Bilary PAH metabolites in Baltic Sea fish as indicators of spatial and temporal contamination trends

Background Polycyclic aromatic hydrocarbons (PAHs) are priority pollutants of high environmental relevance. In fish however, they are quickly degraded into stable metabolites excreted via fish bile. To monitor PAH exposure of marine fish, these bile metabolites are used. The present study gives insight into two PAH metabolite concentrations in 850 samples in three fish species at nine locations in the Baltic Sea fish from 2011 to 2023. PAH metabolites have been measured in flounder ( Platichthys flesus ), dab ( Limanda limanda ) and cod ( Gadus morhua ) by means of HPLC with fluorescence detection. Results PAH metabolite concentrations show spatial as well as species related differences. The overall level of contamination of 1-hydroxypyrene in dab and flounder match with other studies. 1-Hydroxypyrene means measured in the present study were 66.6 ng/ml (flounder), 91.1 ng/ml (dab) and 190.7 ng/ml (cod). Contamination of cod, however, is in some cases higher than found before with levels up to 1595.8 ng/ml bile in single cod from the Bornholm Basin. Regarding mean values, all regions were below environmental threshold value for 1-hydroxypyrene. We found that PAH metabolite contamination in the two benthic flatfish species dab and flounder are of comparable magnitude, but significantly lower than in cod. With the present study we showed two significantly decreasing temporal trends in PAH metabolite contamination of dab and flounder mirroring decreasing PAH concentrations in marine environment. Conclusion PAH metabolites are valuable environmental indicators to describe PAH exposure of marine fish and the environmental status of Baltic Sea regions. This parameter can be used to detect environmental trends. Fish from the southern Baltic Sea off-shore regions are moderately contaminated with PAHs. The results help to design and interpret future monitoring studies on PAH metabolites dedicated to environmental assessment.