Polycyclic aromatic hydrocarbons in tropical mangrove soils affected by a major oil spill: vertical distribution, persistence, and mixed sources

Mangrove ecosystems are among the most vulnerable coastal environments to contamination by polycyclic aromatic hydrocarbons (PAHs). This study evaluated PAH contamination in mangrove soils following the largest oil spill in Brazilian coastal history, which affected thousands of kilometers of shoreline. Soil profiles were sampled at eight sites along an affected mangrove estuary at three depths (0–10, 25–35, and 50–60 cm). Sixteen priority PAHs were identified and quantified using gas chromatography–mass spectrometry (GC–MS) to assess contamination levels, vertical distribution patterns, and potential sources. Total PAH concentrations ranged from 233.85 to 2755.60 ng g −1 . Six sites showed moderate contamination, whereas two sites exhibited high contamination. High-molecular-weight PAHs predominated. Diagnostic ratios revealed mixed pyrogenic and petrogenic signatures, reinforcing the contribution of petroleum-derived residues associated with the spill. Multivariate analyses identified distinct PAH groupings consistent with shared origins and demonstrated the strong influence of soil properties on contaminant retention and distribution, particularly clay content and organic carbon. The vertical occurrence of PAHs across soil depths indicates potential incorporation into subsurface layers, raising concerns about prolonged ecological exposure and delayed ecosystem recovery. Given the ecological importance of mangroves as carbon sinks, biodiversity hotspots, and nursery habitats, the persistence of PAHs highlights the long-term environmental legacy of the event.