Evaluating heavy metal pollution in mangrove sediments via SEM-EDS elemental mapping

Coastal mangrove forests can influence the retention and redistribution of sediments and associated contaminants in coastal environments. The primary objective of this work was to examine the distribution and environmental implications of heavy metal contaminants (lead (Pb), copper (Cu), and nickel (Ni)) in mangrove sediments through a concentration analysis, geochemical pollution indices, and elemental profiling through scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS). Sediment materials were obtained from three locations within a coastal mangrove region. At each station, surface sediments were obtained to represent site-specific conditions. The geoaccumulation index (I_geo), contamination factor (Cf), and pollution load index (PLI) were applied to assess pollution levels. The results indicated that Pb, Cu, and Ni concentrations at all locations were below the sediment quality guideline (SQG) thresholds based on the TEL/PEL and ERL/ERM criteria, indicating a low probability of adverse biological effects according to these selected SQGs, within the scope of the metals analyzed and the sampling period. All I_geo values were negative and classified as class 0 (unpolluted), while Cf values indicated low contamination for Cu and Ni and moderate contamination for Pb at one station. PLI values at all stations were below one, confirming that the sediments were generally unpolluted within the sampled stations and sampling period. SEM-EDS analysis revealed porous and aggregated sediment morphologies with relatively uniform distributions of Pb and Cu. Elemental spectra were dominated by silicate and aluminosilicate minerals, with Pb and Cu occurring only as trace elements. These findings indicate that the sediments currently exhibit low levels of heavy metal contamination and suggesting that the sediment matrix may contribute to the retention of Pb, Cu, and Ni under the conditions investigated. However, this interpretation is limited to the measured total metal concentrations, pollution indices, and SEM-EDS observations from one station and does not directly demonstrate long-term accumulation or an ecosystem-scale sink function.