Reactivity at (nano)particle-water interfaces, redox processes, and arsenic transport in the environment

Massive deleterious impacts to human health are resulting from the use of arsenic-bearing groundwaters in South-East Asia deltas and elsewhere in the world for drinking, cooking and/or irrigation. In Bangladesh alone, a fifth of all deaths are linked to arsenicosis. In the natural and engineered subsurface environment, the fate of arsenic is, to a large extent, controlled by redox potential, pH, as well as total iron, sulfur and carbonate content, via sorption and coprecipitation on a variety of natural and engineered (nano)particles. In the present article, we address: (1) new insights in the sorption mechanisms of As on Fe(II) and Fe(III) nanophases recognized to play an important role in the microbial cycling of As and Fe; (2) artifacts often encountered in field and laboratory studies of As speciation due to the extreme redox sensitivity of the Fe-As-O-H phases; and (3) as a conclusion, the implications for water treatment. Indeed the specific reactivity of nanoparticles accounts not only for the As bioavailability within soils and aquifers, but also opens new avenues in water treatment.