Expanding the Understanding of Environmentally Persistent Free Radicals and Their Influence on Toxicity Using Model Clays and Real-World Soils

Environmentally persistent free radicals (EPFRs) are an organic—transition metal complex, typically associated with combustion processes, that have emerged as a pollutant of interest in recent years due to their associated health risks, and ability to participate in further reactions, generating additional toxic compounds. EPFRS have been proven to react further, producing reactive oxygen species (ROS), highly reactive oxygen-centered radicals, as well as dioxins and furans. In environmental conditions, EPFRs can be generated in the soil due to interactions between transition metals and organic matter. To study environmental formation at an elementary level, cation-exchanged montmorillonite clay treated with phenol was used, with a primary focus on zinc-loaded clay. Using electron paramagnetic resonance (EPR) for detection, EPFR concentrations on the order of 1017 were formed only under high temperature conditions, providing a unique case where phenol can be loaded at room temperature without radical formation. This allows for investigation of the role each component of the EPFR complex plays on ROS generation. The influence of the EPFR complex on ROS generation is observed through spin trapping experiments using 5,5-Dimethyl-1-Pyrroline-N-Oxide (DMPO). Use of the spin-trap allows for EPR detection of the typically short-lifetime ROS radical. Spin-trapping experiments carried out in a number of complex media, including simulated human lung fluid, show significant increases in ROS generation from the zinc samples containing EPFRs. In addition to model-clay systems, this dissertation work also studied real-world soils collected near contamination sources in Colfax, LA. and East Palestine, OH. Concentrations of target contaminants were measured at both locations providing insight into the potential health risks impacting the surrounding communities. These real-world samplings provided access to a spread of organic radical g-values, allowing for studies investigating the influence of radical identity on ROS generation. These vi experiments showed results indicating that oxygen-centered radicals are more ROS generative, as well as furthering the understanding about EPFRs in the g-value range 2.0030-2.0040. This presented dissertation work applied fundamental experimentation to both laboratory and real-world systems to study the mechanistic formation of EPFRs, the related toxicity, and the potential impacts these contaminants could have on affected communities.