Detection of environmentally persistent free radicals at a superfund wood treating site.

Abstract

Environmentally persistent free radicals (EPFRs) have previously been observed in association with combustion-generated particles and airborne PM(2.5) (particulate matter, d < 2.5um). The purpose of this study was to determine if similar radicals were present in soils and sediments at Superfund sites. The site was a former wood treating facility containing pentachlorophenol (PCP) as a major contaminant. Both contaminated and noncontaminated (just outside the contaminated area) soil samples were collected. The samples were subjected to the conventional humic substances (HS) extraction procedure. Electron paramagnetic resonance (EPR) spectroscopy was used to measure the EPFR concentrations and determine their structure for each sample fraction. Analyses revealed a ∼30× higher EPFR concentration in the PCP contaminated soils (20.2 × 10(17) spins/g) than in the noncontaminated soil (0.7 × 10(17) spins/g). Almost 90% of the EPFR signal originated from the minerals/clays/humins fraction. GC-MS analyses revealed ∼6500 ppm of PCP in the contaminated soil samples and none detected in the background samples. Inductively coupled plasma-atomic emission spectrophotometry (ICP-AES) analyses revealed ∼7× higher concentrations of redox-active transition metals, in the contaminated soils than the noncontaminated soil. Vapor phase and liquid phase dosing of the clays/minerals/humins fraction of the soil with PCP resulted in an EPR signal identical to that observed in the contaminated soil, strongly suggesting the observed EPFR is pentachlorophenoxyl radical. Chemisorption and electron transfer from PCP to transition metals and other electron sinks in the soil are proposed to be responsible for EPFR formation.