Heavy metal distribution in water, sediments, and aquatic plants from the middle Songkhla Lagoon: Environmental risk and phytoremediation assessment

Abstract

This study investigated the distribution of aluminum (Al), arsenic (As), and lead (Pb) in water, sediments, and two dominant aquatic plants—morning glory (Ipomoea aquatica) and water mimosa (Neptunia oleracea)—from the middle part of Songkhla Lagoon. Heavy metal concentrations in water and sediments were below national and international standards, indicating low contamination risk. Both concentrations of As and Pb in sediment had severe enrichment (EF > 15) at all stations, suggesting anthropogenic inputs. In contrast, geo-accumulation index (I_geo) values were negative, indicating unpolluted sediments and showing two-index differential sensitivity. In aquatic plants, heavy metals were mainly accumulated in roots, with significantly lower concentrations found in stems and leaves, especially for As and Pb. Morning glory showed greater root uptake of As and Pb than water mimosa, making it a better candidate for bioindication. Despite root accumulation, translocation factors (TF) and bioaccumulation factors (BAF) were closed to zero for all stations and metals, confirming that metals did not effectively move into edible aerial tissues. This pathway from sediment to root, but not to leaf or stem, suggested that the edible parts of these plants remain relatively safe for consumption under current conditions. Low contamination levels in water and sediment limited metal transfer to upward plant parts, and environmental parameters (e.g., sediment pH, organic carbon, and particle size) supporting these species, particularly morning glory for rhizo-filtration and safe, sustainable use in brackish aquatic environments.