Visible Light Induced Photodegradation and Phototoxicity of Phloxine B and Uranine

Key words: 
• Phloxine B /
• Uranine /
• Photodegradation /
• Saccharomyces cerevisiae /
• Phototoxicity /
• TOC

Abstract: Objective To determine the visible light-induced photodegradation kinetics of two xanthene photosensitizers, phloxine B and uranine, in solution and on the surface of silica TLC plates, and to examine the phototoxicity of residues of degradation, which could provide valuable safety data on the two photosensitizers and other xanthene chemicals when applied in the environment. Methods UV-Vis absorption during hotodegradation was monitored with a Unico 2102 spectrophotometer. Organic content of samples was measured with a Shimadzu TOC 4100. Phototoxicity tests were carded out using Saccharomyces cerevisiae with the methods modified from Daniels. Results When phloxine B and uranine degraded in solution, their apparent rate constant k was 0.0019 and 0.0027 min-1, respectively. The total organic carbon (TOC) content decreased by approximately 50% during the 8 h irradiation period, which led to a gradual decrease in phototoxicity of the residues. The photodegradation of photosensitizers on the surface of silica TLC plates was much faster than that in the solution. The apparent rate constant k and the half life of phloxine B were 0.0073 min-1 and 95 min, respectively. Conclusion Visible light can rapidly induce photodegradation of phloxine B and ranine. The phototoxicity of residues is also decreased. The environmental risk of applications of phloxine B and uranine is minimal.