Environmental Context. Sulfur dioxide has long been known as a source of acidity in precipitation and of cloud condensation nuclei, but more recently it has been shown a source of radicals highly reactive with respect to various organic compounds. These radicals are formed as intermediates wherever sulfur dioxide, oxygen, and water come into contact, such as in a sulfur dioxide polluted environment (tropospheric clouds, surface waters, soil) and in living organisms (lungs, digestive tract). This work focusses on the destructive action of such intermediates upon organic compounds essential for life (such as enzymes and vitamins).

Abstract. The oxidation of sulfur dioxide in aqueous media by molecular oxygen is here exploited as a source of sulfoxy radical anions. Experimental evidence is given for the chemical interaction between these radical anions and bioorganic compounds: lysozyme (Lys), haemoglobin (Hb), and cyanocobalamin (vitamin B₁₂). Two opposite effects are described, one leading to the elimination of sulfoxy radical anions and the other resulting in multiplication of the radicals. The former effect is due to lysozyme and haemoglobin, which behave as sulfoxy radical scavengers, whereas the latter is caused by cyanocobalamin, which actively contributes to the formation of these radicals. Possible consequences of the effects for life are briefly discussed with a view to the noxious role of tropospheric sulfur dioxide.