Study On The Accumulation And Remove Of Cadmium And Lead In Oysters

With the rapid development of modern industry and agriculture, large amount ofindustrial wastewater and domestic sewage dumped into water, and the content of heavymetals was continuously increasing in coastal marine environment. Shellfish, which belongto filter feeding organisms, can accumulate heavy metals in seawater, especiallycadmium（Cd） and lead（Pb） which are widely existed and have formed serious potentialdangers to aquatic product safety. Meanwhile, heavy metals have the characteristics of harddegradation and biological magnification, they will be biomagnified and transferred alongwith food chains, which would threaten the health of human beings. At present, theshellfish purification technique is mainly against pathogenic microorganism, there are noavailable methods to purify the shellfish polluted by heavy metals, so study on how todecrease or remove the heavy metal residues in shellfish is of great significance.Chitosan（CTS） has a series of virtues such as abundance in resources, nontoxicity,biodegradability and effcient metal chelater. In this paper, using the method of flameatomic absorption spectrometry, the adsorption property of CTS and its derivateN,O-carboxymethyl chitosan（N,O-CMC） for heavy metals Cd²⁺and Pb²⁺in single andmixed solution were studied, then CTS and N,O-CMC were applied to the study ofcontamination model of oyster with exposing Cd²⁺and Pb²⁺. Through assaying the contentof accumulative heavy metal and inductive metallothionein（MT）, the removal of heavymetals in living oyster was discussed. The main conclusions were shown as follows:（1）CTS and N,O-CMC had preferable adsorbent capabilities for heavy metals Cd²⁺and Pb²⁺in aqueous solution, and the adsorption effect of N,O-CMC was better. The pHvalue, temperature, reaction time, adsorbent dose and initial metal ions concentration hadgreat influence on adsorption of CTS for Cd²⁺and Pb²⁺in single solution. But the effect oftemperature was of no significant on adsorption of CTS and N,O-CMC for Cd²⁺and Pb²⁺in mixed solution, as well as the adsorption of N,O-CMC in single solution. With thechange of metal ions, adsorption effect was different, and the interactions of metal ionswould also affect adsorption.（2）By studying CTS and N,O-CMC adsorption kinetics of Cd²⁺and Pb²⁺in single andmixed solution, it can be found that they were both according with Lagergren equationadsorption model2, and the chemisorption was main processes. The adsorptionthermodynamics of CTS and N,O-CMC for Pb²⁺in single and mixed solution was wellfollowed as the Langmuir isotherm equation, and belonged to monolayer adsorption. For Cd²⁺, the adsorption of CTS in single solution was according with Langmuir adsorptionequation, but in mixed solution was not; the adsorption of N,O-CMC in single and mixedsolution was followed as the Langmuir isotherm equation under the certain concentration.（3）The biological enrichment capacity of oyster to Cd²⁺and Pb²⁺was high, and hadtime and dose effect. The heavy metal content in the oysters in each exposure group weremainly higher than standard limit in2d. Simultaneously, the bioconcentration ability ofoysters for Cd²⁺was significant higher than Pb²⁺.（4）After Cd²⁺and Pb²⁺exposure, the oysters were treated with CTS and N,O-CMC, itwas found that they can remove Cd²⁺and Pb²⁺in oysters. It was same to the in vitroexperiment that N,O-CMC had better removal ability. N,O-CMC played a great role in thepromotion of Pb²⁺discharge for the light pollution oyster with Pb²⁺, it can reach standardlimit in6d and its content was0.73mg/kg.（5）Amounts of MT were synthetized when induced by Cd²⁺and Pb²⁺in oysters, thenCd²⁺and Pb²⁺were binding with MT to form nontoxic or harmfulless complexes, thusthese complexes could alleviated toxicity of heavy metals. The reason why CTS andN,O-CMC could remove heavy metals in oyster may be that the replacement reactionbetween they and heavy metal-MT complex, but further study must be paid into themechanism.Our country has abound resources on shellfish, the total yield of shellfish ranks worldfirst. However, the heavy metal pollution of shellfish is very serious, which was one of theserious hidden danger to seafoods safety. And there are no effectively technology toremove the heavy metals from fresh shellfish, this paper studied the elimination effect ofCTS and N,O-CMC to Cd²⁺and Pb²⁺in polluted oysters, which can provide theoreticalbasis for effectively decreasing or removing the heavy metal residues in fresh shellfish, andprovide guarantee for the aquatic product safety and human health.