Abstract
This study focuses on the ability of commercial natural bath sponges, which are made from the skeletons of marine sponges, to sorb Hg from natural waters. The main component of these bath sponges is spongin, which is a protein-based material, closely related to collagen, offering a plenitude of reactive sites from the great variety of amino acids in the protein chains, where the Hg ions can sorb. For a dose of 40 mg L−1 and initial concentration of 50 μg L−1 of Hg(II), marine spongin (MS) removed ~90% of Hg from 3 water matrixes (ultrapure, bottled, and seawater), corresponding to a residual concentration of ~5 μg L−1, which tends to the recommend value for drinking water of 1 μg L−1. This value was maintained even by increasing the MS dosage, suggesting the existence of a gradient concentration threshold below which the Hg sorption mechanism halts. Kinetic modelling showed that the Pseudo Second-Order equation was the best fit for all the water matrixes, which indicates that the sorption mechanism relies most probably on chemical interactions between the functional groups of spongin and the Hg ions. This material can also be regenerated in HNO3 and reused for Hg sorption, with marginal losses in efficiency, at least for 3 consecutive cycles.
Highlights
The presence of trace metals in water is a threat to the health of humans and to all forms of life
The inorganic Hg tends to be converted into its toxic methyl form, Hg(CH3Hg), and it can make its way to humans through the food chain, mainly by the ingestion of marine fish,[3]
The microstructure of the sample was observed by Scanning Electron Microscopy (SEM), which revealed the expected honeycomb-like structure, with anastomosed spongin fibers that ranged between to 20 μm in diameter.[18,31]
Summary
The presence of trace metals in water is a threat to the health of humans and to all forms of life. Even in trace concentration, is acutely toxic and may affect the central nervous and cardiovascular systems.[4] The presence of metallic or inorganic form of Hg in human has a harmful impact in the immune system, kidneys and lungs.[5] It is imperative to continue searching for new and more efficient materials that can remove Hg from different real water matrixes. In the case of Hg remediation, many examples of the use of natural, or natural-based materials can be found in the literature, including agricultural waste, such as peanut or pistachios shells,[6] onions,[7] parts of plants, such as bamboo or castor tree leaves [8], phragmites,[9] and karaya gum extract from Sterculi Urens,[10] Cladophora algae[11]
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