexylene diamine tetraacetic acid) and 57 ml of glacial acetic acid per litre. Using pH/EC/TDS meter (Hanna HI 9811-5), the EC, pH and TDS of water samples were measured. Calcium, magnesium, chloride, carbonate and bicarbonate were analyzed by a titration methods. Sodium and potassium concentrations were determined using a flame photometer (Systronics, 130). Sulphate and nitrate were determined using a UV-visible spectrophotometer (Spectronic, 21, BAUSCH and LOMB).

Data format Analyzed Experimental factors
The bottles were soaking in 1:1 HCl for 24 h and rinsed with distilled water followed by deionized water and samples were collected after pumping out water for about 10 min to remove stagnant water from the well and then transferred and stored at 10°C.

Experimental features
Determine the content levels of fluoride and other Physiochemical parameters using standard procedure. Data source location Markapur, Andhra Pradesh, South India Data accessibility Data is with this article Value of the data Primarily, this data will be a guide line for the Markapur region people and scientists, hydrogeologists who works on this topic and a basic information for groundwater management studies.
Most of the area population depends on groundwater for their daily needs, without any primary treatment and actually they do not know much about the quality of groundwater, but the nature of consequence of fluorosis is in their lifetime, it is because there no cure for it and taking safety measure of drinking water is always preferable.
Based on this data the people who live on the current region are advised to not to drink groundwater directly for drinking purposes, if who does this constantly for a period of time will surely meet with deadly diseases of fluorosis.
This data will be very useful to develop effective strategies for improving Markapur region water supply and provide scientific evidence for decision and management of the groundwater.

Data
The Markapur provinces is located in central-western part of the Prakasam district (Fig. 1). The area geographically lies between the 79°10′-79°22′ south latitudes and 15°35′-15°50′ east longitudes (Fig. 1). The vast plains of Markapur and of the adjacent areas are occupied by phyllite/ slate. The study area has a hot climate and classified as semi-arid with steppe type of vegetation. However, May is generally the hottest month with 45°C with a mean minimum temperature of 27°C, humid weather is experienced during July-November. Winds are generally light to moderate, except during the late summer and early southwest monsoon season. The average annual rainfall of the Prakasam is 798.6 mm, monthly rainfall ranges from nil in March to 182.9 mm in October. October is the wettest month of the year.
Groundwater quality of Markapur, Andhra Pradesh, was studied and assessed the fluoride contaminants in groundwater. The fluoride concentrations varies from 0.4 to 5.8 mg/L and it is clear that the level of fluoride is higher in 54 groundwater locations than that of recommended upper limit by WHO (Tables 1 and 2). It is clear from the map that except for extreme north and south parts of the study area, all other areas have excess fluoride (Fig. 3). West-central part is having groundwater with highest fluoride concentration and cross plots are shown in Fig. 2. However, fluoride can gain entry into human body through different routes, probable transmission routes and its health effects are shown in Fig. 4; Table 3.

Experimental design, materials, and methods
123 groundwater samples have been collected from bore wells/tube wells in the study area. The bottles were soaking in 1:1 HCl for 24 h and rinsed with distilled water followed by deionized water and samples were collected after pumping out water for about 10 min to remove stagnant water from the well and then transferred and stored at 10°C. All collected groundwater samples were separately labeled with sample ID starting from PDM-1 to PDM-123, and were transferred to the laboratory and analyzed in the laboratory for analysis of major anionic and cationic constituents using standard methods APHA (1995). The pH, electrical conductivity (EC), total dissolved solids (TDS), were analyzed on the site using pH/EC/TDS meter (Hanna HI 9811-5). Total hardness (TH) was measured by titration method using standard hydrochloric acid and standard EDTA solution. Calcium (Ca 2 þ ) and magnesium (Mg þ ) were determined titrimetrically using standard EDTA. Sodium (Na þ ) and potassium (K þ ) concentrations were determined using Flame photometer (Systronics, 130). Chloride (Cl − ) was determined by standard AgNO 3 titration. Bicarbonate (HCO 3 − ) and carbonate (CO 3 2− ) by titration with  ) were determined by using UV-visible spectrophotometer (Spectronic, 21, BAUSCH and LOMB). The fluoride concentration in water was determined electrochemically, using thermo Scientific Orion Star A214 Benchtop pH/ISE meter (9609BNWP fluoride ionselective electrode) using the USEP ion selective electrode method. This method is applicable to the measurement of fluoride in drinking water in the concentration range of 0.1-1000 mg/L. Standard fluoride solutions (0.1-10 mg/L) were prepared from a stock solution (100 mg/L) of sodium fluoride. As per experimental requirement, 2 ml of total ionic strength adjusting buffer grade III (TISAB III) was added in 20 ml of water sample. The ion meter was calibrated for a slope of −59.2 7 2. The composition of TISAB solution was as follows: 58 g NaCl, 4 g of CDTA (Cyclohexylene diamine tetraacetic acid) and 57 ml of glacial acetic acid per litre. Eventually, the accuracy of all chemical analyses was verified by calculating ion-charge balance between cations (Ca 2 þ , Mg 2 þ , Na þ and K þ ) and anions (       Table 3 Effects of fluoride ingestion on human health (Adimalla and Venkatayogi, 2017).

Fluoride concentration (mg/L)
Effect on human health o0.5 Conducive to dental caries 0.5 to 1.5 Promotes development of strong bones and teeth 1.5 to 4.0 Promotes dental fluorosis in children 44.0 Promotes dental and skeletal fluorosis 410 Crippling skeletal fluorosis, possibly cancer