Effects of alkylation on potency of benz[a]anthracene for AhR2 transactivation in 9 species of freshwater fish.

Polycyclic aromatic hydrocarbons (PAHs) are naturally occurring or anthropogenic organic chemicals that can activate the aryl hydrocarbon receptor 2 (AhR2) and induce toxicity in fishes. Alkyl PAHs have been found to be more abundant than non-alkylated PAHs in certain environmental matrices and there is growing evidence that alkylation can increase potency, dependent on the position of alkylation. However, it is unknown if the effect of alkylation on potency is conserved across species. Additionally, relatively little is known regarding the extent of interspecies variation in sensitivity to PAHs and alkyl PAHs. Therefore, objectives of this study were to characterize potency of benz[a]anthracene (BAA) and three alkylated homologues representing different alkylation positions in nine phylogenetically diverse species of fish using a standardized in vitro AhR2 transactivation assay. BAA and each alkylated homologue activated the AhR2 in a concentration-dependent manner in each species. Position-dependent effects on potency were observed in every species, however these effects were not consistent across species. Interspecies variation in sensitivity to AhR2 activation by each PAH was observed and ranged by up to 561-fold. Alkylation both increased and decreased the range of interspecies variation and sensitivity, but potency of each alkylated homologue relative to BAA ranged by less than an order of magnitude among species. These results represent an early step towards the consideration of alkylated homologues for more objective ecological risk assessments of PAHs to native fishes.