As contamination in groundwater from the Ganges-Brahmaputra Delta, Bangladesh Y. Zheng1, M. Stute2,3, L. vanGeen3 1Queens College of CUNY 2Barnard College, Columbia University 3Lamont-Doherty Earth Observatory, Columbia University

Introduction tests on 50,000 wells in Bangladesh have shown that around 40% are too contaminated with arsenic to provide drinking water, according to a World Bank official. Arsenic causes potentially fatal tumours and respiratory problems

Objectives of our study Better understand: constrain processes that mobilize As from the sediment identify geochemical factors that affect spatial and temporal variations of As concentrations identify hydrological factors ……. provide baseline for public health studies

As field measurements As measurements in the field The key to adapting the method of Haywood and Riley (1976) for use in the field is a set of inexpensive 50 ml and 2.5 ml plastic syringes and 3-way luer-lock valves. (a) In steps (1) and (2), 5 ml of sulfuric acid and EDTA solutions stored in two 50 mL syringes are first added sequentially to a third 50 mL syringe containing the sample. (b) The sample syringe is then disconnected from this common rig used for all samples, the contents are mixed by shaking, and the syringe is then attached to individual combinations of 3 syringes and 3 valves. During the gradual addition of sodium borohydride in step (3), the evolved arsine is oxidized and trapped in a another syringe containing iodide/potassium iodate (4). The headspace in the sample syringe is also bubbled through the trapping solution by gently pushing the plunger. The contents of the trapping syringe is then transferred in step (5) to mix with the mixed color reagent and allowed to react and degas for one hour. In step (6), light absorption at 865 nm for sample is measured by attaching the extraction rig to the luer-lock connection of the spectrophotometer. Also shown is schematic of colorimeter cell (c). Fig. 8 NSF 1/99

As contamination in Bangladesh % of water samples with As conc. > 0.05 mg/l (data from Dhar et al., 1997) Fig. 1. Cumulative percentage of water samples with As concentration greater than 0.05 mg/L based on a survery of 28 districts (Dhar et al., 1997) is used to illustrate the distribution of As contamination in Bangladesh. The most promising potential study sites are located south of Dhaka, within a radius of about 200 km where a wide range of As concentration is observed. Two districts (Meherpur, Lakshmipur) with frequent (>80%) ocurrence of high As concentration will be studied by the British Geological Surveyand the Royal Institute of Technology, Sweden. To obtain maximum coverage of the problematic area, we plan to select sites from Chandpur, Noakhali or Madaripur. We will also select sites from fairly uncontaminated area, such as Dhaka, Magura, Norail, Khulna. Solid circles indicate the locations of the sediment cores analyzed for As and Fe (Fig. 3) in the Faridpur district and the Asuganj thana in Brahmanbania district. Fig. 1 NSF 1/99

As concentrations in 3000 wells from 28 districts in Bangladesh Distribution of As concentrations in ~ 3000 ground water samples from 28 districts in Bangladesh up to Jan. 1997 based on Dhar et. al (1997). Frequently high levels (> 0.05 mg/l) of As are found in 10 districts (red and purple, see Fig. 1 for locations). The arrows indicate the WHO provisional guideline value of 0.01 mg/l and the current US drinking water standard value of 0.05 mg/l (maximum contaminant level). Fig. 2 NSF 1/99 (data from Dhar et al., 1997)

Conclusions Wells need to be tested and people have to be made aware of wells with elevated As concentrations alternatives need to be developed