Integrated geochemical and PAH analysis with benthic foraminifera to assess environmental quality in a tropical estuary

Abstract

This study assessed the environmental quality of the Serinhaém River estuary (Bahia, Brazil). The characterization was based on concentrations of chemical elements, total organic carbon (TOC), physicochemical parameters, and polycyclic aromatic hydrocarbons (PAHs) in surface sediments, combined with benthic foraminifera as bioindicators. Samples were collected at multiple sites during two seasonal campaigns conducted in 2013 and 2022, representing pre- and post-spill conditions. Chemical element concentrations showed no significant temporal differences but high spatial variability, with Fe, Al, and Mn predominating, indicating association with oxyhydroxides and aluminosilicates. PAHs in 2022 indicated low-to-moderate contamination, predominantly of pyrogenic origin, and did not exceed threshold effect levels (TEL and PEL). In 2013, benthic foraminiferal distribution was mainly influenced by precipitation, promoting transport toward the estuary mouth. In 2022, salinity and pH became the dominant controlling factors. Significant associations were observed between PAHs and benthic foraminiferal assemblages. Negative associations were observed between naphthalene and anthracene and the diversity and abundance of tolerant species (e.g., Ammonia beccarii and Textularia gramen ), while dibenzo[a,h]anthracene showed a positive association with Ammoglobigerina globigeriniformis . Overall, the estuary remains preserved regarding elemental concentrations; however, PAHs influence benthic assemblages, highlighting foraminifera as effective indicators of environmental quality and hydrocarbon contamination.

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