Effect-directed analysis and nontarget screening for identifying AhR-active substances in black-tailed gull eggs from South Korea

This study identifies major aryl hydrocarbon receptor (AhR) agonists in the eggs of black-tailed gulls (Larus crassirostris) from South Korea using effect-directed analysis and nontarget screening (NTS). Significant AhR-mediated potency is observed in the mid-polar fraction (F2) of the egg extracts, as determined by the H4IIE-luc bioassay, with notable activity detected in subfractions F2.3 and F2.6-F2.9, corresponding to log K_OW ranges of 2.0-3.0 and 5.0-9.0, respectively. Fourteen targeted AhR agonists, including traditional polycyclic aromatic hydrocarbons (PAHs), emerging PAHs (e-PAHs), and styrene oligomers, account for 15-61% of the total AhR-mediated potency. Among them, e-PAHs such as 20-methylcholanthrene (14%), benzo[b]anthracene (8.8%), and 10-methylbenzo[a]pyrene (4.5%) contribute substantially to the overall AhR-mediated potency. NTS using GC-QTOFMS on F2.3 and F2.6-F2.9 identifies 24 AhR agonist candidates through a five-step selection process. Among the candidates with available standards, 1,4-dicyclohexylbenzene shows significant AhR-mediated activity in the H4IIE-luc bioassay. This compound is detected in egg extracts at concentrations ranging from 0.25 to 5.1 ng g^-1 wet mass. However, due to its low relative potency value (7.0 × 10^-4) compared to benzo[a]pyrene, its contribution to overall AhR-mediated potency is only 0.01%, on average. The log K_OW and log K_OA values of the maternally transferred AhR agonists in the eggs range from 5.0 to 8.0 and 6.5 to 11.5, respectively. This study represents the first identification of maternally transferred AhR agonists in the eggs of black-tailed gulls, providing new insights into the ecological and toxicological risks associated with these contaminants.