Effect of tryptophan and phthalate on the germicidal activity of ultraviolet-A radiation in solar water disinfection

A major contributor to disease in developing countries is the lack of clean drinking water. Solar water disinfection is a popular method used in such countries and involves elimination of pathogenic bacteria from contaminated water. SODIS requires the storage of contaminated water in clear plastic bottles and exposing the bottles to sunlight for several days. Sunlight contains mainly ultraviolet-A radiation, which has long been known to damage deoxyribonucleic acid and generate formation of reactive oxygen species, making it a popular tool for killing bacteria. Storage in clear plastic bottles ensures the contaminated water is not continuously exposed to bacteria and that sunlight can pass through and kill the bacteria contained within. It has been observed that trace amounts of aromatic compounds, polyethlylene terephthalate, are released from plastic bottles into the water. This suggests that aromatic compounds could play a role in either assisting or interfering with the efficiency of SODIS. In our study, we performed SODIS on contaminated water within PET bottles, with and without the addition of aromatic compounds, tryptophan and phthalate. Due to their ability to react with ROS, aromatic compounds have been speculated to induce quenching of these ROS, leading to a decrease in SODIS efficiency. Surprisingly, the addition of aromatic compounds resulted in a more rapid decline in bacterial survival. Our results suggested that aromatic compounds could enhance the germicidal effects of ROS.