| China is the world’s largest producer and consumer of melamine. Melamine and its analogues are widely used in industral and agricultural production. These compounds can enter into aquaculture environment through various channels and then accumulate in fishes, and finally threaten human health through the food chain. Therefore, it is necessary to explore their environmental behaviors including residue, migration and fate, and their ecological risks to aquaculture water. The detection method is a key problem to solve in first. Due to the low content of melamine and its analogues in aquatic samples with many complex interfering substances, we must adopt an efficient pretreatment approach such as appropriate extraction, enrichment, separation and purification to detect the melamine and its analogues. The aim of this work is to develop a rapid, sensitive; and accurate analytical method for melamine and its analogues residues in aquatic products, then the new method will be applied to study the accumulation of melamine in tilapia under the simulated aquatic ecosystem. The main work and conclusions are as follows:Chapter1:Clarified the background of this study, research ideas and main content.Chapter2:Summarized the recently developed techniques for analysis of melamine and its analogues and research advances on toxicity of melamine and its analogues.Chapter3:A method for the rapid determination of melamine and its analogues in fish samples by using microwave-assisted derivatization was proposed. Samples was extracted by trichloroacetic acid and methanol and purified by SUPELCO ENVI-CARB solid-phase extraction column, then dried by nitrogen gas and rapid derivatized by N,O-Bis(trimethylsilyl)trifluoroacetamide with microwave, then detected by gas chromatography-mass spectrometry and quantified by the external standard method. Extraction solvent and some important parameters affecting the derivatization such as microwave heating time, pyridine volume and derivatization reagent volume were investigated. The study showed that trichloroacetic acid and methanol can extract the melamine and its analogues effectively in the aquatic products and precipitated the protein. Under the optimized conditions (pyridine volume:400μL, derivatization reagent volume:200μL, microwave heating time:2min with the microwave power of700W), the average recovery of melamine and its analogues was81.3%-103.1%with the relative standard deviation was0.56%-4.11%. The linear range was from0.02to50mg/kg of melamine and its analogues were from0.05to50mg/kg with detection limit and quantification limit was: MEL0.0056、0.018mg/kg, CYA0.0096.0.032mg/kg, AMD0.0126、0.042mg/kg, AMN0.0120、0.040mg/kg. The method is also suitable for the determination of melamine and its analogues in many other aquatic products such as tilapia, grass carp, white shrimp and winkles samples.Chapter4:Use the new method to study the accumulation of melamine in different organs of tilapia and winkles during feed administrating diet under the simulated aquatic ecosystem. There were differences in the distribution and accumulation of melamine for different organisms in tilapia during feed administrating diet. The significant differences of melamine accumulation existed between other viscera tissues, kidney, liver and muscle. It is the highest in other viscera tissues than in kidney, liver and muscle, which may be related to melamine input mode and its metabolism in fish. Later, the concentration of melamine in tilapia was decreased gradually during feed basal blank diet. Melamine was directly discharged through the organization of metabolic of tilapia and some dissolved from administrating diet in the water, which can be detected in water and sediment. The concentration of melamine in water was increased gradually during feed administrating diet, then was decreased gradually and finally tended to steady state during feed basal blank diet. This may be there is no melamine was dissolved in water during feed basal blank diet, on the other hand melamine distributed to sediment, goldfish algae and winkles. The adsorption rate of melamine in sediment was fast during feed administrating diet, and then increased slowly and finally tended to steady state during feed basal blank diet. This may be the concentration of melamine in water was decreased, which the distribution rate and content to srdiment was decreased during feed basal blank diet. The concentration of melamine in goldfish algae is closely related to the water environment and the adsoption mechanism remains to be further research. During the experiment, the concentration of melamine have a great relationship with the living habits in Winkles, which visceras is higher than in muscle, was increased gradually and finally fell slightly and tend to steady state. |
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