Acute-to-chronic ratios of aquatic phototoxicity of polycyclic aromatic hydrocarbons and the prediction of chronic phototoxicity using the phototoxic target lipid model.

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds that can be toxic to aquatic life at environmentally relevant concentrations. The toxicity of some PAHs increases in the presence of ultraviolet radiation (UVR). The phototoxic target lipid model (PTLM) builds on the narcotic target lipid model and predicts acute phototoxicity by accounting for the light absorbed by PAHs. Given the lack of chronic data for PAHs exposed to UVR, an acute-to-chronic ratio (ACR) was proposed as a means for extending this model for predicting chronic toxicity. No information could be found on ACRs derived for phototoxic chemicals and therefore, this study had two objectives: (a) to generate acute and chronic toxicity data with and without exposure to UVR; and (b) to test the ability of the PTLM to predict chronic toxicity using an ACR. Acute and chronic bioassays were conducted on eight species, with each exposed to three PAHs and two light treatments: with and without UVR. Although there was a general trend of higher ACRs in UVR treatments, there was no statistical difference across all species in the ACR values for UVR treatments. Data generated herein were combined with data collated through a literature search to generate a global ACR of 11.6. Twenty of the 24 predicted phototoxic effect concentration affecting 10% of species (EC10) values calculated using the PTLM and ACR were within a factor of 10 of the observed phototoxic EC10 or lethal concentration affecting 5% of species values. This study demonstrates the capability of ACR to be applied in the context of phototoxicity and therefore proposes an unprecedented methodology to predict the chronic phototoxicity of PAHs.