Role of oxygen in sunlight induced photodegradation of organophosphorous flame retardants in river waters

Abstract

The persistence of organophosphorous flame retardants (OPFR) on the aquatic environment has motivated the study of their degradation processes in superficial water, particularly the sunlight induced photodegradation mechanisms. A recent study showed that some of these substances, with a low capacity for solar radiation absorption, became surprisingly photodegraded. Indirect photolysis promoted by the photosensitizer properties of this micropollutants constitutes a suitable explanation for this phenomenon. The objective of this project was to investigate the photodegradation indirect mechanisms of OPFR in superficial water, in which singlet oxygen (1O2) appeared to develop an important role. By means of two different procedures, chemical probe photobleaching and spin-trapping experiments, the specific aim was the detection and identification of this species in the reaction medium. Although photobleaching procedures applied to monitor reactions involving singlet oxygen have been widely used, the reported experimental conditions are quite different from the ones required to observe OPFR photosensitizing effects. Thus, several assays were carried out in first place in order to adapt the experimental settings. In spite of that, results did not shown clear evidences about the generation of singlet oxygen during the experiments, regardless of the chemical probe employed. The great competence for singlet oxygen, stablished in the reaction medium, seems to minimize the concentration of this species in there, thus making difficult its detection. For their part, spin-trapping procedures demonstrated to be useful to reliably detect and identify the singlet oxygen molecules generated along the process. Because of its high sensitivity to excited structures, this method allows to effectively detect the presence of 1O2, even when this species is present at very low concentrations in the bulk solution