Geochemistry and arsenic behaviour in groundwater resources of the Pannonian Basin (Hungary and Romania)

Elevated As levels in the Pannonian Basin are mainly present in very old (Palaeo) groundwater of methanogenic Pliocene/Quaternary aquifers, which is in contrast to Asian regions where arsenic-enriched groundwater is generally much younger. [Display omitted] ► Arsenic originates from Late Pliocene/Quaternary aquifers and some very old waters. ► Arsenic levels are controlled by both mobilisation and retention mechanisms. ► Mobilisation is caused by biogeochemical reductive dissolution. ► Sufficient sulfate supply triggers arsenic retention in sulfide precipitates. ► Nearly 500,000 people are exposed to elevated arsenic in their drinking water. Groundwater resources in the Pannonian Basin (Hungary, Romania, Croatia and Serbia) are known to contain elevated naturally occurring As. Published estimates suggest nearly 500,000 people are exposed to levels greater than the EU maximum admissible concentration of 10 μg/L in their drinking water, making it the largest area so affected in Europe. In this study, a variety of groundwaters were collected from Romania and Hungary to elucidate the general geochemistry and identify processes controlling As behaviour. Concentrations ranged from