The formation of singlet oxygen in surface waters

The photochemical formation of singlet oxygen in some Dutch surface waters has been investigated using the method developed by Zepp (1). However, when monitoring the consumption of oxygen beside that of 2,5-dimethylfuran (DMF), the compound added to chemically snare singlet oxygen, it was found that appreciable, but varying parts of DMF were used up by secondary reactions leading largely to the same products, viz. cis- and trans-diacetylethylene. When taking the oxygen consumption as a measure for the singlet oxygen production on the basis of the stoichiometry of the primary reaction, a fair correlation between the singlet oxygen production and the total organic carbon (TOC) content was found for this selection of Dutch surface water samples. The steady-state concentrations of singlet oxygen determined in this way were about one order of magnitude lower than those found by Zepp (1) and by Zafiriou (2).