The uses of living and nonliving microorganisms for metal reclamation and remediation from heavy metalcontaining waste streams and sludges and for preconcentration of trace metals have recently increased. [1][2][3][4][5][6][7][8][9][10] Two types of metal binding to biomass-based materials can take place; these are passive binding in both living and nonliving cells by very rapid physical adsorption and/or ion exchange with the cell surface, and active binding in living cells by slower metal uptake as a result of metabolic activity. 11 Metal uptake by nonliving cells can occur through sorption processes involving proteins, polysaccharides, many functional groups such as amino, carboxylate, hydroxide, imidazole, sulfate and sulfihydryl groups, and biopolymers found in the cell wall.
5In comparison with the conventional ion-exchange resins, having a single functionality, microorganisms contain numerous functionalities. The polyfunctional groups in the microorganisms exhibit unique metal adsorption abilities, and have been successfully used for ion-selective binding and preconcentration. Microorganisms are capable of selectively sorbing specific metal ions from solutions containing a mixture of several metal ions.
12-18Free microorganisms exhibit poor binding abilities due to chemical attack and structural degradation.12 For that reason, the biomass has been encapsulated in a supporting matrix using alginate microbeads 13 , carrageenan gel 14 , silica-based polymers 15 , or immobilized onto a solid support such as controlled pore glass 16 and sepiolite. 17 The encapsulated and immobilized microorganisms show superior mechanical resistivity and enhanced metal binding capabilities, better chemical resistivity and freer use of them in column or fluidized bed experiments, compared with those of the free cells.
12Most studies using microorganisms for preconcentration and determination of trace metals and other species have been conducted by utilizing algae [19][20][21][22][23] , yeast 17,18,[23][24][25][26] , and bacteria. [27][28][29] Only a few studies were done with fungi. Nakajima et al. 30 have used two different fungi species, Penicillium chrysogonum and Penicillium lilacinum, for the adsorption of metal ions. They have found that these species have adsorbed uranium preferentially but with different affinity values. In their study, these fungi species have showed a different tendency for retention of heavy transition metals, although both of them have low adsorption capability for the mentioned metals. Maquieira et al. 31 have immobilized a fungus, Penicilium notatum, onto two different supports, controlled pore glass (CPG) and sand, by two different methods, covalent immobilization method and ultrasonic immobilization method, for the use in quantitative studies. They have found that both methods were successful for the immobilization of fungus. They also investigated a different method for 1251 ANALYTICAL SCIENCES DECEMBER 1999, VOL. 15 1999 © The Japan Society for Analytical Chemistry
Determination of Trace Metal...
