T192 Arsenic: From Nature to Human I

Wednesday, 31 October 2007
8:00 AM - 12:00 PM

REGIONAL HYDROCHEMICAL STUDY OF GROUNDWATER ARSENIC CONTAMINATION ALONG TRANSECTS FROM THE HIMALAYAN ALLUVIAL DEPOSITS TO THE INDIAN SHIELD, CENTRAL GANGETIC BASIN, INDIA

Paper number: T192-14
Program: Technical Sessions
Time: 11:15 AM – 11:30 AM

Authors

Abstract

Although intensive studies of groundwater arsenic (As) contamination have been conducted in the Bengal (Ganges-Brahmaputra) Basin, information on the regional As distribution in adjoining upstream regions of the Ganges, which could provide insights into provenance and mobilization mechanisms, are extremely limited. Groundwater (66) and surface-water (12) samples were collected along two transects in the central Gangetic plain (states of Bihar and Jharkhand), which extend from the Quaternary Himalayan alluvial fans and plains (Indo-Nepal border) to the pre-Quaternary (Precambrian to Cretaceous) Indian cratonic, igneous and metasediment shield provinces.

Groundwater samples were collected from shallow aquifers (well depths £ 137 m, but mostly 8 to 60 m) and surface-water was collected from the Ganges and its Himalayan (northern) and shield- (southern) originated tributaries. Preliminary results indicate that As concentrations are much higher in groundwater collected from the youngest alluvial terraces (~50% samples have ³0.01 mg/L [WHO Maximum Contaminant Level] As, maximum 0.52 mg/L), than those associated with the shield (all £ 0.005 mg/L). Most (87%) of the As is present as As(III). Redox conditions are highly spatially variable (oxic to methanic, dominated by metal-reduction), with no systematic depth variation. Coexistence of As(III), Fe(II), NH3(dis), elevated HS- and CH4(dis), and other redox sensitive parameters delineate reduced environments, although As is not linearly correlated with these individual solutes. Dissolved oxygen (DO) concentrations were generally <0.5 mg/L in reduced groundwater, however, some of the highest As concentrations were detected in groundwater with DO ~1 mg/L. These initial results suggest much higher groundwater As contamination in aquifers with sediment derived from the Himalayas than in aquifers with sediment derived from the cratonic shields.