A total of 25 surface soil samples (0.3 to 1.2 m or 1 to 4 feet below ground surface, bgs) were collected throughout Bangladesh from July 22 to August 6, 1997. These samples were stored in ice-packed coolers from the moment of collection until the samples were processed at the ICDDR,B laboratory between 3 and 5 days later. Each soil sample was homogenized and analyzed for moisture content by evaporation to a constant mass at 105°C. Following desiccation a mass of field-moist soil equivalent to 100 grams of oven-dried soil was delivered to a clean sample jar, distilled water was added to the jar to make the final mass of water equal to 200 grams, and the contents of the jar were mixed for 5 minutes. For example, if a 12 gram sample of field-moist soil weighed 10 grams after drying, then 120 grams of field-moist soil (this initial condition is equivalent to 100 grams of oven-dried soil and 20 grams of water) was delivered to a clean sample jar with 180 grams of distilled water (this final condition is equivalent to 100 grams of oven-dried soil and 200 grams of water; however, the composition of the soil being leached was never altered by oven-drying). After 24 hours a 50 mL aliquot of water was collected, filtered through a standard glass fiber filter used to remove total suspended solids (5), and submitted for total arsenic analysis. Then a 50 mL aliquot of distilled water was added to the soil/water slurry, and the contents of the jar were mixed for 5 minutes. After a total of 6 days another 50 mL aliquot of water was collected, filtered through a standard glass fiber filter used to remove total suspended solids, and submitted for total arsenic analysis.