臺灣食用稻米砷暴露管制標準探討

Abstract

食米長久以來為亞洲地區之主食。就目前文獻所知，食米中之砷物種主要為三價砷(As(III))、五價砷(As(V))、單甲基砷酸(MMA)和雙甲基砷酸(DMA)。眾多文獻指出，無機砷對人體的毒性較有機砷高，且砷被國際癌症研究署(IARC)歸類為第一級致癌物質，可能導致人體皮膚、肺臟、肝臟、腎臟、膀胱等部位癌症，也可能造成非致癌的健康效應，例如心血管疾病、糖尿病，影響嬰幼兒的神經發育等。目前國內法規只針對食米中重金屬鎘、汞、鉛設立管制標準，卻未有針對砷的規範。因此本研究欲經由健康風險之角度進行國人砷暴露量與所承受健康風險之探討，作為未來食米砷管制標準制定的參考。 本研究採用本實驗室在2011年分析全臺各地區食米之重金屬濃度資料，利用蒙地卡羅方法模擬食米之無機砷濃度分布，並以區間估計方法進行健康風險評估，探討國人攝食食米暴露無機砷之暴露量，並比較國家攝食資料庫中食米與熟飯的攝食量資料對人體砷暴露估計的影響。本研究取得之106筆食米(白米)無機砷濃度資料，經由蒙地卡羅方法模擬檢定判定為對數常態(log normal)分布，再利用風險評估區間估計方法計算國人攝食食米之無機砷暴露量與健康風險值。另假定食米之無機砷管制標準分別為0.25、0.20、0.15、0.10 ppm的情況下，探討國人攝食食米之無機砷暴露量與健康風險值的變化。 本研究分析結果顯示，國人攝食食米之無機砷暴露量為:每人每日每公斤體重1.41x10-4 mg/kg-day、男性人口每人每日每公斤體重1.77x10-4 mg/kg-day、女性人口每人每日每公斤體重1.36x10-4 mg/kg-day。致癌風險部分，全人口為2.13x10-4、男性人口2.66x10-4、女性人口2.04x10-4。危害商數部分，全人口為0.472、男性人口0.591、女性人口0.454。管制標準探討的部分，若將食米之無機砷標準分別設立在0.25、0.20、0.15、0.10 ppm，以目前情況來看，分別有0.07、1.12、14.5、74.8 %的食米之砷濃度會超過標準，而若食米之砷濃度分別降至這些不同的標準值，能將國人攝食食米之無機砷暴露量分別降低0.43、0.85、5.97、25.7 %。將食米之無機砷管制標準設在0.15 ppm時能有效將暴露量降低約6 %，此結果與FAO/WHO在2016年制定糙米之無機砷管制標準為0.35 ppm時所能降低之無機砷暴露量較為相近。 以臺灣目前食米之砷濃度分布情形來看，以食米為主食的國人攝食食米所承受之無機砷暴露量與健康風險仍需進一步評估與重視。在健康風險的部分，以危害商數管制標準為1的情形下約有22.6 %的人會超過此管制風險值而面臨非致癌之健康效應，而在致癌風險管制標準為1x10-4的情形下約有77.2 %會超過此管制風險值而面臨致癌之健康效應。 臺灣屬飲食文化以食米為主食的亞洲國家，相較於普遍攝食麥類的西方國家，國人食米之攝食量高。單從制定管制標準改善食米無機砷濃度著手，無法有效降低國人攝食食米可能承受的無機砷暴露量與風險值。因此若直接引用西方國家之管制方法，而未考量國人的飲食習慣即制定嚴格的管制標準，可能導致實際上難以實行。未來在制定管制標準時，仍需考量實際應用層面，輔以經濟與政治面向探討，並採用成本效益分析方法，以評估建立最適宜的管制情形。

Rice is the staple food in Asia. Previous studies have shown that 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 organic arsenic species. Arsenic is also classified as class I--carcinogenic to humans by International Agency for Research on Cancer. Arsenic can cause adverse health impacts such as skin lesions, lung cancers, liver and kidney cancers, bladder cancers. Regarding the non-cancer diseases, arsenic can cause cardiovascular diseases, diabetes, and influence the neuro developments in children. Presently, there are regulations on cadmium, mercury, and lead in rice in Taiwan, but there is still no regulation on arsenic in rice. Therefore, the objective of this study was to assess the arsenic exposure and the possible resulted health risk posed through rice intake for Taiwanese population in the health risk assessment framework, and this might help in forming the regulation on arsenic in rice in the future. We adopted the rice inorganic arsenic data obtained by our laboratory in 2011 for various districts of Taiwan. With the obtained data, we used Monte Carlo distribution fitting to fit the inorganic arsenic concentration data as a log normal distribution, calculate inorganic arsenic lifetime average daily dose(LADD) value and conduct a probabilistic risk assessment to figure out the possible Hazard Quotients(HQ) and cancer risk. We also set various maximum limit proposals on inorganic arsenic level in rice and monitored the resulted differences in arsenic exposure doses and the health risk, respectively, under various maximum limit proposals. The LADDs results are as follows, 1.41x10-4 mg/kg-day for general population, 1.77x10-4 mg/kg-day for male and 1.36x10-4 mg/kg-day for female. The cancer risks are 2.13x10-4 for general population, 2.66x10-4 for male and 2.04x10-4 for female. In addition, the Hazard Quotients(HQ) are 0.472 for general population, 0.591 for male, and 0.454 for female. Regarding the maximum limit proposals, we set various proposals at 0.25, 0.20, 0.15, 0.10 ppm for arsenic level in rice. Under these circumstances, we need to disqualify 0.07, 1.12, 14.5, 74.8 % of currently produced rice and accordingly cut down people’s inorganic arsenic exposure dose by 0.43, 0.85, 5.97, 25.7 %, respectively. We concluded that setting regulation at 0.15 ppm for arsenic level in rice might reduce 6 % of inorganic arsenic exposure dosage for people in Taiwan, and this value is similar to that FAO/WHO measured in 2016 while they were setting inorganic arsenic regulation on brown rice at 0.35 ppm.

From the present inorganic arsenic levels in rice we have assessed, the health risk assessment results have indicated that the intake of rice for Taiwanese people has posed a health risk which should not be ignored. Regarding the health risk, there were 22.6 % of people facing non-cancer health risk considering the acceptable hazard quotient 1, and there were 77.2 % people facing cancer health risk considering the acceptable cancer risk 1x10-4.

Taiwan, as part of Asia, has been consuming rice as staple food for decades. Compared to western countries, people in Taiwan consume a greater amount of rice. Therefore, cutting down on the arsenic exposure by setting regulation on arsenic levels poses little significance. Apart from setting the regulation on arsenic levels in rice, we should ponder on the economic and politics aspects, and also consider about Taiwanese people’s diet habits, in order to foster the most appropriate regulation on arsenic level in rice.