A new analytical method employed by researchers at the University of Delaware, USA, can follow, on the millisecond timescale, what happens as environmental contaminants such as arsenic begin to react with soil and water under various conditions. Quantifying the initial rates of such reactions is essential for modelling how contaminants are transported in the environment and predicting risks.

The method, based on quick-scanning X-ray absorption spectroscopy (Q-XAS), was developed by a research team led by Donald Sparks and published in Proceedings of the National Academy of Sciences (doi: 10.1073/pnas.0908186106). It was developed using beamline X18B at the National Synchrotron Light Source at Brookhaven National Laboratory in Upton, NY, USA.

“This method is a significant advance in elucidating mechanisms of important geochemical processes, and is the first application, at millisecond time scales, to determine in real-time, the molecular scale reactions at the mineral/water interface. It has tremendous applications to many important environmental processes including sorption, redox, and precipitation,” Sparks said.

For their study, the UD researchers made millisecond measurements of the oxidation rate of arsenic by hydrous manganese oxide, which is a mineral that absorbs heavy metals and nutrients. The toxicity and availability of arsenic to living organisms depends on its oxidation state. For example, arsenite [As(III)] is more mobile and toxic than its oxidised counterpart, arsenate [As(V)].