Ground water toxicity due to ﬂ uoride contamination in Southwestern Lahore, Punjab, Pakistan

The prevalence of dental/bone deformities provides motivation for studying the distribution, severity and sources of the Fluoride (F (cid:1) 1 ). The ground water samples ( n ¼ 77) were collected, from the districts of Lahore and Kasur of approximately 750 km 2 area. The water was analyzed for ﬂ uoride (F (cid:1) ), pH, electric conductivity (EC), alkalinity and hardness. The results revealed F (cid:1) concentration ranges from 0.25 – 21.3 mg. An inverse relation between depth and ﬂ uoride concentration was observed. On the basis of cluster analysis three zones were identi ﬁ ed. Highly toxic zone was a strip of 15 km wide and 3 km long, along Multan Road from Sunder to Phool Nagar bypass, with ﬂ uoride concentration (08 – 21.3 mg/L). The highly toxic zone inhabited a number of industrial units, disposing off their wastewater through soaking pits. These units contribute pollution to the shallow water, which further penetrates to the surroundings. Hence the shallow water (depth of 45 – 50 feet) was the most contaminated. The intensity of toxic effects decreases from highly to mild toxic zone. It was concluded that the problem was actually associated with the industrial wastewater. Therefore, to overcome the issue, measures of supplying fresh drinking water from the deep aquifer as well as treatment of industrial water is suggested.


INTRODUCTION
Fluoride is found in plants, soil, animals and water in trace amount. It helps in mineralization of teeth and bones and formation of enamel in teeth (Singh & Mukherjee ).
Fluoride is required in an optimum concentration to the human body for normal physiological activities (Narsimha ; Kumar ). Consumption of water with fluoride contents above or below a certain limit may cause dental and skeletal fluorosis (Ghrefat et al. ; Narsimha ). As per the World Health Organization, the range of fluoride contents should be 0.6 to 1.5 mg/L (Brindha & Elango ). Its impacts on the human body are irreversible (Jadhav et al. ). The sternness of toxic effects depends upon total dose gulped and period of exposure. The severity of toxic effects also depends upon the body response which varies person to person, depending upon their health status (Amalraj & Pius ).
Fluoride is introduced in water through natural as well as through anthropogenic sources. Most of the fluoride in ground water is natural in origin. Naturally, a trace quantity of fluoride can occur in soils, water, plants, animals and all kinds of vegetables (Narsimha & Rajitha ; Adimalla ). All over the world, fluoride levels beyond the safe limit in groundwater was due to the presence of fluoride bearing rocks and its mobility in ground water increased the fluoride contents above the safe limit, which has so far affected over 200 million people belonging to 25 nations (Ayoob & Gupta ; Adimalla ). In western parts of the twin districts Lahore and Kasur (Punjab province), around 17 villages (1.51 million population) were reported with bone deformities. Most of the affected people were teenagers (Farooqi et al. ). In 2007, the issue was scrutinized for the last time and it was reported that phosphate fertilizer and brick kilns were responsible for fluoride introduction. It needs to be interrogated comprehensively to identify the real culprit as brick kilns and phosphate fertilizer is used throughout the Punjab. In addition, the paradigm shift of the issue also needs to be investigated. The real objective of the study was to identify the actual source of fluoride and its relationship with other factors. Secondly, it was to mark the boundary of fluoride contamination in the area.

Study area
The area under study is situated in the Punjab, the most populous province of Pakistan. The focus of the study was the northwest districts of Kasur and Lahore (being affected with bone and teeth deformities). The populations of the Lahore and Kasur districts is about 11,126,285 and 3,454,996 with areas of 772 and 4,796 km 2 , respectively.
The area under study is mainly lined with fertile silty plains of the River Indus and its tributaries. The study area is located at the left bank of River Ravi and at the right bank of River Sutlej. The ground water recharged mainly through these rivers and canals. Two layers of water exist underground. The shallow aquifer is the main source of water for the population. The deeper layer found at >400 feet. More than 80% of the population consume water from shallow aquifers through home installed hand pumps, motor pumps, etc. at the depth of 70-200 feet. The climate of the area is extreme with cold foggy winters followed by spring starting from mid-February; spring continues until mid-April, followed by a very hot and long summer, extending to September. Heavy rains, also called monsoon, occur from mid-July to mid-September. The annual temperature ranges from À2 to 45 C. Map of the study area is presented in Figure 1. Despite of its tropical climatic conditions, the whole Punjab is under intense cultivation because irrigated agriculture is predominant. Overall, Punjab's share in agriculture production is 56.1% to 61.5%. Here, the agriculture sector engages about 45% of labor and contributes 21.4% to the total GDP of the country. Most of the people are farmers but the study area has numerous industrial units, therefore people work in industry as well. The industrial sector contributes to 24% of the GDP of the Punjab.

