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The objective of this paper is to report the development and life span of cross-linked biopolymers that remove contaminants, resist biodegradation over long periods of time, and resist erosion in dynamic aquatic environments. Biopolymers are polymeric compounds produced by living organisms (e.g., microorganisms, plants, crustaceans). They have repeated sequences that vary broadly in chemical composition including a variety of repeating functional groups (such as carboxyl, hydroxyl, amino, etc.). This makes them reactive and subject to cross-linking. Therefore, biopolymers, a great molecular weight compounds with repeated sequences, may have high opportunity for chemical interaction with other compounds. Depending on their functional groups, biopolymers can bind metals, organic contaminants, or soil particles and form interpenetrating cross-linking networks with other polymers. The ability of biopolymers (cross-linked or not) to bind a large variety of metals is supported by many studies (Chen et al., 1993; Etemadi et al., 2003; Knox et al., 2008 a, b). The capacity of alginate as a crosslinked product (calcium alginate) for Cr(VI) uptake was demonstrated by Fiol et al. (2004), who obtained an uptake of 86.42 mmol of Cr(VI) per L of wet sorbent volume using grape stalk wastes encapsulated into calcium alginate. The Cr(VI) removal ability of cross-linked calcium alginate was also shown by Araujo and Teixeira (1997), and its ability to bind Cu was shown by Chen et al. (1990 and 1993) and Wan et al. (2004). The removal of Cu, Cr, and As from treated wood onto the biopolymers, chitin and chitosan, was shown by Kartal and Iamamura (2004). The use of biopolymers based on elastine-like polypeptides for the selective removal of Hg was reported by Kostal et al. (2003), who also reported their potential for binding and removal of other metals such as As and Cr. Recently, the use of a similar elastin-like polypeptide composed of a polyhistidine tail was exploited as a metalbinding biopolymer with high affinity toward Cd by Prabhukumar et al. (2004). Knox et al. (2007 and 2008 a, b) showed that biopolymers (with and without cross-linking) have the ability to sequester a large variety of metals (e.g., Cu, Pb, Cd, As, Cr, Zn, and Ni) and organic contaminants (e.g., phenanthrene and pyrene). |
