Tellurium (Te) is a toxic element that tends to be very rare in most rock and soil, but is concentrated in Te mines, certain gold mines, and certain types of mine waste.  Te in rock and soil is found in solid form, but it may be transformed by oxidation reactions into soluble, mobile forms which have much greater environmental impact.  These forms may, in turn, be transformed back into immobile, less harmful, solid forms by reduction reactions.  Te geochemistry is not very well studied, and thus fundamental studies are needed to improve scientific understand that will, in turn, improve management and remediation of tellurium-contaminated sites.  Te is heavily used in one type of solar photovoltaic panel and in other industrial applications that may greatly increase.   It is considered a critical mineral resource, and both mining and contamination are likely to increase.  The geochemical processes that create Te ore deposits are not well understood.  

This project was an initial, one-year exploratory effort to develop measurements of the stable isotopes of Te (¹³⁰Te/¹²⁶Te ratios) as a new method to improve understanding of Te geochemistry.  Changes in the relative abundances of the heavy and light isotopes, as captured by changes in the ¹³⁰Te/¹²⁶Te ratio, occur in response to certain chemical reactions.  Measurement of the ratios in soils and/or sediments can be used to track those reactions (most importantly reduction), which are critically important in certain geoscience studies.

The intellectual merit of this project lies in addressing a few key feasibility issues.  First, the project demonstrated that ¹³⁰Te/¹²⁶Te measurements on a variety of soil and sediment samples can be made precisely (0.09 per mil uncertainty) while consuming less than 10 nanograms of Te per measurement (this is an important achievement, as Te concentrations in some samples are very low).  Second, the project revealed that adsorption of dissolved Te onto solid materials found in soils induces a significant ¹³⁰Te/¹²⁶Te shift of up to 0.6 per mil.  This is important basic information that will aid in the interpretation of ¹³⁰Te/¹²⁶Te measurements.  Third, measurement of modern soil and sediment samples revealed a range of 1.2 per mil, suggesting that reduction of Te in modern natural settings can be tracked using the measurements.    Finally, measurements of ancient sediments and soils suggest a shift in the chemical behavior of Te in response to the rise of oxygen in the earth system:  Samples representing the early earth show little variation, whereas samples from later time periods reveal greater variation.  This change coincides with a well-known increase of oxygen in the earth's system about 2.3 billion years ago that had profound impacts on the evolution of life.  This confirms a working hypothesis:  Te isotopes indicate when conditions became oxidized enough to initiate oxidation and reduction cycles of Te on earth.  This suggests that Te isotope measurements should be useful in ongoing studies of the earth's oxygenation history.

The project has broader impacts beyond the focused questions described above.  It generated new basic knowledge about Te isotopes that is essential to their development as a new geochemical tool that can be applied more widely.  For example, Te is currently considered a critical mineral resource, and Te isotope measurements may provide new information about ore formation processes. Also, new isotope methods like the one developed here are being employed by archaeologists to study metal sources in ancient societies.

Also in the realm of broader impacts, the project contributed to the development of human capital and a more diverse scientific workforce.  The Ph.D. student who carried out most of the work is becoming one of the world's experts in the development of new stable isotope methods; she also works on the development of antimony and selenium isotope methods.  Furthermore, she has been trained broadly in environmental geochemistry.  The project also allowed her to develop project design and project leadership skills, and to develop the ability to attain very challenging technical development objectives independently.  The project also helped her recruit an African-American undergraduate student to work in the research group for two years and complete a senior thesis in environmental geochemistry.  This student's science career was greatly enhanced by his research experience, and he has continued in a geoscience career.

Last Modified: 02/15/2020
Modified by: Thomas M Johnson