Acute and chronic sources of polycyclic aromatic hydrocarbons (PAHs) in coastal sediments impacted by the 2019–2020 oil spill in NE Brazil

Abstract

The 2019–2020 oil spill off the Brazilian coast represents one of the largest environmental disasters in the South Atlantic, impacting diverse ecosystems and vulnerable communities. This study investigates the occurrence, levels, composition, and potential ecological risks of polycyclic aromatic hydrocarbons (PAHs) in surface sediments of mangroves affected by the spill along the coast of Bahia, NE Brazil. Fifty-one samples were collected across seven sites, including oil-impacted areas, a control site, and a chronically contaminated area, during three campaigns conducted 12, 18, and 24 months after the spill. Total PAH concentrations (∑16 PAHs) ranged from 39.1 to 595.4 ng g⁻¹ and fell within low to moderate contamination levels. Despite a general decreasing trend over time, spatial and temporal patterns were inconsistent, and PAH distributions appeared to be influenced by both the oil spill and local anthropogenic inputs. Higher alkyl-PAHs/parent-PAHs ratios in Siribinha and Boipeba suggest a long-term influence of petrogenic sources linked to the oil spill, while elevated PAHs in the São Paulo River reflect chronic industrial and urban pollution. Diagnostic ratios and compositional profiles confirmed mixed pyrogenic and petrogenic signatures across sites. Although mean sediment quality guideline quotients indicated low ecotoxicological risk overall, exceedances of threshold values for acenaphthylene and phenanthrene at some sites, particularly those inhabited by traditional communities, highlight the importance of continued monitoring. This study provides the first spatially and temporally resolved assessment of PAH contamination in mangrove sediments following the 2019–2020 oil spill, contributing to a broader understanding of both acute and chronic hydrocarbon impacts in tropical coastal ecosystems.