The primary goal of this project was to determine if supplementing standard laboratory lighting with ultraviolet radiation (UVR) during Whole Effluent Toxicity (WET) tests could modify the toxicity of contaminated groundwater samples to aquatic organisms. Research has shown the toxicity of some polycyclic aromatic hydrocarbons (PAH) to aquatic organisms increases significantly in the presence of sunlight or artificial UVR, a phenomenon known as photoactivated toxicity or phototoxicity. WET tests are frequently employed to evaluate the hazards of surface water and provide a standardized means to characterize the toxicity of those waters; WET testing protocols can also be used for groundwater samples. Despite the known interaction of UVR with PAHs, however, WET test protocols do not require the presence of UVR during testing. The results of the phototoxicity studies suggest that the lack of specific guidance for lighting conditions may result in inaccurate estimates of in situ toxicity when photoactive PAHs are present and UVR is not specifically included in the laboratory lighting.