2.1. Sample collection and preparation: The per capita per day intake of major food items and intakes of individual food items (BBS, 2011) used to characterize the food consumption pattern of both the rural and urban population in Bangladesh. Both findings showed almost same food composition but different consumption pattern for rural and urban residents. Fresh samples of cereals (Oryza sativa, Triticum aestivum), pulses (Lens culinaris, Cicer arietinum), vegetables (Solanum melongena, Daucus carota, Phaseolus vulgaris, Solanum tuberosum, Solanum lycopersicum, Allium cepa, Capsicum annuum L.), fruits (Musa paradisiaca, Mangifera indica, Artocarpus heterophyllus), freshwater fish (Labeo rohita, Pangasius pangasius, Oreochromis mossambicus), meat (beef, mutton, chicken, duck), egg (chicken, duck), milk (cow) were collected from different rural and urban markets occupying the 30 agro-ecological zones of Bangladesh in 2013. These foodstuffs are highly consumed by the Bangladeshi population as their daily diet (BBS, 2011). A composite of at least 10 samples for each food item was prepared and homogenized in a food processor and 50 g test portions were stored at −20 °C in the Laboratory of the Institute of Nutrition and food Science (INFS), University of Dhaka. The pre-processed samples were then brought to the Laboratory of Environment and Information Sciences, Yokohama National University, Japan and analyzed for arsenic content, expressed as mg/kg fresh weight (wt.). 2.2. Analytical methods 2.2.1. Reagents and sample extraction procedure All solutions were prepared with analytical reagent-grade chemicals and ultrapure water. An arsenic (As) standard stock solution (100 mg L−1 ) for the determination of the total arsenic (tAs) was purchased from Kanto Chemical Co., Inc. (Tokyo, Japan). The internal standard solutions containing 1.0 mg L−1 of indium (In), yttrium (Y), beryllium (Be), telium (Te), cobalt (Co) and titanium (Ti) were purchased from Spex Certi Prep® USA. The connected tube of ICP-MS was inserted into the internal standard bottle and automatically added to the samples during analysis. A solution of 10 mg L−1 multi-element solution (Merck, Darmstadt, Germany) was used to prepare a tuning solution covering a wide range of masses of elements. A microwave digestion system (Berghof, Bavaria, Germany) was used to extract elements from the sample. Digestion reagents that were used included 5 mL HNO3 acid (69%) and 2 mL H2O2 (30%). The weighed samples of 0.3 g were then placed into the digestion reagent in a Teflon vessel. The following microwave program was applied: 10 min at 180 °C with 800 W, 10 min at 190 °C with 900 W, and as a last step 10 min at 100 °C with 400 W. After digestion samples were then transferred into a Teflon beaker and total volume was made up to 25 mL with MilliQ water (Elix UV5 and MilliQ, Millipore, Billerica, MA, USA). The digest solution then filtered (DISMIC® - 25HP PTFE syringe filter (pore size = 0.45 mm); Toyo Roshi Kaisha Ltd., Tokyo, Japan), and stored in a crew cap plastic tube. 2.2.2. Instrumental analysis and quality assurance Arsenic in samples were analyzed using an inductively coupled plasma mass spectrometer (ICP-MS, 7700 series). The detailed analytical procedure of ICP-MS is presented in Table S2. All test batches were evaluated using an internal quality approach and validated if they satisfied the defined internal quality controls (IQCs). For each experiment, a run included blank, an internal standard in samples and samples analyzed in triplicate to eliminate any batch-specific error. A multi-element standard solution was used to prepare a standard curve. Before starting the sequence, RSD (b5%) was checked by using a tuning solution purchased from Agilent Co (Tokyo, Japan). Each analytical procedure was accompanied by a quality assurance program to ensure the quality of the data. The certified reference materials INCT-CF-3-Corn flour from the Institute of Nuclear Chemistry and Technology, Poland, and DORM-2-Dogfish muscle from the National Research Council, Canada, were analyzed to confirm the analytical performance of the applied method. The data of certified reference material (CRM) is presented in Table S3. The limit of detection (LOD) was 0.003 mg/kg with a good precision (2%).