Highly phototoxic polycyclic aromatic hydrocarbons (PAHs) are hazardous to the environment and biological organisms. They mediate their phototoxic effects through the generation of reactive oxygen species (ROS) which occurs upon absorption of ultra-violet light. The ROS in turn can oxidize biomolecules including nucleic acids leading to cellular and tissue damage. While a few studies have examined the effects of halide salts on the photodegradation kinetics of PAHs in the aqueous phase, the chemistry of PAH phototoxicity in the environment is not yet fully understood and therefore, more knowledge is needed. This report describes the consequences of high ionic strength on positively charged, water soluble naphthalene, anthracene, and pyrene dyes in the presence and absence of DNA. Fluorescence assays using hydroxyphenyl fluorescein (HPF), a specific ROS detecting probe, indicate that higher amounts of ROS are photosensitized by all three dyes in the presence of high concentrations of the redox inactive salts NaCl and KCl. Dye photodegradation studies conducted via UV-Visible spectroscopy also suggest that these chloride salts can enhance the ROS levels generated by the three dyes. The increases in ROS are consistent with the higher photo-induced DNA cleavage yields that can be seen only in the presence of the NaCl and KCl salts. Thus, our findings may help explain why certain PAHs are phototoxic to living organisms under physiological, high ionic strength conditions.

Photosensitized reactive oxygen species and DNA cleavage generated by polycyclic aromatic hydrocarbons based on naphthalene, anthracene, and pyrene: Chloride salt effects

ACS Spring 2022

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