Illuminating whole effluent toxicity testing: ultraviolet radiation, phototoxicity, and PAH-contaminated groundwater

In this study, the acute toxicity of polycyclic aromatic hydrocarbon (PAH) - contaminated groundwater to Daphnia magna and Pimephales promelas were characterized under both ambient laboratory lighting and ambient laboratory lighting supplemented with ultraviolet radiation (UVR) using USEPA Whole Effluent Toxicity (WET) test methods. Research has shown the toxicity of some PAHs to aquatic organisms increases significantly in the presence of sunlight or artificial UVR, a phenomenon known as photoactivated toxicity or phototoxicity. Based on these findings, the discharge of PAH-contaminated groundwater to surface waters may be a phototoxic hazard to aquatic organisms. Since WET tests are frequently employed to evaluate the hazards of environmental media, they may provide a standardized means to characterize the toxicity of PAH-contaminants when sunlight is present. However, despite the known interaction of UVR with PAHs, WET protocols do not require the presence of UVR during testing. Under these protocols, the USEPA recommends the use of ambient laboratory lighting (10-20 μE/m2/s or 50-100 ft-c). No recommendations are made for: 1) light source spectral distribution; 2) spectral irradiance levels; 3) presence of UVR; or 4) dose of light over time. The results of 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. To evaluate the influence of lighting on groundwater toxicity, acute groundwater toxicity was characterized in this study under the following two light treatments: 1) ambient laboratory lighting; and 2) ambient laboratory lighting plus UVA (320-400 nm) and UVB (280-320 nm). The first treatment was designed to approximate WET test lighting recommendations. The second design was based on measurements of habitat-specific irradiance, and incorporated optical radiation characteristics (UVR) that were more representative of local solar conditions. Results show that the toxicity of PAH-contaminated groundwater increased significantly to D. magna under laboratory lighting supplemented with UVR. Although trends in the P. promelas results suggest greater groundwater toxicity occurred to P. promelas when UVR was present, these trends were not found to be statistically significant. Overall, the study demonstrates that: 1) PAHcontaminated field samples be phototoxic to aquatic organisms; 2) WET testing conditions can induce phototoxicity when laboratory lighting is supplemented with UVR; 3) WET tests can be used to measure the magnitude of acute phototoxic effects; and 4) current WET lighting recommendations can lead to underestimation of sample hazard when phototoxic contaminants are present. The central implication of this study is that WET test estimation of sample toxicity may be improved in some cases by incorporating habitat-specific solar characteristics into current WET testing methodology. Moreover, since this study demonstrates that WET tests can be used to evaluate phototoxic hazards, WET testing methodology may represent a more consistent approach to phototoxicity testing for phototoxicity researchers than what is currently represented in the phototoxicity literature.