Sampling strategy
A total of 77 ground water samples were collected in precleaned, high density polyethylene bottles directly from sources, i.e. hand pumps, motor pumps and tube wells.
The samples were collected after purging for 5 min from a running water source. As the previous studies showed, there are two aquifers in the area, i.e. shallow and deep separated by a less permeable layer (Farooqi et al. ). Most of the community uses water from shallow aquifer. Therefore, almost 90% of samples were collected from first aquifer layer (hand pumps or/and motor pump) and 10% from the second kind of aquifers (tube wells/deep wells).
The soil samples were collected in plastic bags, grinded, and, after drying, were passed through 2 mm mesh sieve and then a suspension was prepared by mixing soil in 1:2.5(g: mL) ratio with deionized water. Later, the supernatant was

Quality assurance and quality control
In order to maintain the meticulousness and accuracy of the results, all of blank, standard, and samples were tested in replicates. The data was rejected if standard deviations were more than 10%. Recovery ratios of the results were calculated for the determination of accuracy. Experimental instruments were calibrated before each sample testing.

RESULTS AND DISCUSSION
The basic statistical analysis of water quality data analyzed is presented in Table 1  in Pakistan and in the region is presented in the Table 3.
In order to discover the linkage between the fluoride with other parameters, the scatter plots were shown in Figure 2(a)-2(f). The scatter plot of F À versus pH   (Figure 2(a)) showed a strong linear association (r ¼ 0.813) of the F À with pH as reported in the literature (Brindha & Elango ). This is because the ionic radii of F À and OH À have same ionic strength and they often substitute each other within minerals, that is why F À is found in equilibrium with hydroxide, i.e. at pH greater than 7.0 (Rafique et al. ). Clay minerals, such as kaolin has the ability to grasp F À ions on its surfaces, but when the pH increases, the OH À ions displace the F À ions, discharging it to groundwater (Pazand ). Moreover, the F À contents were found to be highest in those areas where pH and alkalinity values were high, i.e. Manga Mandi, Chah kalalanwala, Talab saraey, Nath-e-Khalsa localities (Figure 3(b)). The highest ranges of F À values were found to be in coexistence with   The medium toxicity zone consists of areas having F À contents between 4 to 8 mg/L in shallow ground water.
In these areas, dental diseases were prevailing on a large scale among the residents having yellowish and porous teeth. The situation was even worse in Phool Nagar city where arthritis, periodontics, and stiffness of muscles was evident in most of the population. Kaminsky () showed that residents exposed to 4-8 mg/L of F À range may suffer from fluorosis in teeth and osteoporosis.
The mild toxic zone was a strip of 5-10 km in width along Lahore-Raiwind Road, covering Kot Radha Kishan-Phool Nagar road and surroundings, where F À ranges between 1.5-4.0 mg/L. Dental caries were more evident here. The 40% of children at the age of 6-12 years were suffering from dental caries. It was observed that in the highly toxic zone and in the mild toxic zone, industrial units including sugar, plastic, polymers, chemicals, etc. were found disposing their waste into soaking pits, contaminating the ground water, while in the medium toxic zone, industrial units were disposing their waste in rohi nullah.

