1 Arsenic and other water-quality issues affecting groundwater, Indus Alluvial Plain, Pakistan. S. Naseem1 and J.M. McArthur2* 1. Department of Geology, University of Karachi 75270, Pakistan. Tel : +92-2199261300-06.
[email protected] 2. Department of Earth Science, University College London, Gower Street, London WC1E 6BT, U.K. Tel: +44-02031086362. *Corresponding author, e-mail
[email protected] ABSTRACT Groundwater beneath the alluvial plain of the Indus River, Pakistan, is reported to be widely polluted by arsenic (As) and to adversely affect human health. In 79 groundwaters reported here from the lower Indus River plain, in southern Sindh Province, concentrations of As exceeded the WHO guideline value of 10 g/L in 38%, with 22% exceeding 50 g/L, Pakistan’s guideline value. The As pollution is caused by microbially-mediated reductive dissolution of sedimentary iron-oxyhydroxides in anoxic groundwaters; oxic groundwaters contain < 10 g/L of As. In the upper Indus River plain, in Punjab Province, localised As pollution of groundwater occurs by alkali desorption as a consequence of ion-exchange in groundwater, possibly supplemented by the use for irrigation of groundwater that has suffered ion-exchange in the aquifer and so has values > 0 for residual sodium carbonate. In the field area in southern Sindh, concentrations of Mn in groundwater exceed 0.4 mg/L in 11% of groundwaters, with a maximum of 0.7 mg/L, as a result of reduction of sedimentary manganese oxides. Other trace elements pose little or no threat to human health. Salinities in groundwaters range from fresh to saline (EC up to 6 mS/cm).