Spatial variability of biliary 1-hydroxypyrene in European hake (Merluccius merluccius) from the Iberian Atlantic coast: a multi-annual assessment of PAH exposure

Abstract Background Polycyclic aromatic hydrocarbons are pervasive environmental contaminants of regulatory concern in European marine waters. Because parent compounds are rapidly metabolized in fish, biliary metabolites provide a sensitive indicator of recent exposure and are widely used in regional monitoring frameworks, including those under the Marine Strategy Framework Directive and OSPAR. European hake ( Merluccius merluccius ) is an ecologically important demersal species recommended for contaminant monitoring, yet no multi-annual data exist for biliary metabolites in this species. This study presents the first multi-year dataset of biliary 1-hydroxypyrene, the primary metabolite of pyrene, in European hake from three Iberian Atlantic regions (Bay of Biscay, Galicia, Gulf of Cádiz) collected between 2014 and 2019, with the objective of assessing spatial patterns and temporal trends in exposure to polycyclic aromatic hydrocarbons. Results A total of 192 female hake were analysed using high-performance liquid chromatography with fluorescence detection. 1-hydroxypyrene was detected in 74% of specimens, with concentrations ranging from below the limit of quantification to 57.5 µg per kilogram of bile. Clear spatial differences were observed: concentrations were consistently highest in the Bay of Biscay and lowest in the Gulf of Cádiz, with the proportion of samples below the limit of quantification increasing from north to south. No significant temporal trends were detected over the 6-year period. Although species-specific assessment criteria for European hake are lacking, comparison with other demersal fish suggests moderate exposure levels. Conclusions This study provides the first regulatory-relevant baseline for biliary 1-hydroxypyrene in European hake across the Iberian Atlantic coast and demonstrates spatial statistically significant differences in exposure to polycyclic aromatic hydrocarbons. These results support the suitability of M. merluccius for regional contaminant monitoring and offer evidence directly applicable to environmental assessment frameworks, including European marine policy instruments. The absence of species-specific reference values highlights a current limitation for regulatory interpretation and underscores the need for developing assessment criteria to strengthen future monitoring and environmental status evaluations.