Source identification
Principal component analysis (PCA) is an independent technique for capturing the variability of the data, it recognizes the pattern of variation in a large data set of inter correlated variables and transforms them to a smaller uncorrelated set.
The analysis recognizes the most meaningful parameters.
PCA based on factor analysis was applied on the data of all three zones separately to assess the possible sources of the pollution and considerable factors were recognized. For each zone, unrotated principal component with factor loading >0.7 were considered (Table 4). For each zone, PCA with eigen value more than one was considered important.
In the highly toxic zone, the VF1 showed 38.05% of total variance and had a strong positive loading with EC (r ¼ 0.842), F (r ¼ 0.745) and TDS (r ¼ 0.854) and negative loading for Ca þ2 (r ¼ À0.626) which showed variation in the concentration of the F À and increase in the TDS and EC of the water along with decrease in calcium contents, which indicated that the F À has inverse relation with calcium as discussed earlier. A higher concentration of dissolved solids enhances the solubility of F À ions (Rafique et al. ). In this zone, F À as well as the ionic strength is continuously increasing (r ¼ 0.745); mean salts are added to the shallow water from some unknown sources. Previously, Farooqi et al. () argued that the brick production and coal combustion introduce F À into air and its deposition to soil; along with phosphate fertilizer, these were the main sources of F À in the area, but the whole Punjab province of Pakistan is using the same fertilizer and, throughout the Punjab, brick kilns are functional; the problem lies in a specified region while the PCA showed the addition of TDS along with F À , indicating a continuous source of F À in the region which might be the industry.
In highly affected areas, investigation from the local community and concerned departments, i.e. Environment Protection Agency Punjab, etc., it was found that no drai- In the medium toxic zone, VF1 showed 38.24% of the total variance with negative loading of EC, total alkalinity and TDS (r ¼ À0.900, À0.844, À0.899) while F À also had weak negative loading r ¼ À0.417, indicating all these parameters have been decreasing in the region. VF2 of the same region explained 17% of the total variance with only strong negative loading of the Ca þ2 (r ¼ À0.722), indicating a sharp decrease in calcium contents in the region, indicating the source of the problem was in the highly toxic zone.
The VF1 of the mild toxic zone explained a total variance of the 34.4% with negative loading of EC, total alkalinity and TDS (r ¼ À0.892, À0.802, À0.890) while the VF2 had 16.24% of the total variance with negative loading of the F À (r ¼ À0.526), indicating a decreasing trend and strengthened our findings that F À and other dissolved solids were introduced through the highly toxic zone.

Natural sources of fluoride
In most of the studies in the world, it was evident that the most of F À is introduced into the environment through natural sources. In order to investigate the natural contribution, six soil samples were collected from the highly toxic zone to test for F À contents and the results were found in the range of 0.03-1.6 mg/kg. Previously, a detailed study of the soil of the  Table 5.
The adsorption and desorption processes directly affect F À migration and exchange from soil to water and water to soil (Wang et al. ). In most of the cases in the world, the main reason of elevated concentration of F À , in soil and water, was its natural intrusion from dissolution of bed rocks containing F À minerals. In the bed rock, fluoride is as abun-   Another possibility of introduction was canals and drains.
So, six water samples were collected from hand pumps installed at the bank of drains and canals. Results presented in Table 6 were within the WHO permissible limits. While Farooqi et al.
() reported 1.7-2.28 mg/L of F À in canal water with a mean value of the 2 mg/L from the same area, Kausar et al.

CONCLUSIONS
Fluoride contamination in ground water of Southwestern Lahore, Punjab, Pakistan was evaluated for identifying the source of contamination. Overall, 59% of the sample falls in the category of medium risk while 9% falls in the highest risk category. The contaminated area was categorized into three zones, i.e., high, mid and low toxicity zones. The shallow aquifer (80-200 feet) was the most contaminated with F À up to the 100 feet depth. In contrast, deep water was fit for consumption. Most of the highly contaminated areas run along main grand trunk road, i.e. Multan Road, which holds heavy industry having no drainage system. The low concentration of F around the canal and River Ravi indicates  dilution of the water with water having low F contents.
Whereas the soil samples analysis indicated that soil had very low concentration of fluoride as compared to the rest of the world, indicating that the bed rock gave slight contribution. The old residents interviewed indicated that no such disease history prevailed in past. Therefore, fluoride contamination of ground water in the study area was due to industrial waste water intrusion.
Further verification was possible with the industrial wastewater analysis but access was denied. Recently reported bone deformities and dental caries can be linked with the increased F toxicity in the area and needs remedial actions such as treatment of the wastewater before disposal through law enforcement and deep-water utilization for drinking rather than treatment of water before drinking.