Superfund Research Program
Activation, Sensing, and Prevention of Formation EPFRs in Thermal Treatment of Superfund Wastes
Project Summary (2020-2025)
Thermal treatment (TT) of hazardous waste, including Superfund site wastes and soils, leads to the formation of environmentally persistent free radicals (EPFRs) associated with emitted particulate matter (PM). Many metals such as copper, iron, zinc, or nickel present in PM form EPFRs with varying yields and different degrees of stabilization and persistency. Such EPFR entities were shown to be a potentially primary factor causing the observed cardiopulmonary health effects in exposed populations. The researchers’ studies of model systems containing particles with single metal speciation and associated EPFRs have allowed for significant advancement in understanding the formation mechanism of EPFRs as well as the respiratory and cardiac health effects resulting from EPFR exposure. The central hypothesis of this project is that the formation of EPFRs, their biological activation, and their propensity to produce hydroxyl radicals is defined by the constituents of associated particulate matter (PM) and the physico-chemical properties of the media (media pH, ionic strength, and polarity). The researchers are investigating whether changes to the associated PM or media can accelerate or prevent EPFR activation. Major scientific questions explored by the project include:
- How does the persistent EPFR in ambient air transform to very active, redox cycling species in biological systems?
- Can the reactivity of EPFRs be exploited to prevent or control EPFR formation and their detection?
This project takes a systematic approach to addressing these questions, starting with defining the mechanism by which EPFRs transition from persistent radicals to reactive species generating hydroxyl radicals (i.e., activation). A bottom-up approach is used in the studies; results obtained from laboratory-made samples with simple composition are compared and evaluated against more complex combustion-generated EPFRs and, finally, field-collected EPFRs. Capitalizing on the results from previous studies, the researchers propose a method for EPFR prevention formation to be studied in detail. This method is based on the "in situ" deactivation of the metal centers in TT facilities, thus effectively blocking the EPFR emissions. The field sensor development is based on EPFR propensity to generate hydroxyl radicals and is based on the visible light absorption by sensory solution. The results of these studies will provide a basis for technology development to control the emission of EPFRs during TT of Superfund site materials and to develop devices for simple and fast detection and measurement of EPFRs in the field.