Identification of CaCO3 polymorphs of shellfish by FTIR spectroscopy and evaluation of metals adsorption by powdered exoskeleton shell

Abstract

Shellfish are found in the coastal region throughout the tropical, sub-tropic and temperate zone. A variety of shellfish species are known in nature. Being filter-feeding organisms, organic and inorganic substances easily gain entry into them. Very often, heavy metals such as Cd, Pb, Cu, and even Hg can accumulate in their bodies. The presence of these heavy metals in shellfish is an indicator of environmental pollution, and a threat to humanity as these fish are widely consumed in coastal regions. Here, biochemical analysis of exoskeleton shell mainly composed of polysaccharides, proteins and calcium carbonate (CaCO₃) - have been studied. Calcium carbonate (CaCO₃) which is one of the major constituent of the exoskeleton part of the shellfish exists in three polymorphs viz., calcite, aragonite and vaterite. The identification of CaCO₃ polymorphs in shellfish is extremely important as it gives information on the structural arrangement of the calcium carbonate lattice in these organisms. Here, we present a convenient method for the identification of CaCO₃ polymorphs in shellfish collected from Goa, west coast of India, with Fourier-Transform Infrared Spectroscopy (FTIR) and further confirmed by powder X-ray analysis. Additionally, the potential of the powdered shell biomass for metal removal from an aqueous medium has also been investigated.