Generation of SO 3−and OH radicals in SO 32− reactions with inorganic environmental pollutants and its implications to SO 32−toxicity

Abstract

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 (SO 3 2−) with inorganic environmental pollutants. The spin trap used was 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Incubation of SO 3 2− with nitrite (NO 2 −) generated sulfur trioxide anion radical (SO 3 −), whose yield approached saturation levels in approximately four minutes. Fe 2+ promoted SO 3 − 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, CrO 4 2−, VO 2 +, Fe 3+, Mn 2+, Ni 2+, and Fe 2+ enhanced SO 3 − generation from SO 3 2− either through direct SO 3 2− oxidation by metal ions or by metal ions-catalyzed SO 3 2− oxidation by molecular oxygen. Incubation of SO 3 2− with H 2O 2 generated both SO 3 −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 SO 3 2− with H 2O 2 caused 2′-deoxyguanine hydroxylation to generate 8-hydroxy-2′-deoxyguanine, a DNA damage marker. The implications of SO 3 − and OH radical formation in relation to SO 3 2− toxicity are discussed.