Hydroxyl radical induced degradation of salicylates in aerated aqueous solution

• In OH induced reactions of salicylates first products are hydroxylated derivatives.
• With prolonged irradiation dihydroxy derivatives also form.
• In aerated solutions the one-electron oxidant OH induces 3–4 oxidations.
• Toxicity first increases and then decreases with dose mainly due to H2O2 formation.
• The toxicity in tap water is smaller than in pure water.

Ionizing radiation induced degradation of acetylsalicylic acid, its hydrolysis product salicylic acid and a salicylic acid derivative 5-sulpho-salicylic acid, was investigated in dilute aqueous solutions by UV–vis spectrophotometry, HPLC separation and diode-array or MS/MS detection, chemical oxygen demand, total organic carbon content and by Vibrio fischeri toxicity measurements. Hydroxyl radicals were shown to degrade these molecules readily, and first degradation products were hydroxylated derivatives in all cases. Due to the by-products, among them hydrogen peroxide, the toxicity first increased and then decreased with the absorbed dose. With prolonged irradiation complete mineralization was achieved.