Polycyclic aromatic hydrocarbons or (PAHs) are persistent environmental pollutants with known harmful effects on biological organisms. While some PAHs are directly toxic and carcinogenic, exposure to ultraviolet (UV) light can increase the toxicity of some of these compounds since they can generate reactive oxygen species (ROS) upon photon activation. ROS in turn causes oxidative damage to biomolecules including nucleic acids present within cells and tissues. A few studies have examined the effects of halides on PAH photodegradation in the aqueous phase with varying results but the chemistry of PAH phototoxicity in the environment is not yet fully understood. Therefore, more knowledge is needed. This dissertation describes the effects of high ionic strength conditions on four polycyclic aromatic dyes based on: naphthalene, anthracene, and pyrene in the presence and absence of DNA. The effects of NaCl and KCl salts on ROS production and DNA photocleavage yields at salt concentrations similar to those found in the cell nucleus and seawater are also considered. The goal is to determine whether or not photosensitized ROS production by PAHs can be stimulated by the redox inactive chloride salts. Our findings may help explain why certain PAHs are phototoxic to living organisms, especially those in marine environments.