In search of PAH transformation pathways through air, water, sediment and bivalves in a coastal area of the Skagerrak Sea

Polycyclic aromatic hydrocarbons (PAHs) and their derivatives constitute persistent contaminants in marine coastal environments, where their sources, fate, and potential ecological and human-health effects are of increasing concern. While much attention has been paid to parent PAHs, less is known concerning their oxygenated (Oxy-PAHs) and nitrogenated (N-PAHs) analogues, which may arise via atmospheric oxidation, photochemical aging, microbial transformation, or direct emissions (e.g., combustion or fossil-fuel usage). We studied a relatively unexploited coastal area of the Skagerrak Sea and a nearby harbour area. Sediments, terrestrial gyttja, water samples, and caged blue mussels ( Mytilus edulis ) and European flat oysters ( Ostrea edulis ) were analysed for 19 PAHs, 10 Oxy-PAHs and 4 N-PAHs. ΣPAHs in sediments ranged from 500 to 2000 ng g −1 dw, whereas water contained 1–3 ng L −1 . Oxy-PAHs occurred at similar levels as PAHs in water but were an order of magnitude lower in sediments and bivalves. N-PAHs were undetectable in water but present in sediments, gyttja and bivalves, with highest levels in terrestrial gyttja. Each matrix represents a distinct environmental compartment and captures different aspects of pollutant behavior: sediments serve as long-term sinks that reflect historical deposition, water provides insight into ongoing inputs and dissolved-phase dynamics, and bivalves act as bioaccumulators integrating contaminant exposure over time. The use of the relationships between daughter and parent PAHs offered insights into sources and environmental pathways of both conventional and emerging PAH compounds. The combined study of five different matrices enhanced our ability to evaluate contaminant cycling.