108 One Century of the Discovery of Arsenicosis in Latin America (1914–2014) – Litter, Nicolli, Meichtry, Quici, Bundschuh, Bhattacharya & Naidu (Eds) © 2014 Taylor & Francis Group, London, ISBN 978-1-138-00141-1 Evaluation of arsenic and its controlling factors in aquifer sands of district Samastipur, Bihar, India M. Kumar & AL. Ramanathan School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, India P. Bhattacharya KTH-International Groundwater Arsenic Research Group, Department of Sustainable Development, Environmental Science and Engineering, KTH Royal Institute of Technology, Stockholm, Sweden ABSTRACT: A set of 96 water samples from shallow tubewells and 14 sediment samples from Samas- tipur district to know the level of arsenic (As) and its controlling factors were analyzed. Groundwater samples were collected from tubewells of different depths, and a wide range of concentrations in the range 0.19–135 μg L -1 was found. Scanning electron micrograph study of the sediments shows intense chemi- cal weathering. Present study also support reductive dissolution of FeOOH triggered by organic matter oxidation as an As mobility factor in the aquifer sands. community development blocks. The district is linked with Budhi Gandak in the northeast side and Ganga with the southwest side. The district is peneplain, intersected by numerous streams like Budhi Gandak, Baya Nadi and Balan Nadi, etc. The southwestern monsoon brings much needed rainfall, and nearly 70% of the precipitation occurs during the months of July to September. The mean annual temperature lies between 24–26 °C (Kumar et al., 2010). Seven blocks, affected by high As con- tent (Dal Singh Sarai, Vidhyapati Nagar, Mohiud- din Nagar, Mohanpur, Patory, Ujiyarpur, Sarai Ranjan), from the Samastipur district of Bihar, were selected for the proposed research work. 2.2 Sample collection and analysis Ninety six-tubewell water samples from various depth, collected during pre-monsoon season (June, 2013), along with one core sediment of 40 m were analyzed for major cations and other trace elements. An Agilent 7500c (Agilent Technologies) induc- tively coupled plasma mass spectroscopy was used to determine the amount of As and other elements in water and sediment samples. Scanning Electron Microscope-Energy Dispersive X-ray diffraction (SEM-EDS) was used for sediment analysis. 2.3 Analysis of Standard Reference Materials (SRMs) Standard Reference Materials (SRMs) 1640 (trace elements in natural water) from the National Insti- tute of Standards and Technology (NIST) and 2711 (Montana soil) were used to verify the results for a and other elements in water and sediment. 1 INTRODUCTION Arsenic (As) pollution in India was reported in 1976 in four states: Punjab, Haryana, Himachal Pradesh and Uttar Pradesh of Northern India (Datta & Kaul, 1976). Lower Ganga plain of West Bengal was revealed in 1984 (Garai et al., 1984). Chakraborti et al. (2003) reported As in middle Ganga plain of Uttar Pradesh and Bihar. Up to date, As has been reported in many states of India predominantly in alluvial plains. There are some studies done on controlling factors and mobiliza- tion mechanisms, which suggest that microbially mediated oxidation of organic matter triggers reductive dissolution of FeOOH in alluvial plain (Bhattacharya et al., 1997; Nickson et al., 2000; Chauhan et al., 2009; Kumar et al., 2010). However, there are very few studies in middle Gangetic plain. India stands second on most populated coun- tries bearing 17.5% of the population on a limited area of 2.4%. The Gangetic plain of Uttar Pradesh and Bihar shows large area with high As pollution in water. Due to highly fertile and most populated areas, the calamity occurring is also high. This study focuses on As mobility in the aquifer sands in Samastipur district of Bihar, India, taking into account the water-sediment interaction. 2 METHODS AND EXPERIMENTAL 2.1 Study area The study was conducted in the Samastipur dis- trict of Bihar state. The area of Samastipur dis- trict is 2904 km 2 and its population, reported to be 4.25 million (Census, 2011), is segmented in 20