| Summary: | 碩士 === 國立宜蘭大學 === 生物資源學院碩士在職專班 === 103 === Mercury is one kind of heavy metals that do harms to human body, and the mercury exposure is mainly caused by fishes that take in mercury. Therefore, to learn the mercury content in aquatic products and processed products that are sold in markets and then further analyze the risks of mercury intake has become an important topic in recent years. This paper attempts to develop a suitable measurement method of mercury content contained in fish, and then analyzes the mercury content in commercial aquatic products to estimate the risks of mercury by taking in fish, which will be served as references for the standard establishment and suggested intake for consumers. The results show that the microwave digestion oven and cold vapor atomic fluorescence spectroscopy can be used for mercury detection. For the conditions of microwave digestion, it shall add 2 mL hydrogen peroxide into nitric acid with eight decomposition bottles under the condition of 800W and 200℃, which is heated to exclude interference chemicals, then reduced with 7% stannous chloride to convert Hg(II) to volatile Hg(0) in mercury analyzer, by which the appropriate analysis results of mercury contents. In the experiment, it takes oilfish and mahi to conduct the matrix spike experiments, with 5 ppb and 10 ppb mercury added into the samples and the respective recovery rate of 94.1±1.9% and 92.2±4.3%, and it further utilizes the standard reference material DORM-4 and BCR-463 to testify the capacity and recovery rate, showing that the proposed method can produce the fine accuracy rating. Moreover, the limit of detection and limit of quantification of the proposed method are 0.0039 ppb and 0.013 ppb.
With the proposed mercury content analysis method, it detects 23 kinds of aquatic products sold in the market, with 211 samples to be detected in total mercury. The results show that all samples meet the limitation scope stipulated in relevant domestic regulations, among which the average mercury content in large pelagic marine fishes meat, shark, oilfish and swordfish are 0.647 ppm、0.619 ppm and 0.556 ppm respectively, which are higher than 0.5 ppm, belonging to the fishes of highest mercury; however, tuna and mahi have a lower content of mercury, which are 0.204 ppm and 0.126 ppm respectively. In which, the medium- and small-size marine fishes and freshwater aquacultures aquatic product are respectively 0.084 ppm and 0.014 ppm, belonging to the fishes of moderate and least mercury content. In terms of processed fish products, it can be divided into fish floss, canned fish and fish roe, and the corresponding mercury contents are 0.05~5.45 ppm, 0.028~0.079 ppm, and 0.002~0.008 ppm, in which the content in fish floss is the highest. Moreover, fish floss can also be categorized as unlabeled fish floss, swordfish floss, tuna floss and salmon floss, all of which have an average mercury content of more than 0.5 ppm except the salmon floss. In addition, the selected samples are also taken to measure the proportion of methyl mercury in total mercury to estimate the rationality of the risk assessment. According to the experiment, the ratio of methyl mercury to total mercury in shark meat and oil fish meat exceed 95%, so the total mercury value can be used to represent the methyl mercury value, but the ratio of methyl mercury to total mercury in swordfish floss only account for 20%. After estimating the acceptable weekly intake of specified fish and comparing with the recommended PTWI value of 1.6 μg/kg/weekly by JECFA, it suggests that children of 6 to 12 years old shall take in the shark meat, swordfish and oilfish meat less than 85.8-92.2 g, and people above 13 years old less than 140-170 g. As for the fish floss of unlabeled fish specie, the weekly intake shall be no more than 120g for children, and people above 13 years old can take 600 g swordfish floss or 200 g unlabeled fish floss a week.
From the estimated risk value of daily fish mercury intake, the risk percentage for children of 6-12 years old only taking in shark meat, swordfish meat and oilfish meat is 382~445% calculated based on their daily fish intake, which is 4 times higher than the JECFA PTDI value. The risk value of taking in fish floss of unknown species is still 3 times higher than the JECFA PTDI value. In the end, it estimated the maximum acceptable fish mercury intake, finding that mercury content of fish lower than 0.3 ppm is suitable for teenagers and adults above 13 years old, which shall be halved for children of 6-12 years old and elder people. Through comparing the measured value in the paper, the values in blue shark, swordfish, oilfish and unlabeled fish floss exceed the suggested value, which is of high risk of mercury hazard and needed to pay attention to the intake amount.
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