Evaluation and risk assessment of toxic heavy metals in East Grand Bahama and Dover Sound mangrove sediments of Grand Bahama

Abstract

Mangrove ecosystems in The Bahamas provide critical coastal protection and ecological functions but may accumulate contaminants derived from anthropogenic activities. This study quantified concentrations of selected heavy metals, chromium (Cr), manganese (Mn), nickel (Ni), cadmium (Cd), antimony (Sb), lead (Pb), copper (Cu), arsenic (As), and zinc (Zn), in surface sediments collected from two coastal sites on Grand Bahama Island, Dover Sound (DS) and East End (EE). Metal concentrations were determined using inductively coupled plasma mass spectrometry (ICP-MS), and contamination levels were evaluated using multiple ecological and human health risk indices. Mean concentrations exceeding sediment quality reference values at DS were observed for Cd (25.64 mg kg⁻¹), Sb (44.92 mg kg⁻¹), and Cu (195.33 mg kg⁻¹), whereas at EE exceedances were recorded for Cd (442.58 mg kg⁻¹) and Sb (56.62 mg kg⁻¹). The pollution load index (PLI < 1) indicated that sediments at both sites were not classified as polluted overall. In contrast, the ecological risk index (RI > 600) indicated very high ecological risk at most sampling locations, except D2, D3, and D4, largely driven by elevated Cd concentrations. Contamination factor analysis identified moderate contamination by Cu (1 ≤ CF < 3) and very high contamination by Cd and Sb (CF > 6), while geo-accumulation index values (Igeo > 1) supported anthropogenic enrichment of Cd and Sb. Human health risk assessment using the USEPA screening framework indicated that Cd may pose potential non-carcinogenic and carcinogenic risk, particularly for children. Although composite sediment quality indices suggest limited system-wide pollution, elevated concentrations of Cd, and to a lesser extent Sb and Cu, contribute to substantial ecological risk and potential human health concern at localized scales. These findings demonstrate that metal-specific enrichment in small island coastal systems can generate disproportionate ecological and health implications and highlight the importance of continued monitoring and improved baseline characterization to inform environmental management strategies in The Bahamas.