Phytostabilization of potentially toxic elements by mangrove trees in coastal sediments along Pattani Bay, Thailand

Abstract

This study provides an integrated evaluation of potentially toxic element (PTE) accumulation across nine dominant mangrove species at five sites representing industrial, residential, and protected settings in Pattani Bay, Thailand. Sediment risk indices, including enrichment factor ( EF ), geo-accumulation index ( I <inf> geo </inf>), and metal risk index ( MRI ), revealed spatially variable contamination, with pronounced enrichment of Pb, Ni, Cu, and Mn in impacted zones. Statistical analysis demonstrated a decoupling effect between sediment loading and plant accumulation, suggesting that metal mobility is largely governed by internal physiological constraints rather than passive uptake. While roots served as the primary sink for lithogenic elements (Fe, Cr, and Al), distinct species-specific uptake mechanisms emerged. Linear regression indicated that bioconcentration factor for shoots (BCFs) and translocation factors (TF) are strongly modulated by internal regulatory barriers. For instance, Rhizophora apiculata exhibited a restricted transport strategy for Zn; despite high baseline accumulation (TF = 4.2; BCF = 113.3), it demonstrated a strong negative linear relationship under increasing sediment loads, effectively shielding aerial tissues. Conversely, Bruguiera cylindrica and Avicennia species challenged typical stabilization paradigms. B. cylindrica effectively concentrated Cr (Slope = 3.11), while A. marina exhibited notable Cd and Pb translocation, suggesting roles as active bioaccumulators. Furthermore, Thespesia populnea accumulated exceptional Pb concentrations (reaching 61,027.1 μg kg⁻¹ in bark), underscoring its utility as a sentinel bioindicator. Integrating these uptake profiles with sediment data provides a practical framework for targeted coastal pollution management and ecological restoration.