For nearly 20 years, John Zachara led insightful and impactful research into the geochemistry, biochemistry, and environmental fate of technetium-99 (99Tc), a long-lived (half-life: 211,100 years), environmentally mobile contaminant in the subsurface at the U.S. Department of Energy’s (DOE’s) Hanford Site and other sites world-wide. John authored ~20 papers on technetium biogeochemistry, resulting in over 1,000 citations to date. John’s research ranged from 99Tc colloid genesis (and biogenesis) to stabilization of 99Tc in subsurface minerals. His work on 99Tc biogeochemistry not only informed the understanding of 99Tc redox chemistry in the environment, but it also provided mechanistic insights into biogeochemical redox reactions with minerals. John also advanced the use of X-ray absorption spectroscopy to probe 99Tc redox chemistry and chemical speciation to inform mechanistic reactive transport models. John’s insights into the mechanisms and kinetics of the reduction of pertechnetate, 99Tc(VII)O4-, by ferrous iron and metal-reducing bacteria (see figure below), particularly the role of unstable intermediates and the formation of nanoparticles, has informed similar investigations into the reduction and bioremediation of other metals and radionuclides, such as uranium.

200,000-year legacy: John Zachara’s technetium biogeochemistry research

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.