Awarded to: Barbara Sherwood Lollar
View recipient's web page
Abstract: Quantification of Transformation and Transport Across Biogeochemical Boundaries by Multi-Element CSIA
Medal lecture in:
Session 13h in Room 4, Goldschmidt2020 - Virtual Venue on Wednesday 24th June 23:15 - 23:18

Citation: I take great pleasure that the Geochemical Society is honoring Professor Barbara Sherwood Lollar with the Clair C. Patterson Medal and Award. As graduate student I learned of the incredible science that Clair Patterson contributed to society and geochemistry. The debt we owe to those like Clair, Barbara, and others – who develop useful high-level science, execute it, and use it to reveal critical features of the environment we inhabit and point the way for change – is clear. Barbara has done this perfectly, her work not only lays the critical foundation of isotope effects but it uses this to develop applications of isotope (Compound Specific Isotope Analysis- CSIA) and to provide a guide and monitor for bioremediation of contaminated groundwater sites. She is a leader in the study of methane and alkane chemistry and of cycling of halogenated organics. She is also a role model for the community holding key appointments in our Societies and research community, allowing her to guide our directions in highly significant ways.
Professor Sherwood Lollar record includes an impressive collection of now classic foundational geochemical and isotopic studies that document abiogenic pathways of formation for methane and longer chain hydrocarbons and that link the formation of deep methane with hydrogen and deep abiotic chemistry. Her work demonstrates how relationships between isotopic ¹³C content and chain length of C1-C4 alkanes support abiogenic synthesis originating from methane and progressing to longer chain alkanes. Her work with others including Guiseppe Etiope and Ed Young, studies kinetic processes where activation barriers are overcome to form products with unique and potentially diagnostic isotope signatures reflective of rate enhancements for hydrogen that manifest in some of the rarest, doubly-substituted, methane isotopologs. The existence of striking isotopic signatures for methane with multiple isotopic substitutions ¹³CH₃D and ¹²CH₂D2 in these deep abiogenic methane sources will surely lead to novel ways to probe methane formation and to trace the sources of these gases extending deep into the silicate Earth. The work in CSIA is one in particular area where Prof. Sherwood Lollar’s contributions have brought useful science to bear on aspects of the environment that are relevant to us. Compound Specific Isotope Analysis of halogentated organic compounds, such as chlorinated alkenes (PCE, TCE, DCE, and ethylene chloride), alkanes and aromatics (including BTEX compounds) have had a monumental impact on organic environmental geochemistry and remediation practices for contaminated sites. The development of CSIA techniques applies the foundational research calibrating metabolic and abiotic kinetic isotope effects (KIE) to support novel field studies that document processes occurring in contaminated groundwater systems. The roots of this work are deep and have been shaped by her earlier studies on carbon isotope fractionations associated with microbial metabolic transformation of chloroethylene compounds as well as on more recent work examining other pathways that influence these same compounds and expand to other compounds such as the fuel additive MTBE, chlorinated alkanes and aromatics. These studies in sum, form a portfolio of environmental research contributions that fit the definition of useful, high-level science that help us address critical environmental issues.
Prof. Sherwood Lollar has made the point that isotope signatures are critical for understanding processes in nature. With CSIA she has demonstrated the power of isotopic information using examples and applications that solve problems uniquely and lay the groundwork for present and future applications of CSIA and with bioremediation. Her voice in the community has been strong, clear, and compelling when making the case for the value of CSIA approaches to tackle important environmental issues correctly and effectively. The approaches also point the way to methods for demonstrating the efficacy of remediation efforts and guide environmentally-relevant decisions in with a much greater level of certainty than was previously possible. An example of this that I particularly enjoyed learning about, examined the role of reductive dechlorination at the Dover Air Force Base.
To wrap up, Prof. Sherwood Lollar has shaped the field through her research. She is sought as a colleague and collaborator on a spectrum of scientific efforts of our community. Her contributions range from fundamental to applied, are useful, and motivate countless other studies. New applications of related techniques continue to develop from the foundation she has built and will inform understanding of critical environmental issues in groundwater chemistry and organic compounds in the foreseeable future. These broad contributions and are the reason we honor her with the Geochemical Society’s 2019 Clair C. Patterson Medal and Award.

