Photoenhanced transformation of nicotine in aquatic environments: Involvement of naturally occurring radical sources.
Résumé
This work investigated the fate of nicotine (Nico) in aqueous solution upon reaction with singlet oxygen (1O2) and hydroxyl radical (HOradical dot). The second-order rate constants of Nico with 1O2 (View the MathML sourcekNico,O21 = (3.38 ± 0.14) × 106 M−1 s−1) and HOradical dot (kNico,radical dotOH = (1.08 ± 0.10) × 109 M−1 s−1) were determined using competition kinetics. Photochemical modelling showed that the reaction of Nico with HOradical dot would prevail over that with 1O2 in surface waters transformation pathway. The Nico photochemical half-life time could be accounted for by the two reactions. This value would vary in the month-year range depending on the environmental conditions: phototransformation would be favoured in shallow water poor in organic matter and rich in nitrate and nitrite. Irradiation experiments of Nico with nitrite suggested that transformation could not be accounted for by HOradical dot reaction alone. Indeed, a variable fraction of Nico transformation (30–80% depending on the conditions) would take place upon reaction with additional transients, photogenerated NOx being possible candidates. The chemical structures of the transformation intermediates were derived by means of HPLC-MS. The detection of nitroderivatives upon irradiation of Nico with nitrite suggests the involvement of nitrogen dioxide in the relevant photoprocesses.