Red Mangrove Heavy Metal(loid)s Accumulation in Contaminated Sediments of the South Florida Intracoastal Waterway

Red Mangrove Heavy Metal(loid)s Accumulation in Contaminated Sediments of the South Florida Intracoastal Waterway

Alvin Sherman Library

Mangroves, recognized as hyperaccumulators, can tolerate and store high concentrations of heavy metal(loid)s without visible toxicity. While metal accumulation in mangroves has been extensively studied worldwide, data remain limited for North America, particularly in southeastern Florida, where urbanization and port activity increase contamination risk. This study quantified 16 heavy metal(loid)s in roots, branches, and leaves of red mangroves (Rhizophora mangle) and associated surface sediments collected across four sites within Dr. Von D. Mizell-Eula Johnson State Park at Port Everglades using inductively coupled plasma mass spectrometry (ICP-MS). Sediment samples were collected at distances of 0, 10, 50, and 100 cm from mangrove roots. Sixteen elements were detected across all samples, with sediments exhibiting substantially higher concentrations than mangrove tissues. Iron (Fe) and aluminum (Al) dominated concentrations across all sites, followed by Zn, Cu, Mn, and Cr. The highest geometric mean concentrations were consistently observed in sediment at South Turning Basin (STB) and West Lake (WL). In contrast, Dania Cutoff Canal (DCC) and Park Education Center (PEC) displayed comparatively low metal burdens. Nonparametric Kruskal-Wallis and Dunn's tests revealed significant site differences, with DCC and PEC distinct from STB and WL. Tissue-specific patterns indicated greater accumulation in roots and leaves, with average root concentrations dominated by Fe (45.55 μg/g), Al (26.17 μg/g), Zn (15.02 μg/g), and Mn (5.02 μg/g). Bioconcentration factors were >1 for Cd, Co, and Cr at all sites, and for Mn, Pb, Se, and Sn at more than one-half the sites, indicating preferential uptake and retention by mangroves. Geo-accumulation index and pollution load assessments classified DCC and PEC as largely unpolluted, while STB and WL exhibited moderate to strong contamination, particularly for As, Mo, and Zn, with STB identified as a primary contamination hotspot. Sediment quality guidelines (probable effects level and threshold effects level) were exceeded for Pb, Ni, and Zn at impacted sites. Collectively, these findings demonstrate that R. mangle in southeastern Florida actively accumulates multiple heavy metal(loid)s and serves as an effective biomonitor for localized contamination in urban-adjacent mangrove ecosystems.