Polycyclic aromatic hydrocarbons (PAHs) and sterol biomarkers were quantified in Perna perna mussels from the Cagarras Islands Natural Monument (MONA), a federally designated no-take marine protected area off Rio de Janeiro, Brazil. Mussels collected in 2022 exhibited parental and alkylated PAH concentrations (197–1765 ng g −1 dw) up to five- and twelvefold higher than values reported a decade earlier, indicating a marked increase in contamination within this protected coastal system. The predominance of 2–4-ring PAHs and diagnostic ratios revealed mixed petrogenic and pyrogenic signatures consistent with chronic petroleum-derived and combustion-related inputs. Although carcinogenic PAHs were detected in all samples, BaP, Σ4PAHs, and BaP-equivalent toxic values remained below current Brazilian and European regulatory thresholds for seafood safety. Total sterol concentrations ranged from 545 to 3712 μg g −1 dw. Coprostanol was consistently detected, confirming sewage-derived organic inputs, while sitosterol suggests additional biogenic contributions associated with seabird populations inhabiting the archipelago. The co-occurrence of petroleum- and wastewater-related tracers indicates that MONA, despite its strict protection status, remains environmentally connected to the surrounding metropolitan coastal system. These findings demonstrate that no-take designation does not ensure chemical isolation in urban-embedded MPAs and support the incorporation of standardized contaminant biomonitoring into adaptive coastal management and conservation performance assessment frameworks. • PAH concentrations in MONA mussels increased up to twelvefold. • Mixed petrogenic and pyrogenic PAH sources were identified. • Coprostanol confirms chronic sewage influence in a no-take MPA. • MONA remains chemically connected to the metropolitan seascape. • Results support standardized contaminant biomonitoring in MPAs.
Gramlich et al. (Tue,) studied this question.