Study on Arsenic Species and Cadmium Levels in Rice in Taiwan

• Main Authors: Yu-Mei Suei, 隋昱梅
• Other Authors: Yaw-Huei Hwang
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/17518513005237702617

碩士 === 國立臺灣大學 === 職業醫學與工業衛生研究所 === 99 === Rice is the staple food in Asia. The major arsenic species in rice grain include arsenite (As(III)), arsenate (As(V)), monomethyarsonic acid (MMA), and dimethylarsinic acid (DMA). In general, inorganic arsenic species are more toxic than those of organic arsenic species. Therefore, it is necessary to analyze the arsenic species in rice in Taiwan to optimize the exposure assessment for the ingestion of rice. The objective of this study is to analyze arsenic and cadmium in white rice samples and cooked rice in Taiwan, and to determine the optimal extraction procedure for arsenic species in rice. With the obtained data, we used Monte Carlo simulation to calculate cadmium and inorganic arsenic daily intake value. First of all, based on the production of japonica crop, we chose one to three villages/towns with top crop production of japonica in every county in Taiwan and decided the sample number for each village/town, according to the ratio of rice crop production of the individual village/town to the whole Taiwan. In total, 118 white rice samples were collected, and then dried by freeze dryer and ground by a rice miller. Pretreated rice samples were acid digested by microwave. Total arsenic and cadmium concentrations in digested samples were determined by ICP-MS. For arsenic speciation, we first evaluated the efficacy of different solvent mixtures and techniques for the optimal extraction of arsenic species in rice samples. The most appropriate method was ultrasonic process followed by microwave extraction with recovery rate of above 80 % for most white rice samples. The average concentration for total arsenic was 0.17±0.04 μg/g (0.09-0.37 μg/g), for arsenite 0.11±0.03 μg/g (0.05-0.26 μg/g), for arsenate 0.02±0.01 μg/g (0.004-0.06 μg/g), for DMA 0.02±0.01 μg/g (0.01-0.06 μg/g), and for MMA 0.001±0.004 μg/g (ND-0.03 μg/g). There was no difference in the total arsenic concentration for rice samples of different counties in Taiwan. For arsenic speciation analysis, arsenite was the major species determined in rice sample and MMA was the least one. For the analysis of cadmium concentrations in rice samples, the average concentration of cadmium was 0.06±0.05 μg/g (0.007-0.40 μg/g). There were higher cadmium concentrations in Yilan and Nantou, with averages of 0.19±0.10 μg/g and 0.15±0.07 μg/g, respectively. The total arsenic concentration was significantly reduced in cooked rice, with higher percentage of reduction observed for raw rice samples with higher arsenic concentration. With respect to arsenic species in cooked rice samples, the proportion of arsenite rose while that of DMA decreased. We used Monte Carlo simulation to estimate cadmium and inorganic arsenic daily intake value. The results showed that 99% of people did not have cadmium or inorganic arsenic intake from rice exceeding the WHO suggested maximum tolerable daily intake value (MTDI). In conclusion, the concentrations of total arsenic and cadmium in rice samples in Taiwan are acceptable, which would be further reduced through washing and cooking process. Results of the Monte Carlo simulation indicated that, currently, the daily cadmium and inorganic arsenic intake from rice in Taiwan, is still within the acceptable range.