Investigation of the Potential UV-A Enhanced Toxicity and the Potential Inhibition of Catalase by Phthalate Exposed to UV-A

Solar Water Disinfection (SODIS) is a simple process used in developing countries to improve the quality of bacteria-contaminated drinking water. A previous study found that phthalate, an aromatic compound released by polyethylene terephthalate (PET) bottles upon UV-A irradiation, enhanced the germicidal activity of SODIS. In the current study, two possible mechanisms behind this observation were examined: phthalate toxicity to bacteria and phthalate inhibition of catalase activity. The potential toxicity was studied by: 1) observing changes in growth rate in a 90-minute time course study in which irradiated and non-irradiated phthalate were added to Escherichia coli B23 cultures and 2) examining growth inhibition around phthalate saturated filter disks on E. coli B23 lawns. Since no differences in bacterial growth were observed between the control and the phthalate conditions, these experiments suggested that neither irradiated nor non-irradiated phthalate is toxic to E. coli. A third experiment tested the proposed inhibition of catalase by using a simple catalase assay. It was found that without UV-A irradiation, phthalate had no effect on catalase. In the presence of UV-A, when phthalate was at the same concentration as catalase (50 μg/mL), a protective effect on the enzyme was observed. However, at a concentration of 0.4 μg/L, the typical amount of phthalate released in a PET bottle, no protective effect was observed. Neither of the mechanisms proposed in this study proved to be the cause behind phthalate-enhanced germicidal activit of SODIS. y