Effect of Toxic Metal Ions on Photosensitized Singlet Oxygen Generation for Photodegradation of Polyaromatic Hydrocarbon Derivatives and Inactivation of Escherichia coli.

Here, we report an experimental study of the effect of toxic metal ions on photosensitized singlet oxygen generation for photodegradation of PAH derivatives, Anthracene-9,10-dipropionic acid disodium salt (ADPA) and 1,5-dihydroxynapthalene (DHN) and photoinactivation of Escherichia coli bacteria by using cationic meso-tetra(N-methyl-4-pyridyl)porphine tetrachloride (TMPyP) as a singlet oxygen photosensitizer. Three s-block metals ions, such as Na , K and Ca and five toxic metals such as Cd , Cu , Hg , Zn and Pb were studied. The s-block metal ions showed no change in the rate of photodegradation of ADPA or DHN by TMPyP, whereas a dramatic change in the photodegradation of ADPA and DHN was observed in the presence of toxic metals. The maximum photodegradation rate constants of ADPA and DHN were observed for Cd ions [(3.91 ± 0.20) × 10 s and (7.18 ± 0.35) × 10 s , respectively]. Strikingly, the photodegradation of ADPA and DHN was almost completely inhibited in the presence of Hg ions and Cu ions. A complete inhibition of growth of E. coli was observed upon visible light irradiation of E. coli solutions with TMPyP and toxic metal ions particularly, Cd , Hg , Zn and Pb ions, except for Cu ions where a significantly slow inhibition of E. coli's growth was observed.