| With the development of industry, the large amount of heavy metals have polluted the ocean with all kinds of ways, and the content of heavy metal in water environment have been continuously increasing. And the cadmium is one of the mainest marine pollutant, it is easy to be absorbed and accumulated by the creature, which have formed the serious potential dangers to food safety, especially aquatic product, the shellfish. However, people usually like eating the raw or undercooked, and no removal the viscera, the heavy metals invaded the body by the transport through food chain, which have formed potential threat.Now, there are two methods to improve the shellfish cleaning, including temporary raising in clean water and cleaning in factory. Considering the great labour intensity and consuming time, the two methods were difficult to carry out, and it may pollute the water in temporary zone when the shellfish moved the temporary zone from growth zone. The shellfish purification technique is mainly against pathogenic microorganism, there are no available methods to purify the shellfish polluted by petroleum hydrocarbon, heavy metals, pesticide and marine toxin. How to decrease the Cd in shellfish is urgent matter, which have important significance to guarantee the shellfish quality safety.The Cd content in Chlamys ferrari collected in aquatic wholesale market in Qingdao was investigated for one year, the results showed the Cd content in the majority Chlamys ferrari were higher than standard limit, only 33.3% were less than the standard, which illustrated how to remove the Cd residue in the aquatic product is urgent matter. The Chlamys ferrari have the higher enrichment ability to Cd, and the Cd content in viscera is more than in meat by 20 times. The enrichment ability is positive correlation with raising temperature, the Cd enrichment among the different size of Chlamys ferrari has no obvious difference.Chitosan oligosaccharide(COS) has excellent water-soluble, there are some groups, such as–OH, -NH2, -NHCOCH3, which are the optimum ligand of mental ionic. Therefore, 5 kinds of complexes were prepared by the binding between COS and Ca, Mg, Zn, Fe, Ree. And the preparation condition were optimized, including time, temperature, pH, the addition level of metals, the content of reaction solution, the type of metallic salt. Using the UV, IR, Fluorescence spectra, it was proved that metal elements binded with COS through N and O.After Cd exposure, the Chlamys ferrari were treated with COS complexes, it was found that the all complexes can remove the Cd in viscera of Chlamys ferrari. COS-Ca, COS-Mg, COS-Ree have significant removal ability to Cd, the Cd content can be deduced by 46%, 52% and 47.8% respectively in 12 days. The removal rate of Cd reached 17% and 13% respectively by ushing COS-Zn , COS-Fe. The complexes additive dose and raising temperature have effect on removal ability of Cd. 1~1.5kg Chlamys ferrari, exposed with 0.5mg/L Cd , were raised in 40L seawater, the removal rate of Cd were 31%, 27%, 39%, 17%, 13% respectively when treated with COS-Ca, COS-Mg, COS-Ree, COS-Zn, COS-Fe, the additive dose of complexes were 0.35g, 0.21g, 0.21～0.28g, 0.21g and 0.35g respectively.The Cd binding with protein and small molecule substances in kidney and viscera was removed by COS complexes with metal elements. Compared with negative control group, the Cd in kidney were reduced 25.2%, 36.1%, 37.5% respectively in 5 days when treated with COS-Ca, COS-Mg and COS-Ree. The COS-Ca, COS-Mg and COS-Ree have effect on the antioxidant enzyme system of Chlamys ferrari exposed with Cd, such as CAT, POD, SOD, GSH-PX and MDA. The complexes have the ability of antioxidant, maintaining the balance between creating and scavenging the free radicals. Based on physiological, theory the mechanism complexes can remove the Cd from viscera of Chlamys ferrari was proved. The mechanism was further confirmed by the replacement reaction between the complexes and Cd-MT.The COS complexes with metal elements also can remove Cd from other shellfish except for Chlamys ferrari, such as Mytilus edulis, Crassostrea gigas, Sinonovacula constricta, Venerupis variegate, Argopecten irradiams. Our country has the greatest stage on shellfish cultivation. The total yield of shellfish was 10.73 million tons in 2007, account for 60% yield of worldwide raising shellfish. However, the heavy metal pollution of shellfish is very serious, especially Cd, which was the one of food safety. And there are not availably technology to remove the Cd from fresh shellfish. If the problem can be solved availably, which will have great influence to the sustainable development of shellfish farming. The complexes prepared in this paper can remove Cd from fresh shellfish, which is the one of basical study of application of developing the removal of Cd from fresh shellfish, which can provide theoretical basis for exploiting feed additive and special agent of shellfish purification to remove the Cd, providing guarantee for the aquatic product safety and human health.
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