Environmental Nuclear Magnetic Resonance
The main goal of our research is to understand the molecular workings that control the fate and impact of contaminants in the environment.
Our main tool for this is called Nuclear Magnetic Resonance, or NMR. This tool uses the interactions that occur between radio frequency radiation, magnetic fields, and atomic nuclei to peer into the ‘black box’ of complex environmental systems.
Using NMR we have looked at many environmental systems, including contaminant binding in soils, plant-contaminant interactions, contaminated groundwater, and the effect of contaminants in wastewater treatment bioreactors.
Natural Organic Matter
Natural Organic Matter, or NOM, is the product of the biotic and abiotic degradation of plant and microbial organic matter in the environment. NOM is ubiquitous is soil and aquatic environments and plays vital roles in the regulation of the health of these ecosystems. The structure of NOM is complex and varies temporally and geographically. Our research group is interested in the roles that NOM plays in the fate of contaminants and nutrients in soil and aquatic environments.
A typical solution-state 1H NMR spectrum of a Soil Organic Matter Extract (Left). NMR provides an unbiased fingerprint of the types of structures present and can be used to indicate the origin of the material as well as to predict the role that NOM may play in the environment.
Soil Fertility
The figure below show the solid-state 13C NMR spectra of humic acid extracted from the same type of soil that has been treated with different forms of swine manure. The differences between the spectra indicate the occurrence of different organic structures that may influence the role that the soil organic matter plays in the availability of key plant nutrients, such as phosphorus.
The photo above shows the growth of corn in soils amended with different types of organic amendments. The structure of the soil organic matter directly influences the availability of phosphorus by either outcompeting binding sites for phosphate on soil mineral surfaces or by interfering with the formation of stable phosphate minerals that would otherwise not be available. Management of phosphorus in agroecosystems is important for a number of reasons, including mitigating the impact of excess phorphorus run off on aquatic systems, particularly the great lakes, and because phosphorus is a finite resource that is vitally importance in crop production.
Contaminant-Soil Binding
One of the unique applications of NMR is its ability to probe the interactions between molecules by taking advantage of NMR’s ability to manipulate the magnetic interactions between atomic nuclei. At a general level, many common atomic nuclei possess magnetic dipole moments (Similar to how bar magnets have a N and S pole). In the same way that bar magnets have magnetic fields that other magnets will feel, atomic nuclei can also feel the magnetic fields of other atomic nuclei – if they are located close enough.
We have used to property to see how organofluorine compounds interact with soil organic matter by exploring how the fluorine nuclei (19F) of the organofluorine compounds talk to the hydrogen nuclei (1H) of the soil organic matter. Many organofluorine compounds, including the class of compounds known as perfluoroalkyl substances (PFAS), are both extremely persistent in the environment and ubiquitous in nearly every environment and organisms (including humans!) due to their widespread use in consumer products. Our research has shown that PFAS interacts with soil organic matter in a very different manner than other persistent organic compounds. Most notably is that perfluorooctanoic acid (PFOA) shows a strong preference for interactions at structures in the soil that have a protein-like nature.
We have used to property to see how organofluorine compounds interact with soil organic matter by exploring how the fluorine nuclei (19F) of the organofluorine compounds talk to the hydrogen nuclei (1H) of the soil organic matter. Many organofluorine compounds, including the class of compounds known as perfluoroalkyl substances (PFAS), are both extremely persistent in the environment and ubiquitous in nearly every environment and organisms (including humans!) due to their widespread use in consumer products. Our research has shown that PFAS interacts with soil organic matter in a very different manner than other persistent organic compounds. Most notably is that perfluorooctanoic acid (PFOA) shows a strong preference for interactions at structures in the soil that have a protein-like nature.
Environmental Metabolomics
Environmental metabolomics is the study of the changes in the occurrence of metabolites in an organism in response to an environmental stress.
Anaerobic Digestors
The spectra below are 2D 1H-1H Total Correlation Spectroscopy (TOCSY) NMR spectra of water from an anaerobic digester exposed to different concentrations of a common disinfectant. Anaerobic digesters are a key tool used to reduce the impact of food processing facilities that produce a lot of waste water. The role of the digester is to use anaerobic microbes to consume the organic compounds present in the water and convert them into methane gas that can then be used as fuel to produce energy. Disinfectants are common tools used in food processing facilities to maintain food security, however these disinfectants can disrupt the microbial processes at play in the anaerobic digesters. The spectra below show the emergence of different key microbial metabolites indicating disruption of the normal anerobic metabolic processes.
Plant Metabolomics
The 1H NMR spectrum shown below is produced from polar metabolites extracted from the leaves of Arabadopsis thaliana labelled with identified metabolites.
Legend: 1, isoleucine; 2, leucine; 3, valine; 4, threonine; 5, alanine; 6, arginine; 7, γ-aminobutyrate; 8, proline; 9, glutamate; 10, succinate; 11, glutamine; 12, citrate; 13, malate; 14, aspartate; 15, asparagine; 16, ethanolamine; 17, myo-inositol; 18, methanol; 19, sugar region; 20, ascorbate; 21, glucose; 22, maltose; 23, sucrose; 24, fumarate; 25, tyrosine; 26, tryptophan; 27, phenylalanine.
Complex data like this can be used to identify individual metabolites, or it can be used to identify variation in metabolite profiles in response different environmental stressors using tools such as principal component analysis. For example, PCA plots prepared from NMR spectra of Arabadopsis plants exposed to different concentrations of perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are shown below. These two compounds are persistent organic pollutants of significant concern. The PCA plots are used to identify variations in the metabolic profiles in response to these different contaminant exposures. These patterns can be used to identify the specific metabolic profiles being impacted by these exposures.
Principal component analysis (PCA) scores plots of leaf metabolite extracts of A. thaliana plants exposed to PFOA (left) and PFOS (right). Each point represents an extracted sample. Legend: Green, Control; Blue, 10 mg/kg; Orange, 50 mg/kg; Purple, 500 mg/kg.
Groundwater Contamination
Many current and former chemical manufacturing and processing facilities have soils and groundwater impacted by the occurrence of significant quantities of chemical contaminants. Given the diversity of chemical processes often in use over the life of these facilities, identifying the specific contaminants present is not always straightforward. Many contaminants present are unknown, either due to limited records or due to unknown degradation pathways. We are currently developing NMR spectroscopy as a non-targeted tool to help improve the characterization of these contaminants. NMR spectroscopy is able to provide detailed spectra of all key compounds present in contaminated groundwater and soil samples that allows for the unambiguous identification and quantification of structures for known contaminants, the information needed to identify unknown contaminants. We are also currently working on developing bench top NMR as a rapid tool for use in on-site mobile laboratories.
The figure below shows 2D NMR spectra of a Non-Aqueous Phase Liquid found at a contaminated site. This method was able to rapidly and unambiguously identify the key contaminants present at the site.
