Arsenic (As) contamination of the groundwater in the Mekong Delta is a serious problem affecting millions of people who rely on this important resource for drinking and agriculture. In this study, borehole cores up to a depth of 40 m were collected in the Vietnamese-side of the delta and the solid-phase partitioning of As with depth was investigated to understand the factors and processes controlling its release under oxic, acidic and reducing conditions. The results showed that in most of the sediments, substantial amounts of As are partitioned with exchangeable phases that are easily released into solution. Two borehole cores obtained between the Hau and Tien Rivers also had significantly high As partitioned with organic/sulfide phases and one of these cores had abundant As-bearing pyrite in 1-m thick peat layers. Leaching experiments in deionized (DI) water coupled with principal component analysis suggest that As release is controlled by sorption-desorption reactions with clays/phyllosilicates (i.e., kaolinite, muscovite and clinochlore), proton-promoted dissolution of iron-oxyhydroxides, and oxidation of pyrite/organic matter. The release of As was further promoted under acidic conditions in the presence of chloride (Cl⁻), which suggests that seasonal drying/flooding episodes generating acid sulfate soils, as well as salt water intrusion due to excessive groundwater abstraction may exacerbate this problem in the future.

湄公河三角洲地下水的砷污染是一个严重的问题，影响了数以百万计依赖这种重要资源进行饮酒和农业生产的人们。在这项研究中，在三角洲的越南一侧收集了一个深度最大为40 m的钻孔岩心，并研究了As在深度上的固相分配，以了解在有氧，酸性和还原性条件下控制其释放的因素和过程。情况。结果表明，在大多数沉积物中，大量的As被可交换的相分配，这些相易于释放到溶液中。在Hau和Tien河之间获得的两个钻孔岩心也具有显着较高的As，并被有机/硫化物相分隔，并且其中一个岩心在1 m厚的泥炭层中具有丰富的含As黄铁矿。去离子（DI）水中的浸出实验以及主成分分析表明，As的释放是通过与粘土/页硅酸盐（即高岭石，白云母和斜绿石）的吸附-解吸反应，质子促进的铁-羟基氧化物的溶解和氧化来控制的。黄铁矿/有机物。在酸性条件下，在氯化物（Cl⁻），这表明季节性干燥/泛滥事件会产生酸性硫酸盐土壤，以及由于过度抽取地下水而导致的盐水入侵，可能会在将来加剧这一问题。