Exposure of PAHs to solar radiation results in the generation of oxygenated products. Many of these oxyPAHs are more toxic and/or carcinogenic than the parent compounds. Environmental photomodification of PAHs could result in formation of toxic compounds not anticipated by regulatory agencies. We have confirmed the presence of oxyPAHs at toxic levels in sediment samples taken from a known contaminated site. Contaminated sediment samples were taken from Hamilton Harbour (Hamilton, Ontario). A reference site from the harbour, known to be free of contaminants was also analyzed. High performance liquid chromatography (HPLC) was used to fractionate, and analyze individual compounds present. Fractions were tested for toxicity using both short-term, and long-term assays on the bacterium Vibrio fischeri.OxyPAHs were found in sediments at concentrations comparable to intact PAHs. Testing confirmed toxicity in fractions containing oxyPAHs on the order of intact PAH-containing fractions. It is concluded that environmental photomodification of PAHs contributes to the presence of toxic compounds that are not properly addressed by current regulations in the U.S. and Canada.