Natural, HCl-treated, and formaldehyde-treated non-living leaves of Posidonia oceanica, a marine plant, were investigated as potential biosorbents to remove Cd from aqueous solutions. The studied biosorbents were characterized by elemental analysis and Fourier transform infrared spectroscopy (FTIR) and it was observed that the adsorption capacity of the biosorbents strongly depended on the pH, increasing as the pH rises. The adsorption process was fast. The adsorption kinetic was analyzed using five kinetic models: pseudo-first order, pseudo-second order, Elovich, intraparticle diffusion, and Bangham models. The adsorption isotherms were analyzed by the Langmuir, Freundlich, Dubinin-Radushkevich, Sips, Redlich-Peterson, and Toth models. The maximum biosorption capacity was attained by the biosorbent treated with HCl (1.11 mmol g). The distribution equilibrium constant and the Gibbs free energy change were calculated. The effects of the presence of Na, K, Mg, and Ca ions in the solution on Cd uptake were studied. Results indicate that non-living leaves of P. oceanica, natural or treated, can be considered as effective and low-cost biosorbents for the removal of cadmium from aqueous solutions.

This study assesses the potential human health risks posed by six heavy metals (Hg, As, Pb, Cd, Cu, and Zn) found in five of the most consumed fish species (Mugil incilis, Centropomus undecimalis, Cathorops mapale, Eugerres plumieri, and Elops smithi) collected by the riverine population living in Ciénaga Grande de Santa Marta (CGSM), the largest estuary in Colombia. Metal concentrations were low compared with those reported in other regions around the world and the maximum value established by international monitoring organizations. The estimation of the potential risk (HQ) indicated that Cu and Hg could generate negative effects in groups of women of childbearing age (WCA) and the remaining population (RP), because they exceeded their related reference doses, with HQ values > 1; however, Cu and Hg concentrations were not high in fish and EWI, MFW, or MeHgPSL values shows that there is no evidence of a potential health risk from MeHg exposure in the study population. Therefore, the recommendations are to establish continuous monitoring of heavy metals together with strategies that address the high fish consumption, as well as to implement mechanisms for the mitigation of contamination of the watershed, to ensure the safety of organisms in the ecosystem and human health, not only of populations who depend on aquatic resources in the area but also of those that market and consume these resources in the Colombian Caribbean.

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