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Final Progress Reports: Columbia University: Arsenic, Iron, Sulfur and Organic Carbon Speciation and Their Impact on Groundwater Arsenic

Superfund Research Program

Arsenic, Iron, Sulfur and Organic Carbon Speciation and Their Impact on Groundwater Arsenic

Project Leader: Benjamin C. Bostick
Co-Investigators: Brian J. Mailloux (Barnard College), Steven N. Chillrud, Alexander F. van Geen
Grant Number: P42ES010349
Funding Period: 2000-2017
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Final Progress Reports

Year:   2016  2010  2005 

Calibrating a Sequential Extraction Method for Speciation Analysis of As in Natural Samples

PhD candidate Hun Bok Jung conducted a series of laboratory experiments to establish a method that will allow quantitative determination of As oxidation state in natural sediment samples.  This is important because synchrotron X-ray Spectroscopy is not sensitive enough to assay whether As present at natural abundance in sediment is As(III) or As(V).  By adding 0.1 M L-ascorbic acid to 1 M phosphate solution, 80~100% of As(III) sorbed onto various Fe and Mn oxides was recovered under anaerobic conditions.

Mineralogy and Mobility of Fe and As in Meghna River Sediments in Bangladesh

Post-doc Saugata Datta (now assistant professor at W. Georgia State Univ.) undertook a geochemical study of sediment samples taken along the Meghna River in January 2003.   The most surprising finding was that sub-surface sediment samples (depth 1 to 4 m below surface) contained 0.2 to 1300 mg/kg phosphate-extractable As and 0.8 to 23700 mg/kg HCl-extractable As.  In contrast, surficial sediments from the same locations contained 10-20 mg/kg total As. Much of the subsurface sediment As (10-100%) is phosphate extractable, is not likely associated with acid soluble sulfide, and is most likely sorbed to Fe-minerals such as magnetite or goethite determined by EXAFS. Mixed valence states of As are found by XANES and voltammetric speciation of P-ext As analyses.  The source and fate of this As require further study.

Stable Isotope (18O, 2H) and Arsenic Distribution in the Shallow Aquifers in Araihazar, Bangladesh

The Zheng/Stute group monitored the oxygen (18O) and hydrogen (2H) isotopic composition of precipitation in Dhaka, Bangladesh, and of surface waters and groundwaters in a 25 km2 study area in Araihazar upazila or sub-district (90o37’E, 23o74’N), about 30 km east of Dhaka. The groundwater isotopic composition obtained at 6 multi level well sites covers the range between the global meteoric water line and moderately evaporated surface waters.  These data indicate that some groundwaters are recharged directly by precipitation while others show evidence of recharge from evaporated surface waters during the wet and at the beginning of the dry season.  Using the deuterium excess as an estimator of the degree of evaporation, the wells show characteristic changes from more or less evaporated sources of water as a function of depth. The degree of evaporation expressed as deuterium excess does not correlate with As concentrations in the groundwater samples.  This finding suggests that the source of groundwater recharge from either precipitation with a low reducing capacity, or surface waters with a higher reducing capacity, is not an important factor in As mobilization.

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