Where can we find clean drinking water? How can we remove excess carbon dioxide from the oceans? When can a contaminated site be declared clean? Molecular environmental scientists look for answers to big questions like these by zooming in on their smallest components: Chemical reactions taking place at the scale of molecules and atoms.

These reactions, along with processes such as evaporation and adsorption, determine how contaminants and nutrients move through soil, water and air. They’re often complex webs involving many chemical players. Understanding how all of this works may require elements of microbiology, chemistry, environmental engineering, geology and physics.

With a method called X-ray absorption spectroscopy at SLAC's Stanford Synchrotron Radiation Lightsource (SSRL), molecular environmental researchers get a direct look at the chemical processes that affect life on Earth.

X-rays are ideal for studying structures on the molecular scale, and by changing how the experiment is done, scientists can also switch to imaging larger-scale objects. SSRL also offers techniques for examining samples that contain many different chemical components and materials, have highly uneven surfaces or are diluted by water or soil.

In SLAC’s Subsurface Biogeochemistry Research Program, for instance, scientists study how nature handles contamination, in the hope of harnessing those natural processes to speed the cleanup of polluted sites. One such project is looking at natural bacteria that “eat” a reactive form of uranium and convert it to a more chemically stable form that is less likely to move into groundwater. Researchers brought back soil samples from a contaminated site near the Colorado River where uranium has been leaching out of abandoned mine tailings, and used SSRL’s X-ray beams to understand the complicated underlying chemical reactions.