Characterisation of organic matter and microbial communities in contrasting arsenic-rich Holocene and arsenic-poor Pleistocene aquifers, Red River Delta, Vietnam

► First lipid analysis of Pleistocene aquifer sediments from a groundwater As-prone region. ► No difference in lipids between (As-rich) Holocene and (As-poor) Pleistocene aquifers. ► Lack of in situ microbially mediated As mobilisation in any of the sediments. ► Groundwater As at depth controlled by As mobilisation processes elsewhere.