James Farquhar – University of Maryland

Response: Thank you to the Geochemical Society, President Vickie Bennett and the Patterson Medal Selection Committee, and particularly to the colleagues who generously led this nomination. I am very pleased to accept this on behalf of the team of students, postdoctoral fellows and colleagues whose joint work and inspiration contributed to the research honored here. My University of Toronto colleague Dr. John Polanyi tells a wonderful story which I am sure we can all identify with. In his words “it is at these moments, looking out at one’s research team, that one sees a quizzical expression on their faces that must be akin to that on the face of the race horse - who having just successfully run the race - watches the cup being handed to the jockey”.
In all seriousness, it is with feelings of immense pride and privilege that I share this recognition of research in environmental geochemistry with the list of outstanding colleagues who have received the Patterson Medal since its inception. Clair Patterson represents a pinnacle of achievement in our community in so many ways. His work on uranium-lead and lead-lead dating provided, among other fundamental insights, one of the first accurate ages for the Earth. He pioneered work on escalating lead concentrations in the environment, atmosphere and the human body. His career demonstrates the arbitrariness of subdividing our discipline into supposed “low temperature and high temperature” or “soft rock and hard rock”. The list of past Patterson Medalists continues to reflect this vision of great minds working across the breadth of science, with contributions that inform processes that govern earth and planetary science systems and integrate discovery in geosciences, chemistry, biology physics, and more. Clair Patterson’s legacy of applying scientific discovery and data-based decision-making to enact change in society, influence public policy, and protect human health and the environment, resonates more today than ever.
We all stand on the shoulders of giants. I had the immense privilege of working as a young scientist with Dick Holland, Peter Fritz, and Keith O’Nions, and benefiting from more informal but invaluable early support from Chris Ballentine, Kate Freeman, Peggy Ostrom, Steve Macko, Ursula Franklin, Derek York, Michael Whiticar, Warren Wood, and others too numerous to mention. I had the pure good fortune to begin my own academic career at a time when the genius of John Hayes, Willi Brand, and others had translated their discoveries in continuous flow mass spectrometry to commercial instruments that young scientists such as myself could build a new generation of laboratories around. Their insight and work changed the fabric of environmental geochemistry for organic compounds. Continuous flow compound specific isotope analysis for the first time raised sensitivity by up to 5 orders of magnitude, thereby reducing sample size requirements to a level compatible with field investigations where groundwater samples might only be available in milli-liter volumes, and dissolved concentrations of priority pollutants therein are in the range of ppb-ppt. Prior to that time one “could” measure a carbon isotope value dissolved organic contaminants in an aquifer – but their instrumentation breakthroughs provided the first ability to measure at a spatial and temporal scale that was meaningful in the context of contaminant remediation.
The early 90’s were a time of blistering excitement as we seized this technological opportunity and began to explore compound specific isotope analysis, first for chlorinated solvents such as trichloroethylene and petroleum hydrocarbons such as benzene and toluene. These compounds, both man-made and natural, have globally impacted our lakes, groundwaters, and soils in both urban and rural settings as a direct result of society’s industrial expansion post-WWII. As many are carcinogens or mutagens, they are harmful even at trace levels. Hence, for organic contaminants such as these “dilution is not the solution”. The challenge was to find a way to scientifically differentiate environments where decreasing concentrations are in fact due to transformation to more benign end-products, and not simply due to dissemination and transport of contaminants, even at trace levels, further into the environment. Working on opposite sides of the ocean and in different laboratories, but always with a collegiality and openness to communication that reflects the highest levels of scientific collegiality, our own work and discoveries in this field at the University of Toronto emerged at the same time as work by Daniel Hunkeler, Hans-Hermann Richnow and Rainer Meckenstock. We were all inspired by the same scientific challenge:
How to make invisible in situ transformation reactions in the environment, visible?
Compound specific isotope analysis—first for carbon, but rapidly expanding to other major elements including hydrogen, chlorine, and nitrogen—provided that insight. Kinetic isotope effects associated with bond breakage provided not only a dramatic signal of transformation of contaminants, but a means of differentiating and identifying competing reaction mechanisms. A day I can remember vividly was our realization that in many cases the changes in isotopic values observed during contaminant transformation could be fit to a Rayleigh model. Surprisingly, despite the complexity and frequent occurrence of multiple steps involved in enzymatically catalyzed reactions, and despite the potential for masking effects in both biologically and chemical catalyzed transformation reaction, we found that isotope fractionation is often controlled by a single rate-limiting step. Understanding this fundamental basis controlling stable isotope fractionation involved in contaminant transformation therefore provided not only a new and sensitive signal of transformation and remediation, but a novel and independent quantification approach based on the Rayleigh model for establishing rates of clean-up and prediction of remediation end-points. These discoveries provided us with the honour and opportunity to work with and learn from colleagues in microbiology and in industry as CSIA provided a novel means of providing quantitative information on the levels of microbial enzymatic activity and rates of reaction controlling bioremediation. While conventional microbiological tools can identify “who is there” (the components of a microbial population and ecosystem), CSIA proved to be a powerful tool in the arsenal to identify “who is active” (i.e. what microbial processes are active and at what rates and levels of enzymatic activity). These isotopic principles provided vital information to evaluating and optimizing in situ bioremediation potential.
Compound specific isotope analysis is now a mature and global research discipline, continuing to extend applications to novel groups of contaminants including fuel additives, pesticides, and atmospheric greenhouse gases such as CFCs. We have been privileged to be part of that journey as the legacy of John Hayes and Willi Brand’s work has been built upon to establish the fundamental principles and applications for new “natural tracers”. The naturally occurring stable isotope signatures of dissolved organic contaminants in soils and groundwaters provide signals of unparalleled sensitivity, and an innovative means of establishing in situ reaction rates to the investigation of the transformation of hydrocarbon contaminants in groundwater and the environment (without the cost and regulatory hurdles of adding enriched labels or tracers). We are immensely grateful to the “intellectual venture capital” provided for these foundational studies in the early years by the Natural Sciences Engineering Research Council of Canada (NSERC), to ongoing support from industry partners and collaborators, and more recently to the CIFAR program in Earth 4D – Subsurface Science and Exploration.

Barbara Sherwood Lollar CC FRS FRSC FRCGS University of Toronto