Hydrocarbon dynamics influenced by coal-related activities in a South Atlantic River–Estuarine System: Challenges for conventional source apportionment approaches

The Tubarão River-estuarine system (TRES), located in the South Atlantic, Brazil, is essential for water supply, agriculture, fisheries, and industrial activities. It has historically been affected by coal extraction, urbanisation, and industrial discharges, activities that generate significant impacts on ecosystem health, such as decreased water quality, habitat degradation, and potential bioaccumulation of toxic compounds in aquatic organisms. Nineteen sediment samples were collected along the TRES to assess contamination levels and evaluate the sources and spatial distribution of pollution. The study encompassed both aliphatic hydrocarbons (AHs) and polycyclic aromatic hydrocarbons (PAHs). Total AH concentrations ranged from 3.86 to 69.4 μg g −1 (mean: 25.7 ± 20.7 μg g −1 ), with ΣC 10 –C 40 n -alkanes accounting for 0.34–12.0 μg g −1 (mean: 4.65 ± 4.07 μg g −1 ). PAH levels were between 6.42 and 6440.2 ng g −1 (mean: 1370.7 ± 1654.6 ng g −1 for Σ 27 PAHs, excluding retene and perylene) and 3.47 to 1540.8 ng g −1 (mean: 323.4 ± 385.5 ng g −1 ) for Σ 16 PAHs. The TRES is strongly influenced by anthropogenic hydrocarbons, with the most prominent contamination observed in the upper reaches of the river and the Rocinha River tributary. The middle section of the system is moderately affected, likely due to dilution by tributary inputs, while the lower reaches experience consistent pollution from urban and industrial activities. Contamination pattern is potentially influenced by fine coal particles and sorbent nanoparticles derived from mining and other coal-related activities. In this context, these particles may also influence source apportionment analyses, which revealed mixed petrogenic- and pyrogenic-like signatures, consistent with the geochemical characteristics of coal-derived PAHs in coal-influenced systems. These data are crucial for monitoring long-term pollution trends, as environmental conditions and contamination levels typically change gradually, offering valuable insights for future assessments and regional policy development. • - Natural hydrocarbons increase seawards, linked to terrigenous organic matter. • - PAHs in TRES are mainly from fossil fuel combustion and coal-related residues. • - Coal-related PAHs challenge conventional diagnostic ratio source apportionment. • - Coal-related nanoparticles enhance hydrocarbon retention in fine sediments. • - Findings highlight the need for targeted monitoring in coal-impacted estuaries.