Detection and characterization of environmentally persistent free radicals (EPFRs) in soils and sediments from superfund sites

Environmentally persistent free radicals (EPFRs) from combustion-generated PM have been demonstrated to form via reactions of molecular precursors with redox-active transition metals at 150-500C thermal reactions in a few seconds reaction times. While ambient temperatures are much lower, soils/sediments contain similar transition metals, and reaction times of contaminants in soils/sediments are years, rather than seconds. This questions whether EPFRs could be formed at ambient temperatures in soils/sediments from Superfund sites that are contaminated with hazardous materials. Superfund soils contaminated with PCP from Georgia and Montana, and sediments contaminated with PAHs from Washington. Using EPR spectroscopy, EPFR concentrations and structural assignments were determined. Contaminated soils/sediments were ~30x, ~12x, ~2x higher than the background at the Georgia, Montana, and Washington sites, respectively. Conventional humic substances extraction procedures revealed ~90% of the EPFRs originated from clays/minerals/humins fraction. Similarity of EPR signals in the Georgia and Montana PCP contaminated soils were observed (g = 2.00300 and ΔHp-p = 6.0 G), whereas, signals in the Washington sediments were similar to other PAH contaminated soils (g = 2.00270 and ΔHp-p = 9.0G). Several methods of analyses (Total Carbon Content, GC-MS, ICP-AES, Vapor and gas/liquid phase dosing) confirm pentachlorophenoxyl EPFR. Chemisorption and electron transfer from PCP or PAHs to transition metals and other electron sinks in soil are indicated for EPFRs formation. Low temperature thermal treatment of PCP contaminated soil in an open type heating system indicated the formation of a more oxygen-centered structure of the pentachlorophenoxyl radical or new, similar radicals. Both type of heating system, open and closed, demonstrated an EPFR concentrations that peaked at ~10 x 10E+18 spins/g of soil at ~75-100C, with lifetimes of 2 – 24 days at room temperature in ambient air indicating persistency in the environment. Discovery of EPFRs formed in PCP contaminated soils indicates that EPFRs are not only confined to combustion-generated particles. Studies on EPFR similar to pentachlorophenoxyl cause cardiopulmonary dysfunctions via induction of oxidative stress. The existence of potentially toxic EPFRs questions the long held belief that sorption of an organic pollutant to a soil matrix is a method of mitigating its environmental impact