Johnson Research Group: Environmental Geochemistry and Isotope Geochemistry

NEWS:  I am looking for new Ph.D. or M.S. students to join the group in Fall, 2020.  If you are a talented geoscientist or chemist looking for exciting opportunities in geochemistry and environmental geology, read below and contact Tom Johnson (tmjohnsn@illinois.edu) to discuss potential areas of interest!  Graduates of the group work as Professors, environmental consultants, and few other areas- see the Group Members page for details.

The Johnson group is working to better understand the geochemical behavior of several redox-sensitive contaminant elements, including chromium, selenium, uranium, antimony, tellurium, and mercury.  The toxicity, bioavailability, and geochemical cycling of each of these elements depends on valence state; information about redox reactions is very valuable in managing the environmental impact in contaminated settings or understanding geochemical behavior in natural settings.

The stable isotopes of chromium, selenium, uranium, antimony, tellurium, mercury and other redox-sensitive elements often shift in abundance when redox reactions occur, and thus they often provide a record of past redox reactions.  For example, increases in the 53Cr/52Cr isotope ratio in groundwater can be used to track transformation of toxic, mobile hexavalent chromium to the immobile, non-toxic trivalent state- obviously an important reaction!  The isotope ratios may also be useful as tracers of contamination source.

Chromium isotopes have proved to be useful in many contaminated settings.  For information about how to obtain and use chromium isotope data, follow this link.

The group also applies these stable isotope techniques to explore the redox history of the Earth. The shift from an O2-free early atmosphere to the O2-rich conditions of the Phanerozoic was driven by the rise of photosynthesis and other biological changes, but also profoundly influenced biological evolution.  Chromium, uranium, and selenium isotope measurements provide insights into when and how these redox changes took place.

Other interests include  tellurium and antimony isotopes, and strontium isotope ratios as archaeological tracers.


The group uses the department’s multicollector ICP-MS laboratory constantly to make these measurements and often develops or improves measurement methods.

The Lundstrom and Johnson groups in the isotope lab