Baseline investigation of (methyl)mercury in waters, soils, sediments and key foodstuffs in the Lower Mekong Basin: The rapidly developing city of Vientiane (Lao PDR)

• First inventory of mercury (Hg) contamination in Vientiane city ecosystem
• Hg concentrations were low in water, soil, sediments, rice and fish.
• Dissolved monomethyl-Hg concentrations were low in surface and pore water.
• Low Hg levels reflect the essentially non-industrialized status of the capital.
• Low environmental Hg-attributable health risks for the local population

We report here the first inventory of mercury (Hg) contamination in the ecosystem of Vientiane city, a representative emerging city bordering the Mekong River. Total Hg (THg) concentration in soil and sediments of both contrasting non-urbanized (wetland, rice paddy, Mekong River) and urbanized areas (wastewater canal and associated wastewater irrigated wetland) was low (8 to 101 ng g− 1), reflecting the essentially non-industrialized status of the capital. Dissolved THg (2.2 ± 2.2 ng l− 1) and monomethyl-mercury (MMHg) concentrations (0.06 ± 0.09 ng l− 1) were also low in both surface and soil or sediment pore water with higher concentrations (up to 9 ng g− 1 THg and 0.53 ng g− 1 MMHg) measured in wetland and rice paddy suboxic waters. Dissolved organic carbon was identified as the main carrier in surface water for dissolved Hg transport towards the Mekong River. The measurement of low THg concentrations in rice (6.4 ± 1.0 ng g− 1) and fish (51 ± 40 ng g− 1) sampled in rice paddies and in the Mekong River confirmed the pristine state of the ecosystem of Vientiane area. Based on these data, we evaluated a low environmental Hg-attributable health risk for the local population whose diet relies on both fish and rice.