Occurrence And Geochemistry Of High Arsenic Groundwater In Datong Basin, China And Lahore, Pakistan

Water crises have increased in the world in last few decades. It is reported that 80% illness and over one third of all deaths in developing countries are due to water related issues. It is also estimated that about 137,000,000 people in more than 70 countries are probably affected by arsenic poisoning from drinking water. Pakistan and China is also facing elevated arsenic levels in ground water. Lahore is the second biggest city and among one of the highly populated city in Pakistan. Datong Basin is one of the industrial city of China and its population relies on ground water for domestic, agricultural and commercial use. In 2003, there were 36,676 people at risk due to drinking of high arsenic (>50 μg/L) groundwater in Datong Basin, and the sufferers of arsenic poisoning were up to 3296. In this region arsenic concentration upto 1820 μg/L is reported.The research aim is to identify the main genesis and factors influencing As levels in the groundwater of Datong Basin, China and Lahore City, Pakistan, and to reveal the different hydrogeochemical process occurred in the high arsenic aquifers. In this study we assess:water quality of Datong Basin, water quality of Lahore at sources and distribution system, arsenic correlation of trace elements in high arsenic groundwater aquifers in Lahore, Sediment geochemistry of Lahore and we compare hydrogeochemistry of high arsenic groundwater of Lahore-Pakistan and Datong Basin-ChinaA total of 50 drinking water samples (16 from sources, and 34 from distribution system) were examined for physical, chemical and bacteriological parameters to evaluate water quality of Lahore at sources and distribution system. Principal component analysis (PCA) revealed that the concentration of As was strongly associated with that of SO42-. To assess arsenic concentration at sources of Lahore, we collected a total of 474 tube well samples from 7 towns from Lahore, Pakistan. In most cases, the concentration of As was higher than WHO limit value. Investigation of the groundwater type revealed facies in the order:HCO3·SO4-Mg·Ca> HCO3·SO4-Ca.Mg> HCO3·SO4·Cl-Mg·Ca> HCO3·SO4-Ca·Mg> HCO3·SO4-Ca> HCO3·SO4-Mg·Ca. The Hierarchical Cluster Analysis (HCA) showed that pH significantly affected As, F-, NO3-and NO2- while HCO3- contributing most to the observed TDS values in Lahore. It can therefore be concluded that inherent mineral dissolution/precipitation, pH, oxic conditions, anthropogenic activities, atmospheric transport/wet deposition, microbial activities and surface soil characteristics play significant roles in elevating As(III) and As(V) in the groundwater of Lahore. We selected 30 high arsenic sources from Lahore for isotopic and heavy metal analysis. We transported 30 water samples and 150 sediment samples from one borehole (where high arsenic value is reported) to School of Environmental studies, China University of Geosciences to get reliable data for comparison with high arsenic ground water of Datong Basin-China. In isotopic analysis, δ18O and δ2H values typically range from-51.04 to-8.178‰ and-33.92 to-5.846‰ for all ground water sample of Lahore. All point except five points are scattered above LMWL. It indicates that there is no considerable evaporating effect in this region. Such slope results are obtained due to mixing of evaporating soil water with infiltrating rain. On base of lithology data a total of 72 sediment samples were selected for total arsenic analysis. A total of 5 samples were analyzed for XRD and 12 samples were analyzed to know concentration of As in extraction forms. Correlation analysis of arsenic with minerals shows negative correlation with quartz and orthoclase while high positive correlation with chlorite minerals.To assess water quality of Datong Basin and to compare with hydrogeochemistry of Lahore, we analyzed 87 water samples of Datong Basin. Data analysis (Analysis of valiance and descriptive statistics) was done using IBM SPSS Statistics version 21. Five major factors (PCI, PC2, PC3, PC4 and PC5) were realized in the groundwater samples in Lahore which explain 77.07% of the total variance in dataset. Six major factors (PCI, PC2, PC3, PC4, PC5 and PC6) were realized in the groundwater samples in Datong Basin with total variance of 78.3%. Results were compared in the form of tables and graphs.The results show that the concentration of As was affected by the redox reactions, dissolution and evaporation. More variation in element composition is found in the ground water of Datong Basin as compare to Lahore. Na+ and HCO3- are found the predominant ions in groundwater at Lahore and Datong Basin as well. The majority of low As groundwater samples in Datong Basin are classified as HCO3-Mg(Ca)Na and HCO3·SO4·(Cl)-Na(Mg) water, while most of high As groundwater samples have HCO3-Na(Mg), and HCO3·Cl-Na(Mg) water type. In Lahore arsenic has perceptible correlation with Fe, Ba, Zn, Cr, Mn and Si. In Datong Basin arsenic shows weak positive correlation with B and negative correlation with Cr, Cu, Fe, Li, Ni, Pb, Se Sr, V and Zn but this trend is opposite in Lahore. In Lahore water correlation analysis indicate that source of boron and arsenic is different while source of arsenic, iron, chromium zinc and silicon might be same and in reducing environment mobility of arsenic may be increase in ground water of Lahore.Sediment geochemistry was also found different in two study areas as arsenic contents in sediment samples of Datong Basin which are reported in literature ranges from 2.45 to 27.38 mg/kg with an average value of 9.4 mg/kg while in Lahore 0-81mg/kg with mean value 6mg/kg almost two time higher than reported values of As in sediment in Datong Basin while in Lahore depth range for sediment result was 1.6 to 240 meter is comparable to that of modern unconsolidated sediments. In Datong Basin it is reported that arsenic values varies with depth. In Datong Basin ground water samples, arsenic values are increasing with increase of depth but in Lahore it has negative correlation for ground water while in sediments arsenic values is increasing with depth. Reason of this different trend is might be different depth of boreholes at two sites. In Datong Basin predominant part of arsenic is likely in sorbed or co-precipitated state in Fe-bearing mineral phase as iron oxides/oxyhydroxides with residual magnetite and chlorite, illite, quartz coated with iron oxides/oxyhydroxide. Feldspar and ankerite are carrier for arsenic in sediments while in Lahore, illite, quartz and chlorite serpentine are dominant carrier of arsenic in sediments.In this study, all water samples in two study areas were found in unsafe criteria according to WHO guidelines. In Datong Basin high value of boron, arsenic, salinity is responsible for unsafe portable water while in Lahore all water samples exceed permissible limit of arsenic. Higher TDS and HCO3- distribution is more apparent in the north and south part, SO42- distribution is Dominant in northern part of the study area while TH has a sporadic (high to low) distribution observed throughout the area. The drainage system comprising of 14 wastewater collections drains transports sewage and industrial wastewater conveyed westward into river Ravi which is might be major source of contamination in Lahore aquifer including agriculture activities, poor management of land fill. In Datong Basin Coal mining and industrial activities are responsible for high polluted ground water.