Eggshell

9 1994by Humana Press Inc. All rights of any nature whatsoeverreserved. 0273-2289/94/4546--0871503.00

A New Biomaterial, Hen Egg Shell Membrane, to Eliminate Heavy Metal ion from Their Dilute Waste Solution
KYOZO SUYAMA,*'I YOSHITAKA FUKAZAWA, 1 AND YOSHIAKI UMETSU 2

1Laboratory of Molecular Technology of Animal Products, Faculty of Agriculture, Tohoku University, I. 1 Tsutsurnidori,Sendal 981, Japan; and 21nstitute for Advanced Materials Processing, Tohoku University, Sendai, Japan

ABSTRACT
The egg shell membrane (ESM) is an intricate lattice network of stable and water-insoluble fibers with high surface area. ESM accumulates and eliminates various heavy metal ions from dilute aqueous solution with high affinity and in short contact time, depending on pH and characteristicsof the individual ion. Under certain conditions, the level of precious ions, Au, Pt, and Pd accumulation approaches 55, 25, and 22% of dry wt of ESM, respectively. Also uranium uptake 30% of that of ESM. Experiments suggested that ESM is promising to use for the purpose of removal/recovery of metals and water pollution control.
Index Entries: Egg shell membrane; metal ion; biosorption.INTRODUCTION Almost all biominerals, including avian egg shells, have one common feature. They are composed of an inorganic (mineralized) phase, and an organic part consisting of proteins. The hen egg shell membrane (ESM) is an intricate lattice network of fibers and is suggested to be the part where
*Author to whom all correspondence and reprint requests should be addressed.
Applied Biochemistry andBiotechnology

871.

Vol. 45/46, 1994

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Suyama, Fukazawa, and Umetsu

calcium deposition takes place. Although the precise role of ESM on the mineralization of egg shell is not very clear, the insoluble protein would appear to be essential for mineralization to occur (1-3). From the fact of ESM mineralization, we considered that ESM would accumulate various types of inorganic ions. Ithas been well reported that certain types of biomaterials, such as microbials (4,5) and seaweeds (6-8) possess a potential to sequester and accumulate inorganic ions in aqueous solutions. Metal concentration by biomaterials from a solution is termed biosorption, and industrial application of these are so-called "biosorbents." We found ESM protein eliminated various heavy metal ions from theirdilute aqueous solutions in high yield and in short contact time, depending on pH and characteristics of the individual metal ion. ESM protein can be used repeatedly in the sorption-desorption for the accumulation of most heavy metals. ESM is therefore promising to use for removal/recovery of metals and water pollution control. This might also be pertinent to effluents containing radioactive metals.Biosorption is generally considered to be a rapid physical/chemical process and not expensive. The following positive considerations for this process using ESM can be taken into account: 1. Abundant resource (byproduct of egg industry); 2. Highly stable and water-insoluble; 3. Very high surface area with homogeniety and allows metal ions, as well as extremely large organic nutrient crosslinkedprotein molecule, to pass freely through; and 4. Egg shell consisted with calcium carbonate may not be obstacle for the process. It is recognized that two ESMs surround the hen egg, a thick outer membrane attached to the shell and a thin inner membrane. Each of these membranes is composed of a network of fibers (9). The shell is attached to the outer of these membranes by the mammiUae, which areroughly hemispherical knobs composed of large spherulite crystal of calcite (2,10). ESM contains crosslinking amino acids, such as desmosine and a large amount of cystine, suggesting that ESM consists of keratin- or elastin-like protein (11,12). In the recent report, collagen-like proteins were detected in the ESM (9). However, the structural proteins of ESM are still not well characterized. This...