Safety Assessment Of Cadmium Pollution In Aquatic Products And The Research Into The Influence Of Cadmium In Different Forms

Not as an essential but as a harmful microelement to creatures, cadmium is one of the grave enduring pollutants in aquatic products. As the development of the industry and agriculture, the cadmium pollution towards environment and feed has been aggravated. Through the aquatic animals'absorption and the transfer of food chain, cadmium has constituted a potential menace to mankind's health, and even the export of China's aquatic products has been affected. In dealing with this the present problem, the present thesis investigates Cadmium from three respects:Firstly, it carries out a survey towards the cadmium content in some typical aquatic products in partial area. In this thesis, the pollution situation is analyzed and the aquatic products'safety for human consumption is evaluated, with the following aims: to provide a reference for the research into cadmium and the perfection of the relevant criteria, to provide a theoretical foundation for human consumption, to provide a basic data for the establishment and perfection of the standards of aquatic products and for the future inspection and monitoring of the hygienic quality of aquatic products, and meanwhile to provide scientific grounds for different branches of government's establishment and administration.Next, Litopenaeus Vannamei being a subject, based on the research of aquiculture experimental system, this thesis, through the investigation of the influence of cadmium's different forms in feed on the aquiculture of aquatic animals, and through the comparison and contrast of the growth, toxicity, and accumulation rules of the aquatic animals, fills a gap in this specific field, which provides a technical basis for the following three: optimization of the restrictive form and amount-limiting of cadmium in feed, development and perfection of the restriction standards of cadmium in aquatic products for human consumption, and the inspection and establishment of the criteria of aquatic products industry. Finally, in dealing with the present problem that methods of detecting cadmium shape are urgently needed in the study on cadmium and its species, the feed which is used in the aquiculture experiment being the subject, in the thesis, relying on the nature and characteristics of organic cadmium and inorganic cadmium, different extraction systems are utilized to do the pattern analysis, which is supposed to be the preliminary exploration in this field. According to the specific experiment result, the next work suggestion is put forth.The outcome of the research reveals that content of cadmium in the sampled aquatic products shows regional difference and species difference,the order of which is bivalve mollusc>prawns>fishes。Cadmium content in fishes and prawns is in the normal scope and the safety for human consumption has not been affected. However, content of cadmium in partial mollusk in individual area is hiher and the safety for human consumption is being affected to some degree, to which attentions should be paid .From the monitoring result,we can see that cadmium content of mollusc is higher than fishes and prawns, however, mollusk liquid and viscera are widely used as raw material in fishery feed industry at present,the cadmium of which cause further pollution to cultured aquatic animals in the forms of organic cadmium. The difference of toxicity and harm between cadmium in different forms has always been a bone of contention at home and abroad,so the present thesis explore the difference between inorganic cadmium and organic cadmium using cultured prawns as study object.Through the aquiculture of prawns, it is discovered that with the same level of concentration of cadmium, after 131 days'breeding, the death rate of the prawns which is fed with fodder containing organic cadmium is higher than that of the prawns which is fed with fodder containing inorganic cadmium. And this case proves that the toxicity of organic cadmium might be stronger than that of inorganic cadmium, which disagrees with the traditional standpoints. Contrasted with the reference group, as the concentration of cadmium increases, the relation between the feeding stuff containing inorganic cadmium and prawns'growth can be described by a parabola while the feeding stuff containing organic cadmium has an obvious positive effect towards the growth of prawns. And this is another find of the monitoring. Next is the third discovery: (1) the cadmium in two forms in feeding stuff has similar accumulation rules towards three kinds of tissues of prawns; (2) the residual quantity in different parts of prawns is positively correlated with the increment of cadmium and the length of the breeding time; the increasing tendency of the same-concentration cadmium in two forms in the three tissues is nearly the same. Conclusively, the relative accumulation rate of the cadmium in two forms in the tissues of prawns can be depicted as following: shell>viscera>muscle. However, the absolute accumulation volume for the cadmium in two forms in the tissues of prawns is viscera>shell>muscle. Therefore, it is easier to accumulate in prawns for inorganic cadmium. Viscera is the target organ which gathers cadmium in abundance, with 80% of the entire cadmium in the body.Methods of detecting cadmium shape are the foundation of related research, but no method exists for the moment at home and abroad because it is difficult to isolate them from other forms.In this paper, organic solveut extraction,hydrochloric acid extraction and water extraction- ultracentrifugation are taken respectively to do form analysis towards cadmium in different forms, with the discovery that cadmium in organic form in feeding stuff cannot be extracted from the solvent such as Cyclohexane and Ethanol. As for cadmium in organic form, it would be devastated by low-concentration hydrochloric acid, and the detailed degree of disintegration cannot be verified. When separate them by ultracentrifugation cells according to the molecular weight , owing to the complex ingredients of the feeding stuff and the complicated chemical and physical changes in the process of feeding stuff processing, the result one get is quite different from the theoretical figure, meanwhile with a very low recycling rate. In short, the form analysis and the testing of cadmium in feeding stuff need a further probe. According to the nature and characteristics of cadmium in different forms, with proper extraction systems being chosen, and with the prerequisite that form of cadmium not being destroyed for form analysis, the breakthrough of separation technology is an essential key issue which is urgent to be solved.