Natural occurrences of elevated arsenic around the world

At present, most contaminated aquifers in Quaternary delta plains are thought to contain arsenic mobilized under anoxic conditions by bacterial activity, which is driven by high concentrations of NOM (Smedley and Kinniburgh, 2002 Smedley, 2005). Arsenic sorbed on metal (oxy)(hydr)oxides is liberated by reductive dissolution (Chapter 3). The best-known example is the Bengal basin, where arsenic is widely present in Holocene (less than 11 500 years old) sediments, while the underlying, oxidized aquifers with Pleistocene (11500-1.75 million years old) sediments are thought to have very low concentrations of arsenic. Similar conditions may occur in Cambodia, Vietnam, Myanmar, and elsewhere [Pg.313]

Region/country Population exposed Arsenic concentration ranges (ng L 1) Aquifer type Groundwater conditions Year(s) of discovery [Pg.314]

Bengal basin, 35 million 0.5-4730 Holocene Strongly reducing, 1993 [Pg.314]

Bengal basin, West 15 million 1-4100 (same as above) (same as above) 1978 [Pg.314]

Middle Canges plain, 1.4 million in Bihar 3-1 861 in Bihar Holocene flood plain Similar to Bengal 2002 [Pg.314]

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