Photosensitized transformations involving electronic energy transfer in natural waters: role of humic substances

The kinetics of photosensitized reactions involving the transfer of absorbed light energy from humic substances to trace organic compounds (pentadiene and dimethylfuran) in water were investigated in the laboratory. The photosensitized reactions of the pollutants occurred through energy transfer from molecules in their triplet states . Pollutants with triplet state energies less than 250 kJ per mol could participate in these photoreactions; such chemicals included most aromatic compounds with two or more fused aromatic rings, nitro-aromatic compounds, and chemicals with conjugated double bonds, such as diketones and polyenes. The rates of the humus-sensitized reactions depended strongly on di-oxygen concentration. The reactions occurring did not involve binding of the substrate by the humus. The data obtained were used to estimate the maximal rates of reactions photosensitized by humic substances.