Arsenic mobilisation is an important concern in many near-surface soil, sediment and groundwater systems. In such systems, microbial sulfate reduction often dominants anaerobic electron flow, producing aqueous sulfide and facilitating the formation of iron sulfide species. However, the effects of microbial sulfate reduction on arsenic mobility in near-surface environments are complex and difficult to predict. In this presentation, I describe recent discoveries illustrating how arsenic mobility is influenced by microbial sulfate reduction in near-surface environments. The approach has been to conduct (i) abiotic mono-mineralogical batch experiments¹, (ii) advective-flow column experiments² and (iii) anoxic incubation experiments with complex arsenic-contaminated floodplain soil. The results show that microbial sulfate reduction can have contradictory consequences for arsenic; either substantially retarding or greatly enhancing arsenic mobility. The ultimate outcome for arsenic mobility depends on multiple factors, including hydrological flow conditions, the presence or absence of elevated porewater sulfide concentrations, aqueous arsenic concentrations and reaction time. Given that sulfate reduction can both retard or enhance arsenic mobility, depending on environmental conditions, great caution must be exercised when aiming to exploit natural sulfur biogeochemistry as a strategy for mitigating arsenic mobility in near-surface environments.

References:

1.Burton et al., Environ. Sci. Technol. 2013, 47, 2221-2229.

2.Burton et al., Chem. Geol. 2013, 343, 12-24.