Education

B.S., 1984, Georgia College & State University
Ph.D., 1989, Emory University

Honors and Awards

National Academy of Engineering, 2024
Analytical Scientist Power List, 2023, 2021, 2019
Walter J. Weber, Jr. Association of Environmental Engineering and Science Professors (AEESP) Frontier in Research Award, 2021
Herty Medal, 2020
Southern Chemist Award (American Chemical Society), 2020
Fellow of the American Association for the Advancement of Sciences, 2019
Fellow of the American Chemical Society, 2016
American Chemical Society Award for Creative Advances in Environmental Science & Technology, 2008
Honorary Doctorate (Doctor of Letters, honoris causa), Cape Breton University, Sydney, Nova Scotia, Canada, 2006

Research

Environmental analytical chemistry; drinking water disinfection by-products (DBPs); emerging environmental contaminants; per- and poly-fluorinated alkyl substances (PFAS); total organic fluorine; microplastics; (N-(1,3-dimethylbutyl)-N-phenyl-p-phenylenediamine quinone (6-PPD-quinone); pharmaceuticals; impacts of algae on drinking water and human health; new analytical methods and technologies; novel technologies to remove emerging contaminants; mass spectrometry.

Introduction: My research is interdisciplinary (often combines chemistry, toxicology, and engineering) and focuses mostly on improving the safety of drinking water.  Recent work also includes development of new analytical methods and technologies to measure contaminants in the environment.  Examples include (1) Total Organic Fluorine (TOF) methods we created to allow a comprehensive assessment of PFAS in industrial wastewater, river water, and air; (2) Highly sensitive GC-MS(/MS) methods to quantify 72 DBPs in drinking water; (3) Vacuum assisted sorbent extraction (VASE)-GC-MS method to exhaustively extract DBPs from water and urine without solvent and measure them at part-per-trillion levels with only 10 mL of sample.  Mass spectrometry is one of the main tools we use in our research to identify new environmental contaminants and to quantify contaminants.

Background: Drinking water disinfection was a triumph of the 20th Century, allowing the prevention of many waterborne illnesses, however, an unintended consequence is the formation of DBPs in drinking water. Human epidemiologic studies show some adverse health effects from DBPs, yet the DBPs responsible for these effects are still not completely understood. DBPs are different from other traditional contaminants, being formed when disinfectants (e.g., chlorine, chloramines, ozone, and chlorine dioxide) react with naturally occurring organic matter, bromide, and iodide. They can also form through the reaction of disinfectants with anthropogenic contaminants, such as pharmaceuticals.  DBPs are generally found at >1000x higher levels in drinking water than other contaminants like PFAS. 
One of the most important studies of my career involved the discovery of “Forcing Factors” of toxicity in drinking water (Allen et al., 2022), where we discovered that haloacetonitrile and iodo-acid DBPs were the main drivers of toxicity in U.S. drinking waters.  In addition, we recently identified an entirely new class of DBPs:  halocyclopentadienes, which are toxic and predicted to be bioaccumulative (a “first” for DBPs) (Li et al., 2022). We also discovered that the use of iodized salt in cooking pasta can result in the formation of iodinated DBPs during cooking (Dong et al., 2023).  We also recently contributed to important discoveries for the impacts of algae on drinking water and human health, including the identification of natural algal metabolites that may be responsible for auto-immune issues, such as lupus and rheumatoid arthritis, as well as the discovery of 2-fold DBP concentrations and increased nitrogenous DBPs in drinking water when algae is present in water sources.  Finally, we also are interested in contaminants and DBPs in potable reuse (turning wastewater into drinking water), as this is becoming a major thrust with increasing populations and water scarcity.  To that end, we recently investigated DBP formation and toxicity of 7 important wastewater contaminants that are not well removed in wastewater treatment (17β-estradiol, estrone, 17α-ethinylestradiol, bisphenol A, diclofenac, p-nonylphenol, and triclosan) and identified DBPs formed by chlorination, including 28 not previously reported (Cochran et al., 2024).  The impact of chlorination was also evaluated in real samples from a potable reuse facility at different stages of treatment. 

Experimental approach: We use gas chromatography (GC)-mass spectrometry (MS) and liquid chromatography (LC)-MS/MS techniques to identify and measure DBPs and other transformation products in drinking water and wastewater. Mass spectrometry is an ideal analytical tool for measuring trace levels of compounds in complex environmental matrices, and we utilize several different ionization modes as well as high resolution-MS. We currently have 6 mass spectrometers in my laboratory and have access to several others in our department’s Mass Spectrometry Center. We are also using VASE with GC-MS to more comprehensively extract contaminants from water, as well as total organic halogen (TOX) analysis and ion chromatography. 

Current research: My current research continues to investigate DBPs, novel algal toxins from harmful algal blooms, and transformation of emerging contaminants during advanced oxidation treatment for water reuse, including a new UV/Cl2 treatment. We are also developing a new TOF method to analyze new PFAS-free fire-fighting foams.  In addition, we are using mass spectrometry to identify contaminants in real-world microplastics, assessing PFAS, TOF, and 6-PPD-quinone in the state of South Carolina (using new TOF methods created in our laboratory), and even participating in an archaeology study to identify biomarkers in traditional ceremonial drinks from indigenous people in Central America to help determine when residues of these are present in ancient pots discovered.  Finally, we are also developing new analytical methods to enable improved extraction and measurement of contaminants in complex matrices.

Selected Publications

Forster, A. L. B., T. C. Geiger, G. O. Pansari, P. T. Justen, and S. D. Richardson. Identifying PFAS Hotspots in Surface Waters of South Carolina Using a New Optimized Total Organic Fluorine Method and Target LC-MS/MS. Water Res. 2024, 256, 121570. https://doi.org/10.1016/j.watres.2024.121570.  

Justen, P. T., M. L. Kilpatrick, J. L. Soto, and S. D. Richardson. Low Parts Per Trillion Detection of Iodinated Disinfection By-Products in Drinking Water and Urine using Vacuum-Assisted Sorbent Extraction and GC-MS/MS. Environ. Sci. Technol. 2024, 58, 1321–1328. https://doi.org/10.1021/acs.est.3c07097.

Cochran, K. H., D. C. Westerman, C. C. Montagner, S. Coffin, L. Diaz, B. Fryer, G. Harraka, E. G. Xu, Y. Huang, D. Schlenk, D. D. Dionysiou, and S. D. Richardson. Chlorination of Emerging Contaminants for Application in Potable Wastewater Reuse: Disinfection By-Product Formation, Estrogen Activity, and Cytotoxicity. Environ. Sci. Technol. 2024, 58, 704–716. https://doi.org/10.1021/acs.est.3c05978.

Mitch, W.A., S. D. Richardson, X. R. Zhang, and M. Gonsior. High-Molecular-Weight By-Products of Chlorine Disinfection. Nature Water 2023, 1, 336–347. https://doi.org/10.1038/s44221-023-00064-x. (Invited).

Forster, A. L. B., Y. Zhang, D. C. Westerman, and S. D. Richardson. Improved Total Organic Fluorine Methods for More Comprehensive Measurement of PFAS in Industrial Wastewater, River Water, and Air.  Water Res. 2023, 235, 119859. https://doi.org/10.1016/j.watres.2023.119859.

Dong, H., I. D. Nordhorn, K. Lamann, D. C. Westerman, H. K. Liberatore, A. L. B. Forster, M. T. Aziz, and S. D. Richardson. Overlooked Iodo-Disinfection Byproduct Formation When Cooking Pasta with Iodized Table Salt. Environ. Sci. Technol. 2023, 57, 3538-3548. https://pubs.acs.org/doi/full/10.1021/acs.est.2c05234

Li, J., M. T. Aziz, C. O. Granger, and S. D. Richardson. Halocyclopentadienes: An Emerging Class of Toxic DBPs in Chlor(am)inated Drinking Water. Environ. Sci. Technol. 2022, 56, 11387–11397. https://doi: 10.1021/acs.est.2c02490

Allen, J. M., M. J. Plewa, E. D. Wagner, X. Wei, K. Bokenkamp, K. Hur, A. Jia, H. K. Liberatore, C.-F. T. Lee, R. Shirkhani, S. K. Krasner, and S. D. Richardson. Disinfection By-Product Drivers of Cytotoxicity in U.S. Drinking Water: Should Other DBPs Be Considered for Regulation? Environ. Sci. Technol. 2022, 56, 392−402. https://doi.org/10.1021/acs.est.1c07998