Boron and strontium isotopic characterization of coal combustion residuals: validation of new environmental tracers.



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In the U.S., coal fired power plants produce over 136 million tons of coal combustion residuals (CCRs) annually. CCRs are enriched in toxic elements, and their leachates can have significant impacts on water quality. Here we report the boron and strontium isotopic ratios of leaching experiments on CCRs from a variety of coal sources (Appalachian, Illinois, and Powder River Basins). CCR leachates had a mostly negative δ(11)B, ranging from -17.6 to +6.3‰, and (87)Sr/(86)Sr ranging from 0.70975 to 0.71251. Additionally, we utilized these isotopic ratios for tracing CCR contaminants in different environments: (1) the 2008 Tennessee Valley Authority (TVA) coal ash spill affected waters; (2) CCR effluents from power plants in Tennessee and North Carolina; (3) lakes and rivers affected by CCR effluents in North Carolina; and (4) porewater extracted from sediments in lakes affected by CCRs. The boron isotopes measured in these environments had a distinctive negative δ(11)B signature relative to background waters. In contrast (87)Sr/(86)Sr ratios in CCRs were not always exclusively different from background, limiting their use as a CCR tracer. This investigation demonstrates the validity of the combined geochemical and isotopic approach as a unique and practical identification method for delineating and evaluating the environmental impact of CCRs.





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Ruhl, Laura S, Gary S Dwyer, Heileen Hsu-Kim, James C Hower and Avner Vengosh (2014). Boron and strontium isotopic characterization of coal combustion residuals: validation of new environmental tracers. Environ Sci Technol, 48(24). pp. 14790–14798. 10.1021/es503746v Retrieved from

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Heileen Hsu-Kim

Professor in the Department of Civil and Environmental Engineering

Professor Heileen (Helen) Hsu-Kim is an environmental engineer who specializes in environmental aquatic chemistry and geochemistry. Her research tackles problems related to pollutant metals and the biogeochemical processes that alter their distribution in water, soil, and air. The applications of this work include environmental remediation technologies, the impacts of energy production on water resources, global environmental health, and the environmental implications and applications of nanotechnology.

Dr. Hsu-Kim's current research projects are focused on mercury biogeochemistry, the impacts of coal ash disposal on water quality, recovering valuable materials from geological wastes, and health impacts of trace metal/metalloid exposures. A central theme to her work is the utilization of chemical speciation for understanding and predicting the persistence, mobility and bioavailability of metals and minerals in the aquatic environment.

The methodologies her group employs for this research include laboratory techniques for quantifying trace element speciation, functional measures of reactivity and bioavailability of contaminant metals, and techniques to probe interactions at mineral, water and microbial interfaces.


Avner Vengosh

Nicholas Distinguished Professor of Environmental Quality

Avner Vengosh is a Distinguished Professor and Nicholas Chair of Environmental Quality at the Nicholas School of the Environment. He is the chair of the Division of  Earth and Climate Sciences. Professor Vengosh and his team have studied the energy-water nexus, conducting pioneer research on the impact of hydraulic fracturing and coal ash disposal on the quantity and quality of water resources in the U.S. and China. He has also investigated the sources and mechanisms of water contamination in numerous countries across the globe, including salinity and radioactivity in the Middle East, uranium in India, fluoride in Eastern Africa, arsenic in Vietnam, and hexavalent chromium in North Carolina and China. As part of these studies, his team has developed novel geochemical and isotopic tracers that are used as fingerprints to delineate the sources of water contamination and evaluate potential risks for human health. Currently, his team is engaged in studying phosphate rocks geochemistry and the impact of fertilizers on soil and water quality, unconventional sources of critical raw materials, and potential environmental effects of lithium mining from hard rocks and brines. He is a Fellow of the Geological Society of America (GSA) and International Association of Geochemistry (IAGC). In 2019, 2020 and 2021 he was recognized as one of the Web of Science Highly Cited Researchers. He serves as an Editor of GeoHealth and on the editorial board of the journal Environmental Science and Technology. He has published 171 scientific papers in leading international journals. His recent cross-disciplinary book “Water Quality Impacts of the Energy-Water Nexus” (Cambridge University Press, 2020) provides an integrated assessment of the different scientific and policy tools around the energy-water nexus. It focuses on how water use, and wastewater and waste solids produced from fossil fuel energy production affect water quality and quantity. Summarizing cutting edge research, the book describes the scientific methods for detecting contamination sources in the context of policy and regulations.

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