Reactive photoinduced species in estuarine waters. Characterization of hydroxyl radical, singlet oxygen and dissolved organic matter triplet state in natural oxidation processes

Abstract

This paper describes the reactive photo-induced species (RPS) hydroxyl radical (HO˙), singlet oxygen (¹O₂) and chromophoric dissolved organic matter triplet state (³CDOM*) in fresh water (Canal Fumemorte) and estuarine water (Vaccarès), sampled in the Camargue region, southern France. Experiments were conducted with a medium-pressure Hg lamp in a glass photoreactor (λ > 290 nm, 220 W m⁻² irradiance between 290 and 400 nm). Steady-state concentration and initial production rate of RPS were determined for HO˙ and for ¹O₂. HO˙ and ¹O₂ were indirectly identified in the presence of benzene and furfuryl alcohol, respectively, as specific probes. The steady-state measured concentration of HO˙was (1.72 ± 0.01) × 10⁻¹⁶ M and (9.41 ± 0.12)×10⁻¹⁷ M for Vaccarès and Canal waters samples, respectively, and the respective concentrations of ¹O₂ was (2.06 ± 0.22) × 10⁻¹³ M and (5.44 ± 0.04) × 10⁻¹⁴ M. The interference of ³CDOM* or other species in the determination of ¹O₂ with furfuryl alcohol, and of ¹O₂ in the quantification of ³CDOM* with 2,4,6-trimethylphenol was also quantitatively assessed. We developed a kinetic model describing the solar photo-transformation of xenobiotic organic compounds induced by the three different photooxidants HO˙, ¹O₂ and ³CDOM*.