Release of arsenic during riverbank filtration under anoxic conditions linked to grain size of riverbed sediments

• Published in: The Science of the total environment 2023-11, Vol.900, p.165858-165858, Article 165858
• Main Authors: Covatti, Gustavo, Hoang, Thi Ngoc Anh, Grischek, Thomas
• Format: Article
• Language: English
• Subjects: Groundwater hydrochemistry; Red River; Redox reactions; Riverbed; Vietnam; Well management
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2023.165858

Geogenic arsenic contamination of groundwater poses a health threat to millions of people worldwide, particularly in Asia. Riverbank filtration (RBF) is a pre-treatment technique that aims to improve surface water quality through natural processes during water infiltration before abstraction. A study in Hanoi, Vietnam is presented, where the water quality of 48 RBF wells from 5 large well fields located in the Pleistocene aquifer along the Red River was analyzed. >80 % of the wells had arsenic concentrations above the WHO limit of 10 μg/l. The riverbed sediment and riverbed pore-water from 23 sites along a stretch of 30 km of the Red River near the well fields was also analyzed. Muddy riverbeds were found to be a hotspot for arsenic release. Already at a 30 cm depth from the riverbed sediment surface, the pore-water at many sites had high concentrations of arsenic (>100 μg/l). Arsenic concentrations in the pore-water of sites where mud lenses were present in the riverbed were significantly higher compared to sites with sandy riverbeds. At well fields along stretches of the Red River where riverbed was mostly muddy, higher arsenic concentrations were found than at well fields where the riverbed was mostly sandy. This indicates that river muds deposition and river morphology can influence arsenic concentrations in the aquifer in Hanoi and potentially other RBF sites in regions with geogenic arsenic contamination. At the end, recommendations regarding site selection of new potential RBF wells in affected regions is given. [Display omitted] •84 % of the 48 investigated wells in Hanoi had As concentrations higher than 10 μg/l.•As in the wells positively correlated with NH4+, Mg2+ and HCO3− concentrations.•High As concentrations found in the riverbed pore-water of the Red River (>100 μg/l).•Muddy riverbeds proposed as one of the sources of As to RBF wells in Hanoi.•Wells along river stretches where the riverbed was muddy had higher As concentrations.