The remediation potential and kinetics of cadmium in the green alga Cladophora rupestris

This study determined the subcellular distribution, chemical forms, and effects of metal homeostasis of excess Cd in Cladophora rupestris. Biosorption data were analyzed with Langmuir and Freundlich adsorption models and kinetic equations. Results showed that C. rupestris can accumulate Cd. Cd mainly localized in the cell wall and debris (42.8-68.2%) of C. rupestris, followed by the soluble fraction (22.1-38.4%) observed in C. rupestris. A large quantity of Cd ions existed as insoluble CdHPO4 complexed with organic acids, Cd(H2PO4)(2), Cd-phosphate complexes (F-HAC) (43.2-56.0%), and pectate and protein-integrated Cd (F-NaCl) (30.8-43.2%). The adsorption data were well fitted by the Freundlich model (R-2=0.933) and could be described by the pseudo-second-order reaction rate (R-2=0.997) and Elovich (R-2=0.972) equations. Related parameters indicated that Cd adsorption by C. rupestris is a heterogeneous diffusion. Cd promoted Ca and Zn uptake by C. rupestris. Cu, Fe, Mn, and Mg adsorption was promoted by low Cd concentrations and inhibited by high Cd concentrations. Results suggested that cell wall sequestration, vacuolar compartmentalization, and chemical morphological transformation are important mechanisms of Cd stress tolerance by C. rupestris. This study suggests that C. rupestris has bioremediation potential of Cd.