ABSTRACT
This chapter describes some of the methodology used in comparing the effects of O2 exposure specifically with the more complex set of processes in photosensitization. "Specific" quenchers are often used in biological investigations as a first approximation of the mechanism of photosensitized toxicity. Intracellular O2, then, represents the more critical source in assessing O2-mediated damage, although not necessarily in determining potential photosensitized cytotoxicity. Singlet oxygen itself failed to exert direct genotoxic effects, although secondary reactants produced by its reaction with cell components enhanced lethality in some repair-deficient bacteria. Maintaining the sensitizer in dry form typically prohibits charge-transfer reactions with diffusible species such as O2, although with sensitizers that self-quench efficiently it also may be necessary to reduce the sensitizer concentration to ensure rigorous inhibition of charge-transfer processes. Photosensitization by dissolved organic matter can be used as a model for extracellular generation in surface waters.
