Environmental context. The presence of high arsenic concentrations in South and South-east Asian groundwater causes dramatic health issues for the local population. As a consequence, scientists, governments and agencies investigate arsenic-related health issues and arsenic origin, fate and behaviour in ground- and drinking water and have started to provide remediation and mitigation strategies. This review broadly summarises our current knowledge on arsenic biogeochemistry, health and socio-economic effects, remediation and risk predications in Asia and discusses current and future research directions.

Environmental context. Understanding how arsenic is changed from toxic to non-toxic chemical forms in lakes and rivers is important in understanding the overall risk from arsenic. Freshwater plankton exposed in laboratory cultures to different sources of toxic inorganic arsenate formed arsenosugars, but at higher exposure levels, in water and through contaminated sediment, inorganic arsenate remained unchanged. In arsenic-contaminated freshwater bodies, plankton may provide a source of toxic inorganic arsenic to consumers.

Environmental context. Arsenic-rich waters generated from the oxidation of mining wastes are responsible for the severe contamination of river waters and sediments located downstream from mining sites. Under certain environmental conditions, the affected riverbed sediments may represent a reservoir for arsenic from which this toxic element may be released into water, mainly as a consequence of microbial activity.

Environmental context. Arsenic is one of the most common contaminants at US Superfund sites; therefore, establishing techniques to accelerate As remediation could benefit many sites. In a pilot scale study, we determined that addition of oxalic acid to the subsurface has the potential to increase arsenic release from sediments and possibly improve remediation efficiency by pump and treat techniques. Because pump and treat remediation can require many decades to sufficiently decrease contaminant levels, methods for improving remediation could lead to substantial savings in time and resources.

Environmental context. Tens of millions of people worldwide depend on groundwater with naturally high arsenic concentrations for drinking and cooking. We studied simple filters built with locally available and inexpensive iron nails, which can oxidise and bind arsenic in forming iron oxides and rust layers. Filters containing iron are being successfully applied in several regions, but efficiencies depend on the type of groundwater, and sufficiently large iron surfaces and contact times with water are needed for good arsenic removal.

Environmental context. Arsenic contamination of aquifers is a worldwide public health concern and several technologies have been developed to reduce the arsenic content of groundwater. We investigated the efficiency of various materials for arsenic removal from groundwater and found that iron-based sorbents have great affinity for arsenic even if groundwater composition can depress their ability to bind arsenic. Moreover, we showed that the use of microorganisms can enhance the removal of arsenic from groundwater.

Environmental context. Household sand filters are widely used in Vietnam to remove As, Fe and Mn from groundwater used as drinking water. From the solid-phase characterisation of a sand filter that has been used for 8 years, we conclude that As and Fe are retained by a combination of fast sorption reactions, surface-catalysed Fe oxidation and mediated As co-oxidation and that microbial processes are probably involved in effective Mn retention. This study contributes to a better mechanistic understanding of filter functioning as a basis for further improvements in filter design and operation.

Environmental context. Himalayan derived arsenic contaminates groundwater across Asia, ranging from the deltas of Ganges-Brahmaputra of Bangladesh to the interior basins of the Yangtze and Yellow Rivers in China, where more than one hundred million people are drinking water with hazardous levels of the toxin. Our ability to predict the distribution and changes in arsenic concentration in aquifers of affected regions has been limited. Here we provide a dynamic model that captures arsenic migration and can be used to forecast changes in groundwater arsenic concentrations.

Environmental context. Groundwater arsenic is a major environmental risk to human health in many regions of the world, including Cambodia where groundwater is often used for drinking water. We present data for hitherto poorly sampled regions in Cambodia, notably around Tonle Sap and in the coastal provinces, and provide a geo-statistical model of arsenic in shallow groundwater for the whole country.