Myrna Simpson

Academic Title: Associate Professor

Phone: 416-287-7234

Office: SY322

Email:

Research Homepage: http://www.utsc.utoronto.ca/~msimpson/

Research Interests

My research applies advanced and conventional analytical methods to understand environmental and geochemical processes. We mostly use solid- and liquid-state NMR to: characterize natural organic matter from sediments, soils, freshwater and marine environments, examine contaminant-interactions with organic matter, and develop environmental "fingerprints", known as biomarkers, for the study of organic matter cycling and biogeochemistry. Current projects in the group are:

• Sorption of organic contaminants in soil and sedimentary environments

The sorption of problematic organic contaminants to soil and sedimentary organic matter often hinders the bioavailability and clean-up attempts. The mechanisms of contaminant sorption to organic matter are poorly understood and are investigated by combining conventional methods (equilibrium sorption and isotherm modeling) with NMR characterization of organic matter. By applying NMR, we have identified mobile organic matter domains that have a large capacity to sequester contaminants. Furthermore, using a special NMR technique (High resolution magic angle spinning NMR), we are able to examine organic matter at the solid-liquid interface. These experiments have also revealed that aliphatic structures, such as those from plant cuticles, predominate at the surface. Aromatic structures, which are visible in 1-D NMR experiments, appear to be buried and not at the surface of soil colloids. 

• Organic matter interactions with mineral surfaces

Soils and sediments are predominantly composed of minerals but very rarely, do researchers consider how clay mineral surfaces regulate the distribution of organic matter structures at the solid-water interface. The distribution of organic matter at the solid-water interface governs most environmental reactions, but has not been studied in detail. We study organic matter sorption to common soil minerals and apply NMR spectroscopy, along with conventional soil chemical methods, to increase our comprehension of environmental interfaces. Once the physical conformation of organic matter is understood, other environmental processes, such as contaminant sequestration, can be elucidated. 

• Improving biomarker methods for evaluating terrestrial carbon cycling

A significant portion of the earth's carbon is tied up in the terrestrial environment. However, it is unclear as to how much is in a recalcitrant form and how long it resides in the soil before it moves into a different part of the carbon cycle. We apply multidimensional NMR to examine structures that can be used as "fingerprints" or biomarkers to identify different components from plants, animals or from anthropogenic influences (soot and charcoal). The structures identified by NMR are confirmed by mass spectrometric methods. Once new biomarkers are identified, then accurate estimates of refractory carbon in soils and sediments can be made such that global carbon accounting can be improved. 

• Kelleher, B.P., S. F. Oppenheimer, F. X. Han, K. O. Willeford, M. J. Simpson, A. J. Simpson, W. L. Kingery. 2003. Dynamical Systems and Phase Plane Analysis of Protease-Clay Interactions. Langmuir. 19: 9411-9417.
• Simpson, M. J., B. Chefetz, A. P. Deshmukh, and P. G. Hatcher.  Comparison of polycyclic aromatic hydrocarbon distribution and sedimentary organic matter structure in near-shore contaminated sediments from Pensacola Bay, Florida. Marine Environmental Research ( in press ).
• Simpson, M. J., A. J. Simpson, and P. G. Hatcher.  Non-covalent associations between hydrophobic organic contaminants and dissolved organic material observed by NMR. Environmental Toxicology and Chemistry.( in press )
• Simpson, M. J., B. Chefetz, and P. G. Hatcher. 2003 Phenanthrene sorption to structurally modified humic acids.  Journal of Environmental Quality 32:1750-1759.
• Fedorak, P. M., D. I. Coy, M. J. Dudas, M. J. Simpson, A. J. Renneberg, and M. D. MacKinnon.  2003.  Microbially-mediated changes in chemical and physical properties of oil sand tailings. Journal of Environmental Engineering and Science. 2:199-211.
• Gunasekara, A. S., M. J. Simpson, and B, Xing. 2003. Identification and Characterization of Sorption Domains in Soil Organic Matter Using Structurally Modified Humic Acids.  Environmental Science and Technology 37:852-858.
• Simpson (Salloum), M. J., B. Chefetz, and P. G. Hatcher.  2002.  Phenanthrene sorption by aliphatic-rich natural organic matter.  Environmental Science and Technology   36:1953-1958.
• Simpson (Salloum), M. J., M. J. Dudas, and W. B. McGill.  2001.  Variation of 1-naphthol sorption with organic matter fractionation: the role of physical conformation.  Organic Geochemistry . 32:709-719.