Generation of SO3.- and OH radicals in SO3(2-) reactions with inorganic environmental pollutants and its implications to SO3(2-) toxicity.

Electron spin resonance (ESR) spin trapping and high performance liquid chromatography (HPLC) with electron chemical detection were utilized to investigate the generation of free radicals in reactions of sulfite (SO3(2-)) with inorganic environmental pollutants. The spin trap used was 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Incubation of SO3(2-) with nitrite (NO2-) generated sulfur trioxide anion radical (SO3.-), whose yield approached saturation levels in approximately four minutes. Fe2+ promoted SO3.- formation. Molecular oxygen was required for radical generation. This was demonstrated by experiments carried out in an argon environment as well as by oxygen consumption measurements. Transition metal ions, CrO4(2-), VO2+, Fe3+, Mn2+, Ni2+, and Fe2+ enhanced SO3.- generation from SO3(2-) either through direct SO3(2-) oxidation by metal ions or by metal ions-catalyzed SO3(2-) oxidation by molecular oxygen. Incubation of SO3(2-) with H2O2 generated both SO3.- and .OH radicals as verified by spin trapping competition measurements using ethanol and formate as .OH radical scavengers. HPLC measurements showed that .OH radicals generated by reaction of SO3(2-) with H2O2 caused 2'-deoxyguanine hydroxylation to generate 8-hydroxy-2'-deoxyguanine, a DNA damage marker. The implications of SO3.- and .OH radical formation in relation to SO3(2-) toxicity are discussed.