稻米穀粒中鎵及砷元素分布與微量元素(鍶、銫、鈷及釩)含量之探討

Abstract

本研究第一部分主要在了解鎵及現行食米中限量規範之重金屬—砷在稻米中累積與分布情形。首先，收集確知產地之稻穀共29種，包含稉稻15種、秈稻3種以及有色稻11種，將稻穀劃分為稻殼、糙米、麩皮及精白米，除測定其水分、灰分含量外，再以感應耦合電漿質譜儀(Inductive coupled plasma-mass spectrometry, ICP-MS)測定其鎵與砷的含量。第二部分則蒐集69種市售稻米，除鎵及砷外，另測定其微量元素(鍶、銫、鈷及釩)含量，並以砷之含量進行食米之風險評估。第三部分為水耕栽培試驗，探討在不同鎵濃度下(1、8及15 mg/L)對稉稻(台稉九號)、秈稻(台中在來一號及台中秈糯二號)之鎵累積情形。第一部分結果顯示，稻穀各部位之平均水分含量(11.02-13.67%)大致接近，灰分含量則稻殼(14.35%) > 麩皮(9.12%) > 稻穀(4.76%) > 糙米(1.49%) > 白米(0.70%)；鎵之累積趨勢為稻殼(1.431 mg/kg) > 麩皮(1.079 mg/kg) > 糙米(0.144 mg/kg) > 精白米(0.074 mg/kg)，而砷的分布情形則是以麩皮含量(1.00 mg/kg)最高。在第二部分樣品中，砷含量在所有樣品中皆測得，且糙米及精白米間具顯著差異，鈷及銫在1/3的樣品中測得含量，砷、鈷及銫之含量範圍分別為0.048-0.773、<LOQ-0.267及<LOQ-0.162 mg/kg，鍶及鎵則分別在四種及兩種有色米中測得，釩含量皆低於定量極限。另以市售樣品砷之含量及國家攝食資料庫之資料，做為台灣各年齡層間攝取食米之非致癌性與致癌性風險評估。結果顯示，非致癌性風險存在於各年齡族群，累積性之致癌性風險則高於1  10−4，為須關注之議題，顯示未來應持續追蹤砷在食米中之含量及可能造成之健康風險。水耕栽培試驗之結果顯示，稻穀籽粒充實程度與品種可能有關，其隨鎵濃度的提高，稻穀收穫量小幅上升，但未達無顯著差異，而收成之稻穀中，並未測得鎵累積於糙米中。

The first part of this study was to evaluate the distributions of gallium and arsenic in rice grains and to quantify the other trace elements in the rice grains. Collected 29 paddy rice samples from selected origins, including 15 japonica, 3 indica and 11 colored rice. Each rice grain was fractionated into rice, husk, brown rice, bran and polished rice. Moisture and ash contents were determined and inductive coupled plasma-mass spectrometry (ICP-MS) was used to determine gallium and arsenic contents. The second part of this study, 69 commercial rice samples were purchased from local markets and the contents of gallium, arsenic and trace elements (strontium, cesium, cobalt and vanadium) in the samples were determined. The third part of this study was the hydroponic culture. Three varieties of rice (TCN1, TK9, TCSW2) were planted in different concentrations of gallium (1, 8 and 15 mg/L) to investigate the accumulation of gallium during grain filling stage. The results showed that the average moisture contents (11.02-13.67%) of rice grains were similar in each fraction. The trend of ash contents was husk (14.35%) > bran (9.12%) > paddy rice (4.76%) > brown rice (1.49%) > polished rice (0.70%). The trend of gallium contents was husk (1.431 mg/kg) > bran (1.079 mg/kg) > brown rice (0.144 mg/kg) > polished rice (0.074 mg/kg) while the bran (1.00 mg/kg) had the highest content of arsenic. In the 69 commercial rice samples, arsenic was detected in all of the samples and the contents in brown rice were significantly higher than polished rice. Cobalt and cesium were detected in one-third samples. The range of contents of arsenic, cobalt and cesium were 0.048-0.773, <LOQ-0.267 and <LOQ-0.162 mg/kg. Strontium and gallium were only detected in four and two colored rice, respectively. The contents of vanadium in rice samples were all below LOQ. The non-cancer and cancer risk assessments of each age group were based on the arsenic contents of commercial rice samples and the data of National Food Consumption Database in Taiwan. Results showed that the non-cancer risk was in all age groups. Cumulative cancer risk was higher than 1  10−4. The contents of arsenic in rice and the healthy risk should be continuously considered in the future. In the hydroponic culture, the harvest of the filled grains may be various depending on rice variety. The grain yields slightly increased with increasing in the gallium concentration. There was no accumulation of gallium in the hydroponic cultured brown rice.