Effective removal of cadmium (Cd) from Chlamys farreri by introducing ZnSO4, EDTA-Na2, and sodium citrate into seawater has previously been reported. However, some mechanisms underlying this removal are not clear. To address this lack of clarity, the present study aimed to investigate the changes of Cd forms in Chlamys farreri from treatment of these additives and analyze the physiological and biochemical responses by comparing the changes over treatment time in Catalase (CAT), Superoxide dismutase (SOD), and Glutathione s-transferase (GST) activity, as well as Malonaldehyde (MDA) concentration and glycogen level. Three forms of Cd, including protein -Cd, liberated Cd, and amino acid/peptide -Cd, were found, and they were sorted according to their Cd content into the following groups: protein -Cd > liberated Cd > amino acid/peptide-Cd. The removal rates of the three forms of Cd were 43.2%, 59.5%, and 59.0%, respectively, using ZnSO4 and EDTA-Na2. Additionally, a significant increase in Zn content was observed, which may suggest that reduction of bound Cd was partly due to the displacement of Cd by Zn. Moreover, Cd depuration using the additives can mitigate oxidative stress only in the first 12 h. Glycogen content continued to reduce over time, inferring that the healthy status of Chlamys farreri under treatment of the additives containing Zn can only be maintained within 12 h for excreting Cd when linking these physiological responses with the ability of the additives to remove Cd only in a short time, i.e. 12 h. The results indicated that Cd should be removed from Chlamys farreri for practical reasons.
Keywords: Biochemical responses; Cd forms; Glycogen change; Physiological metabolism; Zn-Cdantagonism.
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