A predictive quantitative structure-activity relationship model for the photoinduced toxicity of polycyclic aromatic hydrocarbons to Daphnia magna with the use of factors for photosensitization and photomodification

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants that readily absorb environmentally relevant solar ultraviolet radiation. On absorption of a photon, photoinduced toxicity of PAHs is manifested through photosensitization and photomodification. Both of these processes occur under environmentally relevant levels of actinic radiation. An empirical quantitative structure-activity relationship model previously developed was explanatory of photoinduced toxicity of 16 PAHs in Lemna gibba (duckweed). This model was found to be predictive of toxicity to Vibrio fischeri. The L. gibba quantitative structure-activity relationship showed that a photosensitization factor and a photomodification factor could be combined to describe photoinduced toxicity. To further examine this model, we assessed whether it could be applied to Daphnia magna (water flea), a key bioindicator species in aquatic ecosystems. Toxicity was assessed as median effective concentration and median effective time for immobility. As with L. gibba and V. fischeri, neither the photosensitization factor nor the photomodification factor alone correlated to toxicity in D. magna. However, a photosensitization factor modified for D. magna exhibited a correlation to toxicity (r(2) = 0.86), which was modestly improved when summed with a modified photomodification factor (r(2) = 0.92). The greatest correlation was observed with median effective concentration data. This research provides evidence that models incorporating factors for photosensitization and photomodification have interspecies applicability.