Organic pollutants and phytoplankton dynamics across contrasting coastal environments

Phytoplankton are essential components of marine food webs and play a critical role in biogeochemical cycling. However, their ability to accumulate and reflect the sources of organic pollutants in coastal waters is still not well understood. In this study, we quantified the concentrations, molecular composition, and sources of polycyclic aromatic hydrocarbons (PAHs), phthalate esters (PAEs), and alkylphenols (APs) associated with phytoplankton collected from seven river mouth (RM) stations and seven fishing port (FP) stations in Kaohsiung, Taiwan. Phytoplankton in the 55-120 μm size range were isolated, extracted, and analyzed using gas chromatography-mass spectrometry (GC-MS). At the same time, we evaluated the sources of PAHs using molecular diagnostic ratios (MDR) and Positive Matrix Factorization (PMF). The results showed fishing ports consistently exhibiting higher concentrations of ΣPAHs, ΣPAEs, and ΣAPs than river mouth stations. This finding reflects the impact of maritime activities, fuel combustion, plastic-derived inputs, and wastewater discharge. Despite these differences, high-molecular-weight PAHs were the predominant PAHs in both environments, indicating a common influence from pyrogenic combustion sources. In addition, plasticizers (DEHP, DiNP, BBP) and nonylphenol dominate PAEs and APs, respectively. PMF analysis identified traffic-related and petroleum combustion emissions as the primary contributors, alongside inputs from plasticizers. Diatom-dominated assemblages were associated with elevated accumulation of high-molecular-weight PAHs, suggesting that phytoplankton community composition and functional traits may influence the uptake of organic pollutants. These results indicate that phytoplankton can reflect spatial patterns of chemical exposure and ecological response, supporting their potential use as bioindicators in coastal ecosystems.