Abstract

The present study investigated total arsenic (tAs), inorganic arsenic (iAs) species and fluoride ion (F) contamination in underground water of Mithi and Nangarparkar subdistricts of Tharparkar, Pakistan. Statistical parameters, principal component analysis, cluster analysis, sodium absorption ratio and saturation indices (SI) were used to detect interrelation and sources of concentration of tAs, iAs species (As³⁺ and As⁵⁺), F and others physicochemical parameters. The concentration of As³⁺ was measured by cloud point extraction using ammonium pyrrolidinedithiocarbamate (APDC) as complexing
reagent, while inorganic arsenic (iAs) was determined by solid phase extraction, using titanium dioxide. The positive correlation was observed between F contents with As species and other major ions, found in the underground water of the study area. The resulted data indicated that underground water samples of two areas of Tharparkar were severely contaminated with arsenic (0.100–3.83 mg/L) and fluoride ion (13.8–49.3 mg/L), which were exceeded the World Health Organization provisional guideline values, 0.01 mg/L and 1.5 mg/L, respectively. The SI of fluorite and calcite in the underground water samples showed that most of the samples were oversaturated with respect to calcite and fluorite.

Excerpts:

… Around 200 million people from 25 nations have health risks because of high F in underground water (Ayoob and Gupta, 2006). Pakistan, Bangladesh, Argentina, United States of America, Morocco, Japan, South African Countries, New Zealand, Thailand and Middle East countries are facing the problem of fluorosis (Rafique et al., 2009, RGNDWM,
1993).

The chief sources of F in natural waters are fluoride-bearing minerals (fluorite, fluorapatite, cryolite and apophyllite) as well as F replacing OH in the ferromagnesium silicates (amphiboles and micas), and clay minerals (Dey et al., 2011). Its concentration in underground water depends on the pH, the intensity of the weathering process, and the amount of clay in the aquifer material (Adriano, 1986; Saxena and Ahmed, 2001).

The World Health Organization (WHO) provisional guideline values for As and F concentration in drinking water are 10 mg/L and 1.5 mg/L, respectively (WHO, 2011).

… The present study was carried out on water quality parameters of underground water samples of subdistricts Mithi and Nagaparkar during 2011.

… The saturation indices for fluorite and calcite in underground water samples collected within the study area were calculated and plotted in Fig. 4(a). The resulted data indicated that initially the both calcite and fluorite enhance simultaneously until the saturation point achieved in underground water samples but when the SI of fluorite increases than 1.85, SI of calcite starts to decreases, might be due to fluorite super saturation. Hence calcite and fluorite are the main minerals controlling the aqueous geochemistry of elevated fluoride ion contamination occurring in the underground water samples of subdistrict Mithi and Nangarparkar. This situation of solubility control on the higher concentration of F, can be explained by the fact that F in underground water can be increased due to precipitation of
CaCO₃ at high pH, which removes Ca²⁺ from solution allowing more fluorite to dissolve.

In general, aridity of climate is one of the primary reasons for the origin of high fluoride in underground water. Several processes, namely dissolution of F bearing minerals, ion exchange and evaporative concentration can locally accounts for high F concentration in underground water (Agrawal et al., 1997; Apambire et al., 1997; Saxena and Ahmed, 2003). Thar desert have loaded with mica and granite, which are F bearing minerals, therefore during weathering, F can be leached out and dissolved in underground water (Chandra, 1983; Laghari, 2005). Elevated concentration of F, upto 50 mg/L in groundwater is clearly the cause of tooth discoloration and bone deformation among residents. It is reported that Thar desert area in the Sindh province of Pakistan is severely suffering from dental and skeletal fluorosis and people residing in the area are susceptible to F toxicity (Rafique et al., 2008, 2009).

… Tharparkar is also facing the crisis of water like the other deserts of the world, underground water is available in greater than 15 ft up to 160 ft depth, which is brackish and highly contaminated by F, As species and other ions. So, it is concluded that the underground water is not suitable for drinking as well as domestic uses but SAR values recommended that underground water of subdistricts Mithi and Nangarparkar is suitable for irrigation purposes in these areas soil except M-6 and M-8, while saturation indices values shows that most of underground water samples of study area causing scaling if used in industries.

*PDF of study at http://fluoridealert.org/wp-content/uploads/brahman-2013.pdf

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