Effect of irradiance spectra on the photoinduced toxicity of three polycyclic aromatic hydrocarbons

Photoinduced toxicity of polycyclic aromatic hydrocarbons (PAHs) is depende nt on the concentration of compounds present and the dose of light received . Of the light present, only those wavelengths absorbed by the compound hav e the potential to initiate the photochemical events underlying phototoxici ty. This suggests that variation in light spectra present in natural waters , arising from variation in dissolved organic carbon composition, is an imp ortant determinant of phototoxicity risk in specific, PAH-contaminated wate rbodies. To quantify the effect of environmentally realistic variation in l ight spectra on toxicity, brine shrimp (Artemia salina) assays were conduct ed under various light spectra and with three PAHs (pyrene, fluoranthene, a nd anthracene) of known phototoxicity potential. In these spectral assays, the total ultraviolet light present was equivalent; only the spectral chara cteristics varied. Based on the absorbance spectra of these PAHs, it was pr edicted that toxicity, quantified using immobilization as the endpoint, wou ld vary significantly among light spectra in pyrene assays, but not in anth racene assays, and that variation in toxicity in fluoranthene assays would be intermediate. The results supported these assumptions. In the pyrene exp osures, the glass filter time to 50% population immobilization (IT50) (39.5 min) was 117% longer than the KCr Biter IT50 (18.2 min). In the fluoranthe ne exposures, the glass filter IT50 (49.5 min) was 27% longer than the KCr filter IT50 (39.1 min). In the anthracene exposures, the glass filter IT50 (62.2 min) was not statistically different from the KCr filter IT50 (63.8 m in). Comparison of these results with the results of assays conducted under neutral-density filters (that change intensity but not spectral distributi on) demonstrate that multiplying spectral intensity by wavelength-specific absorbance accurately predicts relative photoinduced toxicity among the exp erimental treatments. These results indicate that quantifying the spectral characteristics of PAH-contaminated aquatic environments may he an importan t component of risk assessment at these sites.