Geogenic Contaminants

Geogenic contaminants in groundwater: Predicting regions at risk

Arsenic contamination of groundwater resources threatens the health of millions of people worldwide, particularly in the densely populated river deltas of Southeast Asia. Maps of areas at risk of groundwater arsenic concentrations have been produced by combining geological and surface-soil parameters in a logistic regression model. They show that Holocene deltaic and organic-rich surface sediments are key indicators for arsenic risk areas and indicate elevated risks in Sumatra and Myanmar where no groundwater studies exist.

Read our research article published in

Nature Geoscience, 1, 536–542 (2008) [...]
and PNAS, 108, January 2011 [...]

• contact: michael.berg@eawag.ch | more information

Arsenic contaminated groundwater and drinking water in the Red River Delta of northern Vietnam

We have found arsenic concentrations above the Vietnam Standard of 50 ug/L in groundwater samples collected in 1998 in the frame of a heavy metal screening conducted in the Hanoi area of Northern Vietnam.

The Red River delta in Vietnam is one of the most densely populated regions in the world. In 1998 the arsenic problem in Vietnam was identified in the capital city of Hanoi and surrounding rural districts and has since been recognized in other locations of the Red River delta [see Berg et al. 2001 and Winkel et al. 2011]. To identify safe and unsafe areas over the entire Red River delta, a large-scale hydrogeochemical groundwater survey was launched in 2005. It included the analysis of arsenic, manganese, selenium, boron, iron, salinity, phosphate, ammonium, sulfate, dissolved organic carbon, and 30 further chemical parameters. Concentration maps and arsenic risk modeling suggest that several million inhabitants of the Red River delta are at risk of chronic arsenic and/or manganese poisoning.

Read more about our hydrochemical studies and arsenic risk modeling of the Red River delta, Vietnam [...]

• contact: michael.berg@eawag.ch | more information

Arsenic Contamination in the Mekong Delta (Cambodia and Southern Vietnam)

Arsenic contamination of groundwater was also identified in Cambodia, where millions of rural families have installed tube-wells for daily water needs. Initially we conducted a survey comprising 124 groundwater samples in the rural floodplain south of the Cambodian capital Phnom Penh (sampling density ≈1 sample per 30 km2). Besides As, Fe, and Mn, a set of 27 parameters was determined and analysed with respect to redox processes leading to the release of groundwater contaminants.

Arsenic concentrations varied from 1–1340 µg L-1 (average 163 µg L-1), with 48% of the tube-wells exceeding 10 µg L-1. Elevated Mn levels are posing an additional health threat to the 1.2 million people living in this area.

The occurrence of high As concentrations was found to be sharply restricted to the close vicinity of the Bassac and Mekong River banks and the alluvium braided by these rivers (Kandal Province). Arsenic in this highly affected area averaged at 232 µg L-1 (median 100 µg L-1), while concentrations to the west and east of the rivers were < 10 µg L-1 (WHO guideline drinking value). Arsenic release from Holocene sediments between the Mekong and Bassac Rivers seems to be caused by reductive dissolution of metal oxides, and, to a lesser degree enhanced by pH values ≥ 7. Low groundwater arsenic concentrations are associated with topography featuring gently increasing elevation to the west and east of a shallow valley.

Detailed information on our studies on groundwater and drinking water quality of the Mekong delta and related health risks can be found in our publications [...]