Arsenic in Mekong putting 1.7 million at risk. irinnews. PHNOM PENH, November 17,  2008  Arsenic contamination of the Mekong River and groundwater is putting millions of residents at risk of severe illness due to arsenic poisoning, the UN and NGOs warned. After surveying wells along the Mekong, which flows through Lao PDR, Cambodia and Vietnam, the UN Children’s Fund (UNICEF) and governments concluded that as many as 1.7 million people were at risk of arsenic poisoning, whose long-term symptoms include skin lesions and cance. [ See ]