Potentially toxic elements (PTEs), including cadmium (Cd) and lead (Pb), are persistent contaminants in marine ecosystems that can accumulate in sediments and organisms, causing ecological impacts and potential risks to human health. Mangrove ecosystems can naturally reduce PTE pollution through sediment trapping; however, their capacity is limited under increasing contamination pressures. Mangrove endophytic fungi (EFs) have shown potential for metal tolerance and biosorption in saline environments, but their efficiency and mechanisms for Cd and Pb remediation remain poorly understood.

This study evaluates the potential of mangrove EFs for Cd and Pb remediation by (1) screening fungal tolerance using colony morphology and tolerance indices, (2) assessing removal efficiency and metal accumulation using bioconcentration factor (BCF), bioaccumulation coefficient (BAC), and translocation factor (TF), and (3) analysing the relationship between fungal performance and different fungal components, including biomass, metabolites, and culture media, to identify species-specific remediation mechanisms.
Seven EFs, including Diaporthe arengae, Diaporthe phaseolorum, Parengyodontium album, Phomopsis sp., Pyrrhoderma lamaense, Simplicillium lanosoniveum, and Zasmidium musae, were isolated from three mangrove species (Avicennia alba, Rhizophora apiculata, and Sonneratia alba) along the Strait of Malacca, Malaysia. These fungi, together with Aspergillus niger and Aspergillus oryzae, were screened for Cd and Pb tolerance. Based on the screening results, D. arengae and P. lamaense were further evaluated in Cd- and Pb-spiked broth cultures. Metal concentrations in fungal biomass, metabolites, and media were quantified using flame atomic absorption spectroscopy (FAAS).

All tested fungi achieved >99.99% Cd and Pb removal, demonstrating strong remediation potential. P. lamaense showed high translocation factors for Cd (42.054) and Pb (21.164), indicating effective extracellular metal sequestration through fungal metabolites. In contrast, D. arengae showed strong intracellular Cd accumulation (BCF: 28.165), suggesting metal storage within fungal biomass followed by gradual detoxification.

Principal component analysis (PCA) and Pearson correlation analysis revealed species-specific metal partitioning patterns. D. arengae was strongly associated with biomass, indicating intracellular accumulation, while A. niger was linked to culture media, suggesting extracellular retention. P. album and A. oryzae exhibited balanced metal distribution, whereas P. lamaense showed a preference for extracellular Pb sequestration.

Overall, this study demonstrates that mangrove EFs employ different remediation strategies, including extracellular chelation and intracellular storage, for Cd and Pb removal. These findings highlight the potential of mangrove-associated fungi as sustainable bioremediation agents for managing heavy metal contamination in coastal ecosystems.

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