Electron spin resonance (ESR) analysis at room temperature of the particles produced during the aerobic pyrolysis of perfluoro polymers (PFP) shows the presence of end-chain peroxyl radicals. These radicals, which would normally have lifetimes of several seconds at most, are stabilized by being immobilized in the particles and decay at a rate of about 20%/day. Normally, radicals with this stability would not be expected to be reactive; however, these peroxyl radicals react with 3-chloropropene, with iodine in benzene, with methyl linoleate in methanol, and with aqueous liposomes from soy phosphatidylcholine. Also, stable radicals of this sort would not be expected to give spin adducts; however, when the particles are suspended in a benzene solution containing alpha-phenyl-N-tert-butylnitrone (PBN), they react to give the same series of spin adducts that are detected when the unfiltered smoke from the oxidative pyrolysis of perfluoro polymers is bubbled directly into PBN solutions. This appears to be the first report of the reaction of radicals entrapped in a solid with a spin trap. The nitroxide species produced by the PBN-particle reaction include a fluorine atom spin adduct, an oxy radical adduct, and benzoyl tert-butyl nitroxide (PBNOx), the oxidation product of the spin trap; all of these appear to arise from reaction of the particle-bound peroxyl radicals with the spin trap. Because the particles are in the highly respirable range (down to 0.01 micron), these entrapped peroxyl radicals may be carried deep within the lung when fumes from PFP pyrolysis are inhaled and would be expected to place an oxidative burden on the lung.(ABSTRACT TRUNCATED AT 250 WORDS)