Characterization and ecological risk assessment of toxic metals in mangrove sediments near Langen Village in Tieshan Bay of Beibu Gulf, China

Abstract A series of coastal development initiatives have been recently implemented in the East Harbor area of Tieshan Harbor, Guangxi Province, China. However, the ecological impacts of these reclamation activities on toxic metal pollution levels in shallow mangrove sediments within the intertidal zones adjacent to Langen Village, Tieshan Bay (Beibu Gulf), remain poorly understood. This study investigated the distribution patterns, ecological risks, and potential sources of seven toxic metals (Pb, Cu, Zn, As, Cr, Cd, and Hg) in surface sediments collected from 26 sampling locations across dead mangrove zones, severely degraded mangrove areas, and currently intact mangrove ecosystems near Langen Village during April 2022. We employed multiple assessment metrics including the pollution load index (PLI), geoaccumulation index (I geo), sediment quality guidelines, individual potential ecological risk factors, and potential ecological risk index (RI) to evaluate contamination status and associated ecological hazards. Results indicate moderate contamination and medium ecological risk according to I geo, PLI and RI in intertidal sediments, with significantly higher toxic metal concentrations in dead and severely degraded mangroves than in temporarily undamaged areas. Total unit toxic index analysis revealed generally low biological toxicity from surface sediment metals, with Hg, Cd, and As identified as dominant ecological hazard factors. These findings provide a critical scientific basis for enhancing mangrove conservation strategies and developing targeted management protocols.