Understanding the influence of environmentally persistent free radical location on reactive oxygen species generation in soils

Environmentally persistent free radicals (EPFRs) are an emerging class of environmental contaminants commonly associated with combustion processes. These free radicals have been connected to a number of adverse health effects. This work aims to analyze soil samples collected at two field locations that recently experienced major combustion activity: Colfax, LA. and East Palestine, OH., for the presence of EPFRs. In Colfax, the last commercially-operated open-burn/open-detonation hazardous waste treatment facility in the country, was permitted to operate for nearly forty years. The East Palestine sample location was the site of the 2023 Norfolk Southern train derailment. Findings from these analyses show the presence of multi-radical systems in these soils with varying concentrations in Colfax (8.17x1015 – 4.39x1016 spins/g) and East Palestine (4.00x1016 – 5.56x1017 spins/g). All soil samples measured in this work had observable radical concentrations. These soil samples were further analyzed using spin-trapping experiments to explore the influence of EPFR organic radical characteristics on reactive oxygen species (ROS) generation. Findings from these experiments support our hypothesis that oxygen-centered EPFRs generate ROS at a higher rate than carbon-centered radicals with more oxygen-centered samples exhibiting a nine-fold increase in normalized ROS generation. Additionally, the results of the spin-trapping experiments provide further insight into the characterization of EPFRs with organic radical g-values of 2.0030-2.0040. This work provides real-world support to laboratory experimentation and marks a novel application of these techniques on field-collected soil samples from locations in which thermal remediation (TR) has taken place.