Arsenic and Manganese Contamination of Drinking Water Resources in Cambodia: Coincidence of Risk Areas with Low Relief Topography

摘要

Arsenic contamination of groundwater has been identified in Cambodia, where some 100,000 family-based wells are used for drinking water needs. We conducted a comprehensive groundwater survey in the Mekong River floodplain, comprising an area of 3700 km~2 (131 samples, 30 parameters). Seasonal fluctuations were also studied. Arsenic ranged from 1 to 1340 μg L~(-1) (average 163 μg L~(-1)), with 48% exceeding 10 μg L~(-1). Elevated manganese levels (57% > 0.4 mg L~(-1)) are posing an additional health threat to the 1.2 million people living in this area. With 350 people km~(-2) potentially exposed to chronic arsenic poisoning, the magnitude is similar to that of Bangladesh (200 km~(-2)). Elevated arsenic levels are sharply restricted to the Bassac and Mekong River banks and the alluvium braided by these rivers (Kandal Province). Arsenic in this province averaged 233 μg L~(-1) (median 100 μg L~(-1)), while concentrations to the west and east of the rivers were < 10 μg L~(-1). Arsenic release from Holocene sediments between the rivers is most likely caused by reductive dissolution of metal oxides. Regions exhibiting low and elevated arsenic levels are co-incident with the present low relief topography featuring gently increasing elevation to the west and east of a shallow valley—understood as a relict of pre-Holocene topography. The full georeferenced database of groundwater analysis is provided as Supporting